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TITLE Nuclear Power and the Environment.INSTITUTTON International Atomic Energy Agency, Vienna

(Austria) .PUB DATE 72NOTE 92p.

EDRS PRICE MF-$0.65 HC-$3.29DESCRIPTORS Bibliographic Citations; *Conference Reports;

*Energy; Environmental Education; Health Education;*Public Health; *Radiation; *Safety; ScienceEducation

ABSTRACTThis booklet is a summary of an international

symposium, held in August 1970 in New York City, on the environmentalaspects of nuclear power stations. The symposium was convened underthe sponsorship .of the International Atomic Energy Agency mum andthe U.S. Atomic Energy Commission (USAFC). The information ispresented in a condensed and readily understandable form, and it ishoped that it will be useful to those interested in a summary view ofthe public health and environmental aspects of nuclear powerproduction. Contents are organized according to major headings asfollows: "The Role of Atomic Energy in Meeting Future Power Needs,""Radiation Protection Standards," "Safe !Handling of RadioactiveMaterials," "Other Impacts," "Public Health Considerations," and"Summary." Included in the summary are lists of "pertinentpublications" of the IAEA, the World Health Organization (WHO), otherinternational bodies, and a list of consultants and contributors. Inaddition to the symposium summary, this booklet also containscontributions supplied by 28 experts from IAEA and WHO and a numberof member states. (LK)

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nuclear power

and the

environmentPrepared by the IAEA in co-operation with WHO

Printed by the IAEA in Austria

table of contents

the role ofatonic me

meetingfinuturepower needs

MeV

The Role of Atomic Energy in Meeting Future Power Needs 1

Future World Energy NeedsWorld Energy ResourcesThe Projected Role of Nuclear Power

The Nuclear Fuel Cycle 4

Environmental Aspects of Nuclear Power ProductionRadioactivityTransportationDecommissioning of Nuclear Installations

5

radiationprotectionstandffds

safe handling

of radioactivematerials

Radiation Protection Standards 8Basic Radiation Concepts 10Biological Effects of Radiation 10Basic Radiation Protection Standards 11Derived Release Limits .13Natural Radioactivity 14ManMade Sources of Radiation Exposure 15

Safe Handling of Radioactive Materials 19

Mining, Milling, Enrichment and Fuel Fabrication 20

Nuclear Power Plants 21Sources of RadioactivityRadioactive Waste Generation and ManagementBoiling Water ReactorsPressurized Water ReactorsGas Cooled ReactorsHeavy Water ReactorsFast Breeder Reactors

Accident Considerations 39Accident PreventionAccident MitigationTypical AccidentsEmergency PlanningSite CharacteristicsOperating Experience in the United States

Fuel Reprocessing 47Origins and Types of Effluents and WastesControl of Effluents and Wastes

Transportation 52 .5

1

otherimpacts

Other Impacts 55

Plant Construction 55

Transmission Lines 55

Thermal Discharges 55Comparison of Thermal Release from Fossil-fuelled and Nuclear PlantsCooling Water Sources and Methods of Heat DisposalPhysical Behaviour of Heated DischargesThermal Effects on Biota and Ecology

public

healthconsiderations

Public Health Considerations 61

Nuclear Power Generation 61MiningMilling, Enrichment and Fuel FabricationReactorsNormal operationsAccidental eventsThermal aspectsChemical aspectsFuel ReprocessingTransportation

Public Health and Safety Programmes 69Operational Health and Safety ProgrammesThe Role of Health AuthoritiesThe Role of International Organizations

Summary 75

Annex I.Pertinent Publications of the International Atomic Energy Agency_80

Annex II.Pertinent Publications of the World Health Organization 83

Annex I I I.Pertinent Publications of other International Bodies 83List of Consultants and Contributors 85

Power demandsbroughout the world

are increasing:energy is essentialto assure public health

and to provide for the quality of life to which manaspires. Nuclear energy, based on fiction, is ina position to fill these needs with less detriment tothe environment than most fossil fuels.In the longer term man may need to evolve othersource' of power such as fusion energy or

solar energy; but these have not yet been de-veloped to a point at which their widespread use inthe next few decades can be foreseen.The nuclear power industry has been developingin an era in which much attention is givento the preservation of public healthand environmental quality. No industry, includingthe nuclear industry, can truthfully claim tobe free from all public health andenvironmental effects, but the nuclear industry hasgiven serious attention to these problems.

4

Probably more factual information on the effectsof radioactivity has been compiled than forany other potential pollutant.

Biologists have shown that radiation doses as lowas 0.5 to 1.0 rad per day administeredcontinuously can give rise toobservable genetic and somatic effects in smallmammals. These levels are about a factorof 1000 higher than the ICRP annual dose limits forthe general public, and nearly 10 milliontimes as high as the average radiation doseincrement resulting at present from the operationof nuclear installations. At the very low levelsof radiation to which members of thepublic are exposed the frequency of effects is solow as to be not observable; as a result it ispossible neither to prove nor to disprovethe actual occurrence of effects at these levels.Radiation protection standards are seton the basis that the effects may occur at low dosesin proportion to the effects observed at higherdose rates, but evidence exists to suggest thatthe effects occur with even less frequency, if at all.

A similar situation exists with respect to accidents.Although there have been malfunctions ofnuclear power reactors, in no case hasu.: re been a release of radioactivity to the environ-ment ;n amounts large enough to result in anoverexposure of the public. Because of the excel-lent recori of safety that has been attained,it is not pinsible to establish quantitatively whatthe probe aility of a major reactor accidentis, excer that it is certainly very low.Eng:l.r.dered safety features continue to be developedto improve even further the reliability ofreactors to operate without incident.

Interest in the environmental aspects of nuclearpower stations led the InternationalAtomic Energy Agency, in co-operation with theUnited States Atomic Energy Commission,to convene a symposium in New Yorkon this topic in August 1970. The enthusiasticresponse both during and after that meeting, andthe interest in environmental mattersevidenced by the convening of the United Nations

V Conference on the Human Environmentin 1972, led to the decision to summarize theinformation presented in New York in a condensedand readily understandable form for thosenot engaged directly in this field ofwork. The World Health Organization has co-operated in the preparation of this booklet, whichis the result. It was planned at a consultants'meeting convened in Vienna in June 1971.Following this meeting contributions to the bookletwere supplied by 28 experts from the IAEAand WHO and a number of Member States,

and compiled by Dr. D.G. Jacobs, who served asscientific secretary. A second consultants'meeting was convened in January 1972 to reviewthe assembled draft. (A list of consultantsand contributors is given at the end.)

Compilation of the booklet presented a number ofdifficulties. The time period between itsconception and its desired date of completionwas quite short, especially in view of the number ofcontributions received. There was an attemptto compile a manuscript which was uniformwhile at the same time maintaining the character ofthe various contributions.Further, the interests and technical backgroundof the prospective audiencepresents a broader spectrum than one wouldnormally try to coverwith a single publication. As a result there ismore repetition and parallel material in thebooklet than one might hope to findthough in part this is deliberate. For example, thethird chapter contains more operational detailsthan most readers would require, and wesuggest that this chapter could be omitted by non-specialists. The information presented may beof considerable interest, however, to othersin the intended audience. The first part of the fifthchapter closely parallels Chapter III with regardto the topics discussed, but the discussionstake the form primarily of an evaluation of thepublic health and environmental aspects ofthe various operations rather than a description ofoperations and procedures. We are hopeful thatin spite of its admitted shortcomings thebooklet will be useful to those interested in a sum- Vmary view of the public health and environ-mental aspects of nuclear power production.

No one can profess to be able to quantify at thistime all of the public health and environ-mental effects of nuclear power for the future.The attitude of the nuclear power industryis to proceed with due caution after giving con-sideration to all facets thought to bepotentially detrimental. Concurrently, programmesare conducted to advance our knowledgeof the impact of the industry and toimprove further its safety aspects, with continuedperiodic reviews on the basis of newinformation. to view of their responsibilityto protect the health of populations, public healthauthorities are following continuouslythe development of new sources of power andtheir effects on the human environment.The nuclear industry has achieved a commendablesafety record to date, and it hopes to continueto set an example of thorough attentionto safety which other industries may follow.

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7

the role ofatomic ene

in me

repower needsCivilization has developed largely as man hasdevised new ways of changing and controlling hisenvironment. He has searched continually for newmeans of producing energy to help him attainhis objectives. In the earliest days he relieddirectly upon the energy from the sun to providehim with warmth. The discovery of fire was thekey to releasing the solar energy locked in plantsand trees, by the burning first of wood and laterof fossil fuels.

Although water power and wind power had beenused industrially for several centuries theindustrial revolution began really when manharnessed energy from the burning of fossil fuelsto drive machines to do his work.

The changes in man's sources of energy and therates at which they are consumed have beenparticularly dramatic over the past century.A hundred years ago wood was the source of mostenergy, but by 1900 it had been replacedlargely by coal. After World War II oiland natural gas supplied an increasing fraction ofenergy.

Economic progress is usually associated closely withavailable energy. This is illustrated by a correlationbetween a nation's per capita energy consumptionand its gross national product (see Fig.1).Thus, it may be expected that a majorcontribution to increases in world energy consump-tion will come from improvements in the

economic conditions and standard ofliving of developing countries as well as fromincreases in the world population. World energyconsumption during the last two decades hasincreased very rapidly, by about 8% peryear - much faster than the rate of populationgrowth, which has been about 2.3% a yearduring the same period. It is interestingto note that, although all sectors of energy consump-tion have been increasing, the greatest growth hasoccurred in the production of electricity.

Since the beginning of the industrial revolutionthe impact of man on his environment hasgrown at an ever-increasing pace. Butthe rate of industrial development in differentplaces has not been uniform, and while themore highly developed countries are nowdebating whether and if so how to control theireconomic growth in order to protect thenatural environment, the less developedcountries must increase their rate of industriali-zation if they are to attain comparable standardsof nutrition, housing, clothing, public health,education and so on.

The great changes irtour environment which haveoccurred in recent years, and the still greaterchanges which threaten as higher living standardsand the increasing world population demandever-increasing rates of energy production,have provoked a call for closer control of thesechanges. This demand is greater at present inthe developed countries, where higher livingstandards and more time for recreation allow manto use his environment more intensively, butthere is no reason to doubt that it will spread tothe developing countries. It seems no morethan common sense to urge that the environmentshould be harmed as little as possible.

In most places the decision is not whetheradditional sources of electrical energy should bedeveloped, but how the additional energywhich is required can be best produced.Only about one-tenth of the water powerpotentially available has been developed, butmuch of the remainder is located in ote areas

1

or is not likely to be developed for economicand aesthetic reasons, Even where hydro-electricpower is economically attractive it must besupplemented usually with power obtained fromother sources, because its availability varieswith the seasons. Solar, tidal and geothermalenergy for electricity production are economiconly in certain locations or in special circum-stances. Thus, most electric power in thenear future will be generated in thermal-electricplants based either on burning fossil fuels(coal, oil, natural gas) or on nuclear fission("burning" uranium, plutonium and perhapsthorium). Usually the selection of plant type isinfluenced principally ay considerations associatedwith the cost of the plant and its operation,taking into account other factors includingthe availability of fuel and the reliability of itssources of supply, foreign exchange requirementsand availability, and possible effects onemployment (for example, in coal mines).

The world needs not only more energy to producepower, it needs as well more efficient means ofenergy conversion. The major portion of theenergy now consumed to produce electricity iswasted as heat, which may affect localecological systems. Development ofmore efficient methods for energy conversion wouldreduce the these losses of energy. Generally lessemphasis has been given to development ofmagnetohydrodynamics and other direct conversionprocesses, which need to be investigatedseriously, than into development ofnew sources of power. More emphasis might alsobe placed on improving fuel for powerproduction, for example by gasifying or liquefyingcoal, in ways which could reduce environmentalchange.

Recently, however, increased emphasis has beenplaced on environmental and public healthaspects of electric power production in the morehighly developed countries. The nuclear powerindustry has developed in an atmosphere ofthe utmost caution; probably no other industryhas been so safety conscious. The design and

.1." operation of nuclear power plants, from their in-ception, has stressed public safety and environ-mental protection. Other industries haveasserted that their activities are safe, withoutqualification; the nuclear industry, growing upwith statistics, has instead set limits at ..hickthe probability of harm is consideredacceptably small. Even so, the current trend istoward increasingly strict regulation ofreleases of both radioactivity and waste heat.

The use of atomic energy as compared withfossil fuel for the production of electricity willaffect the environment in a number of ways:

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drastically reducing the mining and transport offuel;

increasing by some 50% the heat released intowater from power plants which are built initially,though in respect of later plants the increase will benegligible;

introducing a very small risk of local release oflethal amounts of radioactive substances, byaccident;

requiring small restricted areas for disposal offission products and for decommissioned reactors;

slightly increasing the world inventory ofkrypton, and later tritium, but decreasingthe inventory of radon in the atmosphere;

virtually eliminating emission ofparticulates, sulphur dioxide, carbon dioxide andmercury to the atmosphere;

eliminating problems in the disposal of fly ash.

The use of fossil fuels developed in an age whichwas too hungry for energy to care overmuch aboutthe consequences. But those consequences arenow being looked at more closely; there arecalls for low-sulphur fuels and for reductions inemissions of sulphur dioxide. The nuclearpower industry is under similar, butdisproportionately heavy, pressure.

There is need for better knowledge of the relation-ship between levels of environmental contami-nation generally and their effects, and forbetter analysis of environmental problems in termsof costs and benefits. These in turn should beconsidered in perspective with other claimson resources. Only then can the best decisions,everything considered, be made as to where,when, what size and what type of powerplants should be built. The aim of both nuclear

and "conventional" industries should be tochange the environment as little as isreasonably practicable.

Future world energy needs

During the past two decades electrical energyconsumption worldwide has increased atabout 8% per year, and this rate of growth hasshown so far little sign of slowing down. It isexpected that it will be maintained for thenext ten years. At present the consumption ofnon-electrical energy is about three times that ofelectrical energy, but total energy consumptionis growing at a lower rate than electricityconsumption. This is reflected in current growthrates of about 3.6% per year for world coalproduction and of about 6.9% per year for worldcrude oil production.

Projections for the longer term are made usuallyon the assumption that the rate of growth indemand for electricity will decrease as populationgrowth rates decrease and as some "saturation"effects are felt, when per capita consumption ofelectricity reaches higher levels than at present.For example, electricity production in Japanincreased at an average rate of 12.4% per yearfrom 1959 to 1968, but it is expected thatthis rate of increase will fall to about 7% per yearby 1980 and to less than 5% per year by 2000.The growth rate in developing countries islikely to be considerably higher than that inindustrialized countries during this period.

If one assumes average growth rates of 8% peryear until 1980 then of 6% per year untilthe year 2000, world electricity consumption inkilowatts would increase from 4900 X 109 kWh(e)in 1970; to 10 500 X 109kWh(e) in 1980;to 33 600 X 109 kWh(e) in 2000.

World energy resources

It is estimated that reserves of mineable coal totalbetween 4 and 8 X 1012 metric tons. Atpresent rates of increasing annual consumptionthis would all be consumed before the year 2100.More reasonable projections are that the rate ofincrease in consumption will begin to decreasebefore 2000, and that coal production willprobably "peak" at about 2100 to 2150 thengradually decrease. At this rate most ofthe world's coal resources would be exhausted by2300 to 2400.

Estimates of recoverable petroleum are in therange of 1.3 to 2.1 X 101 barrels. Even if presentrates of increase in consumption begin todecrease in the near future it is estimated that oilproduction will peak by 1990 to 2000, at a

level less than three times the present level, andthen decrease. This would exhaust most ofthe world's oil resources by the year 2025.

The world's potential water power capacity isabout 3 X 106 megawatts electrical output (MW(e)),of which less than 10% (principally in Europeand North America) has been developed sofar. Presently this constitutes about 28% of thetotal electrical capacity. By the year 2000 it isestimated that about one third of the potentialwater pc capacity will have been developed, atwhich time it will constitute only about 14%of the total electrical capacity. Increasingly insome developed countries there are objections todevelopment of hydro-electric power in thatthis requires the construction of large artificiallakes. Most of the undeveloped water power is inthe developing countries.

Solar energy, ciespiteits large magnitude, is bothintermittent and of low areal density, and isthus not promising as a source for economic large-scale power production in the near term althoughon the basis of recent development it offers hopefor the future. Geothermal and tidal energypotentials are relatively small, and are availableonly in certain locations.The amount of energy from nuclear fissionpotentially available in world uraniumand thorium resources is several orders ofmagnitude greater than the amount Of chemicalenergy in fossil fuels. Present-day types ofnuclear power reactors using uranium-235,however, release only about 1% to 2% of thepotential energy; and for reasons of currenteconomics can use only high-grade uranium ores.On this basis large-scale nuclear power productionusing uranium-235 would not be expected tolast for more than about a century. Breederreactors are being developed, however, and areexpected to become a commercial reality in the1980s; these reactors will be able not onlyto release most of the potential nuclearenergy, but also to use economically large amountsof uranium-238 and thorium which exist,providing reserves for several hundred yearsor longer depending on assumptions made as topopulation growth and per capitaelectricity usage.

Economic production of electrical energy based onnuclear fusion is at present only a hope for thefuture. If the deuterium deuterium fusionreaction can be harnessed the seas constitute amuch larger potential source of energy thanany of the others mentioned above. If, however,the fusion reaction used is based on deuteriumand tritium produced from lithium-6,which seems to be the easier route, the potential

3

energy available will be limited by the amountof lithium-6 which !./y be drawn upon. Oneestimate is that the potential resources of fusionenergy in this case would be about equal onlyto fossil fuel resources.

The market price of fossil fuels will most certainlyincrease as the more easily recoverable resourcesare used up. The same is true of uranium andthorium ores, but the cost of fuel is a smallfraction of the costs of nuclear power, whereasit is the largest part of the cost of "conventional"power, derived from fossil fuels.

The projected role of nuclear power

The primary role of atomic energy is most likelyto be in electric power production, thoughdual-purpose plants will also supply someheat for desalination, space heating and industrialapplications. Other uses, such as ship propul-sion, will be small relative to electricpower production.Atomic energy is already economically competi-tive for base-load application in electrical gridslarge enough to accept unit sizes of about500-600 MW(e) or larger, and there are indi-cations that nuclear plants in the 200 400 MW(e)range may become competitive in somedeveloping countries. It seems likely that nuclearplant orders will account for half the capacityof all orders in some industrinliiad countriesduring the next decade, and tha,...otal installedgenerating capacity worldwide will be 50% nuclearby 2000. It should be noted that since nuclearplants will be used mostly for base-load appli-cation they will generate then more than 50% ofthe total electricity produced.]

For the reasons listed below it is predicted thatnuclear power will account for an increasingfraction of new plant orders, reaching upto 90% of new plant orders by the year 2000:

the long-term trend in the cost of fuel isupward for both fossil and nuclear fuels, but thecost of nuclear power is much less sensitiveto the cost of fuel. This will be true to an evengreater extent for breeder reactors.transportation costs are a large fraction of thedelivered costs of fossil fuels, but only a smallpart of nuclear fuel costs. In addition, onemust consider not only the costs involvedin transportation, but the feasibility of developingfurther transportation systems to move the hugeamounts of coal that would be required ifnuclear power were not developed.environmental protection requirements mayadd substantially to both capital and operatingcosts of fossil-fuelled plants. In some countries,too, the costs of coal are already increasing as a

4

result of measures taken to improve safetyin coal mires, and the need to restore strip-minedareas. Even with improvement of workingconditions in mines there may be problems infinding enough miners. Nuclear plants, however,have been regulated stringently from thebeginning and additional requirements which maybe imposed are expected to involve relativelysmaller cost increases. Enactment of increasinglymore stringent air quality standards inindustrialized countries could accelerate the trendtoward nuclear power plants.

it is said increasingly often that coal reservesshould be conserved as a resource for use inthe chemical industry, rather than being usedas fuel.

It should be stressed that nuclear and conventionalfuels do have a complementary role to play, aswell as a competitive one. Because of the way inwhich load varies with time in an electrical grid,and the nature of the economic characteristicsof nuclear and fossil-fuelled plants, it is mostlikely that the economically optimal system willconsist of a balanced mixture of base-loadnuclear plants and peak-load fossil-fuelled plants.In some countries the balance may be affectedfurther by alternative sources of energy andthe state of their technological development.

The Nuclear Fuel Cycle

The bask: fuel for nuclear power plants todayis uranium; thorium will become important in abreeder reactdr economy, After uranium oreis mined the uranium is separated from theore in the form of a concentrated oxide. (See Fig.2)For the nuclear reactors most commonly usedat present it is necessary also to enrich thenatural uranium slightly, that is, to increase theratio between the fissionable isotope (uranium-235)and the 140 times more plentiful fissionableisotope (uranium-238), which is not easily fission-able but is fertile. This is accomplished by conver-ting uranium oxide into gaseous uranium hexa-fluoride (UF6) and passing this through diffusionequipment in which the relative abundances ofthe lighter and heavier isotopes are varied. .

Gaseous diffusion plants are operated at presentin five countries. In due course they may besupplemented by gas centrifuge plants foruranium enrichment which are now beingdeveloped.

The enriched uranium hexafluoride is processedchemically to metal or oxide, which are thenfabricated into fuel elements and clad with a gas-tight metal tubing. The fuel elements are

Figure 2: The nuclear fuel cycle

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transported to the power station for loading intothe reactor.

Up to this point in the fuel cycle all of the wasteproducts contain only naturally-occurringradionuclides and products useable as fuel whichare recycled from fuel reprocessing. The radiologicalproblems that arise are due only tothe concentration and re-distribution of theseradionuclides. However, in the reactor the fuelundergoes nuclear fission, in which the fuelsplits into radioactive fragments and energy isgiven off in the form of heat which is usedto convert water into steam for driving the turbineswhich produce electricity ... Radioactivematerials are also produced in the reactor bythe interaction of neutrons emitted during fissionwith corrosion products, impurities, fuelcladding and structural materials.

"Spent" fuel elements, in which only afraction of the uranium has been consumed,are removed periodically from the reactor andreplaced with fresh ones. The remaininguranium, the fission products (including gases)and plutonium formed during reactoroperation are i etained essentially within the fuelcladding. Normally it is desirable from theeconomic point of view to reprocess t::e spentfuel to recover the valuable uranium andplutonium. These can then be returned to afuel element fabrication plant for manufactureinto new fuel elements, or the uranium maybe returned to a gaseous diffusion or other plantfor re-enrichment. The fission products andthe remaining transuranic elements are removedand processed so that some of them can beused in industry, research and medicine;

I

the remainder are contained and managr .- helong term as discussed later in this text.plutonium produced from the uranium-2" , ta theinitial fuel is especially important, for thismay be used as new fuel for presentpower reactorsand also for future fast-breeder power reactors.

Well over 99.9% of the radioactivity generated inpower reactors is retained within the fuelelements until they are reprocessed. Because ofthis, and the fact that one fuel reprocessingplant may serve a large number of powerreactors, it is at this stage of the fuel cycle thatlong-term management of radioactive wastesbecomes especially important. Low-levelwastes may be released to the environment,following appropriate treatment, if they can besafely diluted and dispersed. The major objectiveof the high-level waste management programmeis to keep the great majority of the potentiallydangerous wastes isolated from the humanenvironment for a time long enough to allow themto lose their radioactivity thrcugh decay. Asdiscussed later, the techniques used tvaccomplish this degree of isolation differ dependingon the geologic conditions in the various countrieswhere fuel reprocessing is carried out.

One ton of slightly enriched nuclear fuel willproduce about two hundred million kilowatt hoursof electricity, which is enough to satisfy theneeds of about 70000 people for a year(this figure is based on present-day per capitaconsumption in Europe). [See Fig.3]. Reprocessingof this amount of spent fuel gives rise to about0.4 to 0.8 cubic metres of high-level liquidwastes, or about 0.04 cubic metres ofsolidified waste.

Environmental Aspectsof Nuclear Power ProductionAs in any major technical enterprise there areenvironmental aspects of nuclear powerproduction which require particular attention. Inthis respect the nuclear power industry has beensince its inception fully aware of the need toensure public safety and to prevent damage toproperty and to the environment as a whole.

Radioactivity

One of the most obvious'problems associatedwith the nuclear power industry is ic the generationand potential release of radioactive materials.The rate of generation of radioactive materialsin a nuclear reactor is primarily a function of therate of heat production, and hence electricity

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production after making allowance forthermal efficiency.

Provisions are made in the design and siting ofpower reactors and of ancillary nuclearfacilities to cope with potential accidentalreleases of radioactivity as well as with routinereleases. The principal constraints, in general, areimposed by the consideration that must be givento the highly improbable but potentially dangerousserious accident. As a result, radiation doses tomembers of the public at large during routineoperation have been only a very small fraction ofthose from natural background radiation andof the levels set in internationally acceptedradiation protection standards.The technology required both to prevent accidentsand to mitigate their consequences should theyoccur is fundamental to the designing ofnuclear installations in such a way. as to affordmaximum protection to the environment.The safety record of the nuclear industry hasbeen particularly noteworthy: the few accidentsthat have occurred have been well within thecapability of the installations concerned to containthe abnormality and to protect the public.But the projected growth of nuclear power and thepotential public health risks involved, howeversmall, require that diligent controls shouldcontinue to be practised. The public is quite awareof the risks involved, and it is necessary and

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proper that the nuclear industry keep the publicinformed about the careful controls that areexercised to minimize these risks. The timelypublic acceptance of nuclear power may be as im-portant as is the development of the technologyitself.

Low activity liquid and gaseous wastes are releasedroutinely from reactor power stations, fuelfabrication and reprocessing plants afterappropriate treatment. Low activity solid wastes,including the residues from treatment of lowactivity liquids and gases, are generally disposed ofby burial in the ground, although some are beingdisposed of in the deep seas.

High activity liquid wastes arising from fuelreprocessing are concentrated and isolated veryeffectively in long-term storage; subsequentlythey may be converted to a solid form andstored in some form of deep repository.

Thermal discharges

No method of converting heat to electricity usesall the heat which is available. Modern steamturbines operating with fossil fuels and using highpressure and high temperature steam attainthermal efficiencies of 40% or more. Mostpresent-day nuclear power plants are thermallyless efficient than these modern fossil-fuelledpower plants, although they are comparable inthermal efficiency to the average of all fossil-

fuelled power plants now in operation. In fossil-fuelled power plants part of the excess heat isreleased to the atmosphere in the flue gases,whereas in nuclear power plants essentially all ofthe excess heat is transferred to the cooling water.As a result, a nuclear power plant in which thecooling water is used only in one pass through thecooling circuits (a oncethrough design) willdischarge about 50% more waste heat tothe receiving waters than a fossil-fuelled powerplant producing an equal amount of electricity.Gas-cooled and liquid-metal-cooled advancedreactors of the future are expected to attain higherthermal efficiencies, equal to or exceeding thoseof conventional plants.

There is no doubt that the discharge of waste heatinto public water: .foes modify the aquatic environ-ment. The question is whether this modificationis perceptibly harmful or beneficial, and whether itaffects water use significantly. Knowledge ofthe aquatic life present in the receiving waters,coupled with use of engineering techniquesdesigned to minimize the impact of the'release ofwaste heat, can enable power plants to meetthe desired standards of water quality. If there isnot enough water available to meet thesestandards with a once-through cooling system thenprovision must be made for alternative systems:for example, cooling towers or cooling pondsare being used in many power plants, both nuclearand conventional, to recycle cooling water andthus reduce the effects of the release of waste heatto accepcable levels.

Transportation

The various components of the nuclear fuel cycleare inevitably at different locations a powerstation here, a reprocessing plant there. This mayrequire the transport of nuclear materials, rangingfrom ores to spent fuel elements and solidifiedhigh-level wastes, over large distances. Althoughthe number of such shipments in transit at anygiven time may become quite high, the accidentrate in the transport of hazardous cargoes is muchlower than that for normal shipments. The IAEAhas drawn up regulations applicable to all modesof transport by normal conveyances which havebeen widely accepted by national authoritiesand by organizations concerned with the inter-national transport of goods. The regulations pro-vide for the design and testing of containers forhighly radioactive shipments to standards whichensure that even in the event of a serious accident

there should be no loss of radioactive materialto the environment.

Decommissioning of nuclear installations

This problem is touched on here in order topaint as complete a picture as possible of thedifficulties which can arise in connection withnuclear power; it is not so much that itsimportance is comparable with that of the otherproblems discussed.

Taking into account the 25 to 35 year life ofnuclear power plants, we must expect thatin about 1990 a number of power plants will needto be decommissioned, and that thereafter thisnumber will rise rapidly. The decommissioning ofpower stations, even conventional ones (whichare as a rule larger in size than nuclear powerplants), is a costly procedure. Despite theirsmaller size, nuclear power plants would be morecostly and difficult to decommission becauseof the radioactive substances remaining inthe structure of the reactor and the primarycircuit, although these are only a small part ofthe whole installation. If there has been anaccident in the reactor the problems of dismantlingwill be more difficult, and if a serious accidenthas occurred it may be prudent to abandonthe reactor in place, taking appropriate precautionsto avoid spread of radioactive materials and torestrict access to the area. It can be said thaton the basis of present technology the decommis-sioning of reactors is quite feasible: successfuloperations of this type have been undertaken(the SL-1 and Elk River reactors in the US, andthe Lucens reactor in Switzerland).

The problem now being studied is concernedrather with the ease and cost of operations. It isbelieved and postulated that some extra meansadopted at the design stage could make decommis-sioning much easier. Even the basic need forcomplete decommissioning of nuclear powerinstallations is being discussed. It seems quitepossible to provide for siting of nuclear powerplants in nuclear power "parks" whichwould continue to be used during long periods'of time. New units would be built there toreplace old ones, and public access to the sitecould be restricted, making it unnecessary toremove completely the most complex componentsof obsolete installations. Many factors enterinto this discussion, among them the needfor adequate cooling water resources for operatingfacilities.

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I

radiation protection

standaIntroductionNuclear power stations are designed and operatedin such a way that they release only anextremely small amount of radioactivity to theenvironment during routine operation or even inthe event of a major accident.Almost all radioactivity is preventedfrom bcing releasedby one of the following four mechanisms:

radioactive decay at the station;containment within components during thelife-time of the reactor system;periodic removal to fuel reprocessing plantswithin the used fuel elements; anddisposal in solid waste.

The amounts of radioactivity in gaseous andliquid effluents released to the environment arelimited by law in each country to meet standardsof radiation exposure of the general public, andmake up a very small fraction of the total amountgenerated.

National radiation exposure standards quitegenerally are based on recommendationsby the International Commission on RadiologicalProtection (ICRP) for maximum permissibleexternal and internal (i.e., from the intakeof radionuclides) exposure. These recommen-dations have evolved from numerous studiesin many countries of somatic effectsand hereditary effects (damage to descendants) athigh radiation exposures. Information is alsoobtained from animal research. Doselimits have been established at radiation exposurelevels which are considerably lower, at whichsomatic damage and hereditary effects arebelieved to be at very low incidence. Maximumpermissible body burdens (MPBB) andmaximum permissible concentrations(MPC) of radionuclides in air and water have beencalculated from these dose limits on the basisof observation of the metabolism, i.e.retention, movement, distribution and eliminationof radioactive material from the body of a'references roan'.

8 tt14

The derivation of radiation protection standardshas been clearly formulated in a series ofICRP publications, but it is a complex undertaking.Radiation effects depend on the type of radiation,its intensity, the exposure period, the extent towhich the body is irradiated, and a number of factorsthat affect the radiation susceptibility of a person.In applying information from ahimal studies to humansdifferences in metabolism and response must beevaluated carefully. Further, effects at maximumpermissible values have been computedby assuming that the ratio of effect to exposureis the same as at the much higher exposures at whicheffects were observed (the linear dose-effecthypothesis). This calculation is believed to be safe andconservative, although the actual relationshipscannot be proved on the basis of direct observation.

The radiation exposure of the public at large as aresult of the operation of nuclear power facilities iscontrolled usually by limiting the rates ofrelease and concentration of radionuclides ineffluents so that standards will not be exceededfor the group of persons exposed to the highestradiation levels. Compliance with theselimits is checked by measuring the radioactivecontent of effluents. In addition, environmentalsurveillance may be undertaken to confirm thatenvironmental reconcentration processes donot lead to undue exposure of membersof the public. Although all environmental processesare considered, experience generally has shownthat certain radionuclides and environmentalpathways make the greatest contributionsto radiation dose. These radionuclides and path-ways and the population group receiving thehighest radiation doses are termed "critical" andare subject to special attention in environ-mental surveillance programmes. Theenvironment may also be monitored to check oneffluent data and to provide direct radiationmeasurements in emergencies.

In some countries there has arisen recently agrowing opposition to the building and operationof nuclear power stations. Concern aboutradioactivity discharged routinely in effluent airand water has three foci:

*that radiation effects at reported exposure levelscould be much more severe than indicated inICRP recommendations;

that radiation exposures could be much greaterthan computed from discharge data; andthat radiation effects, although believed onthe basis of the linear doseeffect hypothesis tooccur infrequently, nevertheless could beunacceptable.

Those who challenge the ICRP standards arguethat exposure of a large population group tothe allowable maximum would increasemarkedly the number of cancer cases, and wouldcause thousands of genetic deaths. At leastone research worker has carried this general lineof argument so far as to calculate a correlationbetween very low levels of radioactive emissionsfrom power plants (which are a small fractionof natural background) and infant mortality.

The complexity of the subject does not permit anadequate treatment in a booklet of this type,but several key points should be stressed.

When discussing existing radiation protectionstandards one can state that not all scientists agreeabout them. As one journalist commented:"When scientists disagree, reasonable non-scientists have to fall back on the faith of themajority." The guidance that forms thebackbone of radiation protection standards comesfrom independent scientists chosen specificallyfor their competence in the field. No singleindividual nor single agency has made these basicdeterminations unilaterally.

The radiation protection standards which aregenerally acceptable today are by no meansfixed and final. Data on the effects of radiation,from both national and international programmes,are reviewed by expert committees on acontinuing basis both nationally and internationally.

From the biomedical standpoint arguments as tothe adequacy of current standards centre largelyon the calculation of risk for the very lowdose range; that is, at the level of the naturalbackground and below. To make such calculationsone must make certain assumptions and extra-polate from the region of high dose rates and doselevels, for which there is experimental evidence,to exposure levels at such low dose rates anddose levels that effects, if any, have not beenobservable. All such calculations containa degree of uncertainty, and arguments have arisenas to what that degree of uncertainty is. Someeven ignore this uncertainty entirely andbase their public statements upon the uppervalues calculated by them, treating them as fact.As one observer has stated: "They put forththeir projections not as hypothesis but asfact, saying their mortality rates will notmight occur." All such calculations, to

be meaningful, must refloat the uncertaintiesinvolved. Scientists generally use a lineardose/effect relationship to project from the dosesat which quantitative information has beenobtained to the low dose region. However, ICRPhas cautioned that:

"It must be borne in mind that in some instancesthis may lead to a gross overestimate of theincidence of effects from chronic low levelexposure; indeed, some of the effects may notoccur at all."

The arguments over accuracy of calculation ofrisk from exposure at levels comparable tobackground or lower are somewhat academic fortwo reasons:

They led those who first adopted this approachto the assessment of risk to the conclusionthat until more is known about low level effects,to be prudent one should not expose peopleto any higher levels of radiation than is necessary.Although upper limits were identified as aframe of reference these were recommended inaccordance with a guiding philosophy which gaveencouragement that exposures be kept as lowas was practicable.People are being exposed to only smallfractions of the amounts identified as upper limitsas a result of nuclear power production. Radiationprotection standards as implemented are servingto keep exposures received by the public as aresult of nuclear power production well below thelevels identified as the maximum allowable. Suchexposures averaged over large population groupsare but a small fraction of the natural background,and will continue to remain so for any reasonableprojections of the growth of nuclear power pro-duction that one can now make.

Concern about possible catastrophic accidents hasits source in the expected rapid increase in thenumber of stations. Speculations as to thefrequency of accidents and their possible effectsare extensive but arbitrary, in view of thebrevity of operating experience 15 years for afew small reactors and 10 years for some ofintermediate size. Until now, no widespread acci-dental environmental contamination arisingfrom the operation of a nuclear powerstation has occurred, and no adverse effect onpublic health has been observed to resultfrom operating such stations. The onlysuch incident that has occurred was at a plutoniumproducing reactor (at Windscale in the UK)which was not equipped with theengineered safeguards required for nuclear powerreactors, and even in that situation there wasno demonstrable harm to any member ofthe public.

Basic Radiation ConceptsRadionuclides are formed within nuclear reactorsby several processes. Fission products aregenerated by nuclear fission within the fuel.Activation products arise through interaction ofneutrons with materials coolant medium, reactorvessel, cladding, gases dissolved in liquidcoolant that surround the fuel. Transuraniumelements (neptunium, plutonium, etc.) areformed by neutron activation of the fuel. Thefuel itself is composed of natural radioactivematerial, usually uranium.

Most radionuclides remain in place within fuelor reactor materials. A small fraction leaksfrom fuel through minute imperfections in itscladding or erodes from other materials or recoilsfrom them, and combines with the radioactivityoriginating in the coolant medium. Much ofthis radioactive material, in turn, decays or isretained within the system. A small fractionroutinely leaves the system as gaseous andparticulate effluents to air, in liquid wastesdischarged to rivers, lakes or oceans, and in solidwastes for burial at specially controlled sites.After use, the fuel is first stored at thereactor to reduce its radiation level by decay,and is then taken to a fuel reprocessing plant.

The amount of radioactivity associated withinventories or releases is commonly expressed incuries'. Different radionuclides not onlyhave wide ranges of values for their radioactive"half-lives", the periods during which theiractivity decays by half, but also for the amountsthat may be deposited in different organs ofthe body, if ingested or inhaled, and intheir rates of elimination from the body. Todetermine biological effects one must knownot only about the quantities of the specificradionuclide involved in curies but alsothe type of radiation emitted as the atomsdisintegrate (alpha, beta or gamma), the totalamount of energy emitted per disintegration, therate at which this energy is absorbed in anorgan, the biological and radioactive rates ofelimination and the mass and radiosensitivity ofthe tissue involved.

These factors are then considered in thecalculation of radiation dose. The basic unit ofdose for measuring the ionizing radiationenergy absorbed ir passing through a mediumsuch as body tissue is the rad§ (one-thousandthof a rad is a milliral, abbreviated mrad). For

A curie is a special unit of activity equalling3.7 X 10" nuclear transformations per second.§ A rad is defined es the unit of adsorbed dose equalto 0.01 Joules per kilogram In any medium.

10

radiation protection purposes, it is desirable toconsider the rays of absorbed energy fromeach type of radiation weighted by factors charac-terizing quality, biological effects, distributionfactor and any other necessary modifying factors.The quantity that is obtained by the weightingof the absorbed dose by these modifyingfactors is called the dose equivalent.

In this paper, the shorter term 'dose' is sometimesused for the sake of convenience, even thoughthe meaning is strictly 'dose equivalent'. The doseequivalent is equal numerically to the dose inrads multiplied by the Quality Factor andany other modifying factors recommended byICRP. The unit of dose equivalent is the rem.In this way, the biological effect fromdifferent types of radiation or from a mixture ofradiations can be expressed on a common scale,which has as its unit the rem (one-thousandthof a rem is a millirem, abbreviated mrem).

The Quality Factor for gamma rays and betaparticles is 1; and for alpha particles 10. Thus,assuming other modifying factors to beunity, exposure to 1 rad of gamma rays is equiva-lent to a dose of 1 rem; to 1 rad of alphaparticles, 10 rams. Doses described in terms oframs are additive. A person absorbing1 rad each of alpha and gamma radiation in an organwould receive a total dose of 11 rams inthat organ.

Biological Effects of RadiationBiological damage by ionizing radiation has beenstudied intensively for many decades. The effectsof radiation on biological systems have beenexamined in animal experiments, radiationaccident victims, survivors of atomic bombs atHiroshima and Nagasaki, patients undergoingradiation therapy, and persons exposed toradiation in the course of their work. Biologicaleffects are classified broadly as somatic,occurring within the exposed individual, andhereditary, those affecting descendants byaltering genes. Exposures are classified as acute(brief) and chronic (continuous). An acuteexposure at a radiation dose of hundredsof rads produces almost immediate effects, knownas the acute radiation syndrome. Most personsincur exposures that are chronic at low levels;effects, if any, may be delayed for decades.

Some typical late somatic effects manifested in manfrom high doses include leukemia and othermalignancies among patients treated byX- rays for spondylitis and among atom bomb sur-vivors, lung cancer in uranium miners, andbone cancer among radium watch dial painters.

Alterations (mutations) of genes can be producedby radiation, as well as by chemicalmutagens and physical causes such as heat.Mutations are usually considered to be detrimental.Those occurring in germ cells can be transmittedto offspring; their effects, which range inseverity from inconspicuous to lethal, may notbe revealed until many generations have passed.The United Nations Scientific Committee onthe Effects of Atomic Radiation (UNSCEAR)reports that serious genetic detects are observedin about one per cent of live births and thatnatural radiation can account for no morethan a small fraction of natural mutations in man.

Some questions about the biological effects ofradiation remain unanswered, particularly thoseconcerning somatic and hereditary damage fromcontinuous doses of radiation not much higherthan the natural background. Is there a safethreshold dose for somatic effects that is,a level below which no effects can be observed?Leukemia induction has been demonstratedclearly at doses above 100 rads, according to theICRP, but the existence of a threshold dosebelow this level is still uncertain. UNSCEARindicates that cataract/ occur after chronicexposure to 500 rads of oeta or gamma radiationor 200 rads of mixed gamma and neutronradiation. Because of the limitation ofnumbers in experimental populations, animal studiesof genetic exposure fail to indicate a dose ordose rate below which the probability ofeffect is zero. Some controversy exists amonggeneticists about this; for example, a recentinvestigation indicates that among femalemice there does occur what is for practical pur-poses a threshold dose rate.

Some concern is often voiced that additional here-ditary damage may be incurred by the generalpopulation from proliferating nuclearactivities. Not only the affected individual's mis-fortune but the burden imposed on futuresociety by an increase in the number ofpersons with mutated genes must be considered aswell. A subject of current interest is the amountof exposure equivalent to the "doubling" dose,that is, the additional quantity of accumulateddose to each member of a population withinchild-bearing age that effects an eventual doublingof the mutation rate. Present estimates,according to UNSCEAR, are that a chronicirradiation of 100 rads or possibly higher is neces-sary. Since the dose from natural radioactivity ismuch less than one per cent of this range, it isbelieved that an additional dose on the order ofthat from nature would cause no measurableina ease in the mutation rate.

There is insufficient information at the moment togive unequivocal answers to all questions ofradiation effects. For example, at lowdoses, effects may vary with the dose rate. Not allforms of injury may be known. To what degreedoes tissue repair damage after irradiation? Isthe frequency of effects greater for personscontinuously exposed to higher than normalnatural background radioactivity? In view ofthese incompletely answered questions aconservative approach has been used in arriving atradiation protection standards. In the mean-time work to answer these questions is continuing.

Knowledge about the relationship between doseand frequency of effects is required by thoseresponsible for establishing permissible humanexposure levels. Studies of abnormallyexposed persons mentioned previously haveyielded much information, but dose-responseestimates based on the data cm very approximatedue to uncertainties in total dose deliveredor total exposure period.

Research with animals has been valuable inconfirming the effects from high doses observedin man, but the results canriot be relateddirectly to man due to inherent biologicaldifferences. Radiation sensitivity is too variablebetween species or even strains to enable thedrawing of valid conclusions about threshold levelsor the occurrence of delayed effects fromchronic exposure. Moreover, statistically accept-able studies require vast populations exposedto radiation near background dose levels.

In the absence of definite evidence, frequency ofeffects can be related to low doses in severalways. A conservative method is to assumeno threshold and extrapolate a straight linedownwr -d to zero dose from the higher dose-responsi 1Nels where more data are available. Thisprovides a line of maximum likely risk. On theother hand, one may select a threshold doselevel below which no response is believed to occuran approach used to set tolerance standards formany toxic substances. The latter requiresdecisions concerning the threshold leveland the shape of the dose-response line.

Basic Radiation ProtectionStandardsThe basic standards for radiation protection havebeen recommended by the International Commissionon Radiological Protection (ICRP). The ICRP is anindependent body of 13 internationally recognizedexperts drawn from many countries and a variety ofprofessions genetics, biologyoradiobiology,medicine,

11

chemistry, physics, radiology, engineering, mathe-matics, etc. The ICRP was formed in 1928 underthe auspices of the Second International Congressof Radiology to lay down guidelines to themedical professions for exposures toX-rays and radium. In 1950, the Commission wasreconstituted to provide radiation protectionguides for the increasing application of theatom for power production, in laboratory researchand in industrial processes, and for the handlingof radioactive waste, and so on.

The function of the ICRP is solely advisory; itconsiders fundamental principles upon whichradiation control practices can be based.Recommendations by ICRP have no legal force,recognising that the factors affecting risk-benefit evaluations may vary from nation tonation. Many countries have established nationalcommittees of experts to assess their own national,economic and social considerations for theformulation of policy and regulations.For example, the United Kingdom has the MedicalResearch Council's Committee on ProtectionAgainst Ionizing Radiation, Japan has theRadiation Council, and the U.S. has the NationalCouncil on Radiation Protection andMeasurements. The United Nations has authorizedthe International Atomic Energy Agency toset standards for its operations.

In formulating dose limits the ICRP considersthat, if man wishes to obtain the benefitsof nuclear applications, he must recognize thatthere is a degree of risk involved and thatthe benefits must be worth the assumed risk.According to the ICRP, "the objectives of radiationprotection are to prevent acute radiation effects,and to limit the risks of late effects to anacceptable level". For purposes of radiationprcitection, any exposure is assumed to entail a riskof biological damage, a risk that increases inproportion to the dose accumulated. In otherwords, the frequency of effects such as leukemiaor cataract formation observed at high dosesfor relatively short periods has been extrapolatedlinearly to low chronic radiation doses. Asdiscussed previously, this approach is conservative,expressing maximum likely risk and implyingthat there is no wholly safe radiation dose. TheICRP states in its Report No.9 that, in absence ofpositive knowledge that a threshold dose level

_exists, "the policy of assuming a risk of injury atlow doses is the most reasonable basis forradiation protection" even though suchcalculations may over-estimate the real riskinvolved. Therefore, the basic recommendationof the ICRP is that radiation doses should beas low as is practicable and in any case should notexceed dose limits prescribed for various organs.

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el is

The latest dose limit recommendations for somaticeffects in individuals and for hereditary effectsin whole populations were adopted by theICRP as from 17 September, 1965, and arepublished in Report No. 9, referred to earlier. Thelimits for individuals are expressed as doses permit-ted to various organs and tissues in the body,considering the radiation sensitivity andsize of these tissues.

Two categories of individuals are recognized fordose limit purposes: adults exposed in thecourse of their work and individual members ofthe public. This distinction is made becauseradiation workers constitute a small populationthat has accepted employment voluntarily andundergoes periodic medical ereminations.The hazards to which they may be exposed areanticipated normally and are monitored andcontrolled to ensure that pern:heit,le dosevalues are not exceeded. The general public, onthe other hand, is a much larger populationand therefore may accumulate a greaternumber of radiation effects. Members of thispopulation may have no choice about exposureand may receive no direct benefit from it.They may be exposed environmentally for agreater number of years than the typical durationof employment In addition, the public includeschildren and embryos who are more sensitive toradiation, and adults who may be moresusceptible to damage. For these reasons, doselimits for individual members of the publicare recommended to be 10 per cent of the annualdoses permitted for radiation workers.The ICRP recommendations given in Report No. 9for individual members of the public are listed inTable I.

Table I.Dose Limit for Members of the Public

Organ or tissue Dose limit, rem/year

Gonads, red bone-marrow

Skin, bone or thyroid

Hands & forearms; feet & ankles

Other single organs

0.53.07.5

1.5

Gonads and red bone-marrow are considered to bethe critical organs when the whole-body is exposed uni-formly; dose limits for these omens also apply to allcases of uniform irradiation of the whole body.

For children up to 16 years of age the dose limitfor the thyroid is 1.5 rems/yesr.

The most stringent dose limitation is to ensure thatthe risk of damage to the total present andfuture genetic structure of the generalpublic remains exceedingly low. The ICRP assumesthat hereditary effects are related linearly to thegonad dose. It recommends that the "geneticdose" to the population should be kept tothe minimum amount consistent with necessity aneshould certainly not exceed 5 reins from allsources additional to the dose f;om natural back-ground and from medical procedures over thenormal period of child-bearing, taken to be30 years. The genetic dose limit is to be appliedas an average to the total population, allowingsome members, such as radiation workers, toreceive higher doses since others are likelyto experience lower exposures.

The ICRP deems it important that no oneradiation source, such as nuclear power plants,contribute inordinately to the population dose.The commission recommends that anyunnecessary exposure to radiationworkers and the public alike be avoided and thatall doses be kept as low as is readily achievable,taking into consideration economic andsocial factors.

The dose inc. rred in any organ or tissue is the sumof exposurei.om external and internal sources.The total dc,a, particularly from internaldeposits of radionuclides, is difficult to measuredirectly. Secondary standards have thereforebeen computed by the ICRP to limit concentra-tions of individual radionuclides in inhaledair and drinking water, to be used whenthese represent the major source of radionuclidesfor the exposed group. Such values are basedon primary dose limits coasidering the half-life, types of radiation, transportability and some-times the chemical form of the radionuclide,and the fraction absorbed by each organ(or tissue), the period of retention, organ size, andaverage daily inhalation of air and consumptionof water by a 'reference' man. 'Reference'man is a model representing the averageanatomical and physiological characteristics ofEuropean and North American adults. Theorgan for which the lowest allowable concentrationof a radionuclide is set is referred to as thecritical organ. These MPC values formembers of the public are also one-tenth as largeas those for radiation workers.

Derived Release LimitsThe dose a nuclear facility contributes to eachmember of the public is impossible to determinein actual practice since exposure would need

to be measured individually and distinguishedfrom natural and other, man-made contributions.Instead, derived release limits have been developedfor application in the facility design andoperation to ensure that radioactive dischargesdo not exceed the primary ICRP dose limits forthe public. Such limits consist of upper values forthe rates of release of radioactive materialsfrom an installation or for radioactivity levels inenvironmental media that represent pathwaysfor movement of radionuclides from thesource to humans. Derived limits must bepromulgated and applied with restraint becausea proliferation of them, particularly thosedeveloped for local conditions, could lead toconfusion that would undermine their purpose.

Derived limits sometimes include values for theradionuclide concentrations in effluents andare set as MPC values for air and water atthe boundary of controlled areas around nuclearpower stations, atomic research laboratories,etc. They may be established for individualradionuclides or for gross radioactivity; in the lattercase the limits are more conservative. Inaddition or as an alternative, releaselimits may be set considering the dispersion andconcentration of critical radionuclides alongpathways to critical populations, so that thedischarge limit will not lead to an exceeding of theappropriate dose limit for the general public.For example, at the Windscale reprocessingplant, such release limits have been derived forruthenium-106 concentrations in Porphyraseaweed from which laverbread is prepared, andfor external dose to fishermen from radio-nuclides retained by silt in the local estuary. Theregulatory limits for releases are expressed in curiesper unit time, usually three months or a year.

Figure 4: Podiatry. to men for radioactive rdeeeee to air

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Figure 5: Pathways to man for radioactive releases to water here in Table II pertain to the gonadal dose, whichwas computed because the gonads are theorgan receiving the highest estimated dose.IWATER

I IRTDFOOD

RIGA EEEO ED I

I AQUATICON

IVEGETATN

4!ANIMALS FISH

I I MAN

Various pathways by which radioactivitydischargedto water and air reach man are shownin Figures 4 and 5.

The development of derived secondary standardsrequires quantitative information concerningdischarged radionuclides, their environmentalbehaviour in moving from a source to potentiallyexposed populations, and the characteristicsof the population. Considerable data areavailable on environmental processes such asatmospheric dispersion, reconcentration by fish,and transfer from cow's feed to milk. Invariably,surveys at proposed facility sites are requiredto identify critical radionuclides, pathwaysand populations, and to determine theextent of the effects of local environmentalprocesses on the behaviour of radioactive materials.

Natural RadioactivityThe natural ionizing radiation to which man hasbeen exposed continuously provides a basisfor evaluating potential effects from low-levelman-made sources. Natural radiation results fromcosmic rays which bombard the earth con-tinuously from outer space, and from the decayof radioactive substances on earth. Doserates from these sources to individuals are highlyvariable, depending on elevation above sea level,local geology, seasons, dietary habits, timespent outdoors, type of residential construction,and so on.

The average dose rate received annually by theworld population from natural sources wasestimated for several critical body organsby UNSCEAR in its report to the UN GeneralAssembly for 1988. The data summarized

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Ozo

Cosmic rays striking the atmosphere cause multiplenuclear reactions that yield radiations of manyenergies. . Dose rates to man are highly dependenton altitude and slightly on latitude. At sealevel, the dose rate is estimated to be 28 mrad/yearat middle latitudes and about 10 per cent lower atthe equator. The dose rate approximatelydoubles for each 1.5 kilometres above sea levelfor the first several kilometres. Thus, dosesfrom this source are of greater significanceto populations living at high altitudes, aircraftcrews, air travellers, and space explorers.

Cosmic rays also produce radionuclides throughinteractions with nuclei in air, land and water.These may contribute to internalhuman dose through inhalation or ingestion. Themost abundant long-lived radionuclide in airfrom this source is carbon-14 at a concentrationof 1.3 to 1.8 X 1042 curies per cubic metre,with beryllium-7 at slightly lower concentrationsand considerably smaller amounts of tritium(hydrogen -3), phosphorous -32, and a number of others.

The earth contains other radionuclides believedto have been formed during its creation, long-lived primordial radioactivity derived mainlyfrom uranium and thorium, with small amounts ofpotassium -40, and traces of rubidium-87,vanadium-50,indium-115 and several others. Uranium and thoriumhave many decay products,of which radium-226 andgaseous radioisotopes of radonare of particular interest.

All of these naturally occurring radionuclides aresources of external exposure, mostly fromground deposits and to a certain extent fromconstruction materials such as brick, concrete, andgranite. Dose rates average 47 mrad/year.This value varies for different regions, beingapproximately 4 times higher for certain graniteregions in France and as high as 290 and800 mrad/year in monazite sand regions of Braziland India respectively. Radon gas and itsradioactive daughters in air are also externalsources, but contribute only a small fraction to theexternal gonad dose.

The internal dose from natural long-livedradionuclides results mostly from potassium-40, anisotope of elemental potassium. This is anormal component of the body and is maintainedat its usual level by intake in food and bymetabolic turnover. Carbon-14 and rubidium -87taken in in food and water together contributeabout 1 mrad/year. Radon-222 and a daughterproduct, polonium-210, taken in mostlyfrom air, contribute about 0.6 mrad/year.

Table II.Dose Rates from Natural Radioactivity*

Source Dose. mrad

External Irradiation

Cosmic rays 28.7Terrestrial radiation 50

Internal RadiationsoK

20other radionuclides 1.6

Total 100

estimated by UNSCEAR as average annual doseto gonads received by weld population.

Table Ill.Summary of Annual Whole-Body doses per Capita inthe United Stites from ManMade Sources

Radiation Source

Medical

Diagnostic

Dose, mrem

103Therapeutic 6Radiopharrnaceutical 2

Occupational 0.8

Environmental

Global fallout 4Worldwide 'H and "Kr 0.05AEC installations 0.01Nuclear power reactors 0.002Fuel reprocessing 0.0008

Miscellaneous 2.6

Total 114

Natural 130

estimated for yew 1971 by the US. EnvironmentalProtection Agency

Man-Made Sources of RadiationExposun3The world-wide population dose from man-maderadiation sources is still less than thatincurred from natural radioactivity, although the

background level is being approached in at leastone industrialized nation. The average per capitadose in the United States is estimated for1971 to be 114 mrem, compared to the averagedose of 130 mrem/year from nature. Mostexposure is received as a result of medicalprocedures for diagnosis and treatment of disease.Global contamination of the environment withradionuclides is primarily from atmospherictesting of nuclear weapons, but contributes negli-gibly to average per capita dose. Typicalannual whole-body doses in the United Statesfrom various man-made sources per capitaare summarized in Table I I I, where they are com-pared with that from nature.

Studies conducted by the US Public HealthService showed the main contributor ofexposure in The medical arts to be diagnosticradiography. It is estimated that about 90 per centof the total dose to the US population fromman-made sources in 1971 was received fromthis source. Approximately 5 per cent resultedfrom irradiation for treatment of malignantand non-malignant diseases. Radioactivepharmaceuticals contributed less, and diagnosticdental radiography, negligibly.

Occupational exposure did not add appreciablyto the total population dose. The portion ofthe United States population classified asradiation workers in 1969 was 0.4 per cent; theaverage radiation dose was 210 mrems/year.Most exposures higher than this were incurred bymedical personnel.

External population exposure from fallout arisesfrom radiations of environmental deposits, andinternal exposures arise from contaminatedfood, water, and air passing through or absorbedby the body. Most of the dose is fromstrontium-90 (half-life of 28.5 years) incorporatedin bone tissues. Additional exposure is fromexternal irradiation by caesium-137 (half-life of30 years), and, to a minor degree, from internalirradiation by several long-lived radio-nuclides, mainly carbon-14 (5730 years) andcaesium-137. Atmospheric nuclear testinghas now been reduced significantly hence falloutdebris from recent and older tests has beendiminishing.

Negligible population exposure in the UnitedStates resulted from radioactive releasesfrom 13 operating nuclear power stations. Theestimated average represents a very small fractionof the dose from natural or other man-madesources.

Operation of fuel reprocessing plants and USAECfacilities also resulted in minute exposure to

15

the total population. Larger, but still small, dosesare contributed from worldwide distributionof man-made tritium in surface water andkrypton-85 in the atmosphere. Most of thetritium has arisen from previous atmospherictesting of nuclear weapons; smallerquantities are due to natural tritium andthe amount from nuclear power reactors is a smallfraction of the total.

Miscellaneous sources of radiation exposureinclude colour television sets, luminous watchdials, radiation gauges, static eliminators, and soon. These products contributed an average doseof 1.6 mrem/year. Transport of passengersand crews in aircraft adds 1 mrem/yearto the average population dose, based on theaverage increase in dose equivalent rate from flightat an altitude of 9 kilometres of 0.7 mrem/hour.The average air crewman was estimated toreceive 670 mrem/year.

Doses from man-made radiation in other nationswould appear to be contingent on local medicalpractices involving radiation and their rateof use by the public. Doses from other sourceswould not be expected to differ drasticallysince the major contributor is global fallout.

The average population dose in the United Statesin 1971 from nuclear power reactors and allother nuclear facilities is estimated to be0.013 mrem. This represents 0.008 per cent of thegenetic population dose limit of 5 mrems in30 years. Ocher countries report similarly smallcontributions from nuclear power reactors.In the United Kingdom reactor operation at 11sites in 1970 yielded an estimated dose ofless than 0.003 mrem/year to the average indivi-dual. Monitoring at the site of 160-MW(e) gascooled Tokai and the 330 -MW(e) boiling waterTsuruga stations in Japan has shown nomeasurable addition to environmentalradioactivity since operations commenced. Smallbut distinct increases above background radio-activity levels were reported from operationof the twin 200 MW(e) boiling water reactors atTarapur, India, but concentrations were wellbelow permissible levels.

The experience of many countries in the safeoperation of a number of types of nuclear reactorshas been most impressive and encouraging.Although there have been malfunctionsof nuclear power reactors, in no case has therebeen release of radioactivity to the environmentin amounts large enough to result in overexposureof the general public. However, from thislimited experience, it cannot be assumed thatthe probability of release of large amountsof radioactivity to the environment as a cons.-

16

quence of an accident with a nuclear powerreactor is zero. It is safe to assume perhaps thatthe probability of occurrence of majoraccidents is many orders of magnitude smallerthan that of minor accidents, and majoraccidents will occur very, very infrequently andare not to be expected in the lifetime (approxi-mately 30 years) of any given power reactor.A major accident is commonly consideredto refer to one involving the release of thousandsto a few hundred million curies of radio-activity to the environment. The probability ofmajor accidents with modern nuclear powerreactors of 1000 MW(e) or more is unknown, butguesses range from as low as 104 to as high as10" accidents per reactor per year, depending onthe severity of the accident. The consequencesof an accident would depend, of course, notonly on the amount of radioactivity released tothe environment but upon many otherfactors: for example, the average age of thefission products, the type and quantityof fissile and transuranic elements present, thekind of release (i.e., to river, up the stack,release following meltdown and explosive ruptureof the primary and leakage of the secondarycontainment), the meteorological conditions atthe time (wind speed and direction, inversionconditions, rainout, particle size distribution), thepopulation density in the neighbourhood ofthe plant and the rapidity and efficiency withwhich remedial measures are taken (e g., theimplementation of a well-though-out andfrequently rehearsed emergency procedure thatprovides safe and rapid relocation of the poten-tially exposed population and proper care ofinjured).

Several attempts have been made to determine theconsequences of releases of substantial amountsofthe radioactive products in a reactor accident.Under adverse but possible meteorological con-ditions and with an emergency system andan early implemented evacuation proceduremeeting the minimum requirements of a goodpublic health prigram, it would seem that evenwith 25% release of the iodine isotopes and 100%release of the no. le gases (or a few hundredmillion curies) from a 1000 MW(e) power reactor,the exposure to a typical population in ametropolitan area would be maintained at lessthan 2.5 X 106 man -rams of total body doseand 30 X 106 man-rams thyroid dose. if oneapplied the conservative assumption that there is acompletely linear relationship between thisdose and the number of fatal malignancies, life

A Japanese being examined under a Sdntiscanner,which may be used to delineate the uptake of radioisotopeswithin the body as a port of diagnostic procedures.

4

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17

shortening death equivalents, and firstgeneration genetic deaths and applied thecoefficients of ICRP, this hypothetical worst casedesign (credible) accident would account forsomething less than 500 deaths. This numberwould include both the delayed deaths whenapplying the linear hypothesis and the few promptdeaths from "radiation sickness" of thosereceiving large exposures of greaterthan about 500 rem. The probability of such anaccident is considered to be extremely smallbecause of the engineered safety featuresthat are applied.

At the lower end of the scale of major accidents,a few thousand curies (rather than a few hundredmillion curies) of radioactive materialreleased to the environment would be expectedto contribute a total body dose of only about25 man-rems and, on the same linearhypothesis, this would result in no radiationdeaths.

If one very conservatively assumes that the mostsevere accidents would occur at a frequencyof 10-s accidents per reactor year they mightcontribute, in a system of 500 operating nuclearpower plants, up to two to three deaths peryear. These risks can be compared, for example,with a hundred deaths per year in the UnitedStates of people struck by lightning (88 in1967 and 129 in 1968). The risks are very smallset against the number of deaths in a typical

18

year resulting from accidents in air transportationin the United States (1799 in 1967 and 1904in 1968). Psychological and public acceptancefactors need to be taken into consideration,however, when considering possible nuclear sod.dents. How would the public react to amajor reactor accident every twenty or thirtyyears? and what will be its consequenceson the reactor programme? There is a populartendency to accept familiar hazards whilereacting violently to unfamiliar ones,such as radiation and nuclear contamination. Thepublic is aware that radiation protectionstandards are established on the assumptions,which at present can be neither proved nordisproved, that there may be genetic as well assomatic effects from radiation, that effectsare cumulative and irreversible and thatthere is no threshold level below which effects donot occur. This is felt to be a conservativeapproach but it is prudent to recognisethe possibility of major accidents, however remote,and to undertake public health measures toeducate the public, to assure and convincethe public that proper care has been taken toprotect them by building a safe reactor,caring for its good siting, ensuring its safe operation,being prepared to minimize the effects ofpossible accidents, and undertaking aprogramme to improve power reactors and theiroperations continually, thus reducing furtherthe probability of accidents and profitingfrom experience with minor accidents.

safe handling

of radioactivematerialsIntroductionFission within nuclear fuel creates radioactivesubstances with a wide variety of chemical,biological and radiological characteristics. Thesafety of both plant personnel and the public inthe vicinity of nuclear power plants depends to avery great extent on the containment of theseproducts within the fuel, where they are formedfor the most part. In normal operation verysmall quantities of fission products are releasedfrom the fuel through defects in fuel cladding.Management of these generally imposes no unusualconstraints on facility siting, which dependslargely upon considerations of accidentpotential and consequences.

Exposure of the public to ionizing radiation dueto radioactive effluents from nuclear powerplants can be kept at small fractions ofthe levels set in radiation protection standards forroutine operations, but it is recognised nevertheless

- that nuclear power productions is but one partof the fuel cycle. In order to examine fullythe overall impact of the use of nuclear fuel forelectrical power generation one needs toconsider the whole fuel cycle, beginning withmining and milling and ending with the final dis-posal of wastes from the operations carriedout at various stages. However, reactors are ofmajor interest to most members of the publicbecause there are more of them than ofOther facilities in the fuel cycle, and they are sitedgenerally closer to electricity load centresbroadly, people in towns.

When considering the effective management(control) of radioactive effluents from reactorsand associated facilities one does well tokeep in mind that everything, including effluentsfrom all power plants, whether they use fossilor nuclear fuels, contains some radioactive

material. The management of radioactive wastesis concerned not so much with reducing levelsof contamination to zero or even to the lowestpossible level, as with keeping the total addition ofradioactivity to the environment as low as ispracticable in any case, within the limitsrecommended by ICRP.

The contamination of air by nuclear power plantsis predominantly by radioactive noble gases, whichdo not concentrate in the body but are responsibleprimarily for external radiation exposure. Inorder to assure adequate radiation protection formembers of the public the concentration ofradioactive materials in air, water and food as aconsequence of reactor operations and ancillary ac-tivities must be kept at such a low level thatthe total risks of somatic and genetic injury areexceedingly low, no greater than risksintroduced by other common industries.These risks must be acceptable by the individualand by the society of which he is a part.

Whenever practicable, radioactive materials areconcentrated and contained in isolationfrom man's environment until theirradioactivity has decayed to innocuous levels.When release to the environment is necessary therates of release must be low enough not toexceed the local capacity of the environmentto disperse and dilute the materials to acceptablylow concentrations. In this respect theenvironmental processes that may lead toreconcentration and may provide a pathway forman's exposure to additional radiation mustbe considered.

Radioactive effluents released from nuclear powerplants are always monitored as a means ofcontrol and public protection. Additional, off-site monitoring is carried out as a con-firmatory means of environmentalprotection, but in general releases have been solow that little indication can be found ofradiation above natural background levels.

19

The installations associated with other aspects ofthe nuclear fuel cycle are fewer in number andgenerally more remote from large centres ofpopulation than reactors, but effective managementof radioactive materials to control both occupa-tional and public exposure to ionizing radiation isstill required. In mining and millingoperations on uranium and thorium oresrequired for nuclear fuel fabrication the principalproblems arise in occupational exposures,particularly through the inhalation ofradon gas and the radon daughter products. Infirst cycle enrichment operations wastemanagement involves the effectivecontrol of naturally-occurring heavy elements.However, when spent fuel is reprocessedfor recovery of unburned uranium therecovered product contains plutonium, which isalso valuable as a fuel.The uranium recovered is returned to enrichmentplants for re-enrichment.Fuel fabrication operations also require effectivemanagement of these same elements.In general, the provision of clean working conditionsfor operating personnel and the strictaccountability of the fuel materials contribute tothe control of these materials.

Well over 99.9% of all the radioactivity generatedin nuclear power reactors is contained withinthe fuel elements until they are reprocessedfor recovery of unburned fuel. Thus carefulcontrol of the inventories in reactors and of thespent fuel which must be handledand transported to fuel reprocessing plants isrequired.A reprocessing plant may accommodatethe spent fuel elements from several powerreactors, and it is during the reprocessing of thefuel that highactivity wastes are generated.These wastes must be kept in containment forvery long periods of time, ranging from a few cen-turies to possibly thousands of years, if theycontain substantial concentrations oftransuranic elements. Although storage as liquidsin tanks near the ground surface has been asuitable and reliable method for containmentof these wastes to date processes of solidificationhave been developed,and some countries have already decidedthat such wastes will besolidified to reduce the potential "environmentalmobility" of these wastes during long periodsof time. Consideration is also being givento various means of storage of these wastes, in-cluding their storage in deep, dry and stablegeologic formations in order to assure furthertheir isolation from the Oilcan environment forthe time required.

20.. 26 VS

Mining, Milling, Enrichment andFuel Fabrication

The mining of uranium ores is the starting pointin the production of fuel for nuclear powerplants. These ores contain oxides of uranium.in relatively low concentrations, mixed orcombined with other minerals and rocks.The radioisotopes associated with the uraniumores are naturally-occurring decay productsof uranium, thorium and radium.

Mining gives rise to two types of waste, airbornedust with some radon, and solid tailingscontaining some uranium oxides and a verysmall quantity of radium. The concentration ofradon is controlled by the volume of air usedin ventilation. When airborne dusts area problem the air may be filtered and in specialcases, if necessary, the miners may use respiratorsto limit their exposure to radiation.

The next step in preparing the uranium oxide foruse in fuel fabrication is the milling andconcentration of the oxide. Theuranium-bearing ores are crushed into a relativelyfine form (like sand of fine texture) inpreparation for leaching of the uranium.Since the uranium is only a small fraction gener-ally less than 1% of this material the bulk ofit remains as tailings for disposal as bothsolid and slime-like wastes. The quantities ofuranium oxides and of radium sulphate inthese wastes are limited purposely sincethey are intrinsically valuable and must be ac-counted for; they occur usually in a finely-dividedstate, and wet. The radioactivity of the uraniumis not a controlling factor at this stagemuch more important is its chemical toxicity. Thesolid and slime-like wastes are often depositedon a tailings pile where leaching of radiumand escape of radon can occur. Recent trends aretoward drying these wastes and storing themin dry mines or incorporating them inbitumen, thus isolating them from the environment.The airborne wastes, again, are treated byfiltration and the use of adequate ventilation.The nature of the operations here permits a closecontrol of the airborne materials.

Thorium is not used at present as a fuel for powerreactors, and its mining and milling has notyet become an important source of radio-active wastes. This situation could change in thefuture.

The uranium oxide is commonly converted nextinto uranium hexafluoride (11F6), which canbe maintained in a gaseous state. In this formthe uranium may be enriched in a gaseous diffusion

.::!..",/"...,47.:;6, 'Mr;TO,

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An open pit uranium mine in New Mexico. The spiral dump is of waste. Photo: USAEC

plant in any of a number of countries; enrichmentis necessary to increase the proportion ofthermally fissionable 2350 to non-thermallyfissionable 235U from the natural abundance ofabout 0.7% to about 2.2 3%, to make itmore suitable for use in the most common typesof power reactors. Unburned uranium fromthe reprocessing of spent power reactor fuels mayalso be recycled through the enrichmentplants. Gaseous wastes are filtered prior torelease to the environment.

After enrichment the uranium hexafluoride isconverted again to an oxide or to the metal foruse in the fabrication of reactor fuel elements.Fuel fabrication gives rise to various typesof liquid, gaseous and solid wastes which areslightly contaminated with uranium, itsdaughter products and plutonium (when recycledmaterials are used).

Nuclear Power Plants

Sources of radioactivityBoth nuclear and conventional power plants usemuch the same type of machinery to convertsteam to electricity, and to connect thisto the eiectrical grid: The uniqueness of thenuclear plant lies in the fuel used, and more parti-cularly in the equipment needed to maintainstrict control over the radioactive materialsformed by the fission process that generates heat.

4-

... Fission productsThe principal radioactive materials formed are thefission products. The quantity of fission productsformed is small in terms of mass: in a largepower plant this will amount to only afew kilograms each day. Since some of the fissionproducts decay as others are formed the amountof radioactivity levels off and the inventoryof short-lived fission products reaches essentiallya steady value. Because the shorterlivedradionuclides contribute substantiallyto the total inventory of radioactivity in terms ofcuries after a few weeks of operation of alight-water moderated power reactorusing fuel slightly enriched in 235U the fissionproduct inventory might be up to about 40% ofwhat would exist after a two-year operating period.More importantly, as will be explained rater, all buta very small fraction of the radioactive fissionproducts remain confined within the fuelelement where they were formed. The quantityof fission products within reactor fuel elementswill depend upon:

average operating poWer level of the reactorfuel residence time in the coretime elapsed for radioactive decay.

. Activation productsStructural materials used in the reactor and thecomponents which remove the heat from itscore will corrode and e(pdfkosnly very slightlywith time but enough to create fine2 21

particulates identified broadly as "corrosionproducts". These corrosion products,along with other impurities in thecoolant, circulate through the core of the reactor,where they are exposed to neutrons. Neutronbombardment causes them to becomeradioactive. The quantities of radioactivematerials so formed are small compared with thefission products, and consist commonly ofradioisotopes of elements such as iron,cobalt and manganese. Some reactors use boronin the reactor core and core coolant tocontrol the fission process. Neutronabsorption by boron leads to the formation oftritium, a radioactive isotope of hydrogen.Tritium formation similarly can resultwhere water is used as the corecoolant, through conversion of deuterium anatural isotope of hydrogen found in water.In gas-cooled reactors, cooled with carbondioxide, the activation products include 41Aand II4C.

Radioactive waste generation and management

Although the kinds of radioactive wastes producedas by-products of the fission process arebasically the same for all uranium fuelled reactorsthe characteristics of the effluents from plantscan vary appreciably, depending on thereactor coolant and steam cycles used. The radio-isotopes in the effluent streams in turninfluence strongly the design of particularwaste treatment systems.

Objectives in plant design are so to process andrecycle waste streams as to minimize bothvolume and radioactivity of effluentwherever practical. Releases to the environmentare controlled both by batch processing ofeffluents, and/or by continuous monitoring beforedischarge to ensure that no release exceedsestablished permissible limits.

The waste management techniques now in use forgaseous wastes are delay and decay; filtration;and low temperature adsorption on charcoal.Delay and decay refer to the storage of waste forlong enough to decrease the associated treatmentproblem by permitting some radioactivity todecay before release. The usefulness orefficacy of this technique as a means for reducingactivity levels in gaseous wastes depends on theparticular isotopes precept. Gases are thenfiltered and released through stacks to the atmos-phere. Filters collect radioactive solid particlesformed whfrota gaseous parent nuclide decaysto a particsigte radioactive daughter, or becomeattached to particles; and when particles ofdust are carried by the air stream through

22

the reactor core. Specially-treated charcoal filterbeds may be used to remove iodine. Lowtemperature adsorption may be usefulin providing delay and decay of short-lived noblegases.

Liquid waste management systems employ fourbasic treatment techniques to reduce levelsof radioactivity. These are delay anddecay; filtration; evaporation; and deminerali-zation. In the case of reactors in which once-through cooling systems are used a finalreduction in liquid radionuclide concentrations isachieved by dilution of the wastes in the con-denser cooling water to ensure that radio-nuclide concentrations are at the lowest possiblelevel before reaching the site boundary.

The delay and decay tethnique as used in thetreatment of liquid waste is identical inprinciple to that for gaseous waste, although littlereduction in liquid radioactivity levels isachieved. Radionuclides in liquid radioactivewastes tend to have relatively long half-lives sincethose with shorter half-lives decay duringtheir movement through the plant. A relativelylong delay time would be needed to achieveany appreciable reduction in liquid wasteradioactivity levies it is estimated that it wouldtake about 40 days to reduce the radioactivitylevels of typical liquid waste by a factor ofabout five.

Filtration is commonly used for treatment ofwaste streams containing primarilyinsoluble or particulate contaminants. Filtrationis also frequently employed with othertypes of waste treatment as a pre- or post-treatment step for the process liquid. In pre-treatment filtration the objective is removal of sus-pended solids to prevent interference byparticulates in the subsequent treatment processes.In post-treatment application, filters are usedfor tasks such as the collection of resir>"fines" escaping from ion exchangers. Filter typesused include natural filtration (using sand orother media), activated carbon, vacuumand pressure pre-coat type filtration and fibrousand knife-edge filtration.

Evaporation separates water from non-volatiledissolved and insoluble radioactive wastes byboiling. This concentrates and reduces thevolume of the contained wastes and reduces theactivity level of the effluent, permitting easierultimate disposal. The efficiency of thistechnique for radioactive waste treatment can vary

Part of the interior of the gaseous diffusion uraniumenrichment plant at Capenhunt, in the UK. Photo: UKAEA

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widely depending on the radioactive materialspresent. A reduction of 100 to 1000 in theactivity level can be achieved, depending on themass velocity of the vapour in the evaporatorand decontamination efficiency for non-volatileradioactive contaminants. If volatile radio-active materials such as tritium, iodine orruthenium are present the overall reduction inactivity level may be substantially less on accountof carry-over of these materials. Evaporationis a common method of treatment of liquidwastes because streams having a relatively high con-tent of dissolved solids can be accommodated.It is, consequently, a suitable process foruse in conjunction with subsequent ionexchangetreatment. Care needs to be taken, however,to provide for treatment of any feed streams, suchas laundry wastes which contain organic agents.

The efficiency of demineralizers (ion-exchangeresins) in the treatment of waste streams dependson the type, composition and concentrationof waste liquid, the type of exchange, regenerationmethods, radionuclides present and operatingprocedures. The reduction in activity levelsachieved may be as low as 2 and as high as 103.Only wastes containing relatively smallamounts of dissolved and suspended solids canbe processed efficiently by ion exchange becausebed exhaustion occurs rapidly for liquids witha high total content of dissolved solids.Suspended solids will clog an ion exchanger andalso prevent its efficient operation. Thus, theuse of ion-exchange treatment is restrictedto radioactive wastes with low total dissolved solidsand low suspended solids, and filtration isalways used as a pre-treatment.

Boiling Water Reactors

Boiling water reactors (BWRs) are one of the twotypes of light water reactors which are beingoperated and marketed on a wide scale at present.

through the condenser air ejector. Additions tothe gaseous emission come via the condensergland seal, primary containment air, gases from theradiochemical laboratory at the plant, theradwaste [radioactive waste] treatment area,laundry, decontamination operations and varioustank vents. The gaseous waste containsprimarily the activation product 13N,isotopes of the noble-gas fission products kryptonand xenon, and tritium. About 90% of the13N decays to a non-radioactive isotope in thetime it takes for the gaseous waste to be transferredthrough the plant to the stack and from thereto the site boundary. Consequently, it is ofminimal concern in off site areas. The isotopiccomposition of the krypton and xenondepends on the radiation history of the reactor fueland on the age of the mixture at the time ofrelease, because many isotopes of krypton andxenon have a relatively short half-life. Someradioactive particulates appear in the gaseous wasteas a result of entrainment and decay of noble-gas precursors; isotopes of some of themore volatile elements, such as iodines, will becarried over as vapour.

A typical operating BWR off-gas system,is shownin Figure 8. Noncondensible gases are drawnfrom the main condenser through steamjet air ejectors and condensers into a delay line,where they are retained for 30 minutes or more,depending upon design requirements. Afterthis delay time the gases pass through anabsolute particulate filter and are dischargedthrough the stack. The stack is usually about300 feet high, although its actual height isinfluenced by site topography. Since a majorportion of the activity released from a BWR iscomposed of short-lived gases, an elevated release(as opposed to a ground-level release) con-.tributes to effective dispersal and decay.Off-gases from the turbine gland seals are processedIn a BWR water is circulated through the core of thesimilarly. Because these are metricreactor, where it is converted under pressure into activation gases and the volumetric flow rate

steam (See Fig.6). This high-temperature stream is very large, only a two-minute delay is commonlyis used to drive a turbine to generate electricity, and allowed for before they are discharged throughis then cooled in a condenser and recirculated the stack.through the reactor core. Water is used to cool thecondenser. The basic operation of such a plant,apart from the nature of the fuel, is similar to thatof a fossil-fuelled installation. (See Fig.7)

BWR Waite Management Systems

More than 99% of the radioactive gaseous effluentsfrom boiling water reactors are removed continu-ously with relatively large volumes of air

Provisions can be made in the design of BWRs toreduce greatly the discharge of short-lived noblegases. This can be accomplished throughthe use of activated charcoal beds to delay thenoble gases for a time long enough to permitadditional radioactive decay. This would havelittle influence on releases of 85Krat the reactorsite since this radionuclide has a balf-life ofabout ten years, but its contribution to

Fly-fishing trials taking place radiation doses in the vicinity of the plant is negli-on the lake at the Trawsfynydd nuclear powerstetion,Wales. gible. Like all other fission products,Photo: Central Electricity Generating Board. practically all of the 831(r formed is retained in

25

the fuel elements until they are processedfor recovery of plutonium and unburned uranium.

A typical BWR liquid radwaste processing systemis shown in Figure 9. The unique feature ofthis system is in the segregation of wastesby chemical and physical properties. Influent iscollected and processed according to itsclassification as high-purity (equipment drains),low-purity (floor drains), chemical, orlaundry wastes. Contents of equipment drainsare filtered and demineralized, and can thenbe either used again in the plant, or measured anddischarged. Plant floor drains, chemicalwastes and laundry wastes are filtered anddischarged from the plant. Since the laundrywastes tend to foul filtering media, they are pro-cessed separately through their own filter.The major sources of solid radioactive wastesat BWRs are sludges which accumulate onfilters, and demineralizer resins. Thesewastes are first centrifuged to remove excess waterthen solidified with concrete in 55 gallon(0.2 m3) steel drums. The drums are normallystored for three to six months beforeshipped offsite for permanent burial. About100 175 drums are shipped each yearfrom a typical BWR installation.

BWR Operating Experience

A radiological surveillance study was performedin the United States at an operating BWRpower station. In this study thecharacteristics of the gaseous effluent dischargedto the environment were measured: theaverage fission-product noble-gas release ratewas 12 500 ACi/sec while the plant was operating,which was during 64% of the year. Theprincipal radioactive noble gases found in thelaboratory effluent analyses were Uni Kr,"Kr, 83Kr, 133Xe and 1*5Xe. One day after re-lease only 138Kr, 1"ffIXe and 133Xe were detectedin the sample; after one month the onlynoble gases detectable were 133Xe and 53Kr.Tritium could also be detected in the laboratorysample. The principal non-noble gas fissionproduct found was 1311:

Data for gaseous releases of radionuclides to theatmosphere from ten BWRs operating inseveral countries are shown in Table IV.

The constituents of radioactive liquid wastefrom a BWR are activated corrosion products,and fission products. The fission productlevels are attributable to tramp uranium*, and to

Figure 8: Schematic diagram of a typical boiling-waterreactor

"Tramp" uranium refers tiithe tracers of uraniumthat may be found on the outer surfaces of the fuelcladding.

26 VA,

2

Figure 7: Schematic diagram of a fossil-fuelledgenerating plant

Figure 8: Typical BWR off-gas system

Figure 9: Typical BWR liquid radioactive waste system

WASTEMINTER! W.COLLEC TOR

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Figure 10: Schematic diagram of a typical pressurized.water reactor

Figure 11: Typical PWR gessous waste system

WAIT[ SASCOMMLSSOSS

2 MONTHS

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Figure 12: Typical PWR liquid radioactive wastesystem - dirty wastes

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Figure 13: Typical PWR liquid radioactive wastesystem - dean wastes

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leakage from fuel elements through claddingdefects. The relative contribution ofleaking fuel elements depends, of course,directly upon the number of leaking fuel rodsand the severity of the leaks.

The characteristics of the liquid waste effluentwere also measured in the study mentioned.The average concentration of all detectedsoluble and insoluble radionuclides inthe waste prior to dilution wasapproximately 2 X 10-3 pCi/ml. The radioactiveconstituents at the highest concentrationswere 3H 38t.:o 83Sr, "Sr, 131 I, 134CS,132CS, lquIlla and I"Ce. The average contributionto the total unidentified activity in thewater used for radioactive waste dilutionwas 0.189 X 0-2 pCi/m1 over a one-year period.This may be compared with the ICRPrecommendation for the maximumpermissible concentration of unidentified radio-nuclides in water, (MPCU1w, of 10-7 pCi/m1if neither 226Ra nor 228Ra is present. Thestudy concluded that exposure to thesurrounding population through consumption offood and water was not measurable.

Pressurized Water Reactors

The second type of light water reactor in commonuse is the pressurized water reactor (PWR).Pressurized water reactors operateunder pressure high enough to ensure that thewater passing through the reactors does not boil.This water passes through a steam generatorto make steam to drive the turbine (Fig.10).The water in the primary coolant system does notmix with the steam used to drive the turbine.

PWR Waste Management System

Since the primary coolant in pressurized waterreactors does not boil most of the gasesare contained within the primary coolant system.Gases which do leave the primary coolantsystem are collected and routed to storage tanks.The general composition of the gaseouswaste produced in a PWR is somewhat differentfrom that produced in a BWR. Since PWRgases remain in the plant for a longertime before discharge the shorter half-lifeisotopes are much less abundant in the gaseouswaste of a PWR than in that of a BWR.Occasionally, primary coolant leaks into thesecondary system through defective steam-generator tubes. When this occurs short-lived gas-eous radioactive washiss.may be released throughthe main condenser air ejector.

A typical PWR gaseous radwaste system is shownin Fig.11. The waste gases from various

27

Table IV.Operating Experience of Releases of Gaseous Radionuclides to the Atmospherefrom Boiling Water Reactors in 1970

PlantNominalRating

(MW(ell

GrossElectricalGeneration(106 MWh)

Annual Average EmissionRate

Iv Ci /sec)

Dresden 1 200 1.50 30,000

Big Rock Point 72 0.38 9,000

Humboldt Bay 70 0.43 16,000

Garigliano 150 0.74 16,000

KRB 237 1.84 1,000

Tarapur (2 units) 380 2.17 14,000

Oyster Creek 640 3.56 3,500

Nine Mile Point 600 1.63 < 1,000

Tsuruga 342 1.89 1,800

Dresden 2 809 1.25 8,600

sources are collected in a vent header anddischarged by a waste-gas compressor into one ofseveral decay tanks. When a tank reachesa set pressure and activity level it isisolated and a second tank is placed in service. Gasis held for decay for from one to two monthsbefore being discharged through a filterto the environment from a building vent. Sincethese gaseous wastes are small in quantity andcontain minimal activity dispersal from anelevated stack is not necessary.

A typical PWR liquid radwaste system is shownin Fig. 12 and Fig. 13. Dirty wastes from varioussources (Fig.12) are collected in separatetanks and, when ready for processing, are dis-charged to the wasteholdup tank. Thistank serves primarily as a batching tank for thewaste evaporator. The distillate from theevaporation process is condensed and storedin a condensate storage tank before discharge fromthe plant. The concentrates are collected andstored for processing through the solidradwaste system.

Clean wastes (Fig.13), which consist primarily ofreactor coolant, are collected in holdup tanks.After filtration and demineralization ofthese wastes the boric acid evaporator servesprimaribito recover boric acid and primary grade

-:.!.,,water. The boric acid evaporator condensate,after being filtered and demineralized, can

28

34alf

be recycled to the primary coolant make-up tankor measured and released to the discharge canal.

Solid radioactive wastes from a PWR may beprocessed differently depending upon thesource, the activity and the choice made by theplant operator. Evaporator concentratesare solidifed with a mixture of cementand vermiculite in 55-gallon (0.2 m3) steel drums.

PWRs use cartridge-type filters that consist ofpaper or fibre elements held in a steel cage.Usually only the elements need changing,but occasionally the entire cage assembly must bereplaced. In either case, the component to bedisposed of is placed inside a 55-gallon (0.2 m3)steel drum lined with cement for shieldingpurposes. More cement is added to encapsulatethe component completely. The drum isthen capped. All processed solidradwaste is stored on-site before being shippedto a burial ground for final disposal. These ship-mants range form 100 175 drums a year.

PWR Operating Experience

A recent radiological surveillance studyperformed in the US at an operating PWR powerstation measured the characteristics of thegaseous wastes at several points in the wastemanagement systems. The maximum annual grossbeta-gamma level of activity discharged ingaseous effluents was approximately 22 curies

lo

'

iG

fats

MLI'MIN

The Chapelcross nuclear power station, in Dumfriesshire, Scotland. Photo: UKAEA

for the year 1962 and averaged 5.3 Ci/yearbetween 1962 and 1968. The radionuclides foundin the 9aseous waste were 3H,14C, 8sKr, 133Xeand 133Xe. No gaseous 1311 was found at theminimum detectable level. Based on measuredconcentrations in the surge drum and subsequentdilution, four radionuclides were estimated tobe present at the site boundary in concentrationscorresponding to 0.002%, 1.0%, 0.03% and0.01% respectively of their individualmaximum permissible concentrations. Concen-trations at the site boundary were conservativelyestimated to be 0.01% of the limit for 90Sr.Secondary sources of gaseous waste such as thecondenser air ejector and secondary systemliquid waste-tank vents appear to be themajor contributors to effluent radioacitvity:for example, all but one of the recorded gaseoustritium discharges occurred during monthswhen the vapour container was vented or gaswas released under special circumstances.

Liquid wastes from PWRs are similar to those fromBWRs except that tritium is a much more signi-ficant constituent. This abundance oftritium arises mainly from diffusion of thefission-produced nuclide through stainless steelclad fuel and from extensive use of boronand lithium in PWR coolants. The boron under-goes a neutron-capture reaction with thefission neutrons generating tritium,

which has a relatively long half-life of 12.3 yearsand which combines with oxygen to formwater. Tritiated water is chemically identicalwith ordinary water, making its separationand removal extremely difficult and, to date,impractical.

Diffusion of fission-product tritium into theprimary coolant can be reduced bychanging from stainless steelcladding to zirconium cladding, which reducesleakage from about 30% of the fission-producttritium to 1%. The tritium in the primarycoolant, including that produced byactivation of boron and lithium, would not beremoved regularly but would be recirculated. If itbecame necessary to replace the primary coolantduring the lifetime of the reactor specialprovisions could be made for its handling.

Reactor coolant contributes to the PWR liquidwaste through expansion overflow, reactorletdown flow, component leakage andsampling. Other sources of liquid waste includefloor drains, decontamination and laundrywastes.

The characteristics of PWR liquid radioactivewastes were also reviewed in the study .

mentioned. After release, aside from low 'concentrations of radionuclides found in sedimentand vegetation near the point of discharge, the

I

29

Table V.Operating Experience of Radionuclide Releases from Pressurized Water Reactors

Plant YearTotalLiquid

Released(Curies)

TotalGases

Released(Curies)

TotalTritiumReleased(Curies)

FuelClad

Material

Yankee 1967 0.055 2.3 1690 Stainless Steel(625 MW(t))

1968 0.008 0.68 1170 Stainless Steel

1969 0.019 4.14 1225 Stainless Steel

1970 0.036 16.5 1375 Stainless Steel

Conn. Yankee 1968 3.96 3.74 1740 Stainless Steel(825 MINIt))

1969 12.2 190.0 5100 Stainless Steel

1970 29.5 876.0 7376 Stainless Steel

San Onofre 1969 8.90 251.0 3500 Stainless Steel(1345 MW(t))

1970 3.80 1606.0 4769 Stainless Steel

RG and E 1970 9.35 9974.0 107 Zirconium(1520 MW(t))

only measurable radionuclide in water wastritium. Other major radioisotopes inthe released waste were 14C, 51Cr, and "Co. Lesseramounts of 3213"Mn,..99Fe, 6°Co, 90Sr,"Zr, 95Nb, nomAg, iwsb, ail and

"Ni,Irtswere also discharged. Data on the discharge ofradioactive wastes from four operatingPWRs are shown in Table V.

Gas-Cooled ReactorsThe extensive use of gas-cooled reactors as thebasis for a nuclear power programme hasbeen confined to the United Kingdomand to France. The type of gas-cooled reactorwhich has been operated for power production sofar it the natural uranium fuelled, graphitemoderated, carbon dioxide cooled reactor. In theUK about 85% of the total installed nuclearcapacity of more than 5000 MW(e) isoperated by the Central Electricity GeneratingBoard (CEGB); in France about 94% of theinstalled nuclear capacity of more than1300 MW(e) is operated by Electricite de France(EDF). More advanced gas-cooled reactorsystems are in the prototype stage.

30

A schematic diagram of a typical gas-cooled powerreactor is shown in Fig.14. The fission processtakes place in natural uranium rods whichare sealed in finned magnesium alloy cans. Thefuel elements are arranged in vertical fuelchannels, each containing about eightelements. There are several thousand such fuelchannels together with channels for control andsafety rods in the reactor core, basically agraphite block about 10 m high and 13 m indiameter. The core is contained in a pressure vesselof either steel or pre-stressed concrete. Thecarbon dioxide coolant is circulated through thefuel channels, where it removes heat fromthe fuel, and then through a steam generator.While passing through the core the coolant gas isactivated by neutrons and it also becomescontaminated with particulate erosionproducts of activated reactor components. De-liberate discharges of coolant gas from thereactors takes place from time to time forexample, to maintain correct pressure or coolantor coolant purity and some leakage fromthe coolant circuit also takes place. Thusthe activated materials in the carbon dioxide con-

Figure 14: Schematic diagram of a typical gas-cooledruder

stitute a source of gaseous and particulateradioactive release to the atmosphere.In steel pressure vessel reactors the pressure vesselis surrounded by a concrete "biological shield",and air is blown through the annular spacebetween the two. The main purpose of this air isto cool the concrete of the shield, but it alsosweeps over many of the potential pointsof leakage from the pressure circuit and cariesentrained waste to the atmosphere abovethe reactor roof. Constituents of theshield cooling air itself, and particulate mattercarried by it, are activated while passingclose to the pressure vessel.

Gas-Cooled Reactor Management Practices

The experience of the UK and France has beenthat the arrangements provided in the designof power stations for dealing with radioactivewastes have proved adequate to keep discharges tothe environment within limits imposed by thenational authorizing organizations, and inaccordance with the conditions laid down by theseauthorities.

As is implied in the previous paragraph, measure-ments are made on discharges of radioactivewaste. There has been no requirementfor the regular measurement of gaseous dischargesfrom CEGB nuclear power stations, since theseare dependent largely on reactor powerand are calculable. In practice, radioactivity fromgaseous wastes has proved difficult to detectin the environment. Particulate radio-active gasborne materials are monitoredduring discharge from the principal points ofrelease. At the Electricite de France power stations,at Chinon and St. Laurent des Eaux, bothgaseous and particulate activities aremeasured routinely. Liquid wastes are monitoredbefore discharge while being held in finalmonitoring and delay tanks.

Gaseous wastes originate largely from the plannedrelease of reactor coolant gas, and the discharge

of air used to cool the concrete shield insteel pressure vessel reactors and to ventilate thebuildings containing the reactors and ancillaryplant. The gaseous radioactivity consistsprincipally of argon-41, which is contained in shieldcooling air and in carbon dioxide coolant.Particulate airborne wastes discharged mayinclude fission products but at CEGB stationsconsist mainly of activation products(such as 60Co and s9Fe.

Generally filtration to remove particulate radio-activity is the only treatment given airbornedischarges before their release to theatmosphere, which is usually through a stack.Leakage from the pressure circuit is sweptusually through filters to the atmosphereby ventilation or shield cooling air. An exceptionto the general method of treatment ofairborne waste is that used to treat carbondioxide discharges from Series G reactors atMarcoule, in France, where the coolant is liquifiedand retained for further use.

Aqueous liquid waste produced in the reactoritself is limited to induced activity in thewater used to cool the concrete inconcrete pressure vessel reactors and, in UK reac-tors, tritiated water formed in water vapourpresent in the pressure circuit and tritiumproduced mainly by neutron irradiation of lithiumimpurities in the graphite of the reactor core.This tritiated water is collected in thecircuit driers used to limit moisture levels in thepressure circuit. Wastes are also produced inchanging rooms, active laundry, decontaminationfacilities and so on, though these would notnormally contribute large quantities ofradioactivity to wastes from the station as awhole. By far the largest contributionto the activity of liquid effluent from all but oneof the stations operated by the CEGB ismade by the storage of spent fuel incooling ponds, where it is kept for a time to allowits radioactivity to decay before it is sent forreprocessing. The water from these pondsis circulated through an ion exchange treatmentplant, the regenerant liquors from which, afterneutralization, are handled with other liquideffluents.

Filtration is usually all that is required for treat-ment of liquid effluents. After filtration andmonitoring for radioactive content the effluentsare discharged to a large body of water.Discharges from CEGB reactors are made, afterdilution with the very large volume ofcondenser cooling water (some 90 000 m3 / hourper station, to the sea or to an estuary; inone case, at Trawsfynydd, the discharge

31

is to a freshwater lake. The liquid radioactivedischarges from the French reactor establishmentsat Marcoule, Chinon and St. Laurent desEaux are made to rivers with large rates of flow.At Trawsfynydd the limitations on dischargesare more stringent than at other UK stations,and this installation is provided accordingly withnon-regenerable ion exchange beds in theeffluent treatment plant. At most CEGBpower stations the radionuclides making thegreatest contribution to the radioactivityof liquid effluents are nts and nts,which arise in the cooling ponds. The levels ofthese nuclides at a number of stations havebecome high enough to require theinstallation of ion exchange or preferential adsorption plants especially to removethem. During the past few years isotopic analysesof liquid effluent from the power stationshas been carried out both to establishthe composition and to indicate any changes whichcould affect the critical route of populationexposure to radiation. The sludges, spention exchange materials, filter backwashings and soon, which arise in the treatment of liquidwastes, are themselvet'treated as solid wastes.

In both the UK and France central facilities for theaccumulation of radioactive solid wastes areavailable, but in the case of the CEGB stationssolid wastes ar usually accumulated at thestation at which they arise. The Electricite deFrance stations use this latter arrangementfor large volumes or for high activitywastes. The fuel element fins are removed fromthe spent fuel at CEGB stations before itis despatched for reprocessing, thesemagnesium alloy fins constituting an importantpart of the solid radioactive wastes whichare created. Non-combustible solidwastes include filter backwashings and ion ex-change materials from the pond water andliquid effluent treatment plants, together withmiscellaneous scrap items of plant andequipment which have become contaminatedor activated in use. Substantial quantitiesof combustible solid radioactive wastes areproduced, including active waste from changingrooms and sisal Kraft, paper and plasticsheeting used to minimise spread of contaminationduring certain operations in the power station.

Where possible, it is obviously preferable to reducethe volumes of wastes before accumulating them.The method now used widely in the UK forcombustible waste is incineration. Incinerators aredesigned carefully to prevent significant dischargeof radioactive materials to the environment.The ash from incinerators may be accumulatedin the same way as other solid wastes or, when

32

it is of very low radioactivity, it t,my bedumped at suitable public rutibibti tips. Morehighly radioactive combustible wastesthan those suitable for incineration are accumulated in vaults. In France compression isused in addition to incineration to reduce thevolume of solid wastes before containmentand accumulation.

Non-combustible wastes are also accumulated invaults having adequate :shielding for the typeof material they am to contain. It is ensured thatthe vaults do not allow leakage of radioactivityto the ground, especially when their intendedcontents are wet for example, sludges.

Operating Experience with Gas-Cooled Reactors

The gaseous discharges are mainly of argon-41,of which some 10 mCi/sec may be expectedfrom a typical UK steel pressure vesselpower reactor. The half-life of this nuclide isfairly short 110 minutes and it isdischarged to the atmosphere in such a way thatit is difficult to detect in the environment.At Chinon the average gaseous discharge (again,mainly 41Ar) in 1970 was about 250 tiCi/sec.

Table VI.CEGB Nuclear Power Stations Discharges ofRadioactivity in Liquid Effluent in 1970

Station

Radioactivity Discharged in 1970

Tritium Radioactivity otherthan Tritium

Berkeley 60.1 23.2

Bradwell 95.3 129.2 (0.085)

Hinkley Point 'A' 18.6 127.7

Trawsfynydd 67.7 13.5

Dungeness 'A' 18.6 83.7

Sizewell 20.9 23.4

Oldbury 17.3 7.74

Wylfa 0.551 6.32

Notes

1. Figures shown in brackets for Bradwellrefer to zinc-652. Wylfa discharges of radioactivity other than tritiumwere due almost entirely to bromine-82 dischargedduring tracer tests on cooling water pumps.

Deliberate discharges containing particulateradioactivity mainly of activation productsfrom CEGB reactors amount to onlya few millicuries per month per reactor, andhave had no significant effect on theenvironment.

The radioactive content of liquid wastes dischargedto the aquatic environment is limited to levelslaid down as appropriate for the particularpower station by the competent authorities. AtChinon, where discharge is to the River Loire,the radioactivity released in 1970 was only about2.25 curies. In the UK discharges are mainlyto an estuary or to the sea; Table VI summarizesdischarges from CEGB nuclear power stations in1970. In most cases little or no activity hasbeen measurable in the aquatic environment as aresult of these discharges.

Only very small deliberate discharges of radioactivematerial to the environment, of no radiologicalsignificance, are made in connection with themanagement of solid wastes.

Heavy Water Reactors

The Canadian nuclear development programme isoriented strongly toward heavy water reactors;power plants of this type are also used inIndia, Pakistan and Sweden. Heavy water is usuallyused in tube type reactors, in which it servesas the moderator. Any of several coolingfluids may be used organic compounds, gas,water or heavy water since the heavy watermoderator is separated physically from,the coolant.The net fuel consumption of heavy waterreactors is quite low, and they can operate onnatural uranium.

The heavy water moderator is contained in a tanksurrounding the fuel containment tubes (Fig.15).There is room in the fuel tubes for thecoolant to flow past the fuel elements, thusremoving the heat that is generated in the fuel.The coolant then gives up its heat in a steamgenerator, as in other types of reactor power station

Figure 15: Schematic &porn of a typical heavy-waterreactor

Canadian experience with heavy water powerreactors has been limited so far to theDouglas Point Generating Station(220 MW(e)), which has been operating sinceNovember 1966, and the Nuclear PowerDemonstration reactor (NPD 25 MW(e)), whichhas been converted from pressurized heavywater to a boiling heavy water coolant. The250 MW(e) reactor at Gentilly in the Provinceof Quebec is cooled with boiling light water,and in November 1971 had operated forone year only. The first unit at the Pickeringsite went critical in February 1971.

Heavy Water Reactor Waste Management

With the exception of the rather larger inventoryof tritiated water (about 1 Ci/kilogram in theprimary heat transport system at equilibrium)heavy water reactors are otherwise similarto pressurized water reactors with respect to theirpotential release of radioactive materials to theenvironment. Radioactivity in wastes resultseither from the escape of fission products fromfailed fuel elements or from the neutronactivation of impurities or corrosion productscirculating in the coolant. Soluble radionuclidessuch as those of caesium remain in solutionin the coolant and escape from the reactorwhen the water leaks or during fuel changing.Less soluble radionuclides such as those of cobalttend to be deposited on the surfaces ofpiping and normally do not escape with thecoolant. Instead, they are released when equipmentis decontaminated either in situ or prior toout-ofservice maintenance. Gaseousradionuclides such as those of the noble gases andiodines become airborne if they are presentin the coolant, if and when it leaks.

The rates at which fission products escape fromthe fuel depend directly on the rate of fuelfailure. However, since it is possible tochange fuel without shutdown in the CANDO-type reactor being discussed, with adequateprovision for detecting and locatingfailed fuel it is possible to remove defectiveelements and thus to keep to a minimum theamounts of fission products that escapeto the coolant.

The amounts of activation products formeddepend on the presence of parent atomsin contact with the coolant. 66Co arises in partfrom the presence of cobalt-bearing alloys,especially those of high cobalt contentsuch as Stellite in positions where they are exposedto heavy wear, and also from corrosion ofcomponents which, though low in cobalt, havea large amount of surface area in contactwith the coolant. 6sZn arises from corrosion

33

}

of valve-packing, which may contain asmuch as 50% zinc.

The amounts and composition of radioactivematerials available for release can thusvary considerably from one reactor to anotherof the same type. Similarly, the fractionof the radioactive materials presentin a reactor which may escape to the environmentalso varies depending on a number of factorsassociated with the design details. Ofparticular significance to the heavy water reactoris the economic incentive to reduce heavywater leaks to a minimum. For example, gaseousventilation streams from areas containing high-pressure systems are closed cycles fittedwith molecular-sieve driers to recover heavy watervapour. The driers also remove tritiated watervapour so that the amounts of this radionuclideavailable for release to the atmosphere arevery much less than they might otherwise bewithout special provision for its removal. The driersalso remove iodine and caesium nuclides fromthe air streams, though whether the iodine isretained during the drying cycle is not yetknown. Also all leaks of liquid heavywater from low-pressure systems are collected asfar as possible in tanks for heavy waterrecovery. At the same time dissolved radio-nuclides are also collected, thus providingfor finer control over the subsequent fate of thesewastes.

The need for closed-cycle ventilation to recoverheavy water also provides, incidentally, fordelay in the release of noble gas radio-nuclides. This delay means that radioactive decayreduces significantly the amounts of the short-lived nuclides which are released to theatmosphere.

The NPD and Douglas Point reactors are designedto have air cooling of the space between thecallandria tubes and pressure tubes. Thus,in these reactors 41Ar is produced in substantialamounts, although the fraction whichescapes is generally relatively smallbecause of the closed-circuit ventilation. In thePickering reactors these spaces will be cooledusing dry nitrogen and no 41Ar will be produced.

Delays in the liquid systems similarly allow timefor substantial fractions of the short-livedradionuclides to decay before beingreleased to the environment. In general, radio-

Decontamination facilities for industry: A mobile controlunit carrying a full range of equipment, which can betaken quickly to the scene of a radiation accident.Photo: UKAEA

nuclides having half-lives of less than10 days are reduced by this means to in-significant levels before they are released.

Tables VII and VIII summarise the releases ofradioactivity to the atmosphere and water respecti-vely from the three Canadian power reactors.Although releases from the Gentili);reactor during the first 10 months of 1971 havebeen incligied in the tables it is too early toassess the long-term situation. Indeed,in all three reactors modifications have been madeand continue to be made, affecting to a greateror lesser extent the amounts and compositionof the radionuclides which will be available forrelease to the environment. It is not possible toextrapolate from the limited experience gained sofar in operating the CANDU-type reactor withits many possible variants.

Fast Breeder Reactors

Breeder reactors are those which may be used totransform fertile materials such as " U intofissionable materials such as 239Pu orThorium into 23U by neutron absorption, thuscreating more fuel than they consume.Several designs of reactor have a potential forbreeding. To date all known fast breederreactor projects are based on reactorswith sodium-cooled primary circuits, in which thesodium is blanketed by an inert cover gas(argon) at close to atmospheric pressure.Systems and components for the breeder differfrom those of other reactor types. There isan intermediate heat-transfer loopbetween the reactor coolant system ano the gene-rator of steam to drive the turbine (Fig.16).

Production and management of waste in fast-reactor nuclear power stationsThe waste problems presented by this type ofreactor are associated with sodium andthe technology of handling it, with plutonium andalso with the characteristics of the neutron fluxwithin the reactor, in terms of its energy,density and so on.

Flaws let Schematic diagram of a typical liquid-metalcooled feet breeder reactor

Table VII.Average Releases of Radionuclides to the Atmosphere from Canadian Power Reactors

1967

Average Daily Releases (CO

1968 1969 1970 1971

Douglas Point

Noble Gases 1 110 280 440 NATritium (oxide) 0.6 7 26 30 NA

ND 2 X 10-4 5 X 10-4 6 X 10-4 NA

NPD

Noble Gases -- 45 -- NATritium (oxide)isii

25ND

27ND

28ND

21ND

NANA

Gentilly

Noble Gases TraceTritium (oxide)911

341'ND

ND = Not detectableNA = Not available

= First 10 months onlyt = Includes accidental releases. Excluding accidental spills the average daily release is less than 2 Ci day-'

Table VIII.Liquid-Waste Discharges from Canadian Power Reactors

Douglas Point

Mixed RadioelementstTritium (oxide)

NPD

Mixed RadioelementsTritium (oxide)

Gentilly"Mixed RadioelementsTritium (oxide)

Average Daily Releases (Ci)

1967 1968 1969 1970 1971

15 X 10-3 33 X 10-3 se x 10-3 NA1.2 2.7 2.6 NA

2.1 X 104 4 X 10'3 5 X 10-5 6 X 10-5 NA10.1 15.9 14.8 9.6 NA

1.2X 10-32.9

NA = Not available= First 10 months only

T = The average composition of the mixture during the first six months of 1971 is thought to be typical and isas follows: 337Ci, 58%; "sCs 2096; "Co 17%; "II 4.3%; "Zn 0.2%, "Mn 0.3%; "Co 0.2%; "Sr < 0.05%;"Sr < 0.001%

36

Activation of the primary sodium and its propen-sity to trap iodides (Nal), fission products andactivation products constitute the maincause of contamination. Moreover, most of thenoble gases released by the fuel as a result ofcladding failures turn up in the argoncover gas, and it has been found necessary to designprimary circuits which ensure very effectivecontainment. Two basic designs can beenvisaged at the present time; the primary contain-ment of each is extremely leaktight.

Of these two designs (circuits with external heat-exchangers, and circuits of the integrated type),we shall discuss only the latter in order toavoid dealing with two different examples. It isprobable in any case that routine wastemanagement problems would not besolved very differently in the two cases. The inte-grated circuit type has been chosen in Soviet(BN 600), British (PFR) and French(Phenix) projects.

In this design the main reactor vessel, which alsoencloses part of the handling machinery andequipment, is itself enclosed in a primarycontainment vessel of such a size that rupture ofthe main reactor vessel would not entail lossof coolant from the core.

Fission products liberated from the fuel as a resultof cladding defects, corrosion productsentrained in the sodium and activatedcorrosion products from elements subjected to theneutron flux are normally contained in theleak-tight primary containment vessel.However, the handling of core components anditems from the primary circuits necessitatesan infringement of this integrity. Theprimary sodium and argon circuits for present pro-jects are enclosed only partly in the primarycontainment, but it is foreseeable thatfor large industrial-size reactors theywill be completely within the containment.

Waste management control

... Gaseous wastes

The essential part of the primary sodium circuit iscontained in the main reactor vessel. It has beenaccepted on the basis of experiment that0.1% of the solid fission products and iodine com-pounds (Nal) released into the sodium as aresult of cladding defects would reachthe argon; 90% of these elements, released from thesodium in the form of aerosols, would bedeposited subsequently on cold partsof the primary circuits (the part of the reactorvessel outside the sodium, purificationloops of the primary circuits, and so on).

The argon circuit, whose complex rble is to providea neutral atmosphere in all the parts containingsodium, to regulate the pressure of the argon blan-ket, to allow recycling, scrubbing, scavenging anddischarge of part of the argon, is equippedwith devices allowing the fluid to becleared of entrained sodium aerosols and of thesolid daughter products of the noble gases.The sources will therefore be localizedprincipally at these devices. As noble gases are notretained by the sodium to any appreciableextent, it is found useful generally topostpone the discharge and scrubbing by passingthe recycle gas through baffled delay tanks.

The gaseous releases constitute normally the mainpossible source of contamination of theenvironment, and are subjected tospecial monitoring; their treatment is such thatthese releases can be made very smallwhen necessary.

After decay in the tanks provided for the purposeonly long-lived gaseous isotopes remain; theseare then trapped on activated charcoal atlow temperature before discharge. Any radioactiveparticles that might still remain in the gas arefiltered by highly-efficient absolutefilters in the ventilation system of the reactor

!ding.

After desorption of the charcoal from the purifi-cation plant the gases are stored until the123Xe has decayed; 85Kr is then the onlyimportant remaining isotope. One then has thealternatives either of disposing of it byspreading out the release over aperiod of time and awaiting favourable conditions,or of storing the desorbate in bottles (whichrequires long-term storage since 85Kr hasa half-life of about 10 years'.

Monitoring consists in measuring activity at severalpoints in the argon circuit:

the outlet of the devices used for filtering sodiumaerosols;the outlet of the decay tanks;and the outlet of the scrubbing cell.

The general detector for monitoring the activityof waste in the ventilation gives a finalindication of the character of thegaseous waste. finally, the waste is diluted sub-stantially in the stack.

... Liquid wastes

Liquid wastes arise from decontamination of theinside of the primary circuit devices; from

37

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decontamination of small equipment;from washrooms, showers and change facilities;from hot cells and from workshops; asresidue from combustion of sodium(if a fire were to occur in the primary sodiumcoolant); and, finally, the sodium from theprimary coolant loop if it must beremoved. In addition to the constituents normallyfound in the liquid wastes of other types ofreactors, the liquid wastes of fast breederreactors generally contain sodium hydroxide(NaOH) and traces of plutonium.

Monitoring of liquid wastes is carried out at eachstage by sampling:

intermediate checks before collection;checks before transport to the effluent treatmentplant;checks before treatment (radiochemical analyses);checks before disposal.

It is possible to dilute the effluents once they havebeen collected for storage. After collection andstorage the effluents pass through a sealeddrainage system or are transported in tank cars toan effluent treatment plant, which may serveseveral power stations. In the event of anaccident it is possible to reserve the existing capacity for effluents of high and medium activityand to use auxiliary capacity for lowactivityeffluents.

The treatment of liquid waste depends on theactivity level and the chemical compositionof the waste. Only the large quantities ofeffluents containing soda may cause special prob-lems.

Low-activity effluents are subjected to a simplecheck and neutralized, if necessary, beforedisposal outside the power station.

Medium- and high-activity effluents are filtered toremove suspended material and the filtrate istreated by ion exchange, evaporation orflocculation, as required. After monitoring thelow-activity liquids are discharged into theriver and the concentrates are treatedas solid wastes.

The total activity and the activity level of the wastedischarged are kept within limits based on theminimum dilution volume (taking intoaccount any other releases of radioactive materialsupstream and downstream) in order to ensurethat the maximum permissible concentration(MPC) for drinking water [less than 'IV Ci/m3 foran unidentified mixture of radionuclides ifneither 226Ra nor 228Ra is present] is not exceeded.

The service area of dissolving cells at the Karlsruhe researchcentre. Photo: Ges. far Kernforschung m.b.H., Karlsruhe

Surveillance of the biological environment is carriedout by means of periodic sampling down-stream,and analyses of flora and fauna.

... Solid Wastes

High activity solid wastes consist of the cladding offuel assemblies (when they are dismantled onsite); nonreusable components such aspumps, heat exchangers, rods and rod drives; purification devices and concentrates from theeffluent treatment plant. After contain-ment of contamination and protection from irradiation, which are achieved by the usualmethods, these materials are storedeither on site or, better, at a special storage site.

Lowactivity solid wastes vary in volume and type,but are usually compacted, chopped and packedin drums after being enclosed in vinyl. Theycan be kept at a special storage site. Burnable low-activity waste is incinerated whenever possible.

The various concentrates, filter media, resinsand other solid wastes from the effluenttreatment plant are incorporated in bitumen andstored at a special storage site.

Conventional monitoring methods are used,including external radiation checks by portable orfixed monitors and contamination checksusing monitors or smear tests.

Accident Considerations

All complex systems are subject to a wide varietyof unplanned occurrences which may interferewith their normal operation or, in extremecases, may endanger the health and safety of thepublic. Most accidents that can be envisagedfor a nuclear power plant would haveinsignificant radiological consequences, but inpractice the response of the plant to a variety ofassumed accidents is examined in order tomake certain that all potential avenuesof release of fission products are understood. Theprobability of occurrence of the most seriousaccidents is exceedingly small - but forpublic safety any hazard outside the plant must beprevented. This requirement is accomplishedby two basic approaches: first, the attainmentof thoroughness and assured high quality at everystage from conceptual design to plans forunexpected emergencies; and secondlya parallel effort to prevent accidents which mayoccur from endangering the public, usingseveral lines of defence. Obviously, thefirst approach pervades the second.

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Accident prevention

The most logical way to assure safety in the idealcase would be not to allow accidents tohappen. In practice, accidents may beminimized by making certain that the quality ofeach component and product used in a systemis the highest attainable. The discussionwhich follows describes the approach adopted inthe United States, but the philosophy whichlies behind it is common to othercountries.

"Quality assurance" ensures proper design, fabrica-tion, construction and operation of - and henceconfidence in systems which protect thehealth and safety of the public. A great deal ofstress is laid upon disciplined engineering andquality assurance; guidelines for qualityassurance programmes have been added to the lawsgoverning the construction, licensing andoperation of nuclear installations.These guidelines outline the philosophy to beadopted in design, fabrication, procedures,procurement, handling, storage, identification,inspection, testing, records and audits,and apply at every step in design and construction.

... Attention to designFamiliarity with the system and an appreciation ofthe incidents, large and small, that can occurwithin that system are necessary if itsdesign is to reflect safety consciousness adequately.Consideration is given to such things as

the placement of relief valves so that theirdischarges do not impinge directly upon otherpieces of equipment that might be damaged;

the design of electrical equipment to specifi-cations which ensure that it will continue tooperate in the environment which mightaccompany an accident for example, conditionsof high temperature, pressure or humidity;

multiplication of instrumentation to make upfor data that might be lost because of faultymaintenance or because of an accident;

and piping and pressure vessel design, and plantlayout, so as to avoid potentially hazardoussituations for example, the integrated pressurevessel/piping/steam generator system for the gas-cooled reactor precludes the "double-ended"pipe break accident.

In addition, emphasis is given to designs which allowstraight-forward and uncomplicated performanceof routine tasks, and minimize the possibilityof less hazardous but sometimes more probableaccidents. Accidents such as those involving

Effluent storage tanks at the Windscale reprocessing plant.'hoto: UKAEA

failure within the radioactive waste managementsystem, fuel handling equipment malfunctionsor human error even though these arenot likely to affect the public. have caused moredifficulty in real situations than the large,hypothetical accidents that are plannedfor but have not occurred and are not likely to occurin future.

... Attention to fabrication and construction

Care in workmanship and thorough checking andinspection do much to guarantee the safetyand reliability of each component andultimately of the entire plant. Some of the mostcostly and time-consuming problemsencountered during plant construction andoperation have been caused by failureto adhere to specifications dealing with identifica-tion, cleaning, welding and types of materialsto be used. These may be considereddetails, but they are important details. With theseand other facts in mind many positive actionshave been taken to establish and to enforcequality assurance in nuclear plants to provide fortheir safe and reliable operation.

... Attention to procedures

It is necessary in a complex nuclear plant toestablish, maintain and follow detailed operating,maintenance, periodic in-service testing andinspection, and safety procedures. This programmeshould be conducted normally by the plantoperators in a manner approved by theselevant regulatory body. Variables which are sig-nificant to the overall safety of operation ofthe plant, governing the application ofthese procedures, are identified and monitored.

Safety limits on plant operating variables areestablished to protect barriers preventing the releaseof fission products. If a safety limit is exceededthen the plant is shut down, before the barriercan be breached. Similarly there are limiting systemsettings: settings so chosen that automaticaction is taken to alleviate a potentiallyserious situation before the safety limits are reached.In this case the plant need not be shut down,but its operating condition is changed inorder to maintain an adequate safety margin.Conditions relating to the functional capability ofequipment required for safe operation arespecified, and if performance of thisequipment fails to meet these limiting conditionsthen remedial action must be taken, or theplant shut down. Other requiremehtsof the technical specifications for, the operation ofnuclear installations are surveillanceprogrammes, the various administrative controls

%IL41

necessary to the smooth running of a plant,and allowable limits for the release ofeffluents from it.

Accident mitigration

As noted previously, heavy emphasis is placed onthe prevention of accidents to assure safety;but systems and devices are also providedto minimize further any possible hazard to thepublic by mitigating the effect of anaccident should one occur. This philosophy hasbeen called "defence in depth"; it includesattention to the protection of the publicat every step from design to operation. Specifically,it includes the provision of barriers to therelease of fission products, which areinherent in system design, and special "engineeredsafety features".

... Barriers

The fission process generates radioactive materialsin the fuel, some of which are gaseous orvolatile. Their escape is prevented bythe fuel element cladding (of stainless steel orzircaloy) or, in the ca.,3 of the high-temperaturegas-cooled reactor, by layers of pyrolyticcarbon and silicon carbide on the fuelparticle. The cladding of some of the fuel is subjectto minor faults in normal operation, but majorfailures are unlikely. However, in lightwater reactors any fission products that do escapefrom the fuel cladding are then contained bya very carefully designed and constructedprimary piping system which, in turn,has a very low probability of failure. This is itselfenclosed within the containment building,the final barrier, which is designed andconstructed carefully to withstand the maximumpressure and temperature that could resultfrom the "design basis" accident.

... Engineered safety features

A device or system which prevents an accident orlimits its consequences is called commonly anEngineered Safety Feature (ESF). In thedesign of ESFs the principles of redundancy, diver-sity, freedom from "common mode" fault andsingle failure susceptibility are applied.The largest and most expensive ESF is the contain-ment building which surrounds the nuclearportion of the plant. One of the simplestis the orifice in the main steam line of a boilingwater reactor which restricts flow andlengthens blowdown time in'theunlikely event of a pipe break. Between these twoextremes there are core cooling systems,emergency power systems, containment

42 48

atmosphere cleanup and cooling systems, doublecontained penetrations, control velocitylimiters and many others.

Typical accidents

In the design of nuclear power plants it is commonpractice to consider hypothetical accidentswhich might have severe consequences,then to design the plant and its safety features insuch a way that a hypothetical accident canbe accommodated without risk to thehealth and safety of the public. As experience hasincreased, it has been noted that such "limiting"accidents have not occurred, but failures ofa less severe nature have. Consequently, designersgive just as much attention to the less severeaccident. We will consider here first thefailures that have an appreciable probability ofoccurrence but are not likely to give riseto a significant radiological hazard;then identify the precautions taken for each reactortype. It should be pointed out that no powerreactor can tolerate an accident thatinvolves complete and permanent loss of coolingcapability; as a result, this accident is guardedagainst so well that its probability ofoccurrence approaches zero.

Some events analysed involve abnormal operatingtransients which are not considered to beaccidents since no fuel damage results.Such an event sets in motion a chain of correctiveactions which result either in a reductionpower or the orderly shutdown ofthe reactor.

Occurrences that are analysed generally are loss-of-load (generator trip); loss of condenser vacuum;turbine trip; turbine bypass valve malfunction;and loss of power. Various sensing devices provideinformation to the control room operator andto instrumentation necessary to ensurethat a transient is accommodated in an orderlyfashion.

Other, more serious events that are analysed areconsidered to be accidents. These eventsalso result in the shutdown of the plant,but they may also result in some release of radio-activity from the fuel or the primary system.The types of events analysed are accidentsresulting from: introduction of reactivity to thecore (by sudden withdrawal of control rods,causing the power of the reactor toincrease); refuelling operations; or loss of coolingcapability. In any of these events the ESFsmay be called upon to perform theirdesigned functions.

Figure 17: Safety features of a typical 8WR Figure 18: Safety features of a typical PWR

Such an accident is known as a "design basis acci-dent", and is used to set the criteria forperformance of many ESFs and inconsideration of siting and safety generally. Inaddition, the designer assumes that some ofthe ESFs may fail in part: but the contain-ment and emergency cooling system are assumed towork. These assumptions are thought to bequite conservative, and this type ofanalysis does allow an assessment of the safety ofthe plant to be made in the context of thepossible effect of an accident on thepublic. Even under the adverse conditions assumedthe radiation doses estimated to be likely tobe received by the surrounding population are small.

... Light water reactorsThe most serious hypothetical accident consideredfor light water reactors (both PWRs and BWRs)is that of loss of coolant: a failure in theprimary system allowing coolant to flow unimpededfrom both sides of the break is assumed. TheEngineered Safety Features in this caseprovide for cooling water to be injected, poured orsprayed into the reactor vessel in order tominimize damage to the core (Figs 17 &18). If these systems operate satisfactorily the acci-dent is limited to pressurization of the primarycontainment by the release of high temper-ature water (a significant portion of which will flashto steam), the failure of a portion of the fuelcladding, and the release of some volatilefission products. These fission products would befiltered or scrubbed by one of the containmentcleanup systems and a significant fractionwould be removed. In any event, gross release tothe environment would be prevented by theprimary containment vessel.

... Liquid metal fast breeder reactors

The coolant for the liquid metal fast breederreactor (LMFBR), as noted earlier, isliquid sodium at high temperaturebut at relatively low pressure (Fig.19). Ofseveral hypothetical accidents postulatedthe worst is thought to be loss ofcoolantflow accompanied by failure of the controlsystem to initiate a reactor scram (sudden shut-down). The designer assumes simultaneousfailure of all operating primary sodium pumpmotors, and thus loss of coolant flow. Ifthis combination of failures were tooccur the sodium would boil. Voids within thesodium resulting from this boiling would tendto increase the reactivity of the reactor- in other words, its condition would become super-critical, and its power wouid increase rapidly.This would lead to melting and partialvapourization of the fuel, and eventually to dis-assembly of the core. [The energy releasedin such an event would be limitedby physical factors which are calculable.] Aquantity of sodium coolant would be forcedupward against the reactor plug, leading to aloss of pressure and the release of a fuel/sodiumaerosol to the galleries and compartmentsaround the reactor vessel. Some of thisreleased material could then leak into the spacebounded by the containment shell, wheremost of it would be removed by the aircleanup system. The LMFBR is designed to ensureintegrity of the primary vessel, head and heattransport system; in addition, a containmentshell is provided to ensure that in the event of anaccident such as that described the publicwould not be significantly affected.

4$

43

Figure 19: Safety features of a typical LMFBR

CONTAINMENT BUILDING

NEL !DOWN TRAP

... High-temperature gas-cooled reactors

In a high-temperature gas-cooled reactor (HTGR)helium is circulated at a pressure of 50 atmos-pheres with an outlet temperature of 760°Cthrough a core made up primarily of graphite, withpyrolytic carbon and silicon carbide coateduranium-thorium carbide fuel particles(Fig.20). Many of the very serious accidents nor-mally considered in association with otherreactor types are obviated by basing thedesign on an integrated core and steam generatorsystem, using a prestressed concrete pressurevessel. One of the most serious accidentsconsidered is a depressurization of the primarysystem together with failure of some steamgenerator tubes. In this highly improbableaccident the rate of depressurization would belimited by the access plugs, which wouldact as loose-fitting "stoppers", Steamwould be injected into the core through the breakin the heat exchanger, giving rise to agraphite/steam reaction. This wouldrelease hydrogen, and would probably damage thecore sufficiently to release some fissionproducts from the fuel. Theactivity would then leak from the primary systemand would be partially trapped in the contain-ment cleanup system; gas leakage wouldbe prevented ultimately by the contain-ment shell.

. .Emergency planning

Most accidents are prevented by elaborate safetysystems and designs, and if any does occur theEngineered Safety Features should be ableto reduce the hazard to the public to an acceptable

44

110 lir-

Figure 20: Safety features of a typical GCR

CONTAINMENT BUILDINGNOV COMMON ONGASCOOLED REACTORSI EIC ET US)

COOLER ANDTOL TER

STEAMGENERATOR

minimal level. But, as an auxiliary to QualityAssurance, "Defence in Depth" and ESFs,"Emergency Planning" is also required in respectof each installation. Plant operators arerequired to establish an organizationmade up of designated individuals, from both with-in and without the group responsible for plantoperations, who must prepare for any emer-gency situation that could arise. Inter alia, theyhave the responsibility for ensuring safe shut-down and cooldown of the plant; theestablishment of communication and workingagreements with various community andgovernmental emergency and law enforcementagencies; the identification of the positionand function of each member of theemergency organization together with any specialqualifications they may have; the maintenanceof a means of determining the magnitude ofa release and the establishment of criteria for put-ting into operation various emergency plansand the establishment of procedures fornotifying all involved parties and agencies; provi-sions for emergency treatment of injured atthe site and at local medical facilities;provisions for training and practising the dutiesassigned to each member; and, finally,procedures for determining when itis appropriate to reenter the installation affected.

Site characteristicsChoice of a reactor site often carries with itspecial design requirements, to take account of

Workmen at the Oak Ridge Gaseous Diffusion Plant loada cylinder of uranium hexafluoride, enriched inuranium-235, for shipment. Photo: USAEC

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seismic loadings, foundation conditions, windand weather conditions, floodings and tidalwave considerations, land use and access andvarious other physical factors. In regions of theUnited States where seismic activity is to beexpected a nuclear installation may not belocated nearer than a quarter of a mile to an activefault; and it must be designed to withstand themaximum ground acceleration which hasbeen experienced at the distance of the site fromthe fault. In areas where strong tornadoes areprevalent the assumed design conditionis a 300 mile per hour wind with an associatedpressure drop of 3 pounds per square inchin 3 seconds. The effects of the maxi-mum expected flood or tidal wave are taken intoaccount similarly, to ensure that the plantwill be safe during and after the event.

Special situations arising out of surrounding landuse may require special attention. If the plantis to be built in the vicinity of the flightpath of a nearby airport the containment and otherstructures are designed to withstand the impactof a colliding aircraft. If agricultural con-ditions present an important pathway for thetransfer of radionuclides to man theroutine release ratels) of the important fissionproduct(s) are limited accordingly. If theplant is built near a population centrethen many factors must be taken into account, and

.additional safety features provided. In all cases,any characteristic of the site that may havea bearing on the overall safety of the plant is con-sidered, and appropriate protective measuresare taken if needed.

Operating experience in the United Status

It is now more than a quarter of a century sincethe first chain reaction was achieved. Theintervening years have witnessed theinstallation and operation, in the United Statesalone, of some 25 central station nuclearelectricity generating plants. Duringthis entire period no single member of the publichas been injured by a power reactor accidentin the US - nor in any other country.Failures in the operation of these reactors havebeen experienced, but these failures were ofa minor nature and the Engineered SafetyFeatures of the plants concerned were capable ofdealing with them. When failures occurred theplants were shut down safely, in accordancewith their design.

The containment shell for one of the three reactor units atthe Browns Ferry nuclear power plant, duringconstruction. Photo: Tennessee Valley Authority

Abnormal occurrences and/or unusual eventsexperienced must be reported to the regulatoryagency. Such reports are reviewed to makesure that corrective actions taken areadequate; and, in addition, they are made availableto other facilities and reactor designers through-out the country so that they may be aware ofwhat has taken place. These "experience reports"are also available to the public.

Similar experience in the design and operation ofnuclear power reactors has been obtained inother countries. It is important that suchexperience be gained, and that it be applied in thefurther development of additional EngineeredSafety Features. In this way the reliabilityof reactors for safe operation can be improvedeven further.

Fuel Reprocessing

Fission products build up in fuel elements withinthe reactor, eventually absorbing neutrons tosuch an extent that the fission process isinterfered with. The fuel elements are thereforeremoved from the reactor well before all theusable fuel has been burned, and are sentto reprocessing plants. The main objective ofreprocessing is the safe and efficient recovery ofplutonium (which is produced in the reactor)and unburned uranium in sufficient purityfor re-use in the fuel cycle.

Although much research and development has beencarried out on differing technical approaches tothis objective, all the processes used in theworld's major reprocessing facilities are based uponthe dissolving of the fuel in aqueous acid,followed by a series of solvent extractionand sometimes ion exchange operations which firstremove fission products, secondly separate theplutonium and uranium, and thirdly purifythese two products. The discussion which followstherefore centres on this widely-acceptedapproach, which is unlikely to besuperseded to any great extent for at least a decade.

Origins and types of effluents and wastes

In order to discuss the control of radioactiveeffluents and wastes arising duringreprocessing it will be helpful to summarize themain types of operation, so that the originsof the various wastes are madeapparent.

... Disassembly operations - It is sometimesnecessary to remove external parts of theirradiated fuel assembly by remote

sa 47

1

methods prior to starting reprocessing operationsproper. This gives rise to an accumulation ofmetallic waste which, as a result of neutronactivation in the reactor, is usually radioactive.

... Decladding - Some fuels, especiallyuranium metal fuels, are treated toremove their cladding either by chemical dissolutionor by mechanical processes. In the former case aliquid effluent results, and in the latter, solidwaste in the form of a swarf. In each case the clad-ding activity, caused mainly by diffusion offission products from the fuel into thecladding and by neutron activation, must bereckoned with in the waste.

... Fuel shearing Other fuels, especially thosemade of uranium oxide, are fed to a shear andchopped into small sections which drop intoa dissolver vessel. This operation may release smallquantities of gaseous effluent, including radio-active noble gas fission products.

... Fuel dissolving . Metal fuels, after decladding,are dissolved usually in a boiling aqueous acid.This gives rise to a gaseous effluent containingradioactive fission products such as the noble gasesradiokrypton and radioxenon, together withradioiodine.

Oxide fuels, after shearing into small sections, arealso treated with boiling aqueous acid, givingrise to similar gaseous effluents. Sometimesthe fuel and cladding are dissolved entirely, butmore often only the irradiated uraniumoxide is dissolved, leaving a residue ofleached metallic hulls to be disposed of; these maybe stainless steel activated during residence inthe reactor, or zirconium or other alloysimilarly activated.

... Chemical processing - The dissolver solutioncontaining the uranium, plutonium and fissionproducts is next processed in a series ofsolvent extraction and sometimes ion exchangetreatments with intermediate chemical conditioningstages. At the outset the bulk of the fissionproducts are separated to give an intenselyradioactive waste, which must be stored in someform after further treatment and concentration.As processing fur the recovery of the twomajor end-products - uranium andplutonium - continues a number of liquid effluentsarise. These contain the remaining traces offission products together, with economicallyacceptable trace amounts of lost uranium and plu-tonium; after further treatment these effluentsmust be disposed of safely and economically.Some solid wastes, such as ion exchange resins, usedfilters and so on, of moderate activity level, alsoarise from these operations.

48

... Purification of products for recycling - Thefinal stages of chemical purification of the plu-tonium and uranium products and theirconversion to forms (usually oxides) in which theymay be used again in the fuel cycle result inlimited volumes of liquid and gaseouseffluents containing minute traces of the products.Solid wastes deriving from the mode of handlingthe plutonium in these final purification andconversion phases are also created; these includematerials such as plastic containment wastesand discarded rubber gloves, which implya requirement for recovery and disposal.

Control of effluents and wastes

Having summarized briefly the origins and types ofwaste arising from fuel reprocessing, it is nowpossible to examine its management andcontrol using for convenience as before the threecollective headings solids, liquids and gases.

.. Solid wastes The principal solid wastes arethe metallic discards, cladding swarf and leachedsections of fuel can. Usually these are tooactive for disposal by simple burial, although thisprocedure has been selected at some facilitieswhere it has been established that suitablyimpervious geologic strata exist. More often thesemetallic wastes, which include commonlystainless steel, magnesium alloys andzirconium alloys, are stored in concrete silos on thesite, designed and operated in such a way as notto preclude the possibility of ultimate removaland final disposal after a very long decay period.Other solid wastes are monitored and segregatedinto convenient types - for example,combustible and non-combustible materials, andmedium- and low-level activities. A variety ofdisposal techniques have been adopted forthese wastes in different countries. For the lowerlevels of activity burial in large trenches onthe reprocessing site or on an adjacentsite has been used; long-lived activity is limited inthese disposals, so that the ultimate releaseof the site is feasible. Regular monitoringof water draining from such sites is carried out todemonstrate the continued safety of theprocedure.

Another technique for the disposal of low-levelsolid waste which has been used by somecountries is sea disposal, under carefullycontrolled conditions; the waste is placed in drumswhich are encased in concrete and dumped inselected known ocean areas in water atleast 2700 m deep, often as a combined internationaloperation, well away from fishing grounds.

The Dungeness B nuclear power station, on the Kent coast,during construction. Photo: UKAEA

Combustible waste has been incinerated at somesites, with special attention being paid to thecleansing of the gaseous combustionproducts by conventional scrubbing and filteringtechniques. The resulting ash can either besubjected to chemical recovery treatmentif this is economically feasible, or stored, economi-cally because of its relatively small bulk. It isconceivable (and it is already technicallypossible) that extraction of longer-lived activity,such as that due to plutonium, from such ashcould be undertaken to ease its ultimatesafe disposal in the environment, even though theactual recovery of the plutonium was notitself economic. Medium-level solidwastes are generally stored long-term to allow theiractivity to decay, usually with a view to ultimatedisposal by the most appropriate of the routesalready mentioned.

.. Gaseous wastes - The principal gaseous wastesin reprocessing arise as noted earlier from theshearing of oxide fuels, from the fueldissolving operation and from the air used to ven-tilate such facilities as high activity liquidstorage tanks. Particulate and entrainedactivity may be involved, as well as 1311 and 129I andradioactive noble gases such as UKr.

Invariably, fuel is cooled sufficiently before reproc-essing to allow most of the short-lived nil (half-life 8 days) to decay, so this radionucliderarely presents a significant problem. Particulateand entrained activity is kept to a low level byspecially-designed gas-cleaning equipmentincluding scrubbers and filters; in particular, anumber of specifically developed absorptionsystems are used to trap radioiodine.Release to the environment is ultimately throughhigh stacks fitted with monitoring equipmentwhich registers activity levels and flow rates,so that activity levels in discharged gases may beknown and recorded. As a final check atmost reprocessing sites a programme ofenvironmental monitoring is carried out in the areasurrounding the plant - often extending for somemiles around. The samples taken and examinedinclude those indicative of potential publicexposure, including radioiodine and radiostrontiumin milk. The results of all these measurementsare compared with derived working levelsbased on ICRP recommendations.

Two radionuclides have been studied especially inconnection with their release in gaseouseffluents: these are krypton-85 andiodine-129. The radiological effects, both local tothe reprocessing site and on a worldwide basis,of the release of krypton-85 have beenconsidered; the conclusion is that it will not pose

a significant problem until well into the 21stcentury when, if steps are not taken for itsremoval and containment, the annual genetic dosefrom this radionuclide will probably approach1% of the natural background level.

Methods of removing krypton-85 from the gaseouseffluents from reprocessing are already technicallyfeasible, and can be developed sufficientlyagainst this time-scale to ensure that plants builtafter say about 1990 are equipped to removeand store this noble gas.

It has been established that iodine-129 would notpose a serious problem in gaseous wastes froma reprocessing plant serving a powerprogramme of up to about 100 000 MW(e).

.. Liquid wastes - There are three major catego-ries of liquid wastes from reprocessing:

- low level wastes, such as fuel storage pond water,condensates from evaporators and many planteffluents;

- medium activity wastes, such as those arisingfrom chemical decanning operations, and someplant effluents;

- high activity waste, containing the bulk (usuallymore than 99.9% of the fission products.

Large reprocessing plants produce several cubicmetres of low level aqueous waste each day.After some treatment, which varies fromsimple storage to permit radioactive decay tosophisticated chemical processing, suchwaste is usually released to the sea orto rivers under carefully controlled conditionsdecided upon after many years of investigation.The generally accepted pattern for theresearch which precedes the determination ofallowable releases to the environment is asfollows: the composition of the waste(including likely variations) is established, the pro-posed release procedure is studied and the routesby which the radioactivity may return to manare found and quantified. In practice, one or twoof these routes are normally found to be solimiting that if the resulting radiationexposure is kept within the dose limits recommen-ded by the ICRP the total exposure from allother routes will be quite minor. Thismethod of assessment and control of public expo-sure to radiation from waste disposal is knownas the critical path approach. Examples ofsuch possible critical pathways met in lowlevel liquid waste disposal are:

.

the concentration of radioruthenium in edibleseaweeds

the concentration of radiostrontium in fish

the concentration of radiozinc in shellfishand the adsorption of radiozirconium on silt,which may lead to external radiation exposureof fishermen.

When the research and investigation phases havebeen completed the system becomes one ofcarefully measured releases within aspecific and nationally laid down authorization,followed by systematic and appropriatelywidespread monitoring of the majorcritical exposure pathways. Usually this monitoringis carried out by the reprocessing facilityoperator, and independently by thenational authorizing body responsible for environ-mental control.

One radioisotope is worth special mention in thisdiscussion: tritium, formed during the fissionprocess in the reactor. This tends to appearmainly in aqueous effluents from reprocessing astritiated water. It is virtually impossible toremove tritium from aqueous waste streamsby any reasonably economic method, and most ofthe tritium formed must therefore be dischargedto the environment where it is readily diluted.Although the half-life of tritium 12 years is ratherlong, it is dispersed in the biosphere easily, andcareful evaluation has shown that it presentsno significant hazard to the public in the amountsin which it is released to the sea or to riversystems from reprocessing plants.Nevertheless, measurements are invariably madeboth in discharges and subsequently, ifpossible, in the environment.

Medium activity wastes are very variable in compo-sition but contain usually significant quantitiesof dissolved salts. They are treated by aselection or combination of methods such as eva-poration (with transference of the concentrateto high activity storage), decay storage andchemical precipitation (with the settled floc beingretained as a solid waste) The great bulk ofsuch waste is thus transformed into lowlevel liquid waste.

High activity waste: The bulk of the fission productsgenerated in power reactors are contained inaqueous solutions of nitrate salts of variousmetals after reprocessing. The composition of thewaste varies depending on the reagents used inthe processing, and whether the fuel has beenleached from the fuel cladding or whether claddingand fuel have been completely dissolved.Invariably the first stage in treatmentis concentration by evaporation, but the degree ofconcentration varies considerably depending onthe processing flowsheet used. If only smallamounts of extra salts have been added and thecladding has not been dissolved, then a

volume reduction to about 50 litresper tonne of uranium fuel is achieved, but in anumber of plants 450.900 litres per tonne ofuranium fuel processed result. This intenselyactive liquor is stored in thick walled steeltanks contained in concrete cells up to1.5 m thick, themselves lined with steel; sometimesthese tanks are underground. In order toremove the heat of the decay of the fission productscooling coils are incorporated in the tanks, andsometimes a means of keeping precipitated solids insuspension, such as air jets, is included.

Universally, sufficient spare tank capacity is retainedto accept the contents of a leaking tank. Gaseouseffluent from the storage tanks - mainly airused for agitating the liquid is cleaned byspecially designed gas cleaning devicessuch as scrubbers and electrostaticprecipitators, and is monitored continuously asit is discharged from a high stack.

For a century or more the concentration of radio-nuclides in these wastes will be high enough torequire their nearly absolute isolation fromthe human environment. During this time some ofthe shorter-lived radionuclides will decay,reducing the potential hazard of thesewastes, but the concentrations of long-lived radio-nuclides such as 90Sr predicate a total contain-ment time of several hundred years. If thewastes contain substantial concentrations oftransuranic elements such as "9Pu the requiredcontainment times may range up to manythousands of years.

So far these wastes have been stored safely as liquidsin tanks. Such storage is considered to be safefor many years to come, combined withsurveillance and the use of the "spare tank" philo-sophy referred to above. But it is 'generallyaccepted that in due course some formof solidification of high activity wasteswill have to be adopted for ultimate storage. Agreat deal of research on this topic has beencarried out during the past 15 years inseveral countries, and several alternative systemshave now been developed to a stage at whichthey could soon be adopted fortransformation of liquid high activity waste intosolid. Such solidification would makecontinued surveillance less vital, andwould reduce requirements for the replacement ofexpensive tank storage facilities. But even ifthese wastes were to be solidified it isexpected that interim storage as liquid would berequired and, taking into adcount theprojected continuing growth ofnuclear power, that up to the year 2000 about onehalf of all high-level wastes generated would bein interim storage as liquid.

51

As mentioned at the beginning of this section, dif-ferent processes give rise to rather differenthigh activity liquid wastes, and certainsolidification techniques which have been devel-oped are more suited to some wastes thanto others. Generally, all solidificationprocesses involve heating the wastes to temperaturesbetween 400°C and 1200°C, which drives off allthe volatile constituents - mainly water andnitrates - leaving a calcined solid or a melt that coolsto a solid. In most cases melt-making additivesare included with the heated waste so that glass-likeproducts result.Ideally, the solidified wastes should have- good thermal conductivity;- low leachability;- high chemical stability and radiation resistance, and- mechanical strength

element in the development of nuclear power pro-grammes. Great care is taken, through the useof trained workers and specialized equipment,to guarantee safety during the handling of radio-active materials; the standard of safetyattained must be at least as high intransport, but the precautions taken should not besuch as to hamper the free movement ofconsignments.

Suitably packed, radioactive materials are movedgenerally in normal conveyances by road orrail, in the air or by sea. They comeusually into comparatively close proximity to thegeneral public, and any release of the contentsof packages may lead to contamination ofthe environment and of persons in the neighbour-hood. The packages themselves will behandled in most cases by transportworkers who have neither specialized training norequipment.

Regulations must obviously be laid down to ensurethat the packages are inherently safe, and thateven in the event of serious accidents anyescape of their contents which may occur wouldnot lead to unacceptably high levels ofcontamination. It is also obviouslydesirable that the regulations of different countriesshould be as uniform as possible, so thatpackages can move freely from onecountry to another.

Soon after the IAEA was established it was recog-nised that this Agency was in a very favourableposition to draw up regulations, applicableto all modes of transport, which could be acceptedby national authorities and by organizationsconcerned with the international transportof goods. The Agency's regulations for the safetransport of radioactive materials were firstpublished in 1961; they have been revisedseveral times since. They have now been adoptedas the basis of their own regulations by almostall international transport organizations, andare followed closely in the regulations laid down inmany countries including those that are mostheavily engaged in international trade in radio-active materials.

After solidification the wastes must be suitablycontained. Interim storage of the solid onthe site of the fuel reprocessing and wastesolidification plant will probably be necessary toallow radioactive decay of most of theactivity of radionuclides with shortand intermediate half-lives. In order to dispose ofthe heat from radioactive decay the interimstorage facilities will again need to bedesigned to provide cooling, using either air or water.

In some countries final disposal of the solidifiedwaste in deep geologic formations such as saltmines is now being examined. Storage of the waste incarefully selected formations would ensure that theyare not reached by circulating ground water duringthe time required for decay of their radioactivity toinnocuous levels. Unless fuel reprocessing andwaste solidification plants were located onthe site of the formation used for disposal transpor-tation of the waste would be necessary; as analternative, the solidified wastes could bestored for long periods on the site of the fuelreprocessing and solidification plant in specially-constructed storage vaults.

The total risk associated with the management ofradioactive wastes is the sum of the risksencountered in association with eachstep. The main goal is to reduce the cumulativerisk to the lowest practicable level; as a result,the steps employed in waste managementprogrammes may differ from countryto country depending on the magnitude of the risksassociated with each process used.

TransportationThe safe and rapid transport of radioactive materials,whether in the form of unused or spent nuclearfuel, by-products or waste is a very important

52 Wat58

Potential hazards in transport are first the irradia-tion of persons or of sensitive substances suchas photographic film which may result frominsufficient or damaged shielding, and, secondly,the contamination of the environment andentry of contamination into the bodiesof persons who happen to be nearby which mayresult fronla failure of the containment.These potential hazards are associatedto a greater or lesser extent with the transport ofsmall quantities of radioisotopes used, for

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Face masks for uranium miners being tested. Photo: USAEC

example, in medical practice, of largevolume liquid and solid waste, and of spent fuelcontaining large quantities of fission products.Some radioactive substances are in the formof hard solids that would be unlikely to becomedispersed in the environment to a significant

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4IP.C. tYC '

i

extent even if their containment wereseriously impaired; others are mixed permanentywith a large mass of inactive material and canthus be considered to be of low specificactivity. Some relaxation in requirements for thetransport of such types of substances is permissible.

53

The root principle adopted is that the packagingitself should provide the necessary shieldingand containment. It is not feasible toprovide in all cases sufficient shielding to reduceexternal radiation levels to completelynegligible values without adding excessive weightto the package. Three categories of package,identified by different labels, are specifiedin the regulations: for the first category the label iswhite with one red stripe, and the radiationlevel at any point on the surface does notexceed a value corresponding to 0.5 mrem/hour.For the second, the label is yellow with twored stripes; the radiation level at thesurface of the package does not exceed valuescorresponding to 50 mrem/hour at thesurface and 1.0 mrem/hour at onemetre from the surface. For the third, the label isyellow with three red stripes; the radiation leveldoes not exceed values corresponding to200 mrem/hour at the surface and 10 mrem/hourat one metre from the surface. Each labelalso carries the trefoil symbol whichindicates the presence of radioactive material.Neutron absorbers and. spacers are built intothe packaging for fissile materials inaddition to the radiation shielding. In view of thesafety features that are built in to packages fortransporting fissile materials no speciallabel is required other than those relating to theradioactive properties of the contents.

A large fraction of all consignments of radioactivematerials contain relatively small quantitieswhich would not present an unacceptablehazard even if the package containment wereseriously impaired. It is therefore economicto prescribe two types of package in termsof containment standards; these are referred to asType A and Type B.

Type A packages are designed to withstand normaltransport conditions, including rough handling,without significant loss of shielding andcontainment. To be classified as Type A specimensof the packaging must pass a series of testsdesigned to simulate the effects thatcould be produced by weathering and expectedrough handling. It is accepted that in anaccident the containment may beimpaired, and it is assumed with some experimentalsupport that one-thousandth of the contentswill escape and that one - thousandth of theamount that does escape may find its way into thebodies of persons nearby.. An upper limit,based on its radiotoxicity and radiationemission, is therefore prescribed for the activity ofeach radionuclide that is to be 'transported in aType A package. ita54

Type B packages are designed to withstand verysevere accidents without significant loss ofshielding and containment. To beclassified as Type B specimens of the packagingmust pass both the Type A tests and additionaltests including a 9 metre drop and exposureto fire, these simulating the conditions that mightbe associated with severe accidents in anymode of transport. The design of Type B packagingmust be approved by the competent authorityof the country in which it is produced,There is no regulatory upper limit to the activitythat may be included in a Type B package,but the upper limit for the particulardesign is specified in the approval certificate of thecompetent authority.

Instructions issued to transport workers enable themto segregate packages of radioactive materials insuch a way that the radiation levels in occupiedplaces or near photographic film do not exceedacceptable values. These instructionsare based on the information given on the packagelabels, and in particular on the radiation levelat one metre from the surface 'which isreferred as to the transport index]. Additionalrequirements based on the transport indexare specified for transport by rail, road,inland waterway craft, sea-going vessels and aircraft.

Accidents involving consignments of radioactivematerial have been reported on manyoccasions. Statistics for a wide range of countriesare not available, but a report based onexperience acquired in the UnitedStates has shown that on 146 occasions the radio-logical assistance plan was called upon inconnection with accidents duringtransport involving radioisotopes. In some of theseaccidents relatively minor releases of radioactivecontamination to the environment occurred.However, no release has been detected from anypackage designed to standards which approachthe Type B specifications. This gives groundfor some confidence that the Type B specificationswill indeed ensure that a package will. withstandvery severe accidents without significant lossof its contents.

But it cannot be taken for granted that packageswill always be properly loaded and assembled,and that accidents of unforeseen severitywill never occur. Countries in which there is con-siderable traffic in radioactive materials havetherefore set up systems which give someassurance that efforts will be made at the scene ofan accident to prevent any avoidable spread ofcontamination, and that competentassistance in dealing with the accident will be givenwithin the shortest possible time.

otherimpaThe undertaking of any large-scale enterprise disturbsthe environment. The production of electricalenergy is no exception. Many of thedisturbances which do occur are due not to thenature of the fuel used but arise from thenormal processes of plant constructionand ancillary operations.

Plant ConstructionDuring the building of a large plant it may benecessary to provide new roads to allow access byvehicles used to transport constructionmaterials to the site. The increase intraffic may impair the normal flow of traffic in thearea to a considerable extent.

A site area of the order of 40 to 80 hectares (100to 120 acres) is required for a 2000 MW(e)nuclear power station. Since goodfoundations are required to support the heavyweight of large structures it may be necessary toundertake a considerable amount ofexcavation and grading. Theseactivities can increase considerably the amount ofsediment which enters surface streams whenit rains, and the amount of dust in theair during dry periods while the plant is being built.

The historical significance of the proposedsite of a nuclear power plant, like thatof any other kind of power plant, is consideredcarefully. Care is taken to minimizedisturbance to any prehistoric petrified plants andanimals or to any valuable archeologicalremains of early civilizations, graveyards, oldbuildings, ruins of walls, monuments,aqueducts and so on. Hydroelectricplants have associated with them large manmade lakes, which have replaced freeflowingrivers; fortunately, immense impoundmentsof water like these are not necessary to nuclearpower plants. Often, alternative sitesfor power plants might be selected in order to avoiddamage to or the destruction of naturaltreasures or priceless historic remains;

if this is not possible intensive scientific investiga-tions should be made before the plant isbuilt, and the most valuable scientificand historic treasures removed to museums for safekeeping.

Transmission LinesThe overhead transmission lines associated withelectricity generation and distribution havea highly visible impact on the environment. It isvirtually impossible to conceal transmissionline towers - pylons - and the linesthemselves, but it is possible to do a great deal tomake them less obtrusive and moreattractive. The practices adoptedobviously differ from country to country, becausetypes of terrain and uses of land vary consider-ably; but in general transmission lines canbe placed and oriented in such a way that they neednot have a serious effect on the environment:they cannot be eliminated from the land-scape, but they can be integrated into their surroun-dings. Cables laid underground might be analternative in the longrun, but furtherdevelopment is required if this technique is tobecome practicable in economic terms.

Thermal DischargesAll steampowered electrical generating plants,whether fired by fossil- or by nuclear fuel,have a common potential problem intheir need to release unused heat to the environment.Recapitulating: heat from the combustion offossil fuel or from the fission of nuclearfuel in a reactor is used to produce steam at hightemperature and pressure, which drives aturbine connected to a generator. The'spent' steam from the turbine is condensed by pas-sing it through condensers cooled by largeamounts of water. The heat transferredto the cooling water normally raises its temperatureby a maximum of 5°15°C under full loadconditions. The discharge of this heatedcooling water to aquatic systems is at the origin ofthe 'thermal effects' problem.

Comparison of thermal release from fossilfuelledand nuclear plants

The reactors on the market at preient operate at alower efficiency than most modern fossil-fuelled plants of the same generatingcapacity. For this reason, and also because about10% of the heat from fossilfuelled plants isdischarged directly into the atmospherethrough the stack, nuclear plants reject about 50%more heat to the cooling vial than fossil-

6155

fuelled plants. This difference shouldbe reduced with the advanced reactors now beingdeveloped.

Nuclear plants on average use about 180 litres ofcooling water per second per kilowatt hour,with an average maximum temperaturerise across the condenser of about 10°C. Fossil-fuelled plants require about 115 to 150 litresper second per kilowatt-hour foramaximum temperature rise of about 8°C.

Cooling water sources and methods of heat disposal

Various constraints including economic and biologi-cal costs, aesthetics, statutes on water qualityand cooling water sources govern thechoice of the method of disposal of condensercooling water. One of the most importantfactors is the type of source of coolingwater available for a particular steam/electric plant.The body of water to be used may range fromfreshwater lakes and rivers to estuaries andcoastal marine waters. In many countries or in partsof them there may be little choice but to useestuaries and coastal waters because thereare insufficient lakes or rivers.

Basically there are three methods of disposal ofheated discharges:

- by a closed-cycle cooling system;- by a variable-cycle cooling water system;- and by once-through operation.

In a closed-cycle system the condenser cooling waterwill flow from a condenser to an atmosphericheat exchanger (either a cooling tower or anartificial lake or pond) where it will lose heat beforebeing returned to the condenser for re-use.In large steam/electric plants thesesystems are usually limited to freshwater sources,because when marine waters are used thedrift of salt water may affect plant and animal lifeat considerable distances from the coolingtowers. Two closed-cycle, hyperbolic natural draftsalt water cooling towers have been used at theFleetwood Station, a 90 MW(e) plant situatedon the Irish Sea with minimal local effect; but forpresent-day large modern steam/electricplants (of, say, 1000 MW(e) or more)the use of salt water towers may not be desirable.

A variable-cycling cooling water systemrejects some of the heat from thecondenser cooling water in a cooling tower or flow-through cooling pond before discharge into anatural water body. Some Of these systemsare capable of operating at any point between thetwo extremes of dosed-cycle and once-throughoperation.

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When the supply of water is not a problem plantsusually use the once-through system, in whichthe cooling water is taken from nearbyrivers, lakes, estuaries or coastal waters and returnedusually to the same source. Choice of theonce-through method carries with it the needto select between several methods of minimizingthe impact of thermal discharges upon a naturalwater body. These methods include theuse of

- dilution in long discharge canals, using additionallarge-capacity pumps (to reduce the temperatureof the cooling water by adding cooler waterto it before it is discharged);- jet and mdltiport diffusers;- cold water from intake point deeper than thedischarge point, thus using the naturally-coolerwater available during the summer at thesedeeper points and reducing the temperaturedifference between the discharge waterand the receiving water;- and the release of cold water from upstreamreservoirs.

Physical behaviour of heated discharges

Engineers and biologists are making considerableefforts to take into account the needs of boththe aquatic biological community and thepower plant in developing suitable designs for powerplant cooling systems. Physical studies concerningwater temperatures enable some predictionsof temperature patterns resulting from heateddischarges to be made. Information on temperatureand behaviour of heated discharges is needed:

- to avoid recirculation of heated discharge waters.and thus to increase plant efficiency;- to comply with regulations on water tempereturestandards;- and to provide sufficient basic data to enablebiologists and ecologists to assess thermal effects.

These thermal studies include mathematical simu-lation modelling, physical hydraulic modelling,and field studies at plant sites on lakes,rivers, reservoirs, estuaries and oceans. Theircommon goal is to assist in the designing ofpower plants in such a way that undesiredenvironmental effects are minimized.

A plume formed by heated discharges can be con-sidered to contain three regions: the near field,the joining region and the far field. In thenear field, immediately adjacent to the outfall,entrainment of ambient fluid at theexpense of the initial kinetic energy of the heatedeffluent is most important. From a biologicalpoint of view this region may be importantbecause it is here that the highest temperatures areencountered, even though this region represents

only a small fraction of the total volumeof the plume.

The joining region is that in which entrainmentbecomes important together with buoyancy,advection and surface cooling. Differ-ences in density of as little as 1% can lead to theformation of stable stratified flows in whichmomentum istransmitted easily to thelower regions, but transport of heat and matter isinhibited, as if by an elastic membrane, at thelower boundary of the plume. Theprincipal mechanism by which temperatdre isreduced in this region is by lateral entrain-ment of surrounding fluid.

The far field is that portion'of the plume whereadvection, entrainment and surface coolingdominate: momentum and buoyancyforces are no longer considered important. Of thethree plume regions this is particularlyamenable to analytical approaches;however, empirical values or relationships for thehorizontal and vertical eddy diffusivities arerequired. The initial conditions for thisregime must also be specified. Except in river andestuary situations physical boundaries need notbe considered, since they would generallybe remote to the plume.

Hydraulic modelling used to estimate the temper.ature and velocity distribution within a plumerequires relations between the hydraulicmodel and a prototype. Exact modelling requiresidentically valued dimensionless numbers inthe model and the prototype; in practicethis is seldom achieved and several models must beused, each emphasizing separate considerationsin order to produce the desired results.

The ultimate objective in the modelling of thermalplumes is to obtain spatial and temporal temper-ature and velocity distributions within theaffected receiving water which, in turn, could beused to make biological and ecologicalpredictions. The bodies of waterreceiving the discharge can be put into categories onthe basis of their characteristics. Ponds areshallow and generally quiescent exceptfor winddriven flows. Lakes are larger and deeperthan ponds and show stratification as well ascurrent driven by winds. Larger lakes haveinternal currents. Rivers are characterized by un-directional flows with a velocity profile.Their flow volume shows short-term fluctu-ations due to weather as well as seasonal trends.In deep rivers some stratification is possible.Estuaries are characterized by cyclic flows

due to tidal flushing, and stratification due to theirsalinity. Because of the cyclic movement recircu-lation of the heated water can be a problem.

Oceans are characterized by good mixing due tocurrents and waves, and stratification dueto temperature effects. Each of thesereceiving environments presents special designrequirements and simplifications foranalysis.

Thermal effects or. biota and ecology

Perhaps no other single environmental factor affectsaquatic life as profoundly or in such an all-pervasive manner as temperature.Unfavourable temperature may affect reproduction,growth, survival of larval forms, juveniles andadults, and all the life processes necessaryto maintain a healthy state. A host of biological andecological questions may be asked aboutpossible damage to aquatic life inwaters receiving heated discharges, and no reason-able persdn recommends uncontrolled releaseof heated water. Regulatory agencies atvarious levels of government are developing or haveestablished water temperature standards whichare used to govern heated discharges fromsteam/electric plants so that no catastrophic 'kills'or thermally-polluted waters or completedemise of desired aquatic populationsare to be expected. If discharges of heated waterare controlled then the primary concern isin 'monitoring' effects to make sure thatno serious trends requiring corrective action aretaking place on account of subtle temperatureeffects on populations, communities andecosystems. Several pertinent problemareas in the thermal effects of nuclear power stationsare reviewed briefly below.

Effects on fish - Disproportionate attention hasbeen given to lethal temperatures for aquaticspecies, and not enough to the more subtleeffects of sublethal temperatures on behaviour,reproduction, food web relationships,growth and other factors which mayhave a significant impact on the health of aquaticpopulations and communities. Nevertheless,for practical reasons one of the early tasksin planning for a nuclear power stationis to assess the risks of direct temperature 'kills'.

The utilities give much attention to the predictionof the physical characteristics of the thermalplume from thedischarge structure inorder to avoid recirculation and to comply withtemperature standards. This temperaturedata can give an early idea of thepossible risks of thermal kills. In some cases thetemperatures of the undiluted effluent arewell below the published upper lethaltemperature of the fishes of concern. In other casesthe known avoidance behaviour of the fish

63 57

precludes the risk of thermal kills.Comparison between the isotherms drawn fortemperatures around the discharge structure and theupper lethal temperatures of the fishes ofinterest permits an estimate to be madeof the size of the area in which the water temper-ature is potentially dangerous. But thiscomparison is only a grossly simplifiedexamination of the thermal problem.

Animals and plants respond to the conditions in theirtotal environment in a complex and integratedmanner, although biologists often separatethe various physical and biotic factors such as theeffects of temperature for convenience. Theresponse of marine organisms to theinteraction of temperature, salinity and dissolvedoxygen has demonstrated that a change in oneenvironmental factor is influenced stronglyby others. Lethal temperatures for a particularspecies are thus variable with acclimation,season, sex, age, physiological state,water chemistry and other factors. Predictions asto whether a particular water temperature insitu will kill a wild fish therefore needqualification, unless temperatures well above theultimate, incipient lethal temperatures arebeing considered.

Reports of losses of aquatic organisms caused bynatural or man-made temperature changesappear in the literature, but since thesehave been unexpected detailed measurements orobservations are often lacking. Usually it isnot known what other environmentalstresses may have accompanied elevated temper-atures. Reports on fish kills by heat shouldbe evaluated cautiously with the varioussources of error in mind, unless obvious, extreme,lethal temperatures were observed. Oftenthese kills are reported without otherwater quality measurements taken at the time, andit is not uncommon to find that kills have beenattributed to elevated temperature only todiscover later that some toxic material or otherenvironmental factor was actually thecausative agent. Since heated discharges from apower station are common knowledge anydead fish found near a power stationimmediately renders the power station suspect. Theloss of fish resulting from discharges of wasteheat from steam/electric plants are notfrequent, despite some expressed fears. By far themost fish deaths caused by pollution in theUnited States, for example, are the resultof industrial operations - including the discharge oftoxic materials and wastes from municipalsewage systems.

Many of the published lethal temperatures for fresh-water and other marine organisms have been

58

determined in the laboratory. Since suchfish are not usually subject to other environmentalstresses the published laboratory data mustbe treated cautiously if they are to beapplied in the field. Nevertheless, in the absence ofgood data on the effects of heat on fishes insitu, laboratory data serve as good 'benchmarks', or guidelines, although not as standards. Toobtain data for direct application to a particularnuclear site perhaps the most meaningfulapproach before the plant begins operation is to testthe desired species in heated water on site,realizing at the same time that thebiologically-important relationship to be investigatedis the temperature-time exposure history. Thedischarge structures of many existing powerplants provide for rapid reduction of the temper-ature in the thermal plume by dilution.Therefore the determination of thesublethal and behavioural effects of short-termexposures on the desired species are most applicable.The tolerance to acute lethal temperatures mustbe defined at each site; however, in thetemperate regions proper siting and design cangenerally maintain discharge temperaturesbelow acute limits. [The thermal effectsproblem tends to be less acute in temperate watersthan in tropical waters largely because theambient water temperatures are furtherfrom the lethal temperatures of aquatic species.]

The avoidance behaviour of fishes observed both inthe laboratory and in field studies is an importantfactor often overlooked by those concernedabout thermal fish kills. The general lack of fish killsat several existing nuclear power stations dependsto a large extent on the ability of certaindesired fishes to avoid lethal temperatures successfully. Clearly, if the undiluted effluent temper-ature is in the lethal range this should be causefor concern; but this does not necessarily meanthat the risks of thermal kills are high. Properdesign of outfall structures and an under-standing of fish behaviour in response to temper-ature gradients are important factors tendingto minimize risks. No thermal kills of fishwould be expected even if there were small areas oflethal temperature, if the fish did not experiencehigh temperatures for extended periods oftime.

While many fish demonstrate avoidance behaviourin response to lethal temperatures, fish also tendto congregate about their preferred temper-ature. It is interesting to note that thermal historyor acclimation has a positive correlation withthe preferred temperature in some speciesbut no effect on others. The congregation of fish inthe warmer waters of the discharge canals duringthe cool season has commonly been observed

64

at steam/electric plants. The question whether thewarmer waters are actually beneficial toproduction and health of desired fishneeds to be investigated. It can be stated, however,that in many cases the congregation of desiredfish is beneficial to sportsmen, since theavailability of fish is increased.

Effects on plankton - There are many ways ofassessing the effects of heated discharges onplankton. From a basic biological andecological aspect, biologists may be concernedfundamentally with the same types of thermalthermal effects discussed for fishes,although plankton represent a lower trophic level.Interest is mainly in how heated dischargesaffect the metabolism, physiology,growth, reproduction, population dynamics andother life processes of planktonic species.

Plankton, especially in the marine and estuarineenvironments, present a much more difficultproblem. Relatively little is knownabout the population dynamics of even one plank-tonic species, let alone the numerous speciesrepresented in any body of water.Generally the task of proper identification andsampling is much more difficult for planktonthan for fishes. Of course, it is elementarythat plankton are important in an ecosystem in theirown right, but they also form the important andessential food base for many shell- and foodfishes.

Further studies are needed. But we are faced witha pressing need to make some early assessmentof the effects of heated discharges fromnuclear power stations. Investigators working onthe problem appear to use two approaches,namely, estimates of kills of planktonentrained in the condenser cooling system, andestimates of the kill in the receiving water body.

The significance of plankton killed by apower plant may often be difficult to assessin terms of the effect of the kill on thehealth of the planktonic population as a whole.After all, many pelagic fish larvae suffer greater than99.99% natural mortality. It would seem that anylarge effort expended to answer questionsconcerning the impact of plankton kills by towingplankton nets may be spent more effectivelyin other research areas. For example, ifthere are indications that significant numbers ofclam larvae are killed then an extensive studyof the dynamics of the local clam population beingharvested seems to be practical. If importantfood organisms for desired fish are beingkilled a study of the growth, gut-contents and healthof the desired fish population might be undertaken.Other approaches and methods might be used;

but the point here is that while planktonstudies are needed they should be kept in proportionwith the total support available for research,and the objectives of the project.

Effects on benthos - Since the temperature of theeffluent from a nuclear power station is not'boiling' hot but averages about 10°Cabove the ambient temperature, the receiving waternear a shoreline outfall will not be devoid ofaquatic life. Nevertheless, the diversity ofthe benthic flora and fauna near the influence ofthe heated discharges would be expected tochange. But we have limited knowledge,especially in the marine or estuarine environment,and it is therefore extremely difficult to assessor to predict in the long-term the effect ofthese changes.

The bottom organisms resident in the area of influ-ence of heated discharges are generallyconsidered to be good indicatororganisms for thermal effects. Since macroinverte.brates, rooted plants, and macro-algae areessentially non-mobile - unlike free-swimming fish -these bottom organisms may be exposed toheated discharges continuously. Partlyfor this reason, most ecological surveys for nuclearsites include bottom samples in the pre- andpost-operational studies.

It is frequently suggested that heated dischargesmay destroy bottom organisms which areimportant food organisms for fishes. Itis then often implieri, if not stated explicitly, thatthe populations of d3sired fishes will suffergreat harm since fish obviously dependupon lower trophic levels for food for successfulgrowth and reproduction. The concept of thefood supply being one limiting factor for aparticular fish population is not unsound, but asearch of the literature on field experiencesshows no good example in which a heateddischarge destroyed benthic organisms to such alarge extent that its impact was reflected inthe health of the desired fish populations.

It is common experience that the original bottomorganisms inhabiting the environs of the shore-line outfall of a nuclear power station areusually lost due to the scouring action of thedischarged water, which changes the bottom charac-teristics. Casual observations often attributethis loss erroneously to heat; but obser-vations made on the effects of the velocity ofdischarge water on benthic organisms beforeplant operation confirm that the lossoccurred before heat was added. The bottom areaaffected by the changed water current is usuallyrelatively small, and should have no significantImpact.

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The environment of a power station ',ate must beexamined in detail both before and when astation is in operation to determiru theeffects arising from its operation, 7.t.ltensive andcontinuing ecological studies have !;,,,:om thatth6 discharge of heat from power itationsor, be planned and made without Pausing lard'scale changes in the environmen.,any change; observed so far being localto the poi-it of discharge.

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Both in rivers and in estuaries dischargesare being made at thepresent time which do not in any way hinder themigration of fish past the stations concerned.Mciewer, current interest in the possibilitiesof ccx,inercial fish-farming, using warmwater from power stations to improve the rate ofgrowth of the fish, is an indication that positivebenefit may be obtained from heating ratherthen the reverse.

public

healthcsideratio

These can perhaps be best discussed in the contextof an examination of the fuel cycle, keeping inmind the origins and relative amounts ofradioactive wastes and waste heat described inChapter III.

MiningAs indicated previously, the-underground mining ofuranium can expose the miner to duetcontaining naturally-occurring radionuclides.

These dusts, together with radon(a radioactive gas formed by the decayof radium in the ore), pose an occupa-tional hazard to the miner.More specifically, miners can be

- exposed to daughter productsof radon222 (which is a daughterproduct of 226Ra, which in turn is adaughter of natural uranium).

Before the development of current practices, whichreduce the exposure of miners, over-exposureswere experienced and a number of deathsdue to lung cancers resulted. During the past 20years more than 100 uranium miners havedied of lung cancer in the United States, and it hasbeen estimated that 500 to 1500 miners whowere exposed prior to the establishment ofpresent-day occupational safety standards may diesimilarly of radiation-related disease.

The ICRP recommended in 1959 a limit of3 X 10-8 pCi of 222Rn per millilitre as a maximumpermissible concentration (assuming 100% equi-librium with daughter products and 10% ofRadium-A ions unattached). National workingstandards have been established based on thisrecommendation. [In the United States a workinglevel (WL) corresponds to any combination ofradon daughters in one litre of air that willresult in the emission of 1.3 X 105 MeV ofpotential alpha energy. The numerical vaiue of theWL is derived from the alpha energy released bythe total decay of the short-lived daughterproduproducts in equilibrium with 10-IpCi ofcts

per ml in air. The limit for exposure in USmines is four months at working level peryear.] This subject has been discussedby the ICRP for several years, but no evidence hasbeen presented to suggest that the 1959recommendations should be changed.

From the viewpoint of public health several factorsmust be borne in mind:

Radiation exposures of the lungs of minersbefore national standards were established on thebasis of ICRP recorrpgrybitions are not knownprecisely, but they hiTrbeen estimated as beingseveral thousand times higher than the presentexposure limits.

Some critics advocate stoppage or substantialreduction in the growth of power programmes, outof concern for their impact on natural surroun-dings. Although such stoppage or reductionmight be justifiable in some local contexts, in thewider sense and viewed from a public healthstandpoint they cannot be considered tooffer a universal solution. Just how much peopleare dependent on energy becomes evident when-ever there is difficulty in obtaining conventionalfuel supplies, as occurred recently in theUnited Kingdom and in the north-east of theUnited States. In the public health sense theobligation is not really to deny peopleenergy out of concern for their environment, butto harness energy for man's overall good.Energy use is linked too closely withjobs, and the disposal of wastes with health andsecurity, mobility and comfort, to be putsecond to the preservation of a totallyundisturbed natural world. What must be found isan appropriate balance between the socio-economic aspirations of man, and the amount ofdisturbance of his environment which he iswilling to accept in attaining his goals. Systematicand deliberate planning for the best use ofavailable resources is necessary in order that thepublic interest be best served.

Nuclear Power GenerationThe aspects of nuclear power production whichhave key implications for the public health are:

- low level radioactive releasesthermal effects of waste heat

- long-lived radioactive waste residues- and possible accidents and their mitigation.

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Many studies have indicated that cigarettesmoking by the miners greatly increased their riskof contracting lung cancer though exposure tothe daughter products of 222 Rn is the primaryfactor implicated.

By keeping working conditions well within limitsestablished by the ICRP the risks of lung disordersin uranium miners should be far less than thoseexperienced in the mining of other materials.

The establishment of safe working conditions inuranium mines requires the efficient ventilationof mine galleries to remove radon and its daughterproducts. The radon exhausted from the mineis rapidly diluted by diffusion in the atmosphere,and does not give rise to problems of publicexposure in the surroundings of the mine.

Milling, enrichment and fuel fabricationThe piles of tailings from milling operations giverise to several possibilities of difficulty away fromthe site in assuring public health. If strong windsand dry conditions are common it may benecessary to stabilize the piles in someway to prevent the transport of dust clouds topopulated areas. If the piles are exposed toweathering and to water leaching attention must begiven to the water runoffs, as they are likely tocontain radium. The trend at present istoward storage of tailings within dry mines, or inother protected geologic formations.

Historically, tailings have sometimes been used inroad making and as backfill in buildingconstruction. Uses such as these,especially when coupled with the use of buildingmaterials that themselves contain high levelsof naturally - occurring radionuclides, canresult in inadvertent increases in radiation levelscompared with the normal background.Prudent practice in keeping with the ICRP philo-sophy that the radiation exposures receivedby the public should be kept as low aspossible discourages uses of tailings such asthose described.

Uranium ore concentrate from the mills is refinedand converted to UF6 for enrichment in gaseousdiffusion plants. The chemical processesinvolved, the process control standa;ds invokedand the safety procedures instituted in fuelfabrication and gaseous diffusion plants are suchas to preclude essentially any toxicological orradiological impact on individual membersof the public (except the radiation workers actuallyinvolved) or the population as a-whole.Additionally, the strict accounting requirementswhich attend the processing of fissionablematerials in countries engaged in theproduction of nuclear fuels gives added assurancethat discharges of gaseous and/or liquid

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8

effluents contaminated with slightly-enricheduranium are so small as to be negligible.

When fuels are fabricated only from uranium, withno recycling of fissile materials obtained fromreprocessed fuels, no important environ-mental problems arise: the necessity for goodconditions of work for the personnel involved isgenerally sufficient to guarantee that conta-mination is confined within the plant. In the nearfuture, however, plutonium oxide fuels will befabricated for breeder reactors. Plutonium,because of its very low MPC, must be handled andprocessed using very stringent precautions toprotect operational personnel; this impliesworking in specially equipped and confined work-shops, but in normal operation creates littlerisk to the public. Nevertheless, attentionmust be given to accidental situations at the instal-lation especially those involving fires, whichcould lead to the destruction of filteringdevices and permit the escape of important quan-tities of plutonium.

Reactors

Siting - The selection of a site for a nuclear powerstation involves the same basic considerations asany other power plant project with respect toproximity to load centres, transmission routes andaccesses, waste heat disposal possibilities andother, economic factors. The unique featureof the nuclear plant stems from the radiologicalimplications of the fission product inventoryformed in the core. Operating experiencewith nuclear power stations so far has been that inmost cases plant effluents contain such lowlevels of radioactivity as to be barely perceptible, ifat all, above the natural background in areasoff the sites themselves. Considerations ofradiation exposure of persons in the vicinity ofplants from normal effluents does influenceplant design and operation, but in general they donot affect significantly the location of suchplants. People can live more safely next to theboundaries of the site of a nuclear powerstation in normal operation than theycan near many conventional industrial complexes.

Why, then, have reactors generally been removedfrom the immediate vicinity of large numbersof people? The answer lies usually inconcern about the remote possibility of a majoraccident in which the containment of radio-activity could be breached. Such an accident hasa very low probability of occurrence and, asdiscussed in Chapter III, engineered safetyfeatures have been developed to limit the release ofradionuclides from a nuclear plant should anytake place. Nevertheless, a conservativeapproach has been used in the siting of such facilities.

All nuclear power stations are designed to containabnormal events safely, but emergency plansare always established for each installationin case any abnormal release of radioactive materialoccurs. Although designs differ and therequirements laid down by various nationalauthorities do vary in the individualweightings given to certain remote possibilitiesthere is universal recognition that thepossibility of accident is dominantin assuring the safety of the plant. Siting is one ofthe aspects of plant design that is so influenced.

No fixed distance from living areas is universallyapplied in deciding upon the siting of nuclearinstallations. The distance at which a plantis built from a substantial population group variesconsiderably between countries, and from oneplant to another within any one country. Thisvariability results from the interplay of sitecharacteristics with both the inherentsafety features of individual designs, and the safetyfeatures engineered into them to cater for awide range of abnormal possibilities. There is, how-ever, a commonness in siting which might becharacterized as follows:

Site selection involves an integrated considerationof site characteristics and the safety features ofthe facility concerned.

Facilities are designed and operated in such a waythat they comply with radiation protection guideswhich admonish the responsible authorities tokeep radiation doses as low as is practicable, and inany case within nationally-prescribed upper limits.

Facilities are designed in such a way that accidentsthat could result in meltdown and dispersal ofthe fuel are prevented or made highly improbable.The low probability of fuel meltdown notwith-standing, the authorities require that in theinterests of public safety and environmental pro-tection nuclear plants are capable of confiningany significant effects of an accident of this typeto the plant or its near vicinity.

Normal operations As discussed in Chapter II,experience has shown that it is possible togenerate nuclear power while limitingoffsite effects of radioactive effluents in the vicinityof plants to very small increases in backgroundradiation levels:

The very small amounts of radioactivity which arereleased to the environment include tritium andradioisotopes of iodine, krypton, xenon andsometimes carbon.

Most of the tritium and gaseous fission productsare retained in the fuel elements until they arereprocessed, and their behaviour will bediscussed later in a section dealing with fuel

reprocessing. Carbon-14, however, may beproduced and released at the reaction station, Themain contribution to 14C production is neutronirradiation of 14N which may be used forsparging in a reactor.

Carbon is the structural base for all organicmaterial, and plays a significant Role in all forms oflife. The half-life of 14C is quite long more than5500 years so when It enters the environmentit becomes incorporated into the carbon cycle andthus penetrates every living organism.

Nuclear weapons tests resulted in a near doublingof the amount of 14C in the atmosphere duringthe years 1962-63. Since the cessation ofmajor testing programmes the excess amount of 14Cin the atmosphere has gradually decreased, andis expected to drop to about 3% of thenatural, amount by the year 2000.

The amount of 14C entering the atmosphere fromnuclear power stations is expected to increasecontinuously during the next severaldecades. Depending upon the rate at which atmos-pheric 14C cycles into other compartments ofthe environment, its level may become highenough to warrant serious attention.

Howeyer, the increase in radiation levels in theenvironment which results from the releaseof this and other radionuclides cannotusually be distinguished from the background. Theradiation exposures of population groups fromreactors are considerably less than theirexposures from other sources suchas medical diagnostic procedures and are wellbelow the limits suggested as maxima by nationaland international radiation protectionadvisory bodies.

... Accidental events

Experience acquired in many countries in the safeoperation of a number of different types ofpower reactors has been impressive andencouraging and the abnormal events that haveoccurred have not jeopardized public safety.Nevertheless, the sum total of the experience thathas been acquired is still quite limited, and itcannot be said that the probability of an accidentserious enough to have consequences offsiteis zero.

Many assessments of the potential consequences ofpostulated accidents involving the release ofradioactive materials beyond the siteboundary have been made. In this context a numberof things should be said:

Reactors cannot explode like atomic bombs.Neither the composition of the fuel nor itsphysical configuration permit this to happen.

11 69 63

ct

1

[It is sometimes falsely implied that they can bypeople who observe that a reactor can contain afission product inventory comparable inradioactivity to that created by the detonation ofa nuclear weapon.)

The occurrence of significant offsite effectswould require extremely unusual initiating events,coupled with failure of multiple safety devicesprovided to protect the public against suchpossibilities.

The probability of accidents having serious offsiteeffects is generally believed to be so low as toapproach zero. Although they are not quantifiable,the risks of harmful public exposures are judgedto be much lower than those of natural eventssuch as earthquakes, floods and lightning. If aserious reactor accident were to take place onemight be faced with quite serious contaminationof property and even loss of life.Governmental authorities require generally thatemergency plans be prepared in advance to copewith situations such as a reactor accident. Themain measures to be taken include:

rapid survey to delineate the direction andextent of the plume of released radioactivity;

warnings to and instruction of the population;restrictions on the movement of people, the

consumption of milk, wate( and food fromcontaminated areas, and so on;

prevention (if possible) of the extension of theaccident;

and survey of and medical assistance toirradiated persons.

Thermal aspects

As discussed in detail in Chapter IV, the need tocool the condenser of power plants, whether theyare fossil- or nuclear-fuelled, results in therejection of waste heat to the environment. Thegrowth of electricity production is thus heavilydependent upon access to sources ofcooling water. Where populations are compara-tively concentrated this growth can leadto competing demands upon waterresources those of the power station, and fromothers for recreation., fishing, scenic preservation,irrigation and public consumption. It doesnot appear that the growth of the electricity supplyindustry is being limited unduly by constraintsupon'water availability, but the choices forsites are being narrowed, and the engineeringcommunity is being pressed for innovativesolutions which will minimize the impact of powergeneration on water bodies.

Whether the addltion of heated water to thereceiving waters can be assimilated without signifi-cant effects is dependent upon various factors

64

such as the manner in which the heated water isreturned to its source, the temperature andamount of source water available, and theaquatic biota present in it. There is no doubt thatthis waste heat can be detrimental in somecases, but it does not follow that it mustbe. Each system must be examined on its ownmerits.

Alternatives to the "once-through" cooling systemare being developed in a number of countriesfor use when there is an inadequate supplyof cooling water. These involve the use of artifi-cially-created lakes or ponds, or the erectionof cooling towers. Although these alternatives mayoffer relief from the addition of large amountsof waste heat to natural bodies of receivingwaters, their use can have other environmentaleffects and economic penalties. For example, eachof the methods mentioned results in a higherconsumption of water than a once-throughsystem. Cooling towers add large amounts of waterto the atmosphere and this can result, undercertain conditions, in fog, ice formationon trees, roads and transmission lines or snow.Chemicals including chlorine, zinc, chromium andphosphates are added to the water in coolingtowers to inhibit the growth of organismswithin them, corrosion and the deposition ofdissolved salts. These chemicals, transported intower plumes (spray drift) and in tower blowdown,may have damaging effects on the environment.In addition, cooling towers especiallyhyperbolic natural draft cooling towers can poseaesthetic problems in some cases.

Artificial lakes or cooling ponds may relieve thermaleffects in natural bodies of water, and mayalso be used for recreation and otherpurposes. But they can be used only if enoughland is available: 2000 to 3000 acres of lakesurface are required for a 1000 MW(e) nuclearpower station. Whatever metod of coolingis chosen, the waste heat from both fossil andnuclear plants must still, eventually, be dissipatedin the environment.

... Chemical aspects

Normal operation of a nuclear power plant requiresthe discharge of certain chemicals from theturbine condenser cooling system, theradioactive waste system, the regeneration ofprocess water demineralizers, the laundrywaste system and the sanitary waste system. Thechemical content of the discharge from thesesystems will vary from plant to plant.For example, chlorine or some other biocide maybe added intermittently to cooling water toremove accumulations of organic matterinside the condensers; phosphate and zinc

compounds may be used as corrosion inhibitors;sulphuric acid may be used to adjust thealkalinity of recirculating cooling water;and demineralizers may be regenerated periodicallywith sulphuric acid and sodium hydroxide, theregenerants then being neutralized beforedischarge. The maximum concentrations of someof these chemicals in the discharge canal couldconceivably exceed levels which are toxic toaquatic life. Temperature, as the "master factor"affecting rates of all metabolic functions, caninfluence the speed with which toxicsubstances exert their effects and, in someinstances, can influence the thresholdconcentrations for toxicity.

The technical assessment of the potential impactsof chemical and sanitary wastes from nuclearplants is included in the environmentalevaluation made in the early stages of planning.The sources of potential biological damageconsidered include: moisture from cooling topeplumes and airborne spray drift; chemicalsfrom tower blowdown; chemicals fromairborne spray drift on surrounding land and vege-tation; and chemicals such as chlorine that maybe toxic to aquatic life. Assessments such asthese guide those who must supply solutions tomeet water quality standards.

Fuel reprocessing

As discussed in Chapter III, the major radioactivewastes which have some public health inimplications and which arise in thecourse of normal fuel reprocessing operations canbe broadly categorized according to theirphysical state and activity level.

The management of these wastes is governedbroadly by the application of three widely-acceptedprinciples:

dilute and disperse for low-level liquid and gase-ous wastes;delay and decay for intermediate- and high-levelliquid and gaseous wastes, particularly thosewaste streams that contain short-lived radio-nuclides; and

concentrate and contain the intermediate- andhigh-level solid, liquid and gaseous wastes.

It is not always easy to apply one principle inpreference to the other two, therefore some com-bination of the three is often followed. Thenature and volume of the waste, limitations of thesite for safe disposal, possible radiation risk tonearby populations stemming from release to theenvironment and cost are taken into account.

The principle of dilution and dispersion is basedon the assumption that the environment has afinite capacity for dilution of radionuclidesto an innocuous level. The application of thisprinciple requires an understanding of thebehaviour of radioactive materials in the environ-ment and of the pathways by which thereleased radionuclides, particularly those that areconsidered to be critical, may lead later tothe exposure of man. A large body ofknowledge is available for use in the application ofthis principle, especially in meteorology,geology, geography, hydrology,hydrography, oceanography, ecology, soil scienceand environmental engineering. Applications ofthis principle have been made cautiously, thusensuring that thereleases are minimal and in anycase are well within the capacity of the totalenvironment to receive them.

The second of the three principles is rooted in thefact that radionuclides lose their radioactivitythrough decay. It may be called upon in thetreatment not only of intermediate- and high-levelliquid and gaseous wastes but in some casesalso in that of low-level wastes. The intentis to ease problems in subsequent handling or tolessen risks of releases to the environment,taking advantage of the decay of someradionuclides particularly those having shorthalf-lives with the passage of time: Ifhigh-level waste is held in storage in a liquid formthe risk of accidental release might dictate insome circumstances early conversion tosolid form.

The principle of concentration and containmentderives from the concept that the majority ofthe radioactivity generated in the productionof nuclear power must be kept in isolation fromthe human environment. Since some radio-nuclides take a long time to decay to innocuouslevels some wastes must be contained forextended periods.

This principle is invoked in techniques for air andgas cleaning; the treatment of liquid wastes byscavenging and precipitation, ion exchangeand evaporation; the treatment of low-level, solidwastes by incineration, baling and packaging;the treatment of intermediate-level solidand liquid wastes by insolubilization in asphalt;conversion of high-level liquid wastes toinsoluble solids by high-temperature.calcination or incorporation in glassAank storageof intermediate- and high-level liquid wastes;storage of solid wastes in vaults or caverns;and disposal of solid and liquid wastes-in deepgeological formations.

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65

Experience in the application of these threeprinciples which has been gained so far has beenthat the various wastes arising within thenuclear fuel cycle have been controlled adequatelywith respect to both public health and theminimizing of environmental contamination. But,in the light of the expected expansion of thenuclear power industry as a whole, it is importantthat the responsible agencies improvecontinually their surveillance techniques, reviewwaste management practices in the industry,and evaluate their potential impacts onthe public health and on the environment:

Special mention should be made of four aspects ofthe management of radioactive wastes which havebeen the subject of considerable investigationand which call for some continued supervision. Insome cases further technological innovation atreprocessing plant sites may be needed infuture. These aspects are:

release of the noble gas fission productkrypton-85;

release of tritium;release of iodine isotopes;and storage of highly active fission product waste.

... Release of krypton-85

The health interest in this nuclide, which has a half-life of 10 years, is primarily in the whole bodydose the public at large may receive from itafter its global dispersion. Locally, the concern iswith the skin dose. Although krypton isslightly soluble in body fluids, and evenmore soluble in fatty tissue, it does not enter themetabolism, so does not concentrate in anyparticular organ. -

The rate of discharge of krypton-85 will increaseroughly in proportion to'the overall size of thenuclear power programme; but a recentauthoritative assessment, which projected thegrowth of nuclear power to the turn of thecentury, concludes that national andworld-wide radiation doses would not be likely topose any significant problems. It was estimatedthat in the year 2000 the annual genetic dosefrom krypton-85 would approach 1% of the naturalbackground dose rate. Processes now beingdeveloped could be ready kifxtract noblegases from the gaseous effluent from reprocessingplants when the need arises. Some claim itwould be prudent to make provision forthe later addition of such removal equipment in anyreprocessing plant built after about 1990. Thelong-term storage of the extracted krypton-85should not pose insuperable technical problems;however, one needs to bear mind that this

66k3 e

approach would entail the substitution of a concen-trated source of "Kr at a repository, withattendant risk of accidental release oflarge quantities, in contrast to continuous dilutionand dispersion from a number of distributedsources. A careful risk/benefit assessmentshould be made before one course is chosen inpreference to another.

Release of tritium

The health interest in tritium, which has a half-lifeof 12 years, is again in whole body dose. Mosttritium is released as tritiated water andbecomes rapidly diluted and dispersed in the circu-lating waters of the world. The discharge rateof tritium will also increase roughly inproportion to the size of the power programme.Several recent careful assessments, however,conclude that the quantities of tritiumlikely to be released present no significant hazard tothe public. For example, it is estimated that bythe year 2000 assuming that the presentrate of growth of the nuclear power programmecontinues the accumulatign of fission producttritium will be about 700 Megacuries. Tritiumis produced naturally, by the bombardmentof nitrogen in the upper atmosphere with cosmicrays, at a rate of about 4 to 8 Megacuries ayear, giving a steady state inventory ofnatural tritium of between about 70 and 140 Mega-curies. It is estimated that 1700 Megacuriesof tritium were released to the atmosphereas a result of the large-scale testing of thermonuclearweapons. It is therefore expected that for thenext two decades most tritium in the environmentwill be that which resulted from nuclear weaponstesting, and that the total inventory will declineduring this period. The average annual whole-body dose from tritium is estimated to be of theorder of 0.001 millirem for each 100 Mega-curies of the total inventory.

... Release of iodine isotopes

Iodine isotopes are of significance to public healthbecause their release is followed by a comparativelyquick transport back to man along the pathwaygrass cow milk human thyroid. Thedose to the thyroid is the most important, especi-ally for children because they tend to consumelarger quantities of milk and their thyroidsare considered to be more radiosensitive than thoseof adults. Iodine -131 is of particular concernin the accident situation because of itsbehaviour in the environment.

As mentioned in Chapter III, fuels from thermalnuclear power stations are normally cooledfor periods of the order of 100 days before

reprocessing, so that iodine-131 (8 day half-life)largely decays during storage and its subse-quent release during decanning and reprocessing isextremely small. Most of the iodine appears inthe low-level aqueous wastes, and a smallfraction passes to the atmosphere through the con-ventional, moderately efficient alkali scrubbingsystem; in each case the release is wellwithin the derived working limits. In future, whenfuel from fast reactors is reprocessed, theeconomic incentive for a rapid turn-around in the fuel cycle may prompt the reproces-sing of fuel which has been cooled for ashorter time. This will pose problemsin providing new and very reliable techniques forthe removal of iodine-131 from both gaseousand liquid effluents. Development workon fuel transport, off-loading and reprocessing itselfwill be required; removal of iodine at an earlystage may be desirable.

A recent assessment touching on gaseous and liquidwastes from thermal or fast reactor fuelreprocessing has shown that releases ofiodine-129 17 million year half-life) are likely to bemaintained well within derived working limitsfor this nuclide.

... Storage of high activity fission product waste

Fission product waste, containing traces of pluto-nium and of other transuranium elements, is soconcentrated and contains nuclides with suchlong half-lives that it must be kept isolated fromthe human environment for hundreds or eventhousands of years. The management ofthis waste at the reprocessing plant and duringeventual storage in some man-maderepository must recognise its great potentialimpact on man and his environment, andbe the subject of continuing attention and devel-opment.

Whether the waste is stored for all time as liquid,or is converted ultimately to a solid form forstorage, the major public health concern ispreservation of containment.

It is probably easier from this point of view todemonstrate the overall safety of solidstorage in deep natural vaults thanthat of liquid storage; the need for continuedburdensome surveillance is much reducedand the removal of the waste fromproximity to man's environment is attractive. Butthe hazardous aspects of the process of solidi-fication must be borne in mind, togetherwith the fact that an initial period of storage asliquid is still required.

. Accident considerations

The previous section discusses public health aspectsof normal operations in a fuel reprocessing plant.Brief consideration will now be given toaccident conditions which might affect publichealth or have other implications forprotection of the environment.

The basic chemical operation of a reprocessingplant is, in theory, rather like that of similarindustrial chemical processing operations withregard to the possibility of accident. However, inthe design of a fuel reprocessing plant and inthe development of flowsheets for its operationgreat care is taken to avoid creating thehazard of releasing radioactive materials. Forexample, the use of low-flashpoint flammable sol-vents or of gas compositions which may explodeis normally excluded. The whole design of theplant with respect to shielding, containment, ventilation with discharge through absolute filtersystems, in addition to protecting theoperators, means that incidents which may occurwill tend to be isolated within it.

Fuel dis-assembly, decanning and dissolving canconceivably present a small fire risk in someunusual circumstances. Such incidentswill not result in significant environmental contamination because air extracted from the cellsin which these processes are carried outis filtered efficiently. Subsequent chemicalreprocessing carries with it small risks of fire,explosion or criticality incidents, but againscrubbing and filtration of the exhaustair will keep environmental contamination to lowlevels, and render the problem one of protectionof plant personnel rather than of public health.

The most serious problem would be loss of contain-ment in the high activity storage unit. The riskto the public of this type of event isminimized by the adoption of the "spare tank"philosophy (so that material can betransferred rapidly from a leaking tank) and by thesiting, exceptionally high standards of construc-tion of and vigilant surveillance over thestorage unit. Solidification would reduce the mobi-lity of these wastes, and a further reduction inmobility could be achieved by burying thesolids at levels below which circulation of watertakes place.

Transportation

Elements of the nuclear fuel cycle mines, enrich-ment plants, power stations arid so on willbe spread over large geographic areas, withsome installations possibly in common for groupsof states. This rendersittleroblem of

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Table IX.Shipment Statistics for Elements of the Fuel Cycle in the United States

Mill 4 Converter (as U305)

Number of Shipments

1971 1974

704 1071

Converter + Enrichment Plant (as UF6) 938 1438

Enrichment Plant Powder and Pellet Mfgrs.(as enriched UF6) 781 1347

Powder and Pellet Mfrs. + Fabricators(as enriched U30, powder or pellets) 136 223

Fuel Fabricators + Reactors (as fuel elements) 272 360

Reactors + Spent Fuel Reprocessing(as spent fuel elements) 76 1417

transportation of nuclear materialscrucial to the maintenance of safety and goodeconomic performance of nuclear power systems.As an'example, Table IX shows the number ofdifferent types of shipments in the nuclearfuel cycle in the United States which were madein 1971 and are expected to be made in 1974.

Nuclear fuel for a 1000 MW(e) reactor consiststypically of about 90 metric tons (90000 kg) ofslightly enriched uranium. The fuel is inthe form of elements made up of tens tohundreds of stainless steel or zircaloy clad fuel rods.About one-third of the fuel elements arereplaced each year.

The radioactivity of new, unirradiated reactor fuelis small, about 3 curies per metric ton. Thisamount of radioactivity can have essentiallyno impact on the environment, and very little onindividual transport workers under normalconditions. Even in an accident (except inthe case of accidental criticality) the physical pro-perties and the low specific activity of the fuelwould limit radiation effects to very smalllevels. Although the packaging is designed toprevent accidental criticality under normal andsevere accident conditions there is a verysmall probability that accidentalcriticality could occur. If it did, radiation dosesin excess of 500 rems to individuals in theimmediate vicinity might result, andthe immediate area would require a thorough andperhaps costly decontamination.

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Irradiated fuel elements contain large amounts ofradioactivity generated by fission productswhich decay rapidly during the first fewdays out of the reactor. After 150 days eachirradiated fuel element can still contain millions ofcuries of radioactivity, producing high radiationfields in its vicinity. For shipment, irradiatedfuel elements are placed in shielded, air- or water-cooled casks weighing from 23 000 to68 000 kg or more. Under normalconditions certain transport workers truck drivers,train brakeman, barge operators and so oncould receive significant radiation exposures,especially if they are handling a number of ship-ments each year, and have to be treated asradiation workers; but members of thepublic should not exposed. Impacts on the publicand on the environment as a consequence ofaccidents during shipment of irradiatedfuels involving, for example, leakage of contami-nated coolant, loss of coolant as a result ofmajor damage to the cask, damage fromsevere impact and fire could be severe in terms ofpopulation dose. But no such accident hasoccurred so far and elaborate precautionsas outlined in Chapter III are taken to prevent theiroccurrence.

Under normal conditions the shipment of drums ofwaste from a nuclear plant should have littleradiological impact on the public. Sincethese wastes are of low specific activity even asevere accident would not release a majoramount of radioactivity. Minor releases might cost

a few hundred dollars to clean up, but no signi-ficant public exposure should occur if normalprecautions are taken.

More than'20 years of experience has shown thatthe prevailing techniques, characterized bymultiple means of protection and by largesafety margins, do work. The record of US experi-ence during the past 19 years shows that only119 transportation 'incidents' occurredalthough hundreds of thousands of shipments weremade each year. In 84 of these no radioactivematerial was released from the package. Innone of the 35 cases in which material was releasedwas there any serious resultant exposure toradiation. Only one case resulted indispersal into the air, and only one case requiredcostly cleanup. Other nations report similarexperience.

As the nuclear power industry grows both thenumbers of persons professionally exposedto radioactivity and the number of accidents whichoccur during transportation of radioactive materialcan be expected to increase. It can be said that:

No physical, technical or organizational problemprevents the achievement of a safe and manageabletransport system.

The recognition that accidents in transportationwill occur should not be equated with publicexposure to radiation.

To protect the public and the environment from thepossible adverse effects of the transportation ofnuclear materials responsible national andinternational authorities should continue to reviewand harmonize transport regulations and standards.Additionally, for each proposed nuclear powerplant, a technical assessment of potentialtransportation 'impacts', considering a range ofknown distances between sites and theprobabilities and consequences ofserious accidents, should be made. With thisinformation at hand the overall risk fromtransport accidents can be estimated, and the actionswhich should be taken to minimize them can bedetermined.

Public Health and SafetyProgrammesDespite the unprecedented precautions which aretaken to make nuclear power reactors safe andfoolproof one can reasonably anticipate thataccidents will happen eventually as a result of errorsin design, failures in equipment, mistakes of man,sabotage and acts of God floods, tornadoes,earthquakes and so on. As the number and variety

of power reactors increase a few accidentsranging widely in severity can be expected; it iscertain that major accidents will occur farless frequently than minor accidents or incidents.The vast majority of radiation incidents will resultfrom buildup of radioactivity in the primaryand/or secondary cooling system, leaking ofcontaminated fluid through gaskets, stuck fuelelements resulting in building contamination, slightincreases in the building background radiationlevels, contamination of water in the po51storage area, clothing contamination and so on.

Operational health and safety programmes

The principal objectives of health and safetyprogrammes associated with a nuclear power plantare to assist plant management in reducing thenumber and severity of accidents, to detectat an early stage significant perturbations in reactoroperation which, if not corrected, may lead toreactor accidents, to be alert to increases inlevels of radiation background and to take immedi-ate remedial actions which assure appropriatecorrection before rather than afteraccidents have time to develop. It is generallyaccepted that nuclear power reactors in thefuture can and will ba constructed andoperated in such a way that increases in radiationbackground in the environment due to routinereactor operations will be kept essentially tozero. Public health problems and radiation risksassociated with such plants therefore relatealmost entirely to accident potential, orto the frequency and magnitude of reactor acci-dents. During nonroutine operations such asfreeing a stuck fuel element or cleaning upa high-level surface contamination in a section ofthe pool storage area personnel trained inhealth physics are present throughout inorder to ensure that operating personnel are notexposed unduly to radiation.

Those assigned to radiation protection functions inthe power station organization advise the plantmanagers who are responsible, together withpublic health agencies, for protecting the publicliving in theneighbourhood of these plantsagainst excessive exposure to radiation.Such personnel, under the direction of the plantsenior health physicist, are an integral part ofboth plant management and the plant workforce. The members of this organization are fami-liar with every detail of the design, constructionand operation of the installation and providethe interface between operations of the plant andassociated problems of environmental protection;and they also provide the primary contactbetween the plant and the responsible publichealth agency. The details of organization vary

89

from plant to plant and country to country but, ineach case, clime co-operation and a strong linkbetween the health physics staff of theplant and those of the public health agency areessential in providing for the safety and well.being of plant employees and residents in nearbycommunities.

Radiation risks are not the only concern of thoseresponsible for the prevention of pollution ofthe environment, and protection of the public.Although problems of 'conventional' safety (such asfires, explosions, odours and so on), chemicalwastes, thermal pollution and sanitarysewage of the nuclear power station are of typeswhich are customary in other industrialoperations, they, too, must be kept under propersurveillance and in conformity with publichealth standards. Here, the responsibilityfor safe plant operation and for liaison with publichealth authorities usually rests primarily with theplant medical director but, in some cases andbecause these problems are small, thisresponsibility is placed in the hands of the seniorhealth physicist.

This man, because of his close contact with opera-tions, plays a key role both in protecting thehealth of employees and of members of thepublic who may be at risk of exposure to radiation,and in preventing and limiting the consequencesof reactor accidents. As an adviser to the plantmanager he has a major responsibility for providingeffective and reassuring responses to local expres-sions of public concern, preventing radiationaccidents and minimizing harm they might do thepublic should they occur. Responsibilities forradiation protection begin long before thestart-up of the plant, and the central purpose ofthis programme is to minimize human exposureto ionizing radiation by preventing radiationaccidents, rather than in supervisingappropriate remedial measures after the event.Nevertheless, one of the essential tasks of theradiation protection organization is to develop andimplement an adequaw emergency plan whichshould provide, inter alia, for:

close co-ordination with health physics officialsof local, state and national public health agencies;close co-ordination with organizations andauthorities in local communities such as thepolice, fire and health departments, hospitals, doc-tors, transport officials, communications mediaand so on;frequent up-dating of plant emergency plans andthe conduct of occasional emergency drills whichinvolve the whole plant; andguidance for action to be taken if a major acci-dent takes place.

70 s 76

Specific plans for action during emergencies wouldindicate details of what must be done followingan accident, including important actions whichmust be taken immediately. It may seem mis-placed effort, to prepare elaborate and detailedplans for a major nuclear power reactor accidentinvolving the release to the environment of a fewthousand to several hundred million curies ofradioactivity, when it has been estimatedthat such an accident would not be expected in agiven plant more often than once in 10 000 years;but consideration of all safety aspects andplans to handle all eventualities to theextent that they can be visualized are characteristicof the nuclear energy industry. It has one of thebest safety records of all modern industries.

The role of health authorities

The early applications of ionizing radiation wererestricted mostly to medicine, but at an earlystage it became obvious that radiation couldhave harmful effects. Only the immediate somaticeffects were then recognised, and these affecteda relatively small number of people doctors,nurses, engineers and patients. As the applicationof X-rays and natural radioactive substancesfor various purposes and in biological researchspread, the long-term and genetic effects becameacknowledged; eventually many countrieswere compelled to provide legislation, rules andregulations aimed at giving protection against them.The rapid development in the use of nucleartechniques in the many and varied appliedsciences increased the potential danger of exposureto radiation in a way which had no precedent.This development took place against abackground of nuclear weapon development andtesting, and caused the public naturally tomistrust the use of energy of nuclearorigin. This mistrust is still apparent, 30 years later.

The public health service of any country has abasic responsibility for ensuring, promotingand creating favourable conditions for preservingand improving the standard of health of thePopulation. But it took some time formany health authorities to realise that the increas-ing use of ionizing radiation and radioisotopesand the development of atomic energy openedup new responsibilities in the public health context,and that ionizing radiation and radioactivematerial were new factors in environmentalhygiene and a part of environmental pollution al-though relatively small and of minor importancefor the time being. It is widely acknowledgedthat the control, surveillance and monitoring ofradioactive pollution should, and that theevaluation of results including the drawing of con-clusions must, rest with the public health autho-

rities for two reasons. First, the noxiouseffects of ionizing radiation are cumulative, what-ever their source, and exposure resulting fromthe development of atomic energy shouldtherefore be considered together with radiationexposure from all other uses of ionizing radi-ation; and secondly, authorities concerned primarilywith the promotion of modern techniques ratherthan health might be accused by the public ofexercising biased judgement and' of having a vestedinterest in underplaying the potential hazardsof radioactive pollution which mightaccompany the development of such techniques.

Public health organizations at the local, nationaland international levels must play a leading r6lein easing the impact of all forms of powerproduction on the health, peace of mind,economy and general well-being of the public. Itis obvious that the duties of public healthauthorities cannot be discharged without very closecollaboration with other authorities responsiblefor matters such as agriculture, energy andtransportation. Careful co-ordination betweenthese various authorities is essential to thesuccessful management of the control of radiationexposure. The organization of various govern-ment services no doubt varies according tonational conditions and traditions, but in generalthe public health (or environmental protection)agency or agencies are a single focal pointfor evaluation of the total health impact of allsources of radiation, and can ensure thatadequate health protection measures are taken.Public health and/or environmental protectionagencies can and do work in the followingfive principal areas:

establishment of broad environmental guide-lines and standards within which the industrymust operate;

identification and measurement of sources ofradiation exposure of the population;

assessment and evaluation of these exposureswith respect to the biological hazards to variouspopulation groups (one outcome of this isthe stimulation and conduct of research);

co-operation in the development and applicationof methods of control, including the provisionof a staff suitably trained and equipped toprovide advisory and supervisory services inradiation protection;

co-operation in the conduct of programmes forthe training of appropriate technicians andspecialists, as well as information andeducation of both professionals and public as to thetotal health impact of radiation sources.

If a public health programme is to be effective ineasing the impact of nuclear power production

on a community the competent agency musthave proper authority in its area of responsibility,and appropriate financial support from thegovernment under which it works. It mustdevelop a competence which is recognised andrespected by the public whom its programme isdesigned to protect, and by the nuclearpower station organization with which it is concer-ned. Certainly, it must be backed up byadequate regulations and laws which,if necessary, can be enforced in a court of law. Oncea public health programme conducted by well-trained, competent and highly-qualifiedpersonnel has been established it must become acentre for the exchange of information onquestions of radiation risk raised bymembers of the community and by the variousorganizations of which they are a part. In thisway questions of concern for radiationdangers that are imagined or feared by the publiccan be answered before they become thesubject of major public controversy.But before a public health organization can meritthe complete confidence of the public and beexpected to assume this most importantr6le in a community it must demonstrate its com-petence. It must be able to root its conclusionsand recommendations not solely in calculations,inspections of operations and records of thenuclear plant operating authority but inappropriate measurements and observations madeunder its own auspices. If regulations, codes ofpractice and laws are not sufficient to protectthe public to the necessary extent then thepublic health organization or agency must be instru-mental in making them adequate, and it must seethat such laws are so drafted as to be enforceable.

Environmental monitoring programmes are bestdeveloped on the basis of close co-operationbetween the public health organization andthe personnel of the nuclear power plant. Ade-quate monitoring can reassure members ofthe community that frequent measurements arebeing made by experts from both the powercompany and the local public healthorganization, and that these Measurements eithercontinue to confirm the claim that radiatfanexposures are negligible, or lead to immediateaction by the health authority if they are not. How-ever, excessive monitoring programmes can havethe reverse effect, of creating alarm bysuggesting that widespread measurements arenecessary because of potential or suspectedreleases from the plant.

In addition, the health physicists of the publichealth organization and of the nuclear powerplant must co-operate in working out detailsof the emergency plan, as discussed previously.

aC4 71

714,

The existence of various international recommen-dations and standards has had the beneficialeffect that there is a fair degree of uni-formity in the provisions at the national level as tothe maximum permissible doses for radiationworkers. Some differences do exist, however,particularly in radiation protection limits specifiedfor members of the public. These are generallythe result either of a failure to revise legislationbased upon recommendations which have becomeout-of-date, or of a different philosophy. Legisla-tion on radiation protection can place theburden of implementing different regu-lations on different authorities. Where multiplenational organizations are involved one ofthem should be designated to serve as coordinator.

The role of international organizations

The basic standards for radiation protection havebeen recommended by the ICRP, whichcontinues to meet periodically toreview and up-date these standards. The ICRPstandards are recommended by the WorldHealth Organization (WHO), are used asa basis for the standards published by the Inter-national Atomic Energy Agency (IAEA)and are accepted in the Convention onProtection of Workers Against Ionizing Radiationprepared by the International Labour Organi-zation (110). They are also accepted byregional organizations such as EURATOM and theEuropean Nuclear Energy Agency (ENEA), andhave been used as the basis for regulations ina number of States.

Safety standards, codes of practice and guidebookshave been developed by the IAEA, often in co-operation with WHO, to provide guidance onhow the basic radiation protection standards can bemet. Thirty-six of these manuals have beenpublished in the IAEA Safety Series.Standards, codes of practice and guides have alsobeen issued for specialized applications ofradiation for example, the joint ENEA/IAEApublication Radiation Protection Standardsfor Radio luminous Timepieces and theIAEA/ENEA Guide for the Safe Design, Construc-tion and Use of Radioisotope Power Generators.

International organizations can also play animportant rble in the drafting of modelregulations for use by Member States. This can domuch to assure harmonization of policies andregulations from State to State. For exarrflike; theIAEA has issued transport regulations which'are mandatory for its own work and whichare recommended to its Member States and otherorganizations as a suitable basis for their ownregulations. These have been adopted inthe regulations and recommendations of the Inter-

72

national Air Transport Association (IATA), theIntergovernmental Maritime ConsultativeOrganization (IMCO) and the Council for MutualEconomic Assistance (CMEA). They alsoform the basis for the relevant annex ofthe International Convention for the Transport ofGoods by Rail (CIM), applicable in 24 Europeanand neighbouring countries, the AgreementConcerning the International Carriage of DangerousGoods by Road (ADR) and the draft AgreementConcerning the International Carriage ofDangerous Goods by Inland Waterways (ADN),both prepared by the Economic Commissionfor Europe of the United Nations. The UniversalPostal Union (UPU) has adopted regulationswhich permit the carriage of radioactivematerial by post within the exemption limits provided by the IAEA regulations. The regulationshave also been adopted by a substantialnumber of individual Member States.

The United Nations Scientific Commitee on the .

Effects of Atomic Radiation (UNSCEAR )was established on 3 December 1955 toevaluate the radiation doses and risks from globalcontamination by radionuclides released in theatmospheric testing of nuclear weapons.Assessments for all sources of radiation exposureconstitute an appropriate task for such aninternational body, provided emphasis is places onthe global or international implications of suchexposures. Other specialized agencies canassist in this effort by accumulating and makingavailable the required information; forexample, the IAEA can assembleinformation on releases of radionuclides to theenvironment, FAO can assemble informationon the levels of radionuclides in foodstuffsand WHO can secure information on radioactivecontamination of human tissues. Since theradiation exposures from peaceful usesof atomic energy to date have beenboth negligible and local care is needed to ensurethat international activities do not duplicatenational programmes unnecessarily..

A primary activity of international organizations isin the collection and dissemination of information.One of the simplest methods is through thesponsorship of well-conceived international andregional panels, symposia and congresses

especially those which result in the publication ofproceedings which form a permanent record andmake the information presented available toa much wider audience. In planning such meetingsgreat attention must be paid to the choosing ofappropriate and timely subjects for discussion,and each should be focussed on a specific audience.In many cases co-sponsorship with a scientificor professional society has distinct advantages in

that it identifies the subject area and theaudiences more clearly and, most importantly, ithelps members of these organizations realizethat these are their problems, and that theymust take the initiative and share the responsibilityfor finding acceptable solutions.The IAEA and WHO have both been active in col-lecting and disseminating information onactivities relating to public health andenvironmental aspects of atomic energy program-mes. The IAEA has published directories orwhole-body radioactivity monitors and ofwaste management facilities. They also publishannually research abstracts on waste managementand on health physics; these abstracts fill aspecial need, especially for developingcountries, in that they describe current researchrather than work that is already completed andpublished. The WHO has establishedInternational Reference Centres on Waste Disposal,on Air Pollution and on Environmental Radio-activity. The first undertakes a broadprogramme including collection and disseminationof information, co-ordination of research,training of personnel and provision ofadvisory services related to the collection, treat-ment and disposal of radioactive waste. Oneof the functions of the centres on air pol-lution is to collect data systematically and to con-duct measurements on air pollutants in urbanareas around the world. The third class ofcentre collects data on the environmental levels ofradiation and takes steps to ensure that the dataare comparable by standardizing the samplingand measuring techniques used, and arranging forinter-laboratory comparison.

Yet another effective method of information col-lection and dissemination is in the employmentof experts to prepare handbooks and othertypes of publication on pertinent subjects.

Recently the IAEA established a scheme in co-operation with its Member States using computersto assist in the collection and dissemination ofinformation relatigg to nuclear science andits peaceful appliition. In this scheme, the Inter-national Nuclear Information System (INIS),co-operating Member States are called uponto prepare descriptions of pertinent scientific litera-ture published in their areas, and to submit thisinformation to the IAEA for disseminationthrough INIS to others.

The information disseminated need not be highly"scientific", Publications are quite often preparedin an attempt to give the interested layman asimple and concise but technically accuratedescription and discussion of activities in atomicenergy. The IAEA, other specialized agencies

and national authorities also have activepublic information programmes. The IAEA haspublished, for example, an informationcircular entitled Nuclear Energy andthe Environment which contains a short review ofthe efforts made by the nuclear industry toprotect man and his environment.

One programme carried out by international orga-nizations has been helpful in increasing confi-dence in radiological protection programmes:that is, support of inter-calibration studies. Thiswork has been very valuable, bringingtogether health physicists from public health autho-rities and nuclear power operations to conductexperiments with various sources ofradiation and to determine the accuracy of dosemeasurements of the various systems now inuse. The types of instruments andtechniques that should be compared and evaluatedin such a programme are, for example, whole-body counters, low background environmentalmeasurements, criticality instrumentation,and ecological sampling of the environment of anuclear power plant. Attention might alsobe given to the development of referencemethods for radiochemical analysis, and inter-laboratory comparison of results.When Member States have specific problens onwhich they need expert advice internationalorganizations can provide advisory services andtechnical assistance. Experts from the staffof the organization, or from otherMember States, can be made available to therequesting country for specified periods of timeranging from a few weeks to more than ayear, depending on the time needed to completethe task. Assistance can also be given in theform of specialized scientific equipment.

International organizations can also play an impor-tant role in education and training, in a numberof ways. Fellowships are made available toscientists and engineers from developing countriesto enable them to work or to study for sometime in one of the more highly developedcountries. If these assignments are adequatelyplanned the visiting fellow !lei an opportunity tobecome familiar with a wide spectrum ofactivities related to public health and environmen-tal problems associated with atomic energyprogrammes.

Research contracts are designed to fulfil two objec-tives: first, to encourage and support researchconsidered necessary to complete thegeneral undeistanding of the effects of effluentsfrom nuclear installations on public health andthe environment, and secondly, to give support

especially to young scientists for the

73

initiation of research programmes that are expectedto expand and flourish with private or govern-ment support when the value of theprogramme is recognized.

Training courses on topics which are of particularinterest to a given region are organized. Expertsare made available from the staff of theorganization(s) involved and from Member States.In addition to lectures the participants aregiven the chance to do practical work atthe facilities of the host country. Training filmsmay be produced for use in such courses, aswell as for more general use in MemberStates.

Study tours in which scientists and engineers fromdeveloping countries can visit a number offacilities in more advanced countries areoften organized. The study tour usually includes

lectures and practical exercises, as well as adetailed technical description of theoperation of each facility by local staff memiu,

International organizations have as well the oppor-tunity to convene small groups of e..p4Kts asconsultants to discuss present and ;/;,tureproblems of the most importance to Member ...atesand the world community as a whole. In thisway the programmes of the inter' ' ationalorganization can not only be kept relevant to issuesof current concern, but reflect those that arelikely to arise in the future.

Finally, the international organizations can sendrepresentatives to international meetings. Oftenproblems take on a different character whenviewed from an international, as opposed toa national or regional, standpoint. Participati.mbyrepresentatives of international organizationsin meetings can help to balance views.

74 IR°"i

summaCivilization has developed largelyss man has devised new waysof changing and controlling his environment.Since the beginning of theindustrial revolution the impact of manon his environment has grown at an ever-increasingpace. The great changes in our environmentwhich have occurred in recent years, andthe still greater changes which threaten as thecombination of higher living standards andincreasing world population demandever-increasing rates of energy production, haveprovoked a call for closer control of these changes.It seems no more than common sense to urgethat the environment should be harmed aslittle as possible.

In most places additional power is needed to assistpeoples in attaining improved standards ofnutrition, housing, clothing, public health and so on.In these situations the decision is not whetheradditional power should be produced buthow it can be best produced, considering both thesource of energy and the method used to convertit to electricity.

Several factors enable one to conclude that nuclearpower use will increase and thait will play acomplementary, as well as a competitive,role with fossil fuels in the future production ofelectricity. Economic considerations suggestthat the base-load supply will be providedby nuclear plants, and the peak-load by fossil-fuelled plants.

The untlertakir.g of any large-scale enterprise in-volves disturbance of the environment. Theproduction of electrical energy is noexception, but many of the disturbances are notdue to the nature of the fuel but are associatedwith normal I.Pocesses of plant constructionand with ancillary operations. The environmentaldisturbances associated with the constructionof a nuclear power plant are often lessthan those of coal-fired plants, since considerablysmaller sites are required. Both fossil-fuel andnuclear plants release thermal energy, aswaste haat, and small amounts of radioactivity tothe environment, but with respect to atmos-pheric pollutants nuclear plants aredecisively better than fossil-fuelled plants.

All steam - electric generating plants have a commonpotential problem with the need to release heatedwater to the environment. Heat from combustionof fossil fuel or from the fission of nuclear fuel

in a reactor produces steam at high temperaturesand pressure which in turn drives a turbineconnected to a generator. The "spent"steam from the turbine is condensed by passinglarge amounts of cooling water throughcondensers. Modern steam turbines operating withfossil fuels attain thermal efficiencies of37-38%. Most present-day nuclearpower plants are thermally less efficient than thesemodern fossil-fuelled power plants, althoughthey are comparable in efficiency to theaverage of all fossil-fuelled power plants now inoperation. In fossil-fuelled power plants partof the excess heat is released to the atmosphere inthe flue gases, whereas in nuclear power plantsessentially all of the excess heat is transferred tothe cooling water. As a result, a nuclear powerplant in which once-through cooling isused will discharge about 50% morewaste heat to the receiving waters than a fossil -fuelled power plant producing an equal amount ofelectricity. Gas-cooled and liquid-metal-cooledadvanced reactors of the future are expectedto attain higher thermal efficiencies, equal to orexceeding those of conventional plants.However the problem facing the electrical powerindustry is not only how to produce moreefficient power stations and limit thermal pollutionat the source, but also how best to managethe thermal releases that occur. Localcircumstances, rather than global considerations,will dictate the most appropriate methods ofmanagement.

The use of atomic energy as compared with fossilfuel for the production of electricity will affectthe environment in a number of ways:

drastically reducing the mining and transport offuel;

increasing by some 50 per cent the heat releasedinto cooling waters from power plants which arebuilt initially, though in respect of later plantsthe increase will be negligible;

introducing a very small risk of local release oflethal amounts of radioactive.substances. byaccident;

requiring small restricted areas for disposal offission products and for decommissioned reactors;

slightly increasing the world inventory ofkrypton, and later tritium, but decreasing theinventory of radon in the atmosphere;

virtually eliminating the emission of particulates,sulphur dioxide, carbon dioxide and mercury to theatmosphere;

eliminating problems in the disposal of fly ash.

The basic standards for radiation protection havebeen recommended by the InternationalCommission on Radiological Protection. These

recommendations have been accepted by theWorld Health Organization and theInternational Labour Organization, and are used asthe basis for standards prepared by the IAEA.They have also been translated intoregulations, codes of practice and working stand-ards by individual countries and by internationaland regional organizations. These standardshave evolved from numerous studies inmany countries of somatic effects and hereditaryeffects at high radiation exposures. Maximumpermissible values have been established atradiation exposure levels which are considerablylower, at which somatic damage has not beenobserved and hereditary effects are believedto be at a very low incidence. Effects at these lowlevels have been computed by assuming thatthe ratio of effect to exposure is the sameas at the much higher exposures at which effectswere observed (the linear dose-effect hypothesis).This calculation is believed to be safe andconservative, although the actualrelationships cannot be proved on the basis of directobservation. For this reason the ICRP recommendsthat radiation doses should be kept as low as ispracticable.

A number of reactor types are being developed andmarketed currently. Each presents specialrequirements with regard to handling andcontrol of the radionuclides generated, but for eachtype appropriate systems of control have beendeveloped. This attention to the need toensure public safety and to prevent damage to theenvironment has led to the excellent record ofminimal radiation exposure of the publicdiscussed above.

Provisions are made in the design and siting of powerreactors and of ancillary nuclear facilities to copewith potential accidental releases of radioactivityas well as with routine releases.

The technology required both to prevent accidentsand to mitigate their possible consequencesshould they occur is fundamental to thedesigning of nuclear installations in such a way asto afford maximum protection to the environ-ment. The safety record of the nuclearindustry has been particularly noteworthy: the fewaccidents that have occurred have been wellwithin the capability of the installationsconcerned to contain the abnormality and to pro-tect the public.

However it should be recognized that major reactoraccidents, although very unlikely, may occur.There is a popular tendency to acceptfamiliar hazards while reacting violently to unfami-liar ones. Since radiation hazards are not familiarand may be.cuinulative and irreversible as well

76

as entailing possible genetic risks, it is prudent toundertake public health measures to educatethe public and to assure it that propercare is taken to protect it by

- building a safe reactor;- caring for its good siting;- ensuring its safe operation;- being prepared to minimize the effects of possibleaccidents;- undertaking a programme to improve powerreactors and facilities and their operations continu-ally to reduce further the probability of accidentsand to profit from experience with minoraccidents.

The most serious radiological health problem asso-ciated with atomic energy has been the over-exposure of uranium miners. During thepast 20 years some 100 uranium miners have diedof lung cancer in the US, and it has beenestimated that 500-1500 more of thoseover-exposed prior to the establishment of thepresent occupational safety standards mayalso die of this radiation related disease. The inci-dence of lung cancer was much greater amongminers who were cigarette smokers, but theexposure to daughter products of 222R n was theprimary factor implicated. The present levelsfor working conditions have been establishedat much lower working levels than that to whichthese miners were exposed, perhaps by asmuch as a factor of several thousand,and future risks of lung cancer of uranium minersshould be greatly reduced.

In the atmospheric testing of nuclear weapons alarge fraction of the radionuclides created wereinjected into the stratosphere (the upper partof the atmosphere), where they reside for longenough times (several months to severalyears) to become globally dispersed before deposi-tion on to the surface of the earth. In thenuclear power industry most of theradionuclides are contained rather than released.Atmospheric releases that do occur are to thetroposphere (the lower atmosphere), wherethe residence times are of the order of a few daysto a few weeks. Thus most releases give a riseto contamination problems of a localnature. However, a few radionuclides have suffi-ciently long half-lives and environmentalmobility to become globally dispersed.These include tritium, "Kr, 1291 and 14C. Iodine-131,with a half-life of about 8 days, is not normally

A smoggy morning in downtown Chicago.Smoke, generated by industry,Is being held close to the surface by a temperature Inversion.Photo: Argonne National Laboratory

r ' sE.,404U?e.

.;-::, ;404,-,A7,444.4 <or

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of global concern, but is of special concernin accident situations. These radionuclides are ofspecial interest internationally because theirrelease may affect populations outside theimmediate area of their release. Because of thevery rapid growth projected for the nuclearindustry it is advisable to continue toreview information on the releases and concentra-tions of these radionuclides in various sectorsof the environment. If there arises a needto control these emissions it is more easily done atthe source.

Well over 99.9% of all the radioactivity generatedin nuclear power reactors is contained withinthe fuel elements until they are reprocessedfor recovery of unburned fuel. Thus careful con-trol of the inventories in reactor, and of thespent fuel which must be handled andtransported to fuel reprocessing plants, is required.

The IAEA has issued transport regulations whichare mandatory for its own work and which arerecommended to Member States and inter-national organizations as a suitable basis for theirregulations. Reliance is placed on safetyfeatures built into the packaging and the require-ments are especially stringent for packaging ofhighly active materials to prevent loss ofcontainment in the event of an accident. To dateno country has experienced a release ofactivity from a package of high-level activity.

A reprocessing plant may accommodate the spentfuel from several reactors, and it is during thereprocessing of the fuel that high-activitywastes are generated. These wastes must be keptin containment for very long periods of time,ranging from a few centuries to possiblythousands of years, if they contain substantialquantities of transuranic elements. Althoughstorage as liquids in specially constructedtanks near the ground surface has been a suitableand reliable/method for containment of thesewastes to date, processes of solidification have beendeveloped and some countries have alreadydecided that such wastes will be solidifiedto reduce the potential "environmental mobility"of these wastes during long periods of time.Consideration is also being given to variousmeans of storage of these wastes, including theirstorage in deep, dry and stable geologicformations in order to assure furthertheir isolation from' the human environment forthe time required.

Attention must be given to problems of radiologi- .

cal health at all levels ranging from plantoperations, to local and national publichealth authorities and to international organiza-tions. Plant personnel must institute

78

procedures which ensure that normalreleases of radionuclides are within the limitsprescribed by local and national authorities andwhich reduce the number and severity ofaccidents. In the unlikely event thatan accident occurs they must have developed, inco-operation with local and national publichealth authorities, procedures which willreduce the radiological impact upon local popula-tions.

Public health authorities have a basic responsibilityfor protecting public health and should developthe standards within which the industryshould operate.

International organizations provide forums fordiscussion which allow States to discusscommon problems. Although theyhave no direct regulatory role they can promotethe harmonization of principles on whichnational regulations are based, thushelping to ensure that the degree of protection ofpublic health is uniform from State to State.The international organizations also playan important role in the collection and dissemina-tion of information on key issues.

Man has been exposed continually to naturalionizing radiation resulting from cosmic rays andfrom the decay of radioactive substances onearth. Dose rates from these sources arehighly variable, depending on elevation above sealevel, local geology, seasons, dietary habits,types of residential construction and so on. How-ever, UNSCEAR has estimated that the averageannual gonadal dose received by the worldpopulation from natural sources amountsto about 100 mrads.

The world -wide population dose from man-maderadiation sources is still less than levelsincurred from natural sources, butthe background level is being approached in atleast one industrialized nation. The averageper capita whole-body dose in theUnited States is estimated for 1971 to be 114mrems, compared to the average dose of130 mrems per year from nature. Most of theman-made exposure (more than 90%) isreceived as a result of medical procedures fordiagnosis and treatment of disease.Operation of nuclear power stations, fuelreprqcessing plants and other atomic energy facili-ties resulted in minute exposures to the totalpopulation, about 8.013 mrems per year.Thus, even with a projected increase in nuclearpower production by a factor of a hundredit is not likely that it would contributesignificantly to the total radiation exposure.

This should not imply that the control of radio-nuclides in the nuclear power industry shouldbe relaxed. In keeping with the basicrecommendation of the ICRP, the management ofradioactive wastes is concerned with keepingthe total addition of radiation exposure ofman as low as practicable. Whenever practicable,radioactive materials are concentrated andcontained in isolation from man'senvironment until their radioactivity has decayedto innocuous levels.

When release to the environment is necessary therates of release are kept low enough not toexceed the local capacity of theenvironment to disperse and dilute the materialsto acceptably low concentrations. In thisrespect the environmental processesthat may lead to reconcentration and may.providea pathway for man's exposure to additionalradiation must be considered. Radioactiveeffluents released from nuclear power plants andother facilities are always monitored as ameans of control and public protection.Additional off-site monitoring is carried out as aconfirmatory means of environmental pro-tection, but in general releases have beenso low that little indication can be found of radia-tion above natural background levels.

It may be true that cutting the rate of increase ofpower expansion may reduce detrimentalenvironmental effects. But this is unlikelyto occur, and in most cases is probably undesirable.A better solution would be to improve powerproduction in such a way as to reducedetrimental effects on the environment to an

acceptable level. To that end, and to ensure thattotal doses of radiation in man -rams arelimited:

the nuclear power industry must continue tooperate safely. Internationally agreed guidelinesand codes of practice are desirable for thesiting, design, construction and operation ofnuclear power plants and associatedfacilities. These should refer to preventivemeasures to exclude or minimize accidents as wellas to plans and equipment necessary to mitigatethe effects of accidents and to protect the public.

New and improved methods of management ofradioactive wastes from nuclear facilities withspecial emphasis on environmentally mobile,long-lived radionuclides such as tritium ,"Kr and1291 need to be developed;

there is also a need to assess the impact uponman of releases of radioactive materials fromthe nuclear industry;

and research concerning the environmentalbehaviour of long-lived critical radionuclidesshould be continued.

The projected growth of nuclear power and thepotential public health risks involved, howeversmall, require that diligent controls shouldcontinue to be practised. The public isquite aware of the risks involved, and it is necessaryand proper that the nuclear industry exercisecareful control to minimize these riskswhile maximizing benefits to the public and keepthe public informed about them. The timelypublic acceptance of nuclear power may beas important as is the development of thetechnology itself.

Annex I.Pertinent Publications of the International Atomic Energy Agency

Safety Series

No. TitleDate ofissue Remarks

4 Safe operation of critical assemblies and research reactors(Revised, see S.S. No.35)

5 Radioactive waste disposal into the sea

*6 Regulations for the safe transport of radioactive materials

Revised

w/List of National Competent Authoritiesw/Advisory material on packaging for large radioactive sources(April 1967)

7 Regulations for the safe transport of radioactive materialsNotes on certain aspects of the regulations

8 The use of film-badges for personnel monitoring

Basic safety standards for radiation protectionRevised

*9

10 Disposal of radioactive wastes into fresh water(For Revised Edition 1970 see S.S. No.36)

11 Methods of surveying and monitoring marine radioactivity

12 The management of radioactive wastes produced by radio-isotope users

13 The provision of radiological protection services

14 The basic requirements for personnel monitoring

15 Radioactive waste disposal into the ground

16 Manual on environmental monitoring in normal operations

17 Techniques for controlling air pollution from theoperation of nuclear facilities

18 Environmental monitoring in emergency situations

21 Risk evaluation for protection of the public inradiation accidents

24 Basic factors for the treatment and disposalof radioactive wastes

*26 Radiation protection in the mining and millingof radioactive ores

27 Safety considerations in the use of ports andapproaches by nuclear merchant ships

f.

1961 Guide-book

1961 Guide-book

1961 Safety Standard

196419671970

1961

1962

19621967

1963

Guide-book

Guide-book

Safety Standard

Guide-book

1965 Guide-book

1965 Safety Standard

1965

1965

1965

1966

Safety Standard

Safety Standard

Guide-book

Guide-book

1966 Guide-book

1966 Guide-book

1967 Guide-book(Joint IAEA/WHOpublication)

1967 Guide-book

1968 Code of Practice(Joint IAEA/ILOpublication) '

1968 Guide-book

Date ofNo. Title issue Remarks

28 Management of radioactive wastes at nuclear power plants

29 Application of meteorology to safety at nuclear plants*31 Safe operation of nuclear power plants

32 Planning for the handling of radiation accidents

34 Guidelines for the layout and contents of safety reportsfor stationary nuclear power plants

*35 Safe operation of research reactors and criticalassemblies w/Technical Appendix

36 Disposal of radioactive wastes into rivers lakesand estuaries(Revised Edition of S.S. No.10)

1968

1968

1969

1969

1970

1971

1971

Guide-book

Guide-book

Code of Practice

Guide-book(JointIAEA/I LO / FAO/WHO publication)

Guide-book(Joint IAEA/WHOpublication)

Code of Practice(Joint IAEA/WHOpublication)Guide-book

Safety Standards and Codes of Practice are submitted to the Board of Governors for approvalbefore publication.

Technical Reports Series

No. Title Date of issue

15 A basic toxicity classification of radionuclides 196327 Technology of radioactive waste management avoiding environmental disposal 196431 Training in radiological protection: curricula and programming 196478 Operation and control of ion-exchange processes for treatment of

radioactive wastes 196782 Treatment of low- and intermediate-level radioactive waste concentrates 196883 Economics in managing radioactive wastes 196887 Design and operation of evaporators for radioactive wastes 196888 Aseismic design and testing of nuclear facilities 196889 Chemical treatment of radioactive wastes 1968

101 Standardization of radioactive waste categories 1970106 The volume reduction of low-activity solid wastes 1970109 Personnel dosimetry systems for external radiation exposures 1970116 Bituminization of Radioactive Wastes 1970118 Reference methods for marine radioactivity studies 1970120 Monitoring of radioactive contamination on surfaces 1970122 Air filters for use at nuclear facilities ,1970133 Handbook on calibration of radiation protection monitoring instruments 1971

Proceedings Series

Symbol. Title Date of issue

STI/P1413/113 Disposal of radioactive wastes 1960

STI/PUB/57 Reactor safety and hazards evaluation techniques 1962

STI/PUB/60 Biological effects of ionizing radiation at the molecular level 1962

STI/PUB/63 Treatment and storage of high-level radioactive wastes 1963

STI/PUB/72 Siting of reactors and nuclear research centres 1963

STI/PUB/78 Radiological health and safety in mining and milling of nuclear materials 1964

STI/PUB/84 Assessment of radioactivity in man 1964

STI/PUB/116 Practices in the treatment of low- and intermediate-level radioactive wastes 1966

STI/PUB/126 Disposal of radioactive wastes into seas, oceans and surface waters 1966

STI/PUB/154 Containment and siting of nuclear power plants 1967

STI/PUB/156 Disposal of radioactive wastes into the ground 1967

STI/PUB/159 Assessment of airborne radioactivity 1967 .

STI/PUB/195 Treatment of airborne radioactive wastes 1966

STI/PUB/199 Radiation protection monitoring 1969

STI/PUB/226 Environmental contamination by radioactive materials 1969

STI/PUB/239 Nuclear energy costs and economic development 1970

STI/PUB/261 Environmental aspects of nuclear power stations 1971

STI /PUB/264 Management of low- and Intermediate-level radioactive wastes 1970

STI/PUB/285 Tests on transport packaging for radioactive materials 1971

STI/PUB/289 Rapid methods for measuring radioactivity in the environment 1971

Other Publications

Title Date of issue

Waste Management Directory 1971

Waste Management Research Abstracts, No.1 1965

2 1966

3 1967

4 1968

5 1970

6 1971

Health Physics Research Abstracts, No. 1 1968

2 1969

3 1970

4 1972

82

Annex II.Pertinent Publications of the World Health OrganisationPublic Health Responsibilities in Radiation ProtectionWorld Health Organization, Geneva, 1963

Protection of the Public in the Event of Radiation AccidentsWorld Health Organization, Geneva, 1965

Routine Surveillance for Radionuclides in Air and WaterWorld Health Organization, Geneva 1968

Kamath, P.R.The Environmental Radiation Surveillance LaboratoryWorld Health Organization, Geneva, 1970

Straub, C.P.Public Health Implications of Radioactive Waste ReleasesWorld Health Organization, Geneva, 1970

Annex Ill.Pertinent Publications of other International BodiesList of Consultants and ContributorsUnited Nations Scientific Committee on the Effects of Atomic Radiation(UNSCEAR)

Report of UNSCEAR. General Assembly document, 13th session, Suppl. No.17 (A/3838).United Nations, N.Y., 1958.

Report of UNSCEAR. General Assembly document, 17th session, Suppl. No.16 (A/5216).United Nations, N.Y., 1962

Report of UNSCEAR. General Assembly document, 19th session, Suppl. No.14 (A/5814).United Nations, N.Y., 1964

Report of UNSCEAR. General Assembly document, 21st session, Suppl. No.14 (A/6314)..United Nations, N.Y., 1966.

Report of UNSCEAR. General Assembly document, 24th session, Suppl. No.13 (A/7613).United Nations, N.Y., 1969

International Labour Organization (11.0)

Manual of Industrial Radiation Protection

Part I: Convention and Recommendation concerning protection of workers against ionisingradiations, 1963

Part II: Model Code of safety regulations (ionising radiatiOns), 1959.Part III: General guide on protection against ionising radiations, 1963.Part IV: Guide in protection against ionising radiations in industrial radiography and fluoroscopy,

1964.Part V: Guide on protection against ionising radiations in the application of luminous compounds,

1964.Part VI: Radiation protection in the mining and milling of radioactive ores (Code of practice

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List of Consultants and ContributorsConsultants' Meeting of Experts:

21-22 June 1971 J.J. Di Nunno USAH.J. Dunster UKW. Frankowski PolandJ. Pradel France

Scientific Secretary: D.G. Jacobs IAEA

Consultants' Meeting of Experts:10-14 January 1972 P. Condos France

J.J. Di Nunno USAW. Frankowski PolandA.W. Kenny UK (consultant of WHO)G.W. Mei Iland WHOF.J. Woodman UK

Scientific Secretary: D.G. Jacobs IAEA

Special Consultants for the K.Z. Morgan USAWorld Health Organization A.W. Kenny UK

Contributions provided by P.J. Barry and A.M. Marko CanadaJ.R. Buchanan, H.B. Piper andR.L. Scott USAP. Candela FranceJ.J. Di Nunno USAH.J. Dunster UKYu. A. Israel and E.N. Teverosky USSRD.G. Jacobs IAEAJ.K. Jones UKB. Kahn and H. Kolde USAA.W. Kenny UKG.W. Meilland WHOK.Z. Morgan USAR.E. Nakatani and O.J. Stober USAJ.T. Roberts IAEAV.P. Rublevsky, I.A. Ilyin,A.S. Zykova and A.D. Turkin USSRG.E. Swindell IAEAP.J. West I AEAE.W. Wiederhold IAEAF.J. Woodmen UK

Technical Editors D.G. Jacobs IAEAJ.W. Daglish IAEA

International Atomic Energy AgencyKamtner Ring11, P.O. Box 590, A-1011Vienna, Austria