Development of an Inhalation Intake Model for 241Am Based on Mayak Production Association Worker Data

Abstract

VAmericium-241 is a significant radiation hazard at facilities that handle or reprocess spent nuclear fuels. An inhalation intake model for 241 Am was developed using autopsy data obtained from former workers at the Radiochemical and Plutonium Production Plants at the Mayak Production Association (Mayak PA), Ozyorsk, Russia. Accumulation of 241 Am in the body can occur though direct exposure to 241 Am (termed here ''exogenous'' exposures), usually as an inhaled aerosol, or though exposure to 241 Pu that decays inside the body to 241 Am (termed here ''endogenous'' exposures). Metabolism of endogenous and exogenous 241 Am can differ, with endogenous 241 Am being initially related to the behavior of 241 Pu. For the model, it was assumed that intakes of 241 Am and 241 Pu were functionally associated with intakes of 239 Pu. The current Mayak Worker Dosimetry System model (MWDS-2008) was used to describe metabolism of plutonium and americium in the respiratory tract. The ICRP-30 model was used for the gastrointestinal tract, the ICRP-67 model was used for metabolism after absorption into the blood for americium, and the ''Leggett modification'' of the ICRP-67 model for plutonium was used for systemic, non-pulmonary organs. The proposed inhalation intake model for americium provides estimates for internal doses from 241 Am from both exogenous and endogenous sources. Health Phys. 105(1):21Y30; 2013

ICRP Publication 141: Occupational Intakes of Radionuclides: Part 4

“…For the three transportability categories, ∼14 y after exposure, the fraction of body americium retained in the lungs was slightly less than that of plutonium, but the difference was not statistically significant. Sokolova et al. (2013) confirmed that applying the plutonium absorption parameters to americium resulted in overestimation of the americium lung burden by 48%, on average, over 456 autopsied cases, suggesting slightly faster lung clearance for americium than for plutonium. (908) Informal feedback from French decommissioning worksites is that the dissolution kinetics of an americium and plutonium mixture is intermediate between Type M of americium oxide and Type S of plutonium oxide (SFMT, 2011).…”

“…Notable differences in the systemic behaviours of these two elements include an initially higher rate of urinary excretion of americium and faster removal of americium from the liver. There are also differences in the sites of deposition of americium and plutonium on bone surfaces, and perhaps associated differences in the net rate of removal of these elements from bone. (940) Sokolova et al. (2013, 2014) assessed the potential contributions of direct intake and in-vivo production of 241 Am to its total body content in a group of workers at the Mayak Production Association.…”

“…(940) Sokolova et al. (2013, 2014) assessed the potential contributions of direct intake and in-vivo production of 241 Am to its total body content in a group of workers at the Mayak Production Association.…”

Updated biokinetic model for systemic americium

“…not mixed with a significant amount of its parent 241 Pu) are preferred for modelling Am kinetics but are available only for a relatively small number of subjects, some of whom received chelation therapy (Whalen and Davies 1972, Wrenn et al 1972, Fry 1976, Rosen et al 1980, Heid and Robinson 1985, Breitenstein and Palmer 1989, Doerfel and Oliveira 1989, Kathren et al 2003, Fotjik et al 2003, Malátová et al 2003, 2010. More extensive observations are available for workers whose systemic 241 Am burdens are thought to have resulted from ingrowth of 241 Am in the body following intake of 241 Pu, or from some combination of ingrowth from deposited 241 Pu and direct intake of small amounts of 241 Am (Lynch et al 1989, Popplewell and Ham 1989, Kathren and McInroy 1992, Kathren et al 1988, Suslova et al 2013. Data for Pu workers with little potential for direct intake of 241 Am suggest that ingrown 241 Am migrates from its parent 241 Pu over time, resulting in a urinary excretion rate and a skeleton to liver activity ratio (i.e.…”

“…Thus, 241 Am produced in vivo by decay of 241 Pu may reflect some combination of the biokinetic characteristics of Am and distinctive characteristics of Pu. Sokolova et al (2013Sokolova et al ( , 2014 assessed the potential contributions of direct intake and in vivo production of 241 Am to its total body content in workers at the Mayak Production Association. The analysis was based on autopsy data, biokinetic models for Pu and Am, and consideration of the relative concentrations of 241 Am and Pu isotopes in air over time at different work locations at Mayak.…”