Government of India Bhabha Atomic Research Centre

Health Physics Division

Ref: HPD/PKS/ /# 7 2011 Date: August 16,2011

Sub.: Recommendation of Task Group for providing guidelines for evaluation ofinternal dose due to actinides

The Task Group formed with reference to ORPRS/RGP/2010/06/1445, has reviewed the existing procedures of lung counting, bioassay monitoring and methodology of dose evaluation in case of acute as well as chronic exposure cases. The Committee has brought out its recommendations and provided guidelines in the form of a Manual. To assign dose to chronic cases of < 1 mBq d"' urinary excretion of Pu, the infrastructure of Bioassay Laboratories need to be augmented so as to assign doses at exposure to 1/10th of an ALI.

1. Bioassay Laboratory should have 10 alpha counters and 8 channel alpha spectrometry systems for counting of each sample for a period of 5 days to achieve a Detection Limit of 0.2 mBq d"1 for Type M compounds of Pu.

2. In order to evaluate dose due to acute exposure, one set of bioassay sample needs to be collected before administration of Ca-DTPA aerosol / 1. V.

3. The present detection limit of 1 mBq d'1 corresponds to a CED of 6 mSv (Type M) which is not being added to the external exposure of the individual; hence it is recommended that the external exposure be restricted to 14 mSv a"1.

4. For effective implementation of ICRP recommendations, Bioassay Labs, should be equipped with HR-ICP-MS.

The manual is attached herewith for implementation at Laboratories / Facilities handling actinides. v

(P. K. Sarkar)Head, Health Physics Division

Distributions to:Director, H. S & E. G.

^/Director, NRG Director, NFG Director, NRB Director, RC&IG

Government of India Department of Atomic Energy

Bhabha Atomic Research centre

Manual on Internal Dosimetry of Transuranics

Report of the Task Group for Internal Dosimetry Programme for Transuranics

Issued by

HEALTH PHYSICS DIVISION Health, Safety and Environment Group

BARC

June, 2011

MANUAL FOR INTERNAL DOSIMETRY OF TRANSURANICS FOR OCCUPATIONAL WORKERS

CONTENTS

1 : Introduction 1

2 : Measurement Techniques

2.1 Lung counting technique 2

2.1.1 Principle 2

2.1.2 Methodology of Lung counting

2.1.2.1 Detectors 3

2.1.2.2 Energy calibration 3

2.1.2.3 Efficiency calibration 3

2.1.2.4 Estimation of chest wall thickness (MEQ-CWT) 4

2.1.2.5 Evaluation of activity 4

2.1.2.6 Minimum Detectable activity 4

2.1.2.7 Spectrum unfolding 5

2.1.3 Pu/Am ration evaluation 6

2.1.4 Estimation of intake from lung burden measurement 6

2.1.5 Periodicity of lung monitoring 7

2.1.5.1 Routine monitoring 7

2.1.5.2 Incidental monitoring 7

2.1.6 Sensitivity of lung counting technique 7

2.2 Bioassay

2.2.1 Bioassay technique 8

2.2.2 Sensitivity of the bioassay technique and its limitations 8

3 : Analysis Procedures

3.1 Sampling and analytical procedures for bioassay

3.2 Sample collection procedure

3.2.1 Faeces

3.2.2 Urine

3.2.3 Other samples

3.3 Sample processing

3.4 Radiochemical separation

13

13

13

13

14

14

14

i

3.4.1 Sample preparation 14

3.4.2 Sequential chemical separation for Urine, Faeces and other samples 15

3.4.3 Electrodeposition 15

3.4.4 Reporting of results 15

4 : Quality Assurance Programme

4.1 Introduction 16

4.2 Intercomparison for lung counting laboratories 16

4.3 Intercomparisons among different laboratories of HPD and IDD 16

4.4 Intercomparison with IRC and IAEA 17

5 : Action Plan for Pu-Am Internal Exposure Incidents

5.1 Action plan for Pu-Am inhalation incidents 19

5.1.1 Procedure for taking nasal swabs 19

5.1.2 Flow chart of action plan 20

5.2 Action plan for Pu-Am injection incidents 22

6 : Estimation of Intake based on routine Urine analysis

6.1 Introduction 24

6.2 Recommendations 24

6.3 Dose accounting and control 25

7 : Record keeping and reporting procedures

7.1 Direct method 26

7.2 Urine analysis 26

7.3 Dose record keeping 27

Conclusions 27

Acknowledgements 27

References 27

Annexure - 1 (list of contributors) 28

Annexure - 2 (examples of dose calculation) 30

ii

Executive Summary

Estimation of internal contamination of occupational workers to transuranics is

undertaken based on the results of in-vivo lung counting and/or bioassay measurements.

Head, Health Physics Division constituted a Task Group in 2010 to develop methodology and

procedures for evaluating internal doses from the measurements in view of the complex

nature of the problem. The committee after due deliberations has prepared this manual

featuring measurement techniques and analytical procedures for transuranics, action plan to

deal with Pu-Am inhalation exposure cases, routine monitoring and methodology for dose

calculation, methods to be used for dose control and accounting. The important

recommendations for the action plan, dose assessment, control and accounting are as follows:

A) Action plan for acute Pu-Am inhalation: 1

Suspected acute inhalation to Pu-Am aerosols is indicated by measurement of gross

alpha activity in the nasal swab of the worker.

If alpha activity in nasal swab of the exposed worker is:

i) < 6 Bq :No further action is contemplated as the estimated intake is < 0.1 ALI

ii) 6-18 Bq:Administer Ca DTPA by inhalation under medical supervision in hospital. Collect a urine sample before administering Ca-DTPA. Lay off the worker from radioactive work for 12 weeks. Carry out urine and faecal analysis as per action plan. Estimate intake using ICRP 78/IMBA software and decide redeployment.

iii) > 18 Bq :Administer Ca DTPA by inhalation tinder medical supervision followed by Ca DTPA intravenous injection and lay off worker from radioactive work for 12 weeks. Collect a urine sample before administering Ca-DTPA. Carry out lung counting, repeat urine and faecal analysis as per action plan and decide redeployment.

B) Action plan for chronic Pu-Am inhalation:

Routine bioassay programme is carried out to identify the chronic cases of exposure to Pu-Am aerosols once in a year.

If urinary excretion rate of Pu-Am is :i)

iii) >3 mBq/day:Remonitor for confirmation after two weeks and also carry out lung counting. Further actions are to be based on results of remonitoring.

iv) 1-3 mBq/day for three consecutive years :Carry out follow-up monitoring at 1 month interval for 3 months. Take average of the last three measurements and calculate intake assuming the time of intake as 2 years ago.

C) Dose control and accounting:

The committee recommends the following for individual dose accounting and control.

i) The Committed Effective Dose (CED), resulting from the intake of relevant radionuclides

(fission products and actinides), in a year, by the occupational worker should be added to

the external effective dose received by him/her in the year and the sum of the doses

should be treated as the effective dose for the year. Similarly, the CED, resulting from the

intake in the five year block should be added to the external effective dose received by

him/her in the five year block and the sum of the doses should be treated as the effective

dose for the five year block.

ii) The individual committed effective doses exceeding 20 mSv can be distributed over n

number of years at the rate of 20 mSv/a and the individual will be laid off for n number

of years until the total CED is assigned.

iii) The annual effective dose to an individual worker in any calendar year during the five

year block shall not exceed the limit of 30 mSv.

iv) The cumulative effective dose for the five year block shall not exceed lOOmSv.

The manual is intended to provide a guideline to operational health physicists and

bioassay and lung counting laboratories engaged in evaluation of internally deposited

transuranics. The methodology and action plan given in the document will be reviewed after

three years.

D) A committee will be constituted by Head, Health Physics Division to review the

computed doses for those cases of CED exceedijng 10 mSv.

E) Acute exposure intakes exceeding 1 ALI should be referred to Head, Health Physics

Division for information and further advise regarding dose assignment and follow

up monitoring.

iv

MANUAL ON INTERNAL DOSIMETRY OF TRANSURANICS

1.0 INTRODUCTION:

The nuclear facilities in India that handle transuranics (mainly plutonium), are the

spent fuel processing plants, fuel fabrication plants for production of uranium-plutonium

mixed oxide fuel, uranium-plutonium mixed carbide fuel, plutonium alloy fuel and the

radiochemical laboratories. Different compounds of plutonium e.g. nitrates, TBP complexes,

oxalates and oxides are encountered in the reprocessing plants whereas oxides, carbides,

mixed oxides and mixed carbides of plutonium and uranium are encountered in the fuel

fabrication plants. Inhalation of air-borne plutonium is the main route by which the

occupational workers working in these facilities may receive internal contamination. The

possibility of injection of plutonium into the body also exists. According to ICRP-71 (Ref. 1),

plutonium oxide, plutonium carbide, mixed oxide of uranium-plutonium, mixed carbide of

uranium and plutonium and plutonium hydroxide belong to absorption Type 'S and

plutonium nitrate, Pu-TBP complex and plutonium oxalate belong to absorption Type 'M \

Engineered safety features and the work practices in these facilities are aimed at prevention of

internal contamination. However, inherent in these operations is the probability of

occupational workers getting exposed to air borne transuranic particulate material giving rise

to internal exposure in addition to external exposure. Therefore, prompt detection, estimation

of quantity of Pu present in the body and estimation of intake is necessary. Based on this,

resulting internal dose can be calculated and used for the total dose control (internal and

external dose). There are two methods that are normally used for detection and estimation of

internal contamination due to plutonium/americium. One is in-vivo lung counting which

measures low energy X or Gamma rays emitted by Pu-Am using phoswich and/or HPGe

detectors. The second is the in-vitro urine analysis method, where the quantity of Pu

excreted through urine is estimated. The lung counting method does not have the sensitivity

to detect intake of 1 ALI of 239Pu. Also, it is difficult to estimate intake from the results of

urinary analysis if the time at which intake of 239Pu occurred is not known. In addition to this,

there is considerable diurnal variation in excretion rate of Pu through urine. Therefore, there

was a need for addressing the above mentioned difficulties and evolving a methodology for

estimation of internal dose due to transuranics to the occupational workers. Hence, Head,

Health Physics Division, constituted a task group (Ref: ORPRS/RGP/2010/06/1445 dated 13-

08-2010) to recommend, implement and oversee the internal dosimetry programme for

1

transuranics for occupational workers and to address the above mentioned difficulties so that

a reasonably accurate estimation of internal dose could be made.

The committee has prepared this manual to address the methods used for detection of

internal contamination and their limitations, difficulties in estimation of internal dose,

methodology to be adopted for estimation of internal dose, action plan for acute and chronic

cases of internal contamination, etc. The manual is primarily meant for operational health

physicists, internal dosimetry professionals and plant management.

2.0 MEASUREMENT TECHNIQUES

2.1 Lung Counting Technique:

2.1.1 Principle:

Direct measurement of Pu-Am lung burden is based on the detection of low energy

photons (LEPs) emitted in the nuclear transformation of 239Pu (17 keV L X- rays of 235U) or

59.6 keV y- rays of 241Am using a phoswich detector and array of HPGe detector systems.

The details of instrumentation and methodology are given in Ref. 2 and Ref. 3. The minimum

detection limit for pure 239Pu in the lungs is in the range of 1000 - 2000 Bq, whereas that for

241 Am is about 5-10 Bq. Quite often 241 Am is also present along with 239Pu. Therefore, in all

laboratories, 239Pu lung burden measurement is based on measurement of 59.6 keV y- rays of

241 Am. In this method it is necessary to know the activity ratio of Pu/Am. It may be noted

that, if there is presence of !37Cs and other fission products in the body, they interfere

(especially the 32 keV X- ray of 137Cs) in Pu estimation, particularly in phoswitch detector

system. In such cases repeat lung counting has to be carried out to quantify the contribution

from I37Cs. Also, care should be taken to ensure that there is no external contamination on the

chest. In one case, injury to the finger tip of the worker while handling objects contaminated

with plutonium, resulted in the injection of plutonium into the finger tip. Part of the injected

plutonium migrated to axillary lymph nodes and lung counting gave a false indication of

presence of 241 Am in the chest (Ref. 4). Therefore, if lung counting shows activity, it is

necessary to ask the subject if he/she was injured at any time while handling objects

contaminated with plutonium. If the answer is affirmative it is necessary to investigate the

possibility of migration of plutonium from the site of injury to the axillary lymph nodes as

was done in the case described in Ref. 4.

2

2.1.2 Methodology of Lung Counting:

2.1.2.1 Detectors: Two types of detectors are commonly used for the detection of Pu/Am/U

isotopes. They are: i) phoswich detector of 20.24cm diameter and a sandwich of a 1.2 cm

thick Nal(Tl) primary and a 5 cm thick CsI(Tl) secondary detector, ii) Array of HPGe

detectors consisting of three or more large area (> 70 mm dia and ~ 20 mm thick) HPGe

detectors. The detectors have a 0.8 mm thick carbon entrance window which can transmit all

photons above 10 keV energy to the active area of the detector. For routine operations, the

59.5, 63.3 and 185.7 keV photons are used for calculation o f 241 Am, 234Th and 235U activity

respectively. Spectral information obtained from individual HPGe detectors of the array and

the summed spectrum should be retained and the consistency of counts distribution in

individual detectors be evaluated.

2.1.2.2 Energy Calibration: A well defined formation of peak can only be obtained when

correct energy calibration of the detector is performed, particularly for low level

measurements of near detection limits. The energy calibration factor (ECF) can be fixed

preferably towards the higher side of the factor obtained from ideal conditions. ECF is

dependent on the resolution capability (FWHM) of a radiation detector and is generally

defined as FWHM (keV)/5 channel.

For large area HPGe detectors (example):

ECF = 0.75 keV/5 channels = 0.15 keV/channel or 0.2 keV/channel

Therefore, the 60 keV gamma energy of 241 Am should be located at around 300th

channel in MCA to obtain proper calibration factor. The energy linearity calibration should be

obtained and relationship be used for the identification of unknown radionuclides

encountered in in-vivo monitoring. Care should be taken to have same type of multi channel

analyzers and software for easy summation of the three or more spectra of HPGe array. The

energy resolution of each HPGe detector of the array should be nearly same so as to minimize

the line broadening after summation.

2.1.2.3 Efficiency Calibration of the Actinide Lung Monitor: The efficiency calibration of

the system is carried out by using realistic thorax phantom viz. LLNL or JAERI. The chest

overlay plates provided with the phantom should be used to develop an efficiency calibration

3

equation as a function of CWT. The lung sets uniformly distributed with various

radionuclides viz. 238Pu, Nat. U, Enriched U and 241 Am in the lungs are used to calibrate

actinide lung monitoring system. These lung sets are inserted into the phantom and

measurements are carried out in subject monitoring position. Photo peak area or the integral

counts obtained in relevant energy region are used to calculate calibration factor (count/sec.

per Bq. activity) for the radionuclide.

2. 1.2.4 Estimation of MEQ-Chest Wall Thickness (CWT)The efficiency and hence the MDA for estimating activity in the lung is strongly affected by

the MEQ-CWT of the subject. The CWT is defined as the thickness of the soft tissue from the

exterior surface of the chest to the pleural lining of the lung.

MEQ-CWT = 1.427 (W/H) + 0.014 (Ch) + 0.0025 (y) -0.1562

W = Weight in kg; H = Height in cm; Ch = chest circumference in cm and; y = age in years

The estimated MEQ-CWT is used to derive subject specific calibration factors of the actinide

lung monitoring system.

2. 1.2.5 Evaluation of calibration factor and ActivityThe calibration factors from the measurement of known amount of radionuclides distributed

inside JAERI phantom for an array of three 70 mm dia. HPGe detector used for lung

monitoring of workers at Trombay are given in following Table.

Radionuclide EnergykeV

Calibration factor as a function of CWT cpm/kBq of nuclide*

238Pu 17 0.83515 exp (-0.03721X)241 Am 59.5 270.9329 exp (-0.14525x)

238U Nat. U 63 36.3466 exp (-0.2614x)92.5 47.4339 exp (-0.3122x)

235U Nat. U 185 371.11 exp (-0.253x)

x = MEQ-CWT in cm : * : these are nuclide efficiencies not corrected for energy.

Lung activity due to 241 Am (KBq) = Am net counts(CPM)/ 270.9329 exp (-0.14525x)

2.1.2.6 Minimum Detectable Activity (MDA): The MDA is primarily dependent on the

background count rate and the efficiency factor. The standard deviation of background (orb) is

obtained from the average counts of background spectra of non-radiation worker subjects of

varying body builds. The number of background subjects should be at least 20 and the spectra

4

region (energy band) considered should be equal to 3*FWHM (keV) region. MDA at 95%

confidence level is evaluated from:

MDA - ( l ^ + 2.7)E x l x T

a b: square root of background counts (integral counts of the selected region), T: counting time

in secs, E : efficiency fraction from fitted curve of MEQ-CWT, I: gamma abundance fraction

(can be unity for nuclide specific efficiency).

2.1.2.7 Spectrum unfolding and area determination for activity estimation: The simplest

way of defining a clear gamma peak at the appropriate gamma energy of a radio-nuclide is to

check whether the selected net peak area has counts greater than the minimum detectable

counts as per MDA equation. Care should be taken to correct for the Compton counts or

contribution from higher energy gamma lines when difference in gross counts of subject

spectrum and background spectrum of appropriate energy region are taken for activity

determination. Gamma analysis software based deconvolution techniques can be used to

distinguish the multiplets, if any observed in the spectra.

2.1.3 Estimation of activity ratio of Pu and Am:

The Pu/Am ratio depends on many factors such as fuel bum up, period elapsed after

purification of plutonium, source that has given rise to air-bome activity etc. The ratio can

vary by a wide margin from case to case depending on the source of exposure. Therefore, it is

necessary to estimate this ratio especially in a fuel reprocessing plant. In suspected cases of

inhalation incident, the nasal swab of the exposed individual will be available normally for

Pu/Am ratio determination. Faeces of the exposed individual should also be analysed by

radiochemical methods to determine the ratio. Average of the two ratios should be used for

estimation of plutonium lung burden, wherever possible.

If routine lung monitoring shows detectable Am lung burden, Pu/Am activity ratio

should be obtained from analysis of faeces to evaluate the likely Pu intake. It is, therefore

very important to determine the Pu/Am ratio.

5

2.1.4 Estimation of intake from lung burden measurement:

From the measured241 Am lung burden, Pu lung burden should be calculated using the

Pu/Am activity ratio. If the time of intake is known, then the intake should be calculated

using IMBA software or as per ICRP 78. For example, 1.0 Bq of 239Pu lung burden after 1

month of intake corresponds to an intake of ~ 21 Bq of 'M Type 239Pu aerosols (5 (Jin

AMAD). If the aerosol Type is 'S , it corresponds to an intake of ~ 27 Bq 239Pu (Table - 1).

After calculating the intake, committed effective dose should be calculated using the dose

conversion factors (DCFs) given below (Ref. 7).

Type type DCF (inhalation) DCF (ingestion)

Type M* 239Pu 3.2 x 105 Sv/Bq 2.5 x 107 Sv/Bq

TypeS 239Pij 8.3 x 10"6 Sv/Bq 9.0 x 109 Sv/Bq

If the time of intake is not known, it should be assumed that an acute intake had

probably taken place midway between two monitoring periods as recommended by ICRP

(Ref. 6). In the case of annual lung monitoring, the time of intake should be assumed to be

180 days before the day of lung counting.

In the above calculations it is assumed that the Type of aerosols to which the person

was exposed is known. As examples, plutonium nitrate and Pu-TBP complex aerosols belong

to Type 'M whereas plutonium oxide and plutonium carbide belong to Type 'S . Therefore,

from the knowledge of the work location of the exposed individual or by any other means of

analysis, it is possible to infer the aerosols Type; 'M or 'S or Mixed. The details are

required to be provided by the Health Physicist of the plant/Head of plant at the time of

sending the personnel for monitoring.

Urinary excretion rate for Type S exposure cases will be extremely low and below

the minimum detection limit of bioassay technique (~ 0.2 - 0.5 mBq/d) (Ref. 8). But in case

of inhalation of Type 'M aerosols, the urinary excretion rate is well above the minimum

detection limit and hence for Type M aerosols, the intake estimation should be based on

urinary excretion rate. It is, however, necessary that lung counting is adopted for all

occupational workers so that exposure to Type S cases are also identified.

It is known that plutonium nitrate aerosols belong to Type 'M \ However, in one

inhalation incident, plutonium nitrate aerosols had shown lung retention similar to that for

Type 'S (Ref. 4). It appears that plutonium nitrate aerosols got converted into plutonium

6

hydroxide in this case. Plutonium hydroxide belongs to Type 'S . This unexpected behaviour

was revealed by follow-up measurements. Hence, it is necessary to have follow-up

measurement whenever Pu-Am is detected in the lung.

2.1.5 Periodicity of lung monitoring:

2.1.5.1 Routine monitoring;

The Plant Health Physicist should identify the nature of work that has the potential for

exposure to plutonium aerosols and also the areas where such activities are carried out. The

personnel who are required to carry out these activities and also the personnel who are

required to work in these areas should be identified. Such persons should be routinely

monitored once in a year. For others, the periodicity could be greater than 1 year. However,

if these persons are engaged in any specific jobs having the potential for internal

contamination, they also should be monitored at appropriate time. Similar considerations

apply to urine analysis also. The tentative schedule and list of such personnel should be sent

to the Lung counting laboratory in the beginning of the year so as to maintain the monitoring

. periodicity of once in a year.

2.1.5.2 Incident related monitoring:

The occupational worker exposed in an inhalation/ingestion/injection incident is

referred for lung counting immediately on the next day after the exposure. The subsequent

repeat lung counting is based on the results of first monitoring and is described in section 5

titled action plan for Pu-Am internal exposure incidents (flow chart 2). The name(s) of the

exposed personnel along with details such as nature of exposure and other relevant inputs like

chemical form of compound, particle size, date/time of exposure should be intimated to the

analytical laboratory without any follow-up for this information.

2.1.6 Sensitivity of lung counting technique:

The minimum detectable activity for pure 239Pu retained in the lung is about 1000 Bq.

The corresponding intake for Type M 239Pu compound works out to about 17241

Bq (27.6 ALI) and 15625 Bq (6.5 ALI) in case of Type S Pu one day after the exposure.

However, when plutonium is associated with americium, with a Pu/Am activity ratio of 3, an

intake of 0.83 ALI of Type M 239Pu can be detected one day after exposure assuming MDA

of 10 Bq. Table 1 gives the fraction of intake retained in the lung at various time intervals

7

which can be used to calculate the intake ( ICRP-78). Table 2 summarizes the sensitivity of

lung counting technique. Lung counting retained activity measurements data are used in

conjunction with urinary excretion data for the evaluation of GED.

2.2 Bioassay:

2.2.1 Bioassay technique: The bioassay technique is based on measurement of excretion

rate of plutonium through urine and faeces. From the measured excretion rate, the body

burden and the intake are calculated using the bio-kinetic model for plutonium. Because of

the practical difficulties involved in collection, processing and analysis, faeces samples are

not analysed on routine basis. However, analysis of faeces is very important in case of an

inhalation incident and also for determination of Pu/Am activity ratio of the inhaled aerosols

and it is the only bioassay tool in case of exposure to Type S Pu.

In case of urine analysis the worker should be instructed to collect the urine in a clean

bottle given to him for this purpose. Urine excreted by him, from the time of reaching home

till reporting for duty on the next day, has to be collected. The worker should be instructed to

take bath and change all the clothing that he had worn on duty before he starts collecting

urine. This is necessary to avoid possibility of cross contamination of the urine sample.

Plutonium excreted in urine is co-precipitated with calcium phosphate and separated

using anion-exchange technique and is electrodeposited on a stainless steel disc (Ref. flow

chart 1). The Pu alpha activity deposited on disc is estimated using a ZnS(Ag) scintillation

detector and/or alpha spectrometry using a Si surface barrier detector.

2.2.2 Sensitivity of the Bioassay technique and its limitations:

In a ZnS(Ag) scintillation detector type gross alpha counting system, for a counting

time of 96 h, less than 1.0 mBq of Pu alpha activity can be detected (details given below at

the end of this section 2.2.2). With this sensitivity, it is possible to detect acute intake

corresponding to 3/10 ALI 239Pu Type 'M by analysing a days urine sample for any day up

to 100th day after the day of intake. ICRP-54 has set 3/10 ALI as the investigation level.

Acute intake of 1/10 of ALI can be detected in a single urine sample up to 9 days after intake

(Table 3). In order to detect urinary excretion rate corresponding to 1/10 of ALI of Type 'M

239Pu during the period of 9th day to 30th day after intake, pooled urine sample (3 d) has to be

analysed. It is not possible to detect urinary excretion rate corresponding to intake of 3/10

ALI of Type S 239Pu or chronic exposure cases of Type M 239Pu aerosols at the rate of

8

1/365 ALI per day in a single day sample. However, activity corresponding to DRL for

chronic exposure to airborne 239Pu of Type M at the rate of 1/365 ALI per day with routine

monitoring of once in a year can be detected by pooling 3 days urine for analysis and

counting in alpha spectrometry for 7 days. Table 3 gives the DRL and urinary excretion rate

with respect to acute intake of Type M and Type S 239Pu compounds ( ICRP-78).

MDAs at 95% confidence level for an alpha counting system with ZnS(Ag) crystal

and alpha spectrometry system with PIPS type detector are evaluated as follows.

, (4.65 xcr. +2.7)x24MDA = ---------- --------------- B adE x R x T x 16

Where

Table - 1 : DRL and Lung Retention for Type M and Type S239Pn Acute Inhalation Case (Source : ICRP - 78)

Days after intake

d

Lung retention factorr(t)

DRL 0.1 x ALI x r(t)

(Bq)

Intake in Bq per 1 Bq of measured

retentionType M 239Pu ALI: 625 Bq

1 5.8 x 102 3.6 17.22 5.6 x 102 3.5 17.93 5.5 x 10'2 3.4 18.24 5.4 x lO'2 3.4 18.55 5.3 x lO'2 3.3 18.96 5.3 x 10'2 3.3 18.97 5.2 x lO'2 3.3 19.28 5.1 x lO2 3.2 19.69 5.0 x 102 3.1 20.010 5.0 x110'2 3.1 20.015 4.9 x 10'2 3.1 20.430 4.8 x lO'2 3.0 20.8100 2.3 x lO'2 1.4 43.5180 7.0 x 10'3 0.44 143360 1.5x1 O'3 0.09 670

Type S 239Pu ALI: 2400 Bq1 6.4 xlO-2 15.4 15.62 6.3 x 10'2 15.1 15.93 6.2 x 10"2 14.9 16.14 6.1 x 102 14.6 16.45 6.1 x 10'2 14.6 16.46 6.0 x 102 14.4 16.77 6.0 x 102 14.4 16.78 5.9 x lO2 14.2 17.09 5.8 x 10'2 13.9 17.210 5.8 x 10'2 13.9 17.215 5.0 x 102 12.0 20.030 3.7 x 10'2 8.9 27.0100 2.2 x 10'2 5.3 45.5180 1.7 x 10'2 4.1 58.8360 . 1.5 x 10'2 3.6 66.7

Measured lung burdenIntake = ------------------------------

Lung retention factor

10

Table - 2: Sensitivity of lung counting technique

Exposure to Days after exposure

Estimated 239Pu intake in Bq for MDLType M Type S

PurePlutonium

1 17241 (27.6 ALI) 15625 (6.5 ALI)

5 18868 16393

30 20833 27027

180 142857 58823

Pu-Am (Pu:Am activity

ratio) = 3

1 517(0.83 ALI) 469(0.20 ALI)

5 566 492

30 625 811

180 4286 1765

Pu-Am (Pu:Am activity

ratio) = 10

1 1723 (2.76 ALI) 1563 (0.65 ALI)

5 1887i 1640

30 2083 2703

180 14287 5883

Note: a) Minimum detection limit (MDL) for pure 239Pu taken as 1000 Bq and for that of 241Am as 10 Bq.

b) Lung retention factor are taken from Table 1.

11

Table - 3: DRL and Urinary Excretion Rate for Type M and Type S __________ 239Pu Acute Intake Case (Source : ICRP - 78)__________i

Days after intake

d

Daily urinary excretion rate

e(t)

DRL 0.1 x ALI x eu (t)

(mBq)

Intake in Bq per 1 mBq of measured

excretionType M 239Pu ALI: 625 Bq

1 2.3 x 10-4 14.4 4.32 1.3 x 10"* 8.1 7.73 7.8 x 10'5 4.9 12.84 5.3 x 10-5 3.3 18.95 3.9 x 10'5 2.4 25.66 3.0 x 105 1.9 33.37 2.4x1 O5 1.5 41.78 2.0 x 10-5 1.25 50.09 1.7 x 105

( 1.1 58.810 1.5 x 10s 0.94 66.715 1.1 xlO'5 0.63 91.030 9.5 xlO6 0.59 105100 6.1 x lO 6 0.38 164180 5.0 x 10'6 0.31 200360 3.5 x lO'6 0.22 285

TypeS 239Pu ALI: 2400 Bq1 2.3 x lO6 0.55 4352 1.4 xlO-6 0.34 7153 8.3 x 107 0.20 12054 5.9 x 10'7 0.14 17005 4.5 x 10'7 0.11 22206 3.7 x 10'7 0.089 27007 3.1 x lO7 0.074 32258 2.7 x 10'7 0.065 37009 2.4 x 10'7 0.058 415010 2.3 x lO7 0.055 435015 1.8 x 107 0.043 555030 1.7 x lO7 0.041 5900100 1.6 x lO'7 0.038 6250180 1.55 x 10'7 0.037 6450360 1.5 x 10'7 0.036 6650

Measured urinary excretionIntake = ---- ----------------------------

Daily urinary excretion rate

12

3.0 ANALYSIS PROCEDURES

3.1 Sampling and Analytical Procedures for Bioassay

The most important bioassay samples for estimating the intake of transuranics are

urine and faeces. Sometimes nasal swab is also analysed for radionuclide content. In case of

transuranics, analyses of faecal sample during the initial period is essential, particularly after

planned operations and suspected exposures.

3.2 Sample collection procedure:

3.2.1 Faeces:

Generally, morning void faeces is collected in a wide mouthed polyethylene bag

covered by a second polyethylene bag which is wrapped in a paper envelope. The name of

the person and other details are written on the envelope. Analysis of a faeces sample gives the

amount of insoluble radionuclide inhaled/ingested. In case of persons engaged in power

reactor fuel reprocessing, determination of Pu/Am ratio in the faecal sample is very

important since on most of the occasions Am concentration in urine is not detectable even

when Pu is detected. The analysis of faecal samples is required whenever an investigation of

incidental exposure is undertaken or on a case by case basis for personnel handling insoluble

compounds or for establishing the Pu/Am excretion ratio.

3.2.2 Urine:

The radionuclide excreted in urine represents the soluble portion of the inhaled /

ingested radionuclide. Generally, overnight 16 h urine sample is collected after the working

hours, preferably at the residence of the worker to avoid contamination. The sample is

collected in a 1.2 litre plastic bottle with double cap. The bottle is carried in a suitable cloth

bag with a handle to facilitate easy carrying to the laboratory. The collection of complete 16 h

urine sample should be ensured either from the volume of the sample or by analyzing

creatinine content in Labs where the methodology is standardized. The sample should be

rejected and repeat sample requested if there is a doubt on the complete sample collection.

13

3.2.3 Other Samples:

Nasal swab on filter paper is sometimes analysed to confirm that inhalation exposure

has taken place. Rough estimate of inhalation intake can also be made from this analysis.

3.3 Sample Processing:

Faecal sample is dry ashed in a fumehood. The dry weight and the ash content with **

respect to wet weight are recorded. In case the presence of 241Am is expected, the

homogenised faecal ash is directly counted in a gamma spectrometer. (241Am has a gamma

energy of 59.5 keV; 35.9% intensity).

Urine from the plastic bottle is transferred to a 2 litre beaker, acidified with HN03

and given a serial number. The details of the sample and the name of the person and date of

sampling along with the case history of exposure is written in the register maintained. Urine

sample is, generally wet ashed with H20 2 + HN03.

3.4 Radiochemical Separation:

The analyses of urine and faeces for Pu and Am are carried out as follows:

3.4.1. Sample Preparation:

3.4.1.1. Faeces:

The faecal ash with added tracers (242Pu, 243Am) is fused with fusion mixture in a

stainless steel dish over a burner carefully till the whole mass melts and reaction is

complete. Fusion mixture is in the proportion of 5:1:1 of NaOH : NaN03 : NajCO^ The

fused mass is cooled, leached with distilled water and the residue is dissolved in

HNO, and evaporated to dryness. The evaporated residue is dissolved in 8N HNOs and

taken for ion exchange separation of plutonium and americium ( flow chart 1 ).m

3.4.1.2. Urine:

To the acidified urine, 50 mg of Ca carrier and standard 242Pu & 243Am tracers are

added. The urine is wet ashed with 30% H20 2 (10-15 ml) and HNO, till the colour of urine

becomes pale yellow by heating over burner or hot plate. About 200 mg of hydroxylamine

hydrochloride and 2 ml of concentrated orthophosphoric acid is added to urine. Calcium

phosphate is precipitated by adding ammonia with constant stirring. A little excess ammonia

14

is added to ensure complete precipitation. The content of the beaker is allowed to settle

preferably overnight. The precipitate is centrifuged, washed once with distilled water,

dissolved in HN03 and evaporated to dryness. The evaporated residue is dissolved in 8N

HN03 and taken-up for ion exchange separation of plutonium and americium.

3.4.2 Sequential Chemical Separation for Urine, Faeces and other bioassay samples:

The sequential radiochemical separation given in flow chart-1 (page 18) for urine is

applicable to other bioassay samples also.

3.4.3 Electrodeposition:

Both separated plutonium and americium are electrodeposited in ammonium sulphate

medium. To the evaporated sample 0.3 ml of H2S04 is added and allowed to fume over a

burner. The solution is cooled and 1 ml of 2N H2S04 is added slowly. A few drops of methyl

red indicator is added and 1:1 NH4OH is added drop wise until the colour of methyl red turns

yellow. The solution is acidified with drop wise addition of 2N H2S04 until the colour just

turns red. The solution is transferred to an electrodeposition cell fitted with a 2.5 cm dia

stainless steel planchet (cathode) with 2 ml of distilled water washing. Electrodeposition is

carried out at 300 mA current for 2 h. At the end of electrodeposition the solution is made

strongly ammonical with the addition of 1:1 NH4OH before switching off the current.

The stainless steel planchet is washed, flamed and taken for alpha counting and subjected to

alpha spectrometry.

3.4.4 Reporting of results:

The results of urine samples are expressed as mBq/day with standard uncertainty. The

16 h (overnight) sample activity is corrected for one days sample. In case of hospitalized

personnel it is possible to collect 24 h urine sample. The normalization process can also be

made from the Urine Creatinine content after establishing the variations within a group of

healthy persons. The technique will be more useful for rejecting the sample if the Creatinine

concentration is too low. Faecal sample results are expressed as Bq/sample with standard

uncertainty. Counting time of sample should be chosen in such a way that the degree of

uncertainty should not be more than 30% for samples near the detection limit and should not

be more than 10% for samples having activity concentration of 5 times the detection limit.

15

4. QUALITY ASSURANCE PROGRAMME

4.1 Introduction:

Quality assurance in analytical/radiochemical procedures is an important aspect of

internal exposure monitoring and serve to assure the accuracy of dose estimates being made.

Quality assurance experiments are conducted for both direct (lung counting) and indirect

(bioassay) methods. The laboratories of Health Physics Division (HPD) regularly participate

in intercomparison exercises at least once in a year at either national and/or international

levels. Samples used in bioassay intercomparisons are generally of urine and faeces but at

times samples of tissue and/or of other biological origin are also analysed. A brief account of

intercomparisons carried out is given in the following paragraphs.

4.2 Intercomparison for lung counting laboratories :

The lung counters of IDS (HPD, BARC), Health Physics Laboratory, Tarapur and

Environmental Survey Laboratory (Kalpakkam) were calibrated with standard thorax

phantom developed by Lawrence Livermore Laboratories, USA. They were also calibrated

using JAERI phantom representing chest of Asian reference man. The calibration factors for

different chest wall thickness of subjects were derived for both 239Pu and 241 Am. It is

recommended that the calibration should be carried out using realistic phantom representing

thorax of Indian reference man. Intercomparison exercise of measuring241 Am in lung should

be carried out at least once in two years and records maintained.

4.3 Intercomparisons among different laboratories of HPD:

i) Three sets of urine samples spiked with 239Pu and 241 Am and supplied by IAEA in

an intercomparison exercise were analyzed using standard radiochemical analysis procedures

(2001/2002). The exercise indicated that both 239Pu and 241 Am results were in good agreement

with reference values. [Results of the 2001/2002 intercomparison exercise on the

determination of activity of alpha emitters in Urine samples - R. Cruz Suarez and K. Mrabit,

IAEA, 2001/2002] (ii) Two sets of urine samples spiked with 238U, 234U and 241Ain were

analyzed at Trombay, Tarapur and Kalpakkam Labs in an intercomparison exercise conducted

by Health Physics Division during 2005 (IDD/487/2005). Results were in good agreement

within statistical errors. It is now proposed to analyse bioassay samples once in two years on

periodical basis.

16

4.4 Intercomparison with IRC and IAEA:

The laboratories of Tarapur, Trombay and Kalpakkam have a regular program of

analysing samples sent by International Reference Centre (IRC) a WHO unit, France. The

bioassay laboratories obtain IAEA samples sent by the Agency's laboratory at Seibersdorf,

Austria. The samples consist mainly of biological and environmental materials. The

radionuclides covered are fission products as well as transuranics. The results have been

consistently found to be in good agreement with the organisers values. Whenever any

significant deviations were noticed, corrective measures were taken immediately. Since the

analytical procedures and techniques are same for bioassay, biological or environmental

samples, it can be said that the results of bioassay pass the scrutiny of quality assurance

program at international level as well.

17

FLOW CHART 1

Outline of Sequential Chemical Separation of 239Pu and241 Am in Urine Samples

Acidify + 242Pu+243Am + Ca 50 mgOxidation with H20 2 + HN03, add Hydroxylamine hydrochloride to reduce to Pu(III), Precipitate Ca3(P04)2.

Precipitate- 242Pu,239Pu, Supernatant- 137Cs. Count in241 Am & 243Am. Dissolve HPGe detector Marinelli beakerin HN03 evaporate to dryness. geometry (only in case of investigations)Dissolve in 8N HN03,adjust toPu(IV) by adding NaN02, anionexchange separation.

Pu Am

Ion exchange resin- wash with Effluents + 8N HN03 washings (Am)8N HNOa and 8N HC1. Elute Precipitate Ca-oxalate withwith 1.5 M hydroxylamine hydro- oxalic acid and ammoniumchloride, evaporate to dryness hydroxide at pH 3.5 & stir forfume off, electrodeposit in 30 minutes.(NH4)2S04 mediumfor 2 h at 300 mA current. Countin alpha spectrometer. Yield by i--------- ------------ 1242Pu tracer. * *

Supernatant: Precipitate:discard destroy oxalate with HN03

+ HC104. Dissolve residue in 3N HC1. Carry out cation exchange separation, wash column with 2N HN03.Elute Am with the 10 N HN03. Electrodeposit in (NH4)2S04 medium for 2 h at 300 mA current, count in Alpha spectrometer.Yield by 243Am tracer.

16 h urine sample

18

5.0 ACTION PLAN FOR Pu-Am - INTERNAL EXPOSURE INCIDENTS

5.1 Action plan for Pu-Am inhalation incidents :

Guidelines have been framed to handle/manage suspected and confirmed cases of

internal contamination due to inhalation of Pu-Am aerosols primarily to assist the plant health

physicist in deciding the actions to be taken in dealing with such cases.

The incidences leading to internal contamination due to plutonium can be classified

into two categories namely, prompt and delayed detection.

Normally, the possibility of internal contamination is immediately recognised by the

worker himself, his supervisor or the health physicist. The examples of which are:

i) Loss/failure of respiratory and/or other protection equipment while working.

ii) Spray/spillage of radioactive liquid on body parts (e.g. face) of a worker.

iii) Sudden and unanticipated increases in air borne activity in working areas against which

the worker lacked adequate respiratory protection.

iv) Very high facial/skin contamination.

However, at times, for some reason, the recognition of an incident having resulted in

exposure or having had potential for exposure may get delayed. These can be termed as

delayed category incidences.

Potential for internal contamination should be deemed to be significant if, for example

i) Installed continuous air monitors indicate air borne activity above 100 DAC.h. ii) Spot air

sampling shows air activity concentration above 100 DAC. In both the above cases, it is to

be noted that the exposure would have occurred only if workers were present in the area

during the time of increased air borne activity. Identification of such workers, if any, will

need investigation and detailed enquiries, iii) Persons report with high facial skin

contamination iv) Bioassay result during a routine monitoring programme shows urinary

excretion above 3 mBq/day. (As per ICRP-78; 1 ALI of M Type 239Pu, for 360 d monitoring

interval or 180 d mid point intake)

5.1.1 Procedure for taking nasal swabs:

1. Nasal swabs should be taken as soon as the occurrence of an incident is known /

suspected or as soon as the worker reports to the health physics unit.

19

2. Nasal swabs should be taken before any facial decontamination. If the worker has

already tried to wash his face, this fact should be noted while taking the nasal swab and

recorded on the nasal swab sample envelope.

3. Extreme care should be taken to ensure that nasal swabs collected are from the

nostrils and do not have any cross-contamination from the facial skin or external

regions around the nose.

4. The procedure to take nasal swab sample is as follows. Wrap a tissue paper or a filter

paper around the little finger and rotate it couple of times inside the nostril. Dry it under

an infrared lamp and count in an alpha counter. Preserve the sample with all relevant

details for subsequent detailed analysis.

List of samples to be obtained and preserved for subsequent detailed analysis are give below:

1) Nasal swabs.

2) Filter paper samples from continuous air monitors.

3) Spot air sample filters taken immediately after the incident.

4) Swipe samples from the location of incident, if pertaining to the incident.

5) Ashed faecal samples.

5.1.2 Flow Chart of Action Plan:

The 'Action Plan' in the form of a chart (Flow Chart 2) is given on page 23.

The basis and assumptions are given below:

a) Urinary excretion and faecal excretion values given in ICRP-78 are used in formulating

the action plan.

b) In case of 5 jam AMAD Pu aerosols of Type M deposited in the ET,, 10% of activity is

assumed to have been collected on nasal swabs. About 34% of inhaled material is

deposited in ET1 region.

c) Experience shows that administration of Ca DTPA inhalation increases urinary

excretion by a factor 4 to 20 in case of Type M Pu compounds. A factor of 5 has been

used in the action plan. The urinary excretion rate one day after intake corresponding to

1/10 ALI of 239Pu is 14 mBq/d (Table 3). This rate will be increased by a factor of

minimum 5 by administering Ca DTPA aerosol.

d) Activity collected on the nasal swabs is used to estimate probable intake for taking

immediate action.

20

Based on the above following action levels are recommended:

i) Nasal swab having < 6 Bq a- activity - No action is contemplated.

(This would correspond to an intake of 6 Bq but 18 Bq a- activity - administration of Ca DTPA aerosols

inhalation under medical supervision in Hospital followed by administration of

Ca DTPA intravenously in the hospital.

iv) Urine sample of 8 hours to 16 hours duration (depending on the convenience and

time of exposure) must be collected before the administration of Ca DTPA

aerosols inhalation or intravenously.

In case of (ii) and (iii) mentioned above, the person should be laid off from work in

radioactive area till the dose is assigned. The re-deployment of the exposed individual will be

governed by the conditions stipulated in Section 6.3, which deals with dose accounting and

control.

In those cases where Ca DTPA has been administered either by aerosol inhalation

and/or intravenous injection, the first estimate of intake can be made only after 3 months

because by this time the effect of Ca DTPA will reduce considerably and urinary excretion

rate stabilize. Therefore, it is recommended that about 12 weeks after the last Ca DTPA

administration, 16 h urine should be collected for three consecutive days and pooled for

analysis. From the result of this analysis an estimate of intake should be made using IMBA

software/ICRP-78.

If the estimated intake from an acute exposure is greater than 1 ALI, the matter should

be referred to Head, Health Physics Division for information and further advice regarding

dose assignment and follow-up monitoring.

It is to be noted that if the exposure was to Type 'S aerosols e.g. Pu02, PuC etc,

administration of Ca DTPA either by aerosol inhalation or by injection will not have any

effect. Further, urinary excretion rate of Pu is likely to be below the detection limit.

In case of inhalation exposure to Type 'S aerosols, following actions are therefore

recommended.

1. Nasal swabs < 24 Bq : no action is contemplated.

This would correspond to an intake

2. Nasal swabs >24 Bq : Three consecutive days faecal samples and pooled urine

samples should be analysed.

3. Lung counting should be carried out on the next day after exposure. If activity is

detected during lung monitoring, follow-up counting should be carried out once in 2

weeks for 6 weeks and thereafter at a periodicity of six months.

4. Pu/Am activity ratio in nasal swabs and faeces should be determined.

5. If lung counting does not show 241 Am, then intake should be estimated based on the

analysis of faeces. In order to refine the intake estimate, it is recommended that faecal

analysis at intervals of 1 week, 2 weeks, 4 weeks and 8 weeks should be carried out.

5.2 Action plan for Pu-Am injection incidents:

There is always a potential hazard of injury while working with sharp tools even

inside glove boxes. Besides, sharp edges contaminated with plutonium could also lead to

pricks or small cuts. In case of wounds or cuts contaminated with Pu, bleeding should be

encouraged by pressing the wound/cut. The drops of blood should be dried on a glass fibre

filter paper which should be subjected to alpha counting. Also smear sample on the tools or

equipments that caused injury should be taken and analysed. This will indicate the potential

for internal contamination.

The wound should be first washed with water and then directly checked for

contamination. Ca-DTPA intravenous injection is recommended if the wound shows a-

contamination >40 Bq. If the wound shows a- contamination >150 Bq, excision of the

wound tissue is recommended.

If the tool (source of injury) shows contamination due to Pu but blood drops and the

inflicted wound do not show any detectable contamination, the confirmation of intake should

be obtained by analysis of urine sample collected during the next 24 hours. Subsequent

action will depend on the results of urine analysis.

22

FLOW CHART-2: ACTION PLAN FOR Pu-Am INHALATION INCIDENTS

6.0 ESTIMATION OF INTAKE BASED ON ROUTINE URINE ANALYSIS

6.1 Introduction:

Estimation of internal dose from routine urinalysis data is difficult because, quite

often, the time of intake is not known and there is considerable diurnal variation in the

excretion of plutonium through urine.

In order to estimate the intake based on routine bioassay, ICRP recommends that the

intake should be assumed to have taken place mid-way between two monitoring dates i.e. the

date of previous and present monitoring. In plutonium handling facilities in India, routine

bioassay monitoring for occupational workers is normally carried out once a year. Therefore,

the time of intake should be taken as six months before the day of annual monitoring. With

this assumption and using the IMBA software/ICRP 78, intake estimates have to be made for

those persons whose urinary excretion rate was above the detection limit.

6.2 Recommendations:

Recommendations for estimation of intake corresponding to different levels of urinary

excretion of plutonium, are given below:

1. excretion rate < 1 mBq/day, they need not be considered for dose estimation as the intake

is likely to be less than 1/3 ALI and the corresponding annual dose < 0.6 mSv. (CED < 6

mSv).

2. excretion rate between 1 mBq/day and 3 mBq/day, caluculate the intake based on ICRP-

78/IMBA software. Contribution to the excretion from the previous year to be subtracted

before the evaluation of intake and CED.

3. excretion rate > 3 mBq/day, should be re-monitored for confirmation after two weeks and

lung counting should also be carried out.

4. excretion rate between 1 and 3 mBq/day during routine monitoring for three consecutive

years, follow-up monitoring at one month interval, for three months, is recommended.

Average Pu excretion rate observed in the follow-up monitoring should be used for

estimating the intake with the time of intake taken as 2 years ago (mid point of 4 years).

The actions to be taken based on the results of repeat urinalysis, are shown below:

Repeat ------- >AUrine ------- >BAnalysis ----- >c

24

A: > 3 mBq/d but reduction by a factor of about 2 compared to earlier value, analyse

three days pooled urine after about a month. Since there is a significant reduction in urinary

excretion rate, the intake must have taken place probably about a month back. Therefore, take

the time of intake as one day before the day of routine monitoring or as appropriate with

ICRP-78 excretion fraction pattern and estimate the intake using ICRP 78/IMBA software.i

B: > 3 mBq/d and no significant reduction. This means that the intake took place

probably a few months back. Temporarily lay off the person from work in radiation areas.

Analyze three days pooled urine sample and estimate the intake, taking the time of intake as

six month back.

C: If > 9 mBq/d, lay off the person from work in radiation areas and arrange for

administration of Ca DTPA intravenously. Subsequent actions will be based on the

effectiveness of Ca DTPA in enhancing urinary excretion as shown in flow chart 2.

It may be noted that by ignoring excretion rate below I mBq/day, an intake upto 0.3

ALI or the annual effective dose of 0.6 mSv is ignored. Further, 0.6 mSv is the recommended

recording level of internal dose in case of fission and activation products (Ref. 8 :

BARC/1999/E010).

6.3 Dose accounting and control:

The committee recommends the following for the purpose of individual dose

accounting and control:

i) The Committed Effective Dose (CED) resulting from the intake of relevant radionuclides

(fission products and actinides), in a year, by the occupational worker should be added to

the external effective dose received by him/her in the year and the sum of the doses

should be treated as the annual effective dose for the year. Similarly, the CED, resulting

from the intake in the five-year block should be added to the external effective dose

received by him/her in the five year block and the sum of the doses should be treated as

the effective dose for the five year block.

ii) The individual effective dose exceeding 20 mSv in either due to an acute intake or from

an old exposure will be accounted as given below.

Let, I - intake of a radio-nuclide, X - number of lay-off years, ALI - Annual Limit on

intake of a nuclide

In = -----ALI

25

When X > n, consideration for re-deployment can be made.

In case of exposure due to multiple radionuclides and external exposure, the total

CED can be evaluated and compared to X

CEDjmSv)20mSv

l fX>n consideration for re-deployment can be made.

iii) The annual effective dose to an individual worker in any calendar year during the five

year block shall not exceed the limit of 30 mSv.

iv) The cumulative effective dose for the five year block shall not exceed 1 OOmSv.

7.0 RECORD KEEPING AND REPORTING PROCEDURES

7.1 Direct method:

The results of lung counting for 241 Am should be reported routinely at monthly

intervals. The table of results should indicate the date of counting, unique TLD No. of the

person, name of the person and241 Am content in the lung along with its uncertainty. The

detection limit of the system has to be given as a foot note. Generally, results are below the

detection limits except in case of personnel involved in an incident of acute exposure. Copy

of the report should be sent to the respective Plant Superintendent and Health Physicist.

Whenever 241 Am is detected, the probable intake of Pu should be estimated using Pu/Am

ratio. Officer in charge of Lung counting facility should evaluate the resulting dose due to

intake using methodology described earlier or IMBA software. (Table 2)

7.2 Urine analysis:

Results of urine analysis should be tabulated on monthly basis with details of TLD

Nos., date of sampling, name of the person etc. The results should be expressed as mBq/d

excretion with associated standard error. The detection limit should be indicated as a foot

note. Repeat urine sample should be requested whenever the excretion level exceeds 3 mBq/d

in case of routine sample. Copy of the results should be sent to Plant Superintendent and

Health Physicist of the facility. Results of analysis are to be maintained in a register, stored

in PC and also as hard copies. Unique TLD No. is used to identify the results of repeat urine

samples. Internal dose should be calculated by the Officer in charge of bioassay laboratory

with inputs from plant Health Physicist.

26

7.3 Dose record keeping:

The plant health physicist should keep record of the resulting committed effective

dose due to intake received by the individual occupational worker. The CED should be added

to the external effective dose received by the individual during the year and sum of the doses

should be treated as dose for the year. Copy of the individual dose record should be sent to

Head, RPAD, BARC.

CONCLUSIONS:

1. The manual gives the methodology for assigning internal doses using the bioassay and

lung monitoring results.

2. The action plan for routine and incident related monitoring has been described.

3. The Committee recommends that the procedures and methodolgy of internal dose

assessment given in the manual should be reviewed after 3 years. The recommendations

of this document are final and binding. During this period, any difficulties encountered in

applying the methodology should be brought to the notice of the Head, Health Physics

Division, BARC.

4. A committee will be constituted by Head, Health Physics Division to review the

computed doses for those cases of CED exceeding 10 mSv.

ACKNOWLEDGEMENTS:

The committee members would like to thank Dr. P.K. Sarkar, Head, Health Physics

Division, B. A. R. C. for his keen interest in evolving a standard procedure and critical review of the draft.

27

REFERENCES:

1. ICRP (1995). Age dependent doses to members of the public from intakes of

Radionuclides, Part 4, Inhalation dose coefficients, ICRP-71, Pergamon press, Oxford.

2. Sharma R.C., Surendran T., Haridasan, T.K. and Sunta C.M.(1989). In Vivo

Measurements of Low-Energy Photon (LEP) Emitters, Bull. Radiat. Prot. 12 (4), pp 41-

56.

3. Sharma, R.C., Surendran, T. and Haridasan, T.K. (1999) Monioring Intakes of Pu/Am by

External Counting: Current Status. Proceedings Health Physicists Meet' 99, AERB,

Mumbai.

4. Surendran, T., Haridasan, T.K., Sharma, R.C. and Krishnamony S. (1995). Experiences at

Trombay in Monitoring Actinide Intakes by Occupational Workers by Direct External

Counting. Radiation Protection Dosimetry Vol. 59, No. 1, pp 15-24.

6. ICRP (1997), Individual Monitoring for Internal exposure of Workers, ICRP Pub. No.

78.

7. ICRP (1995). Dose Coefficients for Intakes of Radionuclides by Workers. ICRP

Publication 68, Annals of the ICRP, Vol. 24, No. 4, Pergamon Press, Oxford.

8. AERB (1996), AERB Safety Manual, Radiation Protection for Nuclear Facilities, Rev. 3.

28

ANNEXURE-1Contributors to the manual & Members of the Task Group:

1. Dr. A. G. Hegde Head, ESS, BARC

2. Dr. D. D. RaoHead, IDS, HPD, BARC

3. Shri R. G. Purohit Head, ORPRS, HPD

4. Shri M. D. DeshpandeO-I-C, HP Unit, PREFRE, Tarapur

5. Shri M.R. SankaranO-I-C, HP Unit, KARP, Kalpakkam

6. Dr. I. S. Singh IDS, HPD, BARC

7. Ms. Pramila Sawant IDS, HPD, BARC

8. Dr Ravi JammihaL BARC dispensary, BARC

Member

Member

V v2_

Member v

Invited Member

Member

Member Secretary

( ifg f2-0 i/

The terms and references of the Committee:

1. To recommend a consistent routine monitoring programme comprising of bioassay and

body measurements for occupational workers and suggest an adequate periodicity.

2. To review the sampling and analytical procedure for bioassay and procedures for lung

counting and calibration for counting systems and bring about uniformity in procedures

with respect to techniques, detection limits, etc.,

3. To recommend inter-comparison studies at regular intervals in respect of above for

assuring quality of measurements.

4. To review and adopt the proposed Action Plan for suspected internal exposure cases.

5. To evolve record-keeping procedures both at the plant and at the Internal Dosimetry

Section at Trombay.

6. To deal with any other aspect relevant to the programme.

29

ANNEXURE-2

ILLUSTRATIVE EXAMPLES OF DOSE CALCULATION

Example 1 (Case of Lung monitoring)

A person was sent for lung counting 3 days after suspected acute internal exposure while carrying out maintenance work in a cell containing plutonium oxide. The result of lung counting showed 15 Bq of 241 Am. Average activity ratio of Pu/Am in nasal swab and faecal sample was 8.5. Calculate the intake and CED due to plutonium.

Solution:

241 Am retained in the lung = 15 Bq. Corresponding retention of 239Pu = 15 x 8.5 = 127.5 Bq.

Measured Lung burden239Pu Intake = --------------------------------

Lung retention factor

The lung retention factor for class S plutonium after three days = 6.2 x 1 O'2 (Table-1)

127.5 Bqtherefore, 239Pu intake = ------------ = 2056.5 Bq

6.2 x 10 2

The corresponding CED = Intake(Bq) x Dose conversion factor

for class'S 239Pu (Sv/Bq).

= 2056.5 x 8.3 x 10'6 Sv/Bq = 17.07 mSv.

The person has to be laid off from work in radioactive area for a period of one year. Repeat lung counting is recommended to further refine the intake evaluation and observe the decrease or build-up o f241 Am in the lung.

Example 2 ( Case of Acute inhalation to class M)

A person working in a cell handling plutonium TBP complex was suspected to have been exposed to Pu aerosols and his nasal swab showed 8 Bq of plutonium. He was given Ca- DTPA by aerosol inhalation and repeat monitored by urine analysis. Lung counting did not show 241 Am in the lung. The three days pooled urine sample 100 days after exposure gave 239Pu urinary excretion of 2.5 0.8 mBq/d. Calculate the intake and CED.

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Solution:

The stabilised urinary excretion 3 months after Ca-DTPA inhalation administration is 2.5 0.8 mBq/d. The daily urinary excretion rate for class 'M' Pu aerosols 100 d after exposure is 6.1 x 10'6 (Table-3) .

Measured urinary excretionTherefore, Intake = -------------------------------------

Daily urinary excretion rate

(2.5 0.8) x 10"3 Bq/d

6.1 x lO6 /d

= 409.8 131.1 Bq

Corresponding CED = 409.8 Bq x 3.2 x 10~5 Sv/Bq

= 13.1 mSv.

The CED has to be added to external dose to get the total dose.

Example-3 (Case of routine urine monitoring)

A routine urine sample of a subject during 2010 showed urinary excretion of 4.5 0.7 mBq/d. Calculate the CED.

Solution:

As per recommendations of the method described in chapter 6 of the manual for routine urine sample results of > 3 mBq/d, (Option B): Person was re-monitored and found no significant reduction in the excretion. He was recommended for lay off from radiation work. 3 days pooled sample analyzed and found to have an excretion rate of 4.1 0.7 mBq/d. The time of intake was assumed as 180 days. Previous exposure was less than detection limit.

4.1 0.7 mBq/dTherefore, Intake = ------------------------- = 820140Bq

5 x 10'6

CED - 820 (Bq) x 3.2 x 105 (Sv/Bq) - 0.0262 Sv = 26.2 4.5 mSv

The internal dose has to be added to the external dose received during the year. Lay off should be considered as per dose accounting procedure given in 6.3.

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