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U.S. Transuranium and Uranium Registries Conference Contributions

2020 Health Physics Society Virtual Workshop, September 10 – October 21, 2020

The Health Physics Society replaced its traditional in-person meeting with the 2020 Virtual Workshop, which spanned several weeks. USTUR faculty members were authors on one presentation, which was given by Deepesh Poudel of Los Alamos National Laboratory on September 17th.

Long-term retention of plutonium in the respiratory tracts of two acutely-exposed workers

Deepesh Poudel (LANL), Maia Avtandilashvili (USTUR), Luiz Bertelli (LANL), John A. Klumpp (LANL), Sergei Y. Tolmachev (USTUR)

Inhalation of plutonium is a significant contributor of occupational doses in plutonium production, nuclear fuel reprocessing, and cleanup operations. Accurate assessment of the residence time of plutonium in the lungs is important to properly characterize dose, and consequently the risk, from inhalation of plutonium aerosols. This presentation discusses the long-term retention of plutonium in different parts of the respiratory tract of two workers, who donated their bodies to the US Transuranium and Uranium Registries. Comparison of the activity concentration and total activity in the lungs and the thoracic lymph nodes provided information on the long-term solubility of the material inhaled. The materials inhaled by both workers were found to have solubility in between that of plutonium nitrates and oxides. The post-mortem tissue radiochemical analysis results, along with the urine bioassay data, were interpreted using Markov Chain Monte Carlo and the latest biokinetic models presented in the Occupational Intakes of Radionuclides series of ICRP publications. The data from these two individuals can be explained by assuming a bound fraction (fraction of plutonium deposited in the respiratory tract that becomes bound to lung tissue after dissolution, fb) of 1% and 4%, without having to significantly alter the particle clearance parameters. Effect of different assumptions about the bound fraction on radiation doses to different target regions was also investigated. For inhalation of soluble materials, an assumption of fb of 1%, compared to the ICRP default of 0.2%, increases the dose to the most sensitive target region of the respiratory tract by 258% and that to the total lung by 116%. Possible alternate methods of explaining higher-than-expected long-term retention of plutonium in the upper respiratory tract of these individuals – such as uptake by lungs, and material sequestration into the scar tissues – are also discussed. [USTUR-0543-20A]