fission products radioactivity and their effects

28
30.11.11 FISSION PRODUCTS RADIOACTIVITY AND THEIR EFFECTS K. Periasamy, M.Tech (Chem. Engg), Chennai – 96. &&&&& Introduction The radioactivity of individual fission products and its effect on human being is a function of yield%, half life, the type of radioactive decay and its energy. When the yield % is high the quantity of that particular fission product is high and hence the radioactivity can be high. When the half life is high, the decay rate is slow. Hence, the radioactivity will be less for a given quantity of that particular fission product. The effect of various radioactivity types depend upon whether they are internal or external. For the given type of radioactivity, for the given type of exposure ( internal or external ), higher the energy level, the more will be the damage. Types of Radiation There are three types of radiation encountered in the Nuclear Fuel Cycle which consists of Uranium Mining, Ore Processing, Fuel Fabrication, Nuclear Reactor Operation, Spent Fuel Storage, Fuel Reprocessing and Waste Management. They are Alpha, Beta and Gamma. Alpha radiation is the least penetrating and it can be stopped by just a piece of paper or a few feet of Air. It is naturally emitted by large radioactive atoms like U – 235, Pu – 234, U – 233, Ra – 223, and Transuranics like Np – 237, Am – 241, Cm – 243, etc. The Alpha particle ionizes the medium through which it travels by knocking off the outer most electrons of the constituent Atoms of the medium. It deposits some energy when it is intercepted by any medium, including Air.

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Page 1: Fission Products Radioactivity and Their Effects

30.11.11

FISSION PRODUCTS RADIOACTIVITY AND THEIR EFFECTS

K. Periasamy, M.Tech (Chem. Engg), Chennai – 96.

&&&&&

Introduction

The radioactivity of individual fission products and its effect on human being is a

function of yield%, half life, the type of radioactive decay and its energy. When the

yield % is high the quantity of that particular fission product is high and hence the

radioactivity can be high. When the half life is high, the decay rate is slow. Hence,

the radioactivity will be less for a given quantity of that particular fission product. The

effect of various radioactivity types depend upon whether they are internal or

external. For the given type of radioactivity, for the given type of exposure ( internal

or external ), higher the energy level, the more will be the damage.

Types of Radiation

There are three types of radiation encountered in the Nuclear Fuel Cycle which

consists of Uranium Mining, Ore Processing, Fuel Fabrication, Nuclear Reactor

Operation, Spent Fuel Storage, Fuel Reprocessing and Waste Management. They are

Alpha, Beta and Gamma.

Alpha radiation is the least penetrating and it can be stopped by just a piece of paper

or a few feet of Air. It is naturally emitted by large radioactive atoms like U – 235,

Pu – 234, U – 233, Ra – 223, and Transuranics like Np – 237, Am – 241, Cm – 243,

etc. The Alpha particle ionizes the medium through which it travels by knocking off the

outer most electrons of the constituent Atoms of the medium. It deposits some

energy when it is intercepted by any medium, including Air.

Beta radiation can penetrate through few meters of air. But it does not deposit much

energy when it is attenuated (i.e. stopped). Hence it is safer than alpha radiation. This

also causes ionization but about 100 times lesser compared to Alpha.

Both Alpha and Beta radiation are harmful only if the radioactive substances emitting

these radiations enter our body and stay for long periods. This stay within the body

is measured in terms of another half life called Biological half life. For Cs–137, the

most problematic element, it is 70 days only. That is, even if the Cs–137 enters

Page 2: Fission Products Radioactivity and Their Effects

our body through milk, meat, vegetables, etc. almost all Cs–137 would have been

biologically removed from our body by way of stool, urine, perspiration, respiration,

etc. within about one year. Similarly Iodine which can get accumulated in Thyroid has

biological half life of just 11 days for infants and 80 days for adults.

Gamma Radiation is more intense than Alpha and Beta. Hence, they are able to not

only knock off the outer most electrons, but are able to penetrate to the inner electron

shells and further into the nucleus of the atom itself. During all these three stages

they cause ionization by different mechanisms called, Compton Scattering,

Photoelectric effect and Pair Production.

In effect, when radiation interacts with matter, in particular living tissue, the main

effect is ionization, by which process electrons of constituent atoms of the tissue are

knocked off. This process of ionization is the cause for biological damage due to

radiation.

Damage to DNA

There has been a widespread belief that all radiation will cause human Cell damage,

all Cell damages cause cancer and all cancers lead to genetic modifications ! This

cancer issue needs to be understood in its right perspective.

The human Cell consists of two types – Somatic Cells and Germ Cells. Germ Cells

constitute the Sperm and Ova. All other parts of the body are made of Somatic Cells.

Somatic Cells contain 46 Chromosomes and Germ Cells contain 23 chromosomes. The

combination of the 23 each in Sperm and Ova make up the 46 chromosomes required

for the Somatic Cells.

The chromosomes in turn are composed of linear sequence of genes. Mamalian Cells

contain 60,000 to 70,000 genes. These are made up of DeoxyriboNucleic Acid ( DNA )

molecules. Each DNA molecule contains about 10 million atoms. It is made up of 2

molecular chains that are entwined around each other as a Double Helix as shown in

the Figure. These two chains are interlinked by Hydrogen Bonds.

Page 3: Fission Products Radioactivity and Their Effects
Page 4: Fission Products Radioactivity and Their Effects

Suppose a Cell in human body is exposed to radiation. One or more atoms are ionized

as per the type and energy intensity of radiation. The ionizations can cause 1)

Damage to the Hydrogen Bonds 2) Damage to one chain ( Single Strand Break) 3)

Damage to both chains ( Double Strand Break ).

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In many cases the Cells are able to repair these damages by themselves. Sometimes it

is left unrepaired. Alpha particles attack the chains directly and damage them. Hence

are more dangerous. This can be seen from the figure given below.

Even with low Dose, the Cell Surviving fraction drastically falls for Alpha. But the other

two radiations cause damage by indirect means through generation of radicals and

the Cell Surviving fraction does not fall even at high Doses. The effect of radiation on

human body is measured in terms of equivalent dose. Alpha radiation has 20 times

higher effect on human body than that of X-Ray, Gamma Ray, and Beta Radiation. This

is an important aspect to take cognizance of. Among the three types of radioactive

substances, we have the least possibility for Alpha emitting particles coming into

public domain, even under accident conditions.

These DNAs left unrepaired, especially the damaged chains can combine in

uncommon positions leading to new type of Cells. The damaged Cells can multiply in

the body with damaged information. This kind of proliferation of damaged Cells which

do not behave like normal Cells is the root cause of cancer.

Page 6: Fission Products Radioactivity and Their Effects

If the DNA of Germ Cells gets damaged and is not repaired in time, and if they happen

to meet the Sperm or Ova as the case may me, then there could be offsprings carrying

the Cells containing this damaged information. It need not always be deformed limbs,

insane kids, double headed babies, etc as projected by common media.

This is the essence of radiation effect on human Cells.

As explained earlier, Alpha radiation is the most dangerous in terms of cancer, as they

break the main chain. Also the Alpha emitting atoms being larger they will be sitting at

one place and bombarding the same cells again and again unlike in case of Cs-137

which is mobile within the body. But, fortunately, the atoms which emit Alpha particles

( U-235, Pu-239, Am-241, Np-237,etc) seldom come in picture even under accident

situations due to their very low volatility. Even if they come out of the reactor, it will

be in the form of heavy particles and it will fall close to the reactors. Hence, there is

very little possibility for it to be spread wider.

Most of the Cells which are damaged are automatically repaired by the self repair

mechanism like in any other self defense mechanism available in the body for various

diseases. We shall understand that, for cancer to manifest, several coincident

probabilities are required like 1) The radiation particles / atoms shall attack the

sensitive organs 2) Sustained presence and attack of particular Cells 3) Exception

from natural death of attacked Cells 4) Exception from death of Cells by excessive

radiation itself 5) Possibility of damaged Cells joining at wrong locations 6) Possibility

of the wrongly formed Cells not being attacked by the radiation again, etc.

So, it is not that as and when there is radiation, there will have to be cancer ! As and

when there is cancer, there has to be deformed baby births !

Hence, there is no surprise that the radiation effect on human beings is much less

compared to the “predictions” made by “experts” who simply keep arguing that every

radiation causes cancer, every radiation kills people, there is no threshold lower limits

for any effect on human beings for radiation, etc. They do not want to understand

these basic concepts.

This has been proved beyond doubt in Hiroshima, Nagasaki and Chernobyl. We have

data for almost 60 years now. Even in cancer treatment by radiation, we are exposing

the good Cells adjacent to the cancer affected Cells to very high doses. We don’t see

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any cancer development in those Cells. Those Cells simply die in most cases. Similar

thing happens in other radiation exposures also.

OK, but why there is so much fear for radiation if it is not all that dangerous ?

History of Nuclear Radiation Fear

There has been a gross misunderstanding over the years on Nuclear power leading to

some sort of fear psychosis. This misunderstanding has been generated and sustained

by the ill informed and half truth media hypes created over several decades. Since

historically Nuclear Energy has always been linked to defense applications apart from

power, Nuclear energy has always been kept under the wrap of Government secrecy

throughout the world. Even when the media was writing many absurd stories on

nuclear energy, the scientists and officials associated with Nuclear energy were asked

not to react. With the result, media writings gained more credibility in the minds of

general public, especially the educated lot who are not directly associated with

Nuclear Energy.

There is another dimension to the whole issue. Since the consequences of radioactive

contamination / accidents are higher compared to the conventional chemicals /

pollutants / accidents, etc, and it is invisible, the nuclear scientists have always kept

the safety on top priority. For every new employee who enters the nuclear industry,

the first training they undergo is on the dangers of radioactivity. In fact, they are

“intoxicated” with a fear for radiation so that they do not take the safety issue as a

casual one as is normally done in other industries. Sometimes exaggerated phrases

are used during the training to sensitize the workers on the importance of sticking to

the procedures in their duties. These phrases are transferred verbatim to the media by

the lower and middle level employees in their enthusiasm to display the importance /

critical nature of their work. The media in turn takes it to the gullible public with

further exaggerations as part of their professionalism !

The miscommunication and misunderstanding between the media and the Nuclear

Industry started with the confusion created by Nuclear Regulatory Commission (NRC)

of USA during the Three Mile Island accident. There were three conflicting directions

given by NRC to the public within 48 hours. Initially people were asked to vacate. Later

they were told it is better to stay in-door. Again they were asked to vacate, especially

the pregnant women and children. This sowed the seeds of mistrust between the

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nuclear energy and the general public. There were rumours after rumour on Three

Mile Island Accident. There were reports after report on what happened and what can

happen in future.

If we Google for “ TMI Accident” there will be about 23 million hits ! The fact is that not

a single person died in this accident neither immediately nor later due to radiation

release. This accident has released about 2.5 million Curies of Xenon and Krypton and

about 15 curies of I-131. So, for an accident which has not killed even one person and

which has not affected even one square KM of land mass, we have so much publicity !

Further, there was a Fiction film release in USA titled “China Syndrome” wherein it was

shown and made to believe that, if a Nuclear Reactor goes out of control, the fuel will

melt, it will penetrate through the Earth and come out at a location in China diagonally

opposite of USA ! Coincidently, this Film was released just 12 days prior to the Three

Mile Island accident. We can imagine what terrible reaction it would have generated

among the general public, especially the young minds !

The mix up between the effect of Nuclear Bomb of Hiroshima and Nagasaki and the

effect of Nuclear reactor accidents is yet another dimension to the issue. Now again in

Fukushima, though not a single person has died due to the nuclear incident, the 15000

tsunami deaths ( or atleast part of it !) are brought under the Nuclear accident

category ! The fact is that in all probabilities, no one is going to die also in future due

to the Fukushima nuclear accident since there were timely actions by the authorities

concerned, contrary to the media hypes on the “callous” attitude of the authorities in

dealing with the situation. They have distributed Iodine Tablets, they have moved the

people away in phases, they have banned the milk & meat produced in the region,

they have banned the export of food products, etc. Whatever sporadic cases of

contamination news we come across in the media are just few exceptions /

deviations / mistakes / omissions, etc.

This is how there has been a build up of fear psychosis about nuclear energy and

nuclear radiation throughout the world.

Now today, the importance of nuclear weapons has slowly faded away. It is no more

necessary (and any longer possible !) to keep the secrecy of nuclear weapons

program. The Nuclear Industry is allowed to break its silence and explain the whole

thing right from scratch. Naturally, the nuclear industry is opening up its veil. But the

Page 9: Fission Products Radioactivity and Their Effects

pity is that, the mistrust which has been created over several decades is coming in the

way of proper communication. Especially the media, which is run by the middle age

people, whose minds have already been loaded with the negative image of Nuclear

energy right from their childhood, does not want to trust the words of the Nuclear

Industry. For example, whenever there is a discussion about nuclear power, the media

brings up the Hiroshima, Nagasaki and the Mushroom Cloud of Nuclear weapon

crosses their mind, even without their knowledge !

Whether we like it or not, this is the reality. For a healthy discussion and knowledge

dissemination we need to break this barrier in the minds of media people.

Having understood the effect of radiation in a broad perspective and the history of

radiation fear, now let us look at the areas where radiation is handled, how and what

kind of radioactive substances are released during the accidents, how they are

managed, etc.

Radiation Possibilities and the effect on Human beings

There are two areas where there is Radiation. One, where there is Radiation

generation – that is in Nuclear Reactors. The second is in Waste Management

( Fuel Reprocessing and Waste Immobilisation Plants ). Let us analyze these two areas

and understand the consequences of accidents in both these areas.

Having understood a bit of the history behind the fear for Nuclear power, let us keep

our mind in “open mode”, shut the “weakness” part of the heart responsible for

whipping up the fear of unknown, and try to understand the real consequences of the

accidents. Let us see what is the worst that can happen.

a) Nuclear Reactor Accidents

Unlike in the conventional chemical industries, coal power plants, etc., the

consequences of accidents in Nuclear Power Plants are large and it is well known.

Hence, there is very high design margins, safety redundancies, passive shut down

systems, etc. Above all, always fail safe concepts like Negative void coefficient,

Page 10: Fission Products Radioactivity and Their Effects

Negative reactivity coefficient, no means of operator overruling of safety systems, etc.

have been evolved over the last 50 years of nuclear power industry. Hence, Nuclear

Reactor accidents, only three of them in total, over 14000 Reactor years of operation

have happened. All three accidents involved only the Ist Generation Reactors which

were built 30 to 40 years back. Subsequently, many developments have taken place in

terms of Computer Simulation, materials development, knowledge sharing between

countries, etc. Obviously, that is the reason why no accidents have taken place in

Reactors built in the recent decades, which are 2nd and 3rd Generation Reactors. This is

in line with any technology which matures over the time.

Despite all these developments should there be an accident in Reactors what

happens?

Firstly there will be breach of fuel clad (Zircoalloy). The radioactive gases and volatile

fission products will escape through the Stack after passing through the HEPA filters.

Still if there is further heating of fuel, there will be reaction of Zircoalloy with Steam

leading to damage to fuel and there could be escape of some fuel as particles along

with more amount of volatile fission products. These fuel particles can carry fission

products and Actinides. But the chances for these particles escaping the primary

containment are remote unless the primary containment itself opens up like in

Chernobyl. In none of the reactors other than the RMBK type which was used in

Chernobyl, this can happen. In Fukushima accident, even though the reactor building

only exploded, it did not expose the fuel to the atmosphere since the Reactor vessel

was in tact. The fuel was well contained within the reactor vessel itself, though there

was substantial damage to the core. Some prefer to call it as “melt down”. But it is not

a melt down in nuclear parlance. It is only a damage to the fuel elements due to

residual decay heat. The total radioactivity release in Fukushima was only about 25%

of that of Chernobyl even though 3 Reactors and some Spent Fuel ponds were

involved in Fukushima as against one reactor only in Chernobyl.

What are the real consequences of Nuclear Reactor accidents ?

The open secret is that the Nuclear accidents are not catastrophic, not unmanageable,

not unpredictable and not to be worried for centuries, as we all made to believe till

today. Nuclear Reactor is different from Nuclear Bomb. For a clear understanding of

the whole issue, the real consequences of radioactive substances coming out of the

Reactor in Nuclear power accidents is discussed below in detail.

Page 11: Fission Products Radioactivity and Their Effects

The only radioactive gas with significant yield % and higher half life is Krypton-85.

Though Xenon is also a gas, the Xenon isotopes have very low half lives of few

minutes to few hours. Krypton-85 being a Beta emitter with reasonably high half life, it

does not pose any major health hazards. Moreover, Krypton being a Beta emitter, it

matters much only if it enters the body. But being a light gas it always rises up as

soon as it is released through the Stack. Moreover, being an inert gas, it can never

enter the biological cycle. They move up in the atmosphere and go to the polar region.

Hence Krypton does not pose any hazard at all.

There are two important volatile fission products which come out in case of Reactor

accidents. They are I-131 and Cs -137. Since I-131 has a half life of just 8 days, it dies

down very fast and it will be negligible within 2 months. During this period, if children

happen to inhale the contaminated air or drink contaminated milk, then it can

accumulate in the Thyroid leading to Thyroid doses. This I-131 intake and

accumulation in Thyroid can be avoided simply by using paper nose masks and by

taking normal Potassium Iodide Tablets as a precaution. Even after the accumulation

of I-131, this Potassium Iodide Tablet intake will replace the I-131 with non-radioactive

I-127 very fast. Another aspect is that the Biological half life of I-131 itself is only 11

days for children. Hence I-131 exits on its own from the body, albeit slowly.

Hence I-131 issue is very simple to handle. It has been proved beyond doubt in

Chernobyl and Fukushima. In Pripyat town close to Chernobyl, enough Iodide Tablets

were distributed. Hence there was very little effect due to I-131 in this town. But, due

to lack of official co-ordination, sufficient quantity of Iodide tablets were not

distributed in rural areas surrounding Chernobyl. This lead to high Thyroid doses

among about 4000 children in this region. Subsequently they were all treated and

only 15 died due to Thyroid cancer. It has been well documented by several

independent studies including WHO and Chernobyl Forum.

In Fukushima they have distributed enough Potassium Iodide Tablets. Hence there is

no problem here also.

The second isotope Cs-137 has lesser volatility compared to I-131. Boiling point of Cs-

137 is 671’ C compared to 184’ C for Iodine. Hence, the quantity that can escape will

be much less compared to Iodine. But since Cesium isotopes are formed by beta

decay of Xenon, which is a gas which accumulates at the top of the fuel pin as and

Page 12: Fission Products Radioactivity and Their Effects

when it is formed, good amount of Cesium will be there at the top of the fuel pin.

Hence, there is a good probability for it to escape in the first instance of clad failure.

In Chernobyl case, the situation was conducive for the escape of not only this Cesium

which is accumulated at the top but also the Cesium present in the main body of the

fuel pin. In Chernobyl Reactor, the fuel and the Graphite( Moderator) were burning in

open air with extensive damage to the fuel elements resulting in physical carry over of

the fuel particles by the rising inferno. This kind of situations can arise only in RMBK

type of Reactors where Graphite is used as Moderator. In other PWRs(Kudankulam)

and PHWRs ( Kalpakkam) water only is used as Moderator instead of Graphite.

Hence, there is nothing to burn other than the small quantity of Zircollaoy clad.

Cs-137 is a Beta & Gamma emitter with moderate energy levels. A few meters

distance away from the Cs-137 bearing particle lying on the floor, there will not be

much effect due to Beta. Even if we step on the particle containing Cs-137 with

Chapel / Shoes, there will be no radiation to our body from Beta. But there will be

some dose due to Gamma. It has been estimated that the cancer risk for 1,00,000

people continuously exposed to a thick layer of soil containing Cs-137 radioactivity

of 1 pCi/gm, is hardly 0.006%. That is, only 6 people out of 1,00,000 are likely to get

cancer in their old age. In contrast, in USA, Japan, Europe, etc. the normal death due

to cancer caused by natural radiation, carcinogenic chemicals, food toxins, etc. for this

1,00,000 population is about 20,000. So, the effect of external radiation of Cs-137 is

obviously insignificant. If the radioactivity is 1000 times of 1 pCi/gm, then the effect on

cancer is not 1000 times. It is much lower. It has been proved with extensive data. We

shall keep this in mind. For argument sake, even if we take it in proportions also, the

number is only 6000 as against the normal death toll of 20,000.

Please note, with the advent of new technologies in Medical field, there is early

detection of diseases, better medicines, better surgical methods, organ transplants,

etc, there is increase in the life expectancy. The proportion of casual deaths by normal

diseases, heart attacks, organ failures, etc is declining. This leads to higher average

age and this ultimately results in increase in cancer death proportion. This is a natural

phenomenon.

Only if Cs-137 enters our body there will be higher level of radioactive dose due to

both Beta and Gamma. Cs-137 can enter the body in several ways like 1) Intake of

contaminated food (2) Drinking of Milk which was obtained from the animal which has

Page 13: Fission Products Radioactivity and Their Effects

eaten animal feed or vegetation containing radioactive particles (3) Eating Meat which

was cut from the animal which has eaten animal feed or vegetation containing

radioactive particles.

The possibility of radioactive substances coming in direct contact with food items like

Rice, Wheat, Cereals, etc. is not there since there are outer husks which are removed

before food is consumed. In case of vegetables it is washed and consumed. Hence

the possibility Cs-137 entering the body through the intake of contaminated food

route is very limited. We can also exercise administrative control and control by

publicity to minimize the contaminated food consumption during accidents.

Regarding the Milk and Meat, it should be understood that (1) The probability for Cs-

137 getting assimilated and going into the blood stream of animals is hardly about few

percent, like any other minerals. (2) Out of this about 30% goes to the Bone and only

the remaining 70% goes to the Milk and Flesh. (3) The Biological half life of Cs-137

in the animals is about 70 days, meaning after about one year almost nothing will be

left out in the animal.

So, the probability of Cs-137 going into human body through the Milk and Meat route

is very limited since only a few percentage of what the animal has taken in can come

to human food chain. Here again we can exercise Administrative and publicity

controls and further reduce the chances of Cs-137 getting into our body.

Despite all this, whatever Cs-137 enters the human system gets excreted completely

within about one year due to the Biological half life of 70 days in the human beings. In

case of children drinking milk containing Cs-137, the assimilation probability is higher.

Only this needs to be taken care during accident situation. Is it really an

unmanageable situation ?

One thing must be understood here. Just because we are able to detect some

radioactivity in soil, animal meat or milk here and there, we need not press any alarm

bell. The radiation measurement instruments are so sensitive that they can detect

even 1/1000th of value which is of any concern to us. Moreover, the radioactivity

levels reported are specific hot spot values where some mist particles carrying Cs-137

must have settled or a particular animal farm would have used the fodder which would

have been found indoor, but originally it would have been lying outdoor at the time of

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accident, etc. It should not be construed as if it is spread uniformly between any two

hot spots or it would have been true with every animal grown in that region !

The Government reactions by way of ban of even the slightest contaminated food

produced or animals reared in the entire region shall be understood as a matter of

abundant caution and prudence to ensure that no one is affected even by the

remotest probability. Moreover, the limits set for health and safety intervention by

Government agencies are orders of magnitude lower than the values which really can

cause any health hazards. We can see this in the later pages. But the media is using it

to spread fear psychosis !

Some NGOs and “experts” make cryptic questions like, if it is not dangerous or

harmful, “ Why the Government should not allow people to eat contaminated food ?” ,

“Why people should be evacuated in such vast area ?”, “Why there is Exclusion Zone

in Chernobyl”, etc, etc. Just because some one is exercising their power and initiating

certain actions based on their wisdom, as a matter of extra caution in an emergency /

unusual situations, we should not draw technical conclusions based on such actions.

We need to differentiate between the genuine questions and this kind of cryptic

questions for a healthy dialogue and better understanding.

Also, in case of accidents the media people get to know some value of the total

radioactivity releases. They do not know what kind of radioactive substance it is,

whether it is within the Reactor island or it is in Air or it is in water. They simply

assume as if ALL the “Thousands of Curies” of radioactivity which has escaped the

Reactor core will come to public domain and is going to “attack” ALL the population

ALL 24 Hours on ALL 365 days. Based on this assumption, they estimate “so much

millisievert dose” will be received by “Millions of people” and so many “thousands”

will die of cancer!

From the details provided above we can conclude how far this assumption is true and

one can easily understand what will be the real consequences, in case of nuclear

Reactor accidents.

b) Nuclear Waste Management

In Nuclear Waste Management area, there are two Plants – One is Fuel Reprocessing

Plant and the other is Waste Immobilisation Plant.

Page 15: Fission Products Radioactivity and Their Effects

The following Table provides information on the Yield % and the Half Life of various

Fission Products. This information is essential for better understanding of the

radioactivity in Waste Management.

Table – 1

No Isotope Yield,% Half-life Unit Remarks

1. I – 135 6.33 6.57 Hours 10 –50% becomes Xe –135. Balance converts to Cs –135

2. Mo – 99 6.10 65.94 Hours

3. I – 131 2.83 8.02 Days

4. Ru – 106 0.39 1.02 Years

5. Cs – 133 6.79 2.07 Years Gets converted into Cs-135

6. Pm – 147 2.27 2.62 Years

7. Sb – 125 0.03 2.76 Years

8. Eu – 155 0.033 4.76 Years

9. Kr – 85 0.27 10.78 Years

10. Cd -113m 0.0003 14.1 Years

11. Sr – 90 5.75 28.9 Years

12. Cs – 137 6.09 30.2 Years

13. Tc – 99 6.05 2,11,000 Years Suitable for destruction by transmutation

14. Sn – 126 0.024 2,30,000 Years

15. Se – 79 0.051 3,27,000 Years

16. Zr – 93 6.29 15,30,000 Years

17. Cs -135 6.91 23,00,000

18. Pd – 107 0.16 65,00,000 Years

19. I – 129 0.66 1,57,00,000 Years Suitable for destruction by transmutation

In Nuclear Fuel Reprocessing Plant, by the time the fuel is taken up for processing, it

would be about 10 years since it was taken out of the Reactor. Hence almost all short

lived isotopes which are volatile would have died down. Only I-129 which has a very

long half life will remain, in the volatile fission products category.

There are specific process steps for handling this. The vapour containing Iodine is

scrubbed, filtered and contained with redundant passive systems. Hence there is no

scope for it to come to the environment. Even if it comes out due to any accidental

reasons, it can be handled easily with Iodide Tablets intake. Since the yield of I-129

itself is low and since it has high neutron absorption cross section leading to the

Page 16: Fission Products Radioactivity and Their Effects

transmutation to stable isotopes, the quantity of I-129 involved is very less compared

the I-131.

In the remaining fission products, there are two groups which are of concern :

a) Medium half life Fission Products – Specifically Kr-85 (10.78 years), Sr-90

(28.9 years) and Cs-137 (30.2 years)

(b) Long lived Fission Products – Seven of them discussed in detail below.

All these fission products, except Kr-85 are handled within the Reprocessing plant and

the Waste Immobilization Plant in liquid form under several barriers including about

1m thick concrete wall. The entire plant is designed with fail safe concept so that

under any circumstances like, mal-operation, power failure or natural calamities, there

will be no radioactive discharge into the atmosphere. Since the complete plant Cells

are made of 1 m Thick concrete (including the Floor) with leak proof SS Plate lining,

there are no possibilities for the liquids to seep even if they come out of process

vessels (most of them are Double walled).

There are several Fuel Reprocessing Plants operating throughout the world including

India, for several decades without any accidents. A few Waste Immobilization Plants

are also operating including a few in India.

Out of the three major Medium Half Life Fission Products, Kr-85 is a gas with very low

yield of 0.27% ( as against about 6 % for Sr-90 & Cs-137). It’s half life is also relatively

low at 1/3 rd of Sr-90 & Cs-137. Hence, in the first step of Reprocessing itself it is

diluted and let out into the atmosphere at very high altitudes. Being light, it can never

settle down. Also being inert, it does not take part in any of the biological activities. Its

radioactivity is mainly from Beta. As we know, as long as beta emitting particles do

not enter our body, and they are away from us at least about few feet, they are

harmless. So, Kr-85 is of no concern.

The remaining Medium Half Life isotopes, St-90 & Cs-137 are immobilized along with

other Long Lived Fission Products.

The Seven Long lived Fission Products are discussed in detail in the following pages for

a better understanding of the phrases like, “wastes need to be managed for millions of

years”, “we are making our children vulnerable”, “there are no technologies available

Page 17: Fission Products Radioactivity and Their Effects

to handle them”, etc which are coined by people whenever nuclear energy is

discussed.

Seven long lived Fission Products

Now with the background of the effect of radiation discussed earlier, let us look at the

seven long lived fission products which are left out after Reprocessing. These are the

ones which are of concern after several decades of cooling. The Table given below

provides information on the yield, the intensity values of the radiation in KeV, Type of

Radioactivity and half life for each of the Fission Products. Higher the KeV value more

will be the penetration.

As can be seen from the Table below, the first three, Tc-99, Sn-126 and Se-79 have

half lives of 2,11,000, 2,30,000 and 3,27,000 years, which are more or less close by.

Table- 2

S.No. Isotope Yield % Radiation Energy

KeV

βγ Half Life years

1 Tc – 99 6.14 294 β 2,11,000

2 Sn – 126 0.11 4050 βγ 2,30,000

3 Se – 79 0.04 151 β 3,27,000

4 Zr – 93 5.46 91 βγ 15,30,000

5 Cs – 135 6.91 269 β 23,00,000

6 Pd – 107 1.25 33 β 65,00,000

7 I – 129 0.66 194 βγ 1,57,00,000

But the yield of Tc-99 is 60 Times higher than Sn–126 and 140 Times higher than Se–

79. Hence in this top three, Tc-99 only is important. But again Tc-99 is only a Beta

emitter, meaning only if it goes into our body it is more harmful. Though Sn–126 is a

strong gamma emitter, the radioactivity release per unit time is only 5% of Tc–99.

Since all are fixed in a glass matrix and embedded in unleachable and impermeable

concrete, there is no scope for any of these fission products getting into the biological

system.

The 4th and 5th elements Zr-93 and Cs-135 have high yields at 5.4% and 6.9%

respectively. Zr-93 decays 7.5 times slower than Tc-99. Though Zr-93 is a Gamma

emitter, since the intensity is only 1/3rd of that of Tc-99, the overall radiation effect of

Page 18: Fission Products Radioactivity and Their Effects

Zr-93 is hardly 4% of Tc-99. Also, Zirconium is inert to most medium in the

environment, and hence it is relatively insignificant.

Cs – 135 decays about 12 times slower than Tc-99 and it is a Beta emitter with more

or less the same energy level as that of Tc-99. Hence Cs – 135 will have about 1/12 th

of Tc-99 effect only. Cs-135 is not inert like Zirconium. But since everything is in

glass form and secure it can not enter the soil. Being a Beta emitter its effect is

negligible in soil.

The 6th element Pd-107 has very long half life, yield is low, and it is only a Beta emitter

with very weak radiation intensity. Hence, it is insignificant.

The 7th element I -129 has the longest half life. Though the yield of I -129 is

appreciable at 0.66%, due to its moderate absorption cross section (barn) for

neutrons, part of the I-129 absorbs neutron and gets converted to Xe – 130, a stable

isotope, within the Reactor itself. Hence only balance of I – 129 produced remain in

the fuel. It decays about 75 times slower than Tc-99. Though it is a Beta & Gamma

emitter, the intensity is relatively lower compared to Tc-99. Hence I -129 is also

relatively insignificant.

The issue of I-129 getting into the Thyroid and causing thyroid disorders does not arise

even in accident conditions since the I-129, if any escaping after capture by Silver

Nitrate is absorbed in HEPA Filters in both Reprocessing Plant and Waste

Immobilization Plant. The HEPA Filters containing Transuranics and / or I-129 are

treated as High Active waste and immobilized. Moreover only 30% of any Iodine which

goes into the body gets accumulated in the Thyroid and balance is excreted very

quickly. As mentioned above this Iodine which goes to Thyroid is also cleared with a

biological half life of 11 days for infants to 80 days for adults. This excretion can be

further accelerated with the intake of normal Potassium Iodide Tablets. Hence the

effect of I-129 is not significant, and is well manageable in any eventuality.

Hence, out of the Seven Isotopes, only Tc-99 is of major concern. I-129 being a volatile

isotope with gamma radiation, it needs to be taken care.

Conclusion

Page 19: Fission Products Radioactivity and Their Effects

From the above discussion, it is clear that the probability for radioactivity release from

Nuclear Reactors or from the Waste Management is almost Nil in the 3rd Generation

Nuclear facilities being built. The other existing facilities also have been analysed

based on the current knowledge on the risk probabilities and found to be safe. What is

important is that, should there be any release due to any unforeseen reasons, the

effect of the radioactivity released into the atmosphere in the event of an

extraordinary accident also is not of any catastrophic proportions as made out to be.

The consequences are well understood and we can handle the situation without any

damage to anyone, including those living in the vicinity.

The oft repeated phrase “It has ramification for millions of years” needs to be

understood in the right perspective from the quantity of such fission products

generated in the Nuclear Reactor, how they are handled and how they can be

managed. The myth that “ No one can go near radioactive areas for thousands of

years” have been shattered by the complete rebuilding of Hiroshima and Nagasaki

cities, where Nuclear Bombs were exploded and the complete fission products are

dispersed everywhere. Now hundreds of thousands are living there. Millions of

Tourists are also visiting these cities every year.

It will be interesting to know the following information about Hiroshima and Nagasaki.

In Hiroshima and Nagasaki, out of the 2,84,000 survivors of Nuclear Bomb attack, as

on March 31, 2011 there are 2,19,410 living. Among the 1,90,000 survivors, there

were additional deaths of only 94 due to Leukemia and 848 due to cancer over and

above the normal average deaths due to these causes. It works out to just about 0.5%

increase over normal for the total survivors of Hiroshima. This Data on Nagasaki is not

available. As on 2006, after about 61 years of atom bomb explosions, 165 persons

who had been there in the vicinity of both the explosion sites were found to be alive !

At the time of explosions, some of these people were as old as 30 years and as young

as few years.

One Double Bomb survivor died recently at the age of 93 years due to stomach

cancer. He had been there within about 2 to 3 KM of Ground Zero of both the Bombs.

All these people have been exposed to thousands of times higher radiation, and that

too over a short duration, compared to the limits set by the IAEA and further reduced

by various Governments.

Page 20: Fission Products Radioactivity and Their Effects

These are undisputable scientific proofs that the radiation from radioactive substances

is not all that dangerous as made out to be. People mix up the Atom Bomb effect

which is more due to explosion, heat and the momentary high intensity radiation

exposure with that of the much lower levels of radiation from fission products.

Moreover, we are very much aware of the consequences and we are prepared to

mitigate in case of accidents from Nuclear facilities. it unlike in the case of Atom

Bomb. Please note, the death of few lakh persons during the bombing is nothing to do

with the radioactivity of the fission products left out, which is of concern in Nuclear

power.

Moreover, in Hiroshima and Nagasaki, till date there is no single case of genetic

disorders of any kind, even though as on date there are more than 50,000 second

generation people who were born to the radiation survived parents. Most of this

50,000 are about 35 years old. Their off springs also do not have any effect.

With regard to the Exclusion Zones in Chernobyl and Fukushima, it is a matter of

public confidence and precautionary measures taken by the Governments who are

also subjected to media hypes. Otherwise, majority of the exclusion zones are livable

even today. They will definitely be made livable in due course once there is enough

confidence that all hot spots have been identified and cleaned up.

Further it is clear that in terms of long term concern, there are only two Isotopes (Tc-

99 and I-129) which ultimately matter and both are perfectly immobilized in vitrified

glass matrix, contained in large mass of impermeable concrete and buried in deep

underground geological repositories. Absolutely there is nothing to worry about the

radioactivity of fission products though they exist for long periods. In fact, once we go

for transmutation of fission products in Fast Breeder, even these are tackled within the

reactor and there will be no major long term fission products to worry about.

&&&&&&.