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U.S. Transuranium and Uranium Registries Conference Contributions

Health Physics Society Meeting, Salt Lake City, UT, June 26 – July 1, 2010

Idaho State University (ISU) student, Maia Avtandilashvili, presented progress toward her PhD research at the 55th Annual Meeting of the Health Physics Society in Salt Lake City, UT, June 26- July 1, 2010. Ms. Avtandilashvili is a member of the USTUR/ISU Internal Dosimetry Research Team, and is using Bayesian techniques to study the biokinetics of accidentally inhaled refractory PuO2 in USTUR Registrants.

Health Physics Society

Bayesian analysis of bioassay and autopsy data from 18-y follow-up of an acute accidental inhalation of refractory PuO2
M. Avtandilashvili (ISU), A.C. James (USTUR), A. Birchall (HPA), M. Puncher (HPA), D. Gregoratto (HPA-RPD), R. Brey (ISU)

The International Commission on Radiological Protection (ICRP) is currently reviewing and updating the Human Respiratory Tract Model (HRTM) recommended in Publication 66. It is important to test proposed changes to the HRTM against human data. Case 0202 was the highest exposed of 18 U.S. Transuranium and Uranium Registries’ tissue donors involved in the 1965 Pu fire at the Rocky Flats Plant. This study analyzed the extensive bioassay data (counts of 241Am activity in the lungs and urinary excretion of Pu through 8 y after intake) and radiochemical analysis in tissues sampled at autopsy (18 y after intake) to evaluate the applicability of the current ICRP model and a proposed revision to represent these data. Substantial revision of the HRTM structure and parameter values are needed to represent the exceptionally long retention of plutonium particles in the lungs observed in this case. Particle transport from the AI region to the bronchioles occurred in two distinct phases: 20% of the initial alveolar deposition was cleared with a half-time of about 100 d and 80% was cleared very slowly (half-time about 60 y). About ⅓. of this material was cleared to the bronchioles and ⅔ to the thoracic lymph nodes. With appropriate adjustments of AI deposition fractionation and associated particle transport rates, the simplified particle transport model derived recently by Gregoratto et al. yielded an excellent fit to all of the Case 0202 data. The PuO2 particles produced by the fire are extremely insoluble. About 0.6% of 238/239Pu is absorbed from the respiratory tract relatively rapidly, with a half-time of about 8 h. The remainder (99.4%) is absorbed extremely slowly (half-time about 400 y). About 97% of the total committed weighted dose equivalent is contributed by the lungs. The committed weighted dose equivalent per unit intake (about 9 x 10-5 Sv Bq-1) is an order of magnitude higher than the recommended dose coefficient for Type S plutonium (8.4 x 10-6). Bayesian analysis was used to calculate the posterior probability distributions of critical parameter values for the different models tested. This worker’s prior occupational exposure to coal dust (and prior lung disease) are likely to have impaired lung clearance, and thus contributed to the high lung tissue doses (3 Gy to his alveolar-interstitial tissue and 6 Gy to his thoracic lymph nodes). [USTUR-0289-10]

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