|Year : 2010 | Volume
| Issue : 3 | Page : 120-122
Assessment of internal exposure due to acute intakes of radioactivity at waste management facilities under special operational monitoring
Ranjeet Kumar1, Smita Thakur1, JR Yadav1, DD Rao1, Lal Chand2
1 Health Physics Laboratory, GSO Complex, BARC, Tarapur, India
2 Health Physics Division, BARC, Trombay, Mumbai, India
|Date of Web Publication||22-Oct-2011|
D D Rao
Health Physics Laboratory, GSO Complex, BARC, Tarapur
Source of Support: None, Conflict of Interest: None
Assessment of internal exposure to the two acute exposure cases at waste management facilities have been carried out by whole body counting (in-vivo) and bio-assay (in-vitro) monitoring technique. These subjects were administered Ca-DTPA aerosol immediately after exposure. The initial whole body counting results showed internal contamination due to 137 Cs. Urinary excretion rate of 239 Pu and 241 Am in these cases are determined by means of standard radiochemical separation and estimation using 236 Pu and 243 Am tracers. The paper deals with the assessment of internal exposure to the radiation workers from waste management facility at Tarapur. It is observed that the assessed CED due to 137 Cs was very low while the actinides namely, 239 Pu and 241 Am, were the main contributors to the total CED. The CED for Case-I and Case-II was estimated as 8.54 mSv and 6.48 mSv respectively.
Keywords: Whole body counting, urine samples and ICRP-78
|How to cite this article:|
Kumar R, Thakur S, Yadav J R, Rao D D, Chand L. Assessment of internal exposure due to acute intakes of radioactivity at waste management facilities under special operational monitoring. Radiat Prot Environ 2010;33:120-2
|How to cite this URL:|
Kumar R, Thakur S, Yadav J R, Rao D D, Chand L. Assessment of internal exposure due to acute intakes of radioactivity at waste management facilities under special operational monitoring. Radiat Prot Environ [serial online] 2010 [cited 2022 Jan 17];33:120-2. Available from: https://www.rpe.org.in/text.asp?2010/33/3/120/86277
| 1. Introduction|| |
In the waste management facilities, 137 Cs and 90 Sr radioisotopes are of major concern in working environment along with actinides like 239 Pu and 241 Am. During routine plant operations in waste management facilities, occupational workers are likely to get exposed to these radionuclides mostly through inhalation. Subjects are periodically monitored for body burden measurement due to internally deposited 137 Cs isotope by whole body counting (in-vivo) technique. In normal circumstances, when the 137 Cs body burden is below the minimum detection level activity of 0.1 kBq, internal contamination due to 239 Pu and 241 Am is also expected to be low and hence urine analysis for internal contamination due to actinides is not carried out. However in the case of acute exposures having body burden due to 137 Cs above 10 kBq, 239 Pu and 241 Am are also monitored through bio-assay of urine and faecal samples under special operational monitoring programme. This paper deals with the importance of the synchronization of whole body counting and urine bioassay monitoring programme for occupational workers engaged in the management of high level waste. A small and measurable fraction of internally deposited Pu and Am of acute exposure cases is excreted through urine. To estimate the internally deposited Pu and Am at an intake level of about one ALI (ICRP-78, 1997) of occupational workers, urine bioassay is the preferred technique. Urine sample of exposure cases from such facilities may contain radio-nuclides like Cs, Sr, Pu, Am and U etc. A standardized radiochemical method for separation and estimation of plutonium and americium is used to evaluate the urinary excreted activity (Ranjeet Kumar et al., 2005).
| 2. Materials and Methods|| |
During the periodical leak checking of the annular pipes carrying waste, some quantity of radioactive waste water got splashed out into the working environment and got airborne. The personnel working at the maintenance job got exposed to the airborne radioactivity. After assessing the levels of contamination of working area, the personnel were given Ca-DTPA aerosol and sent for whole body counting for assessment of internal contamination. Whole body counting was carried out using 'shadow shield' type of whole body monitor consisting of a NaI (Tl) detector with dimensions of 10.2 cm dia × 7.6 cm height, coupled to a multi-channel analyzer (Sharma, 1995). The energy and efficiency calibration of the system was carried with sealed point sources of 137 Cs and 60 Co incorporated in water filled BOMAB phantom. Sensitivity factors for photo-peak area were obtained with an energy and efficiency calibration of 10 keV/channel and 1 cps/kBq (Cs 137 ) respectively. The minimum detectable activity of the system was 0.1 kBq for counting duration of 1200 seconds.
The urine bioassay was carried out by radiochemical analytical procedures. It involves spiking with tracers ( 236 Pu and 243 Am), wet oxidation with Conc. HNO 3 and H 2 O 2 , co-precipitation of actinides and 90 Sr along with Calcium-phosphate Ca 3 (PO 4 ) 2 , separation of Pu-Am by anion exchange resin column, electro-deposition of the samples on stainless steel planchette (Kamala Rudran, 1969) and activity estimation by alpha spectrometry using PIPS detector. The efficiency of alpha spectrometric system was 22.5% and the average radiochemical tracer recovery was 85% for 236 Pu and 45% for 243 Am. The minimum detectable activity (MDA) of urine bioassy is 0.5 mBq/day and 1 mBq/day for 239 Pu and 241 Am respectively for a counting period of 86400 seconds and at 95% confidence limit of 3.29 times the standard deviation of background (Ranjeet Kumar et al.,2009).
| 3. Results and Discussion|| |
The results of whole body counting and urine bioassay of Case-I and Case-II with assessed intake and CED are given in [Table 1] and [Table 2] respectively. The intake and CED due to incorporated radionuclides is computed as ICRP-78 methodology. Briefly,
|Table 1: Results of Whole body counting and urine analysis for 137Cs of Case-1|
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|Table 2: Results of Whole body counting and urine analysis for 137Cs of Case-2|
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I : Intake (Bq), A (m) , Measured Activity (Bq), m(T): Retention factor (ICRP-78) at T days, CED: Committed effective dose (mSv), DCF i : Dose conversion factor of i nuclide (Sv/Bq), 1000: Conversion of Sv into mSv.
Body burden of 137 Cs estimated from whole body counting observed to give higher intake during the initial period (i.e., 1 st day to 10 th day) of monitoring, as compared to the later period. It is evident that when initial data are used for intake assessment, estimate is found to be higher by a factor of 2 to 3. Since the data of 1 st and 10 th day monitoring of case-1 showed inconsistency with the latter long term data, the intakes obtained from these measurements are considered as outliers and hence not used for average intake estimation. This gives an upper level of estimate by whole body counting or by urine bioassay analysis during initial period for temporary assessment. However, later data need to be used for final assessment. From whole body counting measurement, the average intake and CED of case-1 is 4567 Bq and 0.03 mSv respectively. The average intake and CED of case-2 is 3428 Bq and 0.023 mSv respectively. Urine bioassay analysis of 1 st day sample, showed an intake and CED of 26787 Bq and 0.18 mSv and for case-2 these are 8786 Bq and 0.059 mSv respectively. The higher estimation could be due to external contamination while collecting urine sample over the day. This being very high compared to whole body counting assessment and also as being single analysis, the whole body counting based CED and intake is considered and average dose is assigned.
The assessed data, analysis results of urine bioassay for 239+240 Pu and 241 Am are given in [Table 3]. Piechowski et al have shown average enhancement factor of 50 in plutonium excreted activity due to Ca-DTPA with a range of 25 to 100 (Piechowski et al., 2003). However, our experiences at the laboratory showed an average enhancement factor of 20 and 10 for Pu and Am respectively. Accordingly, the computed intake based on measured data was reduced by 20 times (divided by 20) for 239+240 Pu and 10 times (divided by 10) for 241 Am and assessed intake is obtained. Excretion fractions per unit intake given in ICRP-78 are applied to assess intake for the case-1 and case-2. The assessed intakes were found to be 23.1 Bq and 14.4 Bq for 239 Pu and 289 Bq and 223 Bq for 241 Am for case-1 and case-2 respectively. A look at the initial urinary excretion data for the two cases showed that there was an enhancement in the urinary excretion rate of actinides due to Ca-DTPA and the excretion rates were found to be below MDA (<0.5mBq/day) at 90 days after exposure.
|Table 3: Results of urine analysis administered by Ca-DTPA aerosol of two acute intake cases|
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| 4. Conclusion|| |
The analysis of the data indicated that whole body counting is the method of choice for assessment of body burden due to 137 Cs instead of bioassay analysis. Urine bioassay is used for assessment of intake and CED due to 239 Pu and 241 Am. The two acute exposure cases of waste management facility are found to have insignificant level of intake/CED due to 137 Cs as compared to actinides. The assessed intakes were found to be 23.1 Bq and 14.4 Bq for 239 Pu and 289 Bq and 223 Bq for 241 Am respectively for case-1 and case-2. The total CED due to actinides intake was found to be 8.54 mSv and 6.48 mSv respectively for case-1 and case-2. The administration of Ca-DTPA aerosol was found to be effective as urinary excreted activity was below minimum detectable activity (0.5mBq/day) after 90 days from exposure. The CED due to the intake of radionuclides during this exposure scenario was estimated to be less than 40% of annual dose limit.
| 5. Acknowledgements|| |
The authors are thankful to Dr. P.K.Sarkar, Head, Health Physics Division for the guidance and Mr. H.S.Kushwaha, Director, HSEG for the continued encouragement in carrying out the work.
| 6. References|| |
- ICRP (1997), Individual monitoring of internal exposure of workers, ICRP-78.
- Piechowski J., Menoux B., Miele A., Grappin L., Guillermin A.M., Fottorino R.and Ruffin M., (2003), Implication of the company doctor and the expert in the management and the dosimetry of the incident of contamination: example of a wound contaminated by plutonium, Radioprotection, Vol.38 (1), 29-50.
- Ranjeet Kumar, Yadav J.R. and Lal Chand, (2005), Standardization of technique for separation of Plutonium in urine samples with tracer using anion exchange resin, Radiation Protection and Environment, Vol.28 (1-4), 264-265.
- Ranjeet Kumar, Yadav J.R., Rao D.D and Lal Chand, (2009), Determination of Uranium isotopes in urine samples from radiation workers using 232 U tracer, anion exchange resin and alpha spectrometry, Journal of Radio-analytical and Nuclear Chemistry, Vol. 279 (3), 787-790.
- Rudran K.(1969), A comparative study of electro-deposition of actinides from aqueous ammonium sulphate and isopropyl alcohol, AERE-R 5987, Health Physics and Medical Division, Atomic Energy Research Establishment, Harwell, Berkshire.
- Sharma, R.C., (1995), Internal dosimetry by whole body counting technique, Bulletin of Radiation Protection, Vol.18 (3), 34-47.
[Table 1], [Table 2], [Table 3]