senv guidelines for management of norm

8/3/2019 Senv Guidelines for Management of Norm

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Annex I

GUIDELINES FOR

MANAGING NATURALLY OCCURRING

RADIOACTIVE MATERIALS

IN PRODUCTION OPERATIONS

H. BASHAT, SENV Environmental Advisor

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Managing naturally occurring radioactive materials in production operations Annex I

GUIDELINES FOR MANAGING NATURALLY OCCURRING

RADIOACTIVE MATERIALS (NORM) IN PRODUCTION OPERATIONS

SUMMARY

Naturally occurring radioactive materials, NORM, have been known to be present in

varying concentrations in hydrocarbon reservoirs. These

NORM, under certain reservoir conditions can reach hazardous contamination levels. The

recognition of NORM as a potential source of contamination to oil and gas facilities has

become widely spread and gaining increased momentum from the industry. The contents of

the Annex which wee extracted mainly from References 1 to 3, address the various

problems with NORM and provides the recommended procedures for managing these

materials.

INTRODUCTION

There are two types of NORM contamination which are commonly known in the

oil and gas operations:

1) Radium contamination which is common to formation water and produces

low specific activity scale known as LSA.

2) Radon contamination which is common to natural gas production.

Both of these elements when accumulate in significant concentration will form serious

health and environmental hazard in addition to the operational problems. Thereforeperiodic analyses to detect and identify these contaminants at an early stage is becoming an

acceptable industry practice. The following sections will address each type separately.

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I. NATURALLY OCCURRING RADIOACTIVE MATERIALS FROM

PRODUCTION WATER

BACKGROUND

Naturally occurring radioactive materials NORM in formation water are soluble

radionuclides, may precipitate, under certain operational environment, as low specific

activity scale, known as LSA scales. These scales tend to be barium sulphate and strontium

sulphate which co-precipitate with naturally occurring radium leached out of the reservoir

rock; such scales emit alpha, beta and gamma radiation and this, together with the physical

properties of the LSAS, can give rise to a number of problems if such scales or sludges have

to be removed, handled or disposed.

Once LSA scales are formed within the production system two main problems are

presented: the scale will tend to foul valves and restrict the well fluid stream, and secondly,

the levels of radiation on the outside of the flowline or vessel may be so high that thesurrounding area may have to be designated as a restricted area and be cordoned off.

Scale formation can be prevented with some success by the use of scale formation

inhibiting chemicals. However, if the removal of LSA scale is necessary it can be difficult

and expensive because LSA scales (unlike calcium carbonate scale) are insoluble in

inorganic acids. Scale will either have to be removed (by hand or mechanically), or the

scaled up equipment taken out of service and put into safe storage. Therefore safe systems

of work and proper procedures which recognise the hazards, protect the workers from

harmful exposure, minimise interference with the environment and ensure compliance with

government and international regulations are essential.

1. ORIGIN AND FORMATION OF RADIOACTIVE SCALE

1.1 Naturally occurring radioactive rocks

The main radioelements found in the common sedimentary rocks include potassium,

uranium and thorium and the highest concentrations are normally found in shales as

indicated in Table 1.


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Table 1 Radioelement concentration in sedimentary rocks

K-40(ppm)

U-238(ppm)

Th-232

(ppm)

Sandstones

a) Orthoquartzites 1.7 0.45 1.7

b) Arkoses 1.5 5.0

Shales

a) Grey and green 2.9 3.2 13.1

b) Black 8-20

Limestones 0.4 2.2 1.1

Evaporites


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formation water or the injected seawater together with the occurrence of injection water

"breakthrough" may lead to deposits of mineral scale containing measurable quantities of

natural radioactivity concentrated by this scaling process.

Sand and silt deposits

These are potentially a greater problem in topside equipment (e.g. production separators).

This material can act as an absorbtive surface for radionuclides present in the production

fluid. An exchange mechanism between cations can then give rise to radioactive sludges

and deposits.

Radon-222 gas is part of the decay chain of radium-226. In most cases where radioactive

scale is produced radium-226 as well as some of its daughter nuclides including radon-222

may be found entrapped within the scale. Normally, radon-222 would be carried away with

the normal gas. There are fears that where sludges are formed, the entrapped radon-222 gas

may be given off in relatively large quantities, particularly when this sludge is being

disturbed. Therefore precautions must be taken to protect the people working with suchmaterials.

Iron (rust) deposits

It has been noted that occasionally a matrix like iron oxide in oily-water separators has

exhibited low levels of radiation. The mechanism is unclear, but there is some speculation

that radium-226 could be locked into rust itself.

Lead deposits

In some cases lead deposits occur which have high Pb 210 contents. They can occur with

gas wells producing from carboniferous strata. Often they are characterised by high sodium

chloride concentrations in the formation water. The deposits are usually found in well

tubing and well heads.

2. ENVIRONMENTAL PROBLEMS

Radioactive scales and sludges or contaminated equipment may have to be

removed at some time for storage or disposal. Since this could cause

environmental problems strict precautions have to be taken to prevent the

irradiation and contamination of people, animals, plants and other materials.

The problems involved are:2.1 Radioactive scales tend to be highly insoluble in acids. They contrast with

most common non-active shales (e.g. calcium carbonate) which are readily

soluble in acids. Difficulties experienced in dissolving scale with inorganic

acid should prompt to check for the presence of radioactivity.

2.2 LSA scales invariably emit alpha and beta particles and gamma rays.

Their presence in production systems and equipment can give rise to

occupational hygiene problems. A particular concern is with dust particles

which can be released in cleaning operations. This dust can be trapped in

the tissues of the lung and emit alpha particles which can cause long-term


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health problems. Where LSA scale is present in production trains or in

items such as tubulars or wellheads, concern mainly centres on any effect

that the gamma radiation could have on those working close by.

2.3 Radioactive scale on the insides of the tubing strings may interfere with thenatural radioactive levels of the surrounding strata, causing anomalies in

the readings from gamma ray logs. The observation of such gamma ray

anomalies can be an early indicator of the presence of radioactive scales.

3. UNITS OF MEASUREMENT

The units used for Activity, Absorbed Dose and Dose Equivalent have recently changed

following the introduction of SI units and are:

3.1 Activity

The activity of an amount of radioactive nuclide at a given time is the number

of spontaneous nuclear transformations in the time unit. The SI unit of activity

is the becquerel (Bq) equal to 1 nuclear transformation per second.

3.7 x 1010 Bq equals 1 Curie (Ci) exactly

37 M Bq equals 1mCi (millicurie)

37 k Bq equals 1Ci (microcurie)

The units generally used for measurement are Bq/g for solids and Bq/l for liquids and gases.

3.2 Dose

A term denoting the quantity of radiation energy absorbed by a medium.

Although the terms "dose" or "radiation dose" are often sued in a general sense,

they should usually be qualified, for example as absorbed dose, dose equivalent,

etc. The dose is still usually measured in pre SI units. Three pre SI units are

used, viz:

3.2.1 the Roentgen which measures the radiation dose in air and is sometimes

called the exposure dose;

3.2.2 the Rad which is a measure of the absorbed radiation dose, and

3.2.3 the Rem which is the unit of dose equivalent. For all practical purposes,

it is assumed that doses measured in Roentgen are equal to doses

measured in rads at the same position in the radiation field.

Only dosimeters for measuring neutrons are normally calibrated in rem units.

The unit of dose equivalent takes into account the fact that some types of

radiation, particularly alpha particles and neutrons, are much more efficient at

killing or damaging cells per unit amount of absorbed dose. The rem dose is

related to the rad dose by the following relationship:

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Dose in rem = Dose in rad x QF

(dose equivalent) (absorbed dose) (quality factor)

The value of the quality factor can be as high as 20 for alpha particles and 10 for neutrons.

For gamma and beta particles, it is 1. These units are large and for operational purposes

measurements are made in mR, m rad or mrem, which are 1/1000 of the principal unit.Under SI units, the Roentgen does not have an equivalent. The unit of

absorbed dose replacing the rad is of the Gray or Joule kg-1 and the unit of dose

equivalent replacing the rem is the Sievert. These SI units are related in the

same way as the rad and the rem, i.e.:

Dose in Sieverts (Sv) = Dose in Grays (Gy) x QF

By definition:

1 Gray = 100 rad

1 Sievert = 100 rem

The SI unit is thus even larger than the existing unit and measurements will be made in Gyor Sv (1/1,000,000th of the principal unit).

4. FIELD EQUIPMENT FOR RADIATION DETECTION

Generally there are two broad types of detectors available; contamination meters for

measuring surface radiation such as alpha and beta, and the dose rate meters for measuring

gamma radiation. There are also devices capable of measuring both beta and gamma

radiation simultaneously.

4.1 Contamination meters

These are very sensitive devices for measuring surface radiation. They indicate level of

radiation in "counts per second" and should be able to measure alpha, alpha and beta, and

beta radiation. The ability to measure these three ranges is necessary because if the LSA

scale is damp, if there is moisture in the atmosphere or LSA scale is overlayed with calcium

carbonate scale, then the alpha particles may be absorbed. However, by measuring alpha

and beta emissions together the alpha emissions of the LSA scale may be inferred, i.e. as far

as LSA scale is concerned alpha and beta particles are always emitted together. If an

indication of LSA scale contamination is given by such a meter it must be confirmed by

radiochemical analysis or gamma spectrometry.

Contamination meters should be calibrated against a range of sources of known activity and

of similar isotopic composition; the calibration chart then produced will enable, say, areading of five counts per second to be converted to 0.37 Bq/cm 2 which would only be true

for that particular meter. However, personnel trained in the use of such meters will soon

become adept at interpreting readings correctly.

Contamination meters, if treated with care, will give an early indication of a contamination

problem, provided that the scale is not shielded.

4.2 Radiation monitors or dose rate maters

These meters are reasonably robust and are used to measure radiation levels throughout

industry. Generally they indicate measurements in Sievert/hr and measure gamma

radiation. They are not as sensitive as contamination meters at measuring levels near


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background but are a very useful tool to establish whether or not LSA scale with higher

levels of radiation is present inside pipelines, wellheads, vessels, etc. This is because the

steel will stop the alpha and beta particles but allow a certain percentage of the gamma ray

to pass; levels of radiation inside a steel pipeline or vessels may be in excess of two to three

times those indicated outside, depending on the thickness of the steel.

4.3 Available devices

The available devices to measure gamma and beta radiation in the field

equipment and facilities during operations and maintenance are:

sodium iodide scintillation counters (SC);

energy compensated geiger mueller (GM);

thin window geiger mueller Pancake (PK).

4.4 General considerations

Both types of meter are available from a number of manufacturers world-wide

but there are some basic precautions which must be taken when either or both

are used:

the meters should be calibrated by a suitable laboratory and either, in the

case of a contamination meter, a conversion chart supplied for that

particular meter or, in the case of a dose rate meter, the meter adjusted to

read as accurately as possible across the range; meters should be overhauled and calibrated at least once a year;

if a meter is dropped or damaged it should be recalibrated;

meters should not be abused and should be switched off and kept securely

when not in use;

personnel who use such meters should be trained in their operation, be able

to interpret readings properly and be able to recognise when meters may not

be working properly;

indications of LSA scale should be confirmed by radiochemical analysis ofgamma spectrometry so that a completely accurate record of the levels of

radiation may be kept.

Note:

LSA scales with high levels of contamination, and therefore posing potentially high health

risks of inhaled/ingested, may not register as such on dose rate meters and ideally, if the

presence of LSA scale is suspected, both kinds of meter should be used together.

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5. RECOMMENDED LIMITS

5.1 Dose limits

The basic recommendations of the International Commission on Radiological Protection(ICPR) are laid down in its publications No. 26 and 30. However the "dose equivalent

limit" recommended by ICPR is 50 mSv over one year according to the defined working

conditions. Table 2 summarises these recommendations.

5.2 Activity limits

When radioactive materials are handled, they should be classed as a radioactive substance

when the specific activity level (the activity per unit of mass) is greater than 100 Bq/g. This

limit only refers to the activity level of the material itself. This must be clearly

distinguished from the limit that is used for decontamination purposes: the allowable

contamination level for alpha emitters on a surface is usually 2 Bqcm-2.Therefore, when either of these limits is exceeded, proper operation, handling and disposal

are required.

6. OPERATIONAL PROCEDURES DISPOSAL ASPECTS

6.1 Scale handling

When handling scale or scaled items, during such operations, as when pulling

tubing, entering production separators or produced water skimmers, removal of

Xmas trees, valves, meters and flowlines, etc. The following measures should

be considered:

contain contamination as near as possible to its site or production;

limit the possibility of ingestion or inhalation;

control and restrict direct exposure of workers;

measure and record the levels of activity where scale is found;

follow the recommended method of disposal.


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Table 2 Activity and radiation dose limits

Involvement

Term

Classified workers

Working condition 'A' (1)

Controlled area (2)

Non-classified workers

Working condition 'B' (1)

Supervised area (2)

Public and workers with no

involvement (special

requirements for

transportation)**Dose limits (1) (2)

for whole body 50 mSvYr-1 3/10 x 50mSv =

15 mSvYr-1

1/10 x 50 mSv =

5 mSvYr-1

for individual organs/tissues 500 mSvYr-1 3/10 x 500 mSv =

150 mSvYr-1

1/10 x 500 mSv =

50 mSvYr-1

Derived levels

Hourly limit for external

expose of the whole body (2)2000 Sv h-1 (recommendedmaximum for radiographers)

15 mSv

= 7.5 Svh-1

2000 hours

5 mSv

= 2.5 Svh-1

2000 hours

"Annual limit of intake"* ALI

of radioactive material (1)

Radium 226 by inhalation is

20 kBq Yr -1Radium 226 by ingestion is

70 kBq Yr-1

3/10 ALI, e.g. for Radium 226

by inhalation 3/10 x 20 kBqYr-1 = 6 kBq Yr-1

1/10 ALI, e.g. for Radium 226

by inhalation 1/10 x 20 kBqYr-1 = 2 kBq Yr-1

Surface contamination level

likely to result

ALI (2), e.g.

8 Bq cm-2 for Ra 226

3/10 ALI (2), e.g.

2.4 Bq cm-2 for RA 226

1/10 ALI (2), e.g.

0.8 Bq cm-2 for Ra 226

Airborne contamination+ ALI (2), e.g.

3 Bqm-3 for Ra 226

3/10 ALI (2),

e.g. 1 Bqm-3 for Ra 226

1/10 ALI,

e.g. 0.3 Bqm-3 for Ra 226

Radioactive substance

Specific activity 100 Bq g-1 and any other substance having a lower activity

concentration that cannot be disregarded for the radiological

protection of persons at work (2).

0.4 Bqg-1 used for pollution

control and disposal

authorisations.

Precautions Use only classified workers ornon classified workers workingto a strictly controlled written

system of work (dose limit

15 mSv per annum, i.e. 500 hrs

per year at 30 Sv-hr); containcontamination.

ALARA***. Regularmonitoring of affected areas.Contain surface contamination.

Prevent airborne

contamination.

ALARA*** and 'not

significantly above background

levels'. Controls on radioactive

substances as pollutants.

Controlled disposal of radioactive substances. Occupational

hygiene precautions to prevent inhalation and/or ingestion.

* Annual limit of intake (ALI): an ALI is the amount of radioactive material which if taken into the body would delivery a

committed dose equivalent to the annual dose limit for either the whole body or individual tissues whichever is the more

restrictive. Each isotope has its own ALI, e.g. Radium 226 by inhalation is 20 BqYr-1.

** Transport packages contain limit. On external surfaces of transport packages/containers the limit is 4 Bqcm-2 (3).

70 Bqg-1 is limit used in transport regulations (3) (but check with national regulations for applicable limits).*** ALARA: as low as is reasonably achievable.

+ Airborne contamination: very different limits can apply to different isotopes,

e.g. 3 Bq m-3 Ra 226; 0.01 Bq m-3 natural thorium

(1) Internal commission on radiological protection limits for intakes of radionuclides by workers, ICRP Publication No. 30,

Part 2, Pergamon Press, Oxford, 1980.

(2) EURATOM Directive of the Council about radiation protection of workers and the public.(3) International Atomic Energy Agency, Safety Series No. 6, Regulations for the Safe Transport of Radioactive Materials

1973, Revised Edition (as amended), Vienna 1979.

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6.2 Containment, disposal and the environment

Disposal of LSA scale and sludges can be difficult and expensive, due to the

occupational hygiene and environmental protection considerations discussed

earlier. The following courses of action should be considered:

containment;

disposal.

6.2.1 Containment

If tubulars are pulled and are found to be scaled, then provided that the scale is thin, hard,

tenacious and smooth and offers little resistance to well fluid production, and provided that

the tubing does not need to be reworked, then the scaled tubulars can be re-run back into the

well. Similarly if a vessel is opened up for inspection and is found to contain LSA scales orsludges which are not interfering with production and the material does not have to be

removed, then the vessel can be closed up again.

6.2.2 Disposal

The decision logic for disposal is presented in Figure 1.

Method of disposal include:

Disposal to the sea

Scales exhibiting levels of activity above background may be disposed of to the sea either

from offshore installations or from onshore facilities with their own direct flushed outfall.

Generally a maximum particle size (say 1 mm) could be specified together with a limit on

the total activity (specific activity times weight) expressed in Gigabecquerels.

Because particles of this size will obey Stokes Law, if this method is employed where there

are reasonably strong tides and currents, there should be no detectable increase in the level

of radioactivity in the sea or the surrounding seabed. In such instances, however, seabed

surveys (much like those for oil-based mud cuttings) may be required.

Disposal on land

Listed below are methods of disposal on land:

In specially dug pits, abandoned mines and oil wells: where such

facilities are available, burial of scale in mines, pits or abandoned wells are

possible methods of disposal.

Storage in secure yards or warehouses: in many cases where it is

considered too difficult or expensive to descale such items as tubulars, filter

baskets, valves, etc., it may appear cost-effective to put them into long-term

secure storage. Such storage must only be used with the agreement of the

relevant authorities.


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However, the following produced offshore, should be considered:

the risks of exposing other workers to the hazards of LSA scale are increased

(e.g. seamen, dockers, transport workers);

if LSA scales are stored onshore, thought must be given to keeping such

stores secure for generations in order to prevent workers from being exposed

to risk in the future the half-life of Radium 226 is 1620 years;

if methods such as mixing 'concentrated' LSA scale with cement and then

pumping the slurry into drums or down abandoned wells are used then again

additional risks are incurred by the workers handling the scale.

6.3 Scale inhibition and scale dissolution

6.3.1 Inhibition

Generally, it can be said that scale inhibition of Ba/SrSO4 using the correct programmes,

appropriate solutions and clean suitable equipment, will be successful. Scale inhibitor

squeezes will usually be performed when it is known that barium is present in the formation

water following the first indication of injection water breakthrough. An increasing sulphate

ion count in the produced water is the usual indicator of the onset of breakthrough.

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Otherwise, the produced water must be monitored closely for other indications. Inhibitors

can also be injected into the well fluid stream in the production train to help prevent scale

formation in valves and production manifolds, etc.

6.3.2 Dissolution

Scale dissolution, usually in the production train manifolds, has been attempted, most often

using organic chemicals. Some of these organic chemicals show promise, but dissolution of

the salts has still to be proven effective, due to their almost chemically inert nature.

7. PROCEDURE FOR A FIELD SURVEY

The initial survey for a NORM at a site is typically performed along the exterior of on-line

intact equipment such as vessels, piping, compressors, and other production equipment. Of

the three types of radiation present in NORM (alpha, beta and gamma), gamma rays alone

can penetrate the steel and be detected outside the equipment. As discussed in the detection

equipment section (section 4.3), the SC probe is used to identify areas of potential concern

and the GM probe is used to quantify potential human doses.

Both measurements can be made during the same survey using a meter that can support the

two probes. The results of the survey should be documented and assigned one of the four

categories (A, B, C, D) described in Table 3. Cut-offs of 2.5, 25 and 500

microSieverts/hour (uSv/hr) are used to define requirements needed to ensure a safe work

environment9 such as limiting access, posting of signs, and other follow-up actions. (Note:

10 uSv/hr = 1 mR/hr). It is recommended that sites with NORM contamination be

resurveyed every two years to identify changing conditions.

Table 3 Determination of area NORM category

uSv/hr (GM) Category Definition Requirements

500 D High radiation Limit worker access

Post with "high radiation" sign

Train workers

Personal dosimitry

Work permit required

Notify EA

8. DECONTAMINATION

Any equipment, tools, or personal protective equipment (PPE) that has contacted NORM or


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LSAS contaminated surfaces needs to be evaluated to determine whether they have been

contaminated. Similarly areas where NORM-related work has led to possible

contamination also need to be evaluated.

The decontamination decision logic is presented in Figure 2. Measurements are made using

the GM probe and the PK probe (direct measurement or a wipe sample depending on theconfiguration of the surface). If both measurements are less than the criteria, the material is

not considered to be NORM contaminated.

For materials that do not meet the stated criteria, decontamination and repeat monitoring are

one possible option. The other option is packaging for disposal.

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II.

RADIOACTIVE ELEMENTS IN NATURAL GAS

Occurrence of radon

Natural gas contains small quantities of the gaseous radioactive nuclide Radon-222 formed

from the decay of Radium-226, which is a daughter nuclide of naturally occurring Uranium-

238. Radon enters natural gas in the earth by diffusion from a formation. Uranium

minerals are often associated with carbonaceous deposits, therefore radon can be expected

to occur in natural gas.

Radon-222 has a half life of 3.8 days and produces upon decay a series of short and long

lived daughter nuclides as shown in Figure (1). When propane is separated from natural

gas, radon tends to be concentrated in the propane process stream since the boiling point of

radon is close to that of propane. Consequently, it is typically enriched in propane by a

factor of the order of 10.

In natural gas condensate the long lived daughters of radon (particularly Lead-210 and

Polonium-210) are generally present.

Figure (1) Decay scheme of the 238Unatural seriesNotes:

1) Half-lives are indicated in years a, days d, minutes min, and seconds.

2) The nature of the radiation is indicated by , , and (only energetic

radiations with high yield).

Recent reports of radon contaminated buildings through out the world, attest to the wide

distribution of radon in the environment.

Once formed by the radioactive decay of radium-226, radon is free to migrate as a gas or

dissolve in water without being trapped or removed by chemical reaction. Migration

through rocks and soil, radon is produced with natural gas at the wellhead. Table 1 shows

that radon contamination of natural gas is a worldwide problem, and particularly high

concentrations of radon are reported in the US and Canada.


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Table 1 - Radon concentrations in natural gas at the wellhead *

Location of Well Radon concentration (pCi/L)

Borneo 1 to 3

Canada

Alberta 10 to 205

British Columbia 390 to 540

Ontario 4 to 800

Germany 1 to 10

The Netherlands 1 to 45

Nigeria 1 to 3

North Sea 2 to 4

US

Colorado, New Mexico 1 to 160

Texas, Kansas, Oklahoma 1 to 1,450

Texas Panhandle 10 to 520Colorado 11 to 45

California 1 to 100

*) From "Radon Concentration in Natural Gas at the Well, UN Scientific

Committee on the Effects of Atomic Radiation; Sources and Effects of

Ionizing Radiation, United Nations, New York City (1977).

When radon-contaminated produced gas is processed to remove the NGL's, much of the

radon is removed also. Radon's boiling (or condensing) point is intermediate between the

boiling points of ethane and propane. Upon subsequent processing, radon tends to

accumulate further in the propylene distillation stream. Table 2 shows the boiling points of

radon, the lighter NGL's, and propylene. As expected radon usually is recovered morecompletely in plants with high ethane recovery. The radon is concentrated in the lighter

NGL's and is detected relatively easily with radiation survey meters.

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Table 2 - Boiling points at 760 mm Mercury

F

Methane -258.0

Ethane -124.0

Radon -79.2

Propylene -53.9

Propane -44.4

Butane +31.1

As long as it is contained and controlled within vessels, equipment, and piping, radon

generally is not a health hazard to employees and the public. Even if radon-contaminated

propane were released, the threat of fire or asphyxiation would far outweigh the hazard of a

short-lived radiation exposure.

NORM in NGL facilities

Although entire natural-gas and NGL systems may be contaminated with NORM, some

facilities will be contaminated to the extent that they present significant decontamination

and disposal problems. Gasoline plants and other NGL facilities will be among the most

highly contaminated areas in a system.

During processing in a gasoline plant, the levels of external radiation from radon in propane

1 ft from a liquids pump may be as high as 25 milli-roentgens (mR)/hr. Radiation levels up

to 6 mr/hr have been detected at outer surfaces of storage tanks containing fresh propane.

Sludges in gasoline plants are often contaminated with several thousand picocuries of lead-

210 per gram.

Table 3 shows vessels and equipment in NGL service that may be significantly

contaminated with NORM. Although NORM contamination will be general throughout anNGL facility, the contamination usually will be greatest in areas of high turbulence, such as

in pumps and valves.

Table 3 - Priority areas of concern for high radon and radon decay product

contamination

NGL facilities

De-ethanizers

Stills

Fractionators

Product condensers

Flash tanks

Pumps in liquid service

Piping in liquid service

NGL storage tanks

Truck terminals

Filter separators

Dessicants

Waste pits

Pipelines

Filters

Pig receivers

Machine shops


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In-house Contract

When employees open equipment and vessels, precautions must be taken to prevent

exposure to radioactive contamination. Maintenance procedures should include the use of

respirators and good hygiene to prevent inhalation of radioactive dust. Grinding, if

necessary, should be done wet to minimise dust.Occasionally, a plant or other facility that has been processing light hydrocarbons,

particularly ethane and propane, is taken out of service and the facility sold or dismantled.

Any equipment with internal surface deposits of NORM must receive special consideration

when scrapped, sold, transferred, or otherwise disposed of, particularly when the facility is

being released for unrestricted use. Analyses for lead-210 usually will be required to verify

the extent of contamination and to determine if special handling is needed. Particularly care

must be used to prevent employee exposure to NORM contamination.

There are potential liabilities involved if contaminated equipment, vessels, and other parts

of the facility are released or sold for unrestricted use without first being cleaned and tested

to be essentially free of NORM contamination according to state and federal regulations.

Much of the material wastes from a facility contaminated with NORM must be handled aslow-level radioactive waste and disposed of accordingly. Contaminated wastes should be

consolidated and separated from non-contaminated waste to keep radioactive waste

volumes as low as possible. Consolidated contaminated wastes should be stored in a

controlled-access area. The area should be surveyed with a radiation survey meter and, if

required, should be posted.

The investigation level

Normally, the amount of radioactivity in the natural gas and its products is insufficient to

cause health hazards during handling and subsequent use by consumers.

However, it is recommended that the radon content of natural gas and Polonium-210 in thecondensate of wells should be monitored prior to production. A record should also be kept

of radon and polonium in gas and condensate from reservoirs which have been in

production for a long period. The results of such measurements should be compared with a

'Derived Investigation Level'. A derived investigation level, as defined by the international

Commission on Radiological Protection (ICRP), is a value of concentration of radioactive

material. It is usually set in relation to a single measurement, which is the resulting

radiation dose to humans sufficiently important to justify further investigation.

It is important to recognise that an investigation level is not intended to be a limit. Should

an investigation level be exceeded, this should be reported to the Central Offices EP Health,

Safety and Environment Department (SIPM-EPO/6) who will contact the radiological

specialists for advice. A close investigation of the (local) circumstances will be required.

The investigation will often be no more than a recognition that the circumstances will not

cause any hazard as the investigation level is based on a 'worst case' estimate. Below the

investigation level, the information need not be further studied by experts.

Calculation of the investigation level

Two types of radioactive exposure to humans resulting from radioactivity in

natural gas or condensate can be identified:

a) During the use of the natural gas by consumers, e.g. heating and cooking.

b) Relating to gas handling at gas processing stations.

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In both cases, a derived investigation level will be specified.

Natural gas and LPG for Domestic Consumption

When natural gas or LPG is burned in domestic appliances (cooking and heating) radon will be emitted into the atmosphere and contribute to the radiation level already naturally

present. Radon (and its daughter nuclides which are formed by decay) become attached to

aerosol particles and may subsequently be inhaled.

To calculate the derived investigation level for radon in raw natural gas, the

following 'worst case' conditions are assumed:

- Minimal ventilation and maximal invented appliances of LPG in which

radon is enriched.

- The combustion products will all contribute to the radon concentration in

indoor air.

The maximum permissible yearly dose to members of the public is 5 mSv/a (milliSievert

per year, a unit for the ionising radiation dose to human beings). As a base for the derived

investigation level, one twentieth of this dose equivalent is taken, i.e. 0.25 mSv/a. This

dose equivalent is not exceeded when the concentration in the natural gas is below 2

kBq/m3 (50 pCi/dm3). For comparison, the average yearly dose from the natural

background and medical radiation is around 3 mSv/a. This level can be considered as the

derived investigation level for radon in raw natural gas taking into account the use of

recoverable LPG when converted into fuel gas.

For use of natural gas as an industrial fuel gas, the same investigation level should be used,

provided that the investigation level for surface contamination is not exceeded.

Contamination of Gas Processing Equipment

Inner parts of gas processing equipment may be contaminated with the long lived daughter

products of Radon-222 as a result of deposition of the solid daughters (particularly the long

lived Pb-210 and Po-210) at places where the stream is dispersed over a large surface or

where high turbulence occurs. An additional effect is the enrichment in the propane stream

(see 3.8.1) which causes an increased chance of contamination in the propane stream

equipment.

Similarly, Polonium-210 present in the condensate may be deposited in pumps, distillation

columns, heat exchangers, etc.

The chance of contamination above a certain level is related to the initial concentration of

radon or polonium in natural gas or natural gas condensate. However, possible enrichment

and the throughput of gas or condensate are also important factors.

The long lived daughters of radon (e.g. Polonium-210) mainly emit alpha radiation which

cannot penetrate steel walls of equipment. Only the short lived Bismuth-214 may be

detectable at the outside of the equipment. In view of the short half-life, however, the

external radiation level will always be minimal and will disappear after shut-down of the

installation.

Thus, radiation hazards, if present, may only occur when opening equipment, by inhalation

or ingestion of the contamination. Before workers enter equipment which has been exposed

to condensate containing polonium or propane containing radon, it may be advisable to


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monitor the inner surfaces to avoid the risk of contamination of the personnel involved. For

a derived investigation on surface contamination of equipment, 4 kBq/m3 (10 pCi/cm2)

should be used.

Since the mechanism for deposition of solid daughters of radon (e.g. Polonium-210) cannot

be quantitatively described, it is not possible to calculate investigation levels for liquidconcentration of radon or Polonium-210 resulting in contamination. However, from

experience, contamination of inner surfaces of equipment is unlikely when the level of

Polonium-210 in natural gas condensate is below 20 kBq/m3 (0.5 pCi/cm3).

Monitoring

Radon-222 in natural gas can be detected using an ionisation chamber. Radon

concentration determination is usually carried out as one of the routine tests during

production testing of new gas reservoirs.

Several methods for determination of Polonium-210 in natural gas condensate are available.

One of the accurate methods consists of extraction of Po-210 from the condensate and aciddestruction followed by plating Po-210 on a silver disc. The alpha activity on the silver

surface is determined using, for example, a surface barrier detector.

For detection of contamination of inner surfaces of equipment, a simple technique

developed by KSLA of applying a film sensitive to alpha radiation is available.

Suggested programme for the control of NORM

The following are suggestions for use in establishing a programme for the control of

NORM contamination.

1) Determine whether there is a NORM contamination problem.

2) Determine areas of potential NORM exposure and contamination.

a) Make gamma radiation surveys of facilities and equipment.

b) Make wipe tests on accessible interior surfaces of selected equipment

and vessels, especially any in NGL service.

c) Obtain samples of sludges and scale and analyse for radium and lead-

210.

d) Obtain samples of other waste materials, such as dessicants and filters.

e) Analyse produced water and waste pond water for radium.

3) Establish programmes to ensure personnel safety, products quality,

customer satisfaction, and protection of the environment.

a) Establish policy on periodic surveys, inspection and maintenance

procedures, product controls, and record keeping.

b) Provide safety-manual material that informs employees and details

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required procedures, particularly for maintenance personnel.

c) Recommend a management and audit system.

d) Develop plans and procedures for the disposal of contaminated wastematerials, equipment, and facilities.

REFERENCES

1. Low specific activity scale: origin, treatment and disposal

E&P Forum Report No. 6.6/127, 1988

2. E.C. Thayer and L.M. Racioppi

Naturally occurring radioactive materials: the next step

SPE 23500, 1991

3. P.R. Gray "NORM contamination in Petroleum Industry" JPT Jan. 1993.

4. G.E. Jackson

Formation and inhibition of scale in offshore oil productive systems

Offshore Radioactivity Seminar, OYEZ London, 1983

5. K.S. Johnson

Water scaling problems in the oil production industry

in Chemicals in the Oil Industry, Ed. P.H. Ogden, 1983

6. UKOOA Reference Manual on naturally occurring radioactive substances on

offshore installations

UKOOA, London, 1985

7. W.A. Kolb and M. Wojcik

Enhanced radioactivity due to natural oil and gas production and related

radiological problems

Science of the Total Environment 45, 77-84, 1985

8. A.L. SmithRadioactive scale formation

OTC 5081, Offshore Technology Conference, Houston, 1985

9. P.R. Gray "Radioactive materials could pose problems for the gas industry" Oil &

Gas J. (June 25, 1990) 45-48.

10. J. Summerlin Jr. and H.M. Prichard "Radiological Health Implications of Lead-210

and Polonium-210 Accumulations in LPG Refineries" J. American Industrial Hygiene

Assn. (1985) 46, No. 4, 202-05.

11. E&P Form Report no. 6.6/127, 1988.Low Specific Activity Scale.

12. E.C. Tayler & C.M. RaciopiNORM; "The Next Step", SPE 23500, 1991.


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RADIOLOGICAL UNITS SI CONVERSIONS

CONVERSION TABLE

Activity units

1pCi = 37mBq 1mBq = 0.027pCi = 27fCi

1nCi = 37 Bq 1 Bq = 27pCi1Ci - 37KBq 1KBq = 27 nCi

1mCi = 37MBq 1MBq = 27Ci1 Ci = 37GBq (37E+09Bq) 1GBq = 27mCi

1KCi = 37TBq 1TBq = 27Ci

Curies to becquerels

1 pCi 1 nCi 1 Ci 1m Ci 1 Ci

37 mBq 37 Bq 37 KBq 37 MBq 37 GBq

Becquerels to curies

1 Bq 1 kBq 1 MBq 1 GBq 1 TBq

27 pCi 27 nCi 27 Ci 27 mCi 27 Ci

Absorbed dose units

1rad = 0.01Gy 1Gy = 100rad

1mrad = 0.01mGy 1mGy = 100mrad

1 rad = 0.01 Gy = 10mGy 1 Gy = 100 rad

1Krad = 10 Gy 10 KGy = 0.1Mrad1Mrad = 10 KGy 1MGy = 100 Mrad

Dose equivalent units

1rem = 0.01Sv 1Sv = 100 rem1mrem = 0.01mSv=10Mv 1mSv = 100 mrem

1 rem = 0.01 Sv=10mSv 1 Sv = 100 rem1Krem = 10 Sv 1KSv = 0.1Mrem

1Mrem = 10 KSv 1MSv = 0.1Grem

(H)rem mrem mrem mrem mrem

1 1 10 10 1

1 10 100 1 10(H)Sv Sv Sv mSv mSv

Prefixes

k kilo - thousand (103) m milli - thousandth (10-3)

M mega - million (106) micro - millionth (10-6)

G giga - thousand million (109) n nano - thousand-millionth (10-9)

T tera - million million (1012) p pico - million-millionth (10-12)

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GLOSSARY

Activity The quantity of a radionuclide described by the number of nuclear

transformations occurring per unit time (see becquerel and curie).

ALARA As low as is reasonably achievable.

Alpha particle ( ) A charged particle emitted from the nucleus of an atom having a

mass and charge equal in magnitude to that of a helium nucleus,

i.e. two protons and two neutrons.

Becquerel The SI unit of activity. One Becquerel (symbol Bq) equals one

nuclear transformation per second.

Beta particle ( ) Charged particle emitted from the nucleus of an atom, with a mass

and charge equal in magnitude to that of the electron.

Coelestobarite Ba/Sr(Ra)SO4 solid solution of RaSO4 in Ba/SrSO4.

Contamination(radioactive)

Radioactive material in any place where it is not desired

particularly where its presence may be harmful. The harm may be

in inhaling or ingesting the radioactive material which may cause

internal radiation dose.

Controlled area A defined area in which the occupational exposure of personnel (to

radiation) is under the supervision of the Safety/Radiation Adviser

and the dose rate is above 7.5 Sv/hr.

Counter (Geiger-Muller) A glass or metal envelope containing a gas and two electrodes.

Ionising radiation causes discharges, which are registered as

electric pulses in a counter. The number of pulses is related to the

dose.

Counter (Proportional) A similar device as a Geiger-Muller counting tube; the intensity of

the electric pulses produced is proportional to the energy of the

primary ionising particles.

Counter (Scintillation) A device containing material that emits light flashes when exposed

to ionising radiation. The flashes are converted into electric pulses

by a photo-multiplier.

Curie The pre-SI unit of activity. One curie (abbreviated Ci) equals 3.7 x

1010 nuclear transformations per second, i.e. it equals 37

gigabecquerel.

Decay Disintegration of the nucleus of an unstable nuclide by

spontaneous emission of charged particles and/or photons. It

causes the decrease in activity or radioactive substances.


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Detector (Radiation) Any device for converting radiant energy to a form more suitable

for observation. An instrument used to determine the presence,

and sometimes the amount, of radiation.

Dose A general term denoting the quantity of radiation or energyabsorbed. For special purposes it must be appropriately qualified.

If unqualified, it refers to absorbed dose.

Collective effectivedose

The quantity obtained by multiplying the average effective dose

equivalent by the numbers of persons exposed to a given source of

radiation. Expressed in man-sievert. Frequently abbreviated to

collective dose.

Cumulative radiationdose (radiation)

The total dose resulting from repeated exposures to dose.

Dose equivalent(symbol H)

A quantity used in radiation protection. It expressed all radiationon a common scale for calculating the effective absorbed dose such

that biological effects can be compared. It is defined as the product

of the absorbed dose and the quality factor (see Quality factor and

Sievert).

Effective doseequivalent

The quantity obtained by multiplying the dose equivalents to

various tissues and organs by the risk weighting factor appropriate

to each and summing the product. This procedure makes it

possible to compare this number with a whole-body dose

equivalent.

Maximumpermissible doseequivalent (MPD)

The greatest dose equivalent that a person or specified part thereof

shall be allowed to receive in a given period of time. This quantity

has been rejected in ICRP 26.

Dose rate Absorbed dose delivered per unit of time.

Dosimeter Instrument to detect ad measure a dose received. For example, a

pencil-size ionisation chamber with a self-reading electrometer,

used for personnel monitoring.

Exposure A measure of the ionisation produced in air by X or gammaradiation (see Roentgen).

Gamma ray ( ) Short-wave length electromagnetic radiation of nuclear origin

(range of energy from 10 KeV to 9 MeV) emitted from the nucleus.

Gray (symbol Gy) The unit of absorbed dose. One gray equals one joule per

kilogramme.

Half-life (radioactive)(symbol t1/2)

Time required for a radioactive substance to lose half of its activity

by decay. Each radionuclide has a unique half-life.

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IAEA International Atomic Energy Authority.

ICRP International Commission on Radiological Protection.

Ionising radiation Radiation that produces ionisation in matter. Examples are alpha

particles, beta particles, gamma rays, X rays and neutrons.

Irradiation Exposure to radiation.

Isotopes Nuclides having the same number of protons in their nuclei, and

hence the same atomic number, but differing in the number of

neutrons, and therefore in the mass number. Almost identical

chemical properties exist between isotopes of a particular element.

The term should not be used as a anonym for nuclide.

Joule The unit for work and energy, equal to one Newton expended along

a distance of one metre (IJ = 1N x 1m).

Monitoring Periodic or continuous determination of the amount of ionising

radiation or radioactive contamination present.

Nuclide A species of atom characterised by the number of protons and

neutrons, and the energy content.

Rad The pre-SI unit of absorbed dose; equal to 0.01 J/kg (see Gray).

Radiation The emission and propagation of energy through space or through

a material medium in the form of waves; for instance, the emission

and propagation of electromagnetic waves. The term radiation orradiant energy, when unqualified, usually refers to electromagnetic

radiation. Such radiation commonly is classified, according to

frequency, as hertzian, infra-red visible (light), ultraviolet, X ray,

and gamma ray (see Photon).

Background Radiation arising from radioactive material other than the one

directly under consideration. Background radiation due to cosmic

rays and natural radioactivity is always present. There may also

be background radiation due to the presence of radioactive

substances in other parts of the building, in the building material

itself, etc.

External Radiation from a source outside the human body.

Internal Radiation from a source within the body (as a result of

incorporation and deposition of radionuclides in body tissues).

Radioactivity The property of certain nuclides of spontaneously emitting

particles or electromagnetic radiation.

Radionuclide An unstable nuclide that emits ionising radiation.


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Radon In the context of this report Radon is taken to mean either Radon

222 or Radon 220 radioactive gases produced by decay of Ra 226

or Ra 224.

Rem The pre-SI unit of dose equivalent; equal to 0.01 J/kg (see Sievert).

Risk factor In connection with ionising radiation, the probability of cancer and

leukaemia or genetic damage per unit dose equivalent. Usually

refers to fatal malignant diseases and serious genetic damage.

Expressed in Sv.

Roentgen (R) The pre-SI unit of exposure. One Roentgen is the dose given by a

radiation field that produces ionisation, due to secondary electrons,

of one electrostatic unit of charge per cm3 (NTP) of air. It is equal

to 2.58 x 10-6 coulomb per kilogramme of air.

Sealed substance(or source)

A radioactive substance sealed in an impervious container which

has sufficient mechanical strength to prevent contact with and

dispersion of the radioactive substance under the conditions of use

and wear for which it was designed.

Shield A body of material used to prevent or reduce the passage of

particles or radiation.

SI Abbreviation of "Systme International d'Unites", the International

System of Units, recommended for general use.

Sievert (symbol Sv) The unit of (effective) dose equivalent. The sievert has the

dimensions of joule per kilogramme. The dose equivalent in

sieverts is numerically equal to the absorbed dose in grays

multiplied by the quality factor (see Gray and Quality factor).

Specific activity Total activity of a given nuclide per unit mass of the specific

material.

Tracer (isotopic) The isotope or non-natural mixture of isotopes of an element which

may be incorporated into a sample to permit observation of the

course of that element, alone or in combination, through a

chemical, biological, or physical process.

Tritium The hydrogen isotope with one proton and two neutrons in the

nucleus. (Symbol 3 H or H-3, sometimes T).

X rays Electromagnetic radiation of which the wave lengths are shorter

than those of visible light. They are usually produced by

bombarding a metallic target with fast electrons in a high vacuum,

as occurs in an X ray machine.

senv guidelines for management of norm

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