Uncertainty analysis of doses from ingestion of plutonium and americium

Uncertainty analyses have been performed on the biokinetic model for americium currently used by the International Commission on Radiological Protection (ICRP), and the model for plutonium recently derived by Leggett, considering acute intakes by ingestion by adult members of the public. The analyses calculated distributions of doses per unit intake. Those parameters having the greatest impact on prospective doses were identified by sensitivity analysis; the most important were the fraction absorbed from the alimentary tract, f ₁, and rates of uptake from blood to bone surfaces. Probability distributions were selected based on the observed distribution of plutonium and americium in human subjects where possible; the distributions for f ₁ reflected uncertainty on the average value of this parameter for non-specified plutonium and americium compounds ingested by adult members of the public. The calculated distributions of effective doses for ingested ²³⁹Pu and ²⁴¹Am were well described by log-normal distributions, with doses varying by around a factor of 3 above and below the central values; the distributions contain the current ICRP Publication 67 dose coefficients for ingestion of ²³⁹Pu and ²⁴¹Am by adult members of the public. Uncertainty on f ₁ values had the greatest impact on doses, particularly effective dose. It is concluded that: (1) more precise data on f ₁ values would have a greater effect in reducing uncertainties on doses from ingested ²³⁹Pu and ²⁴¹Am, than reducing uncertainty on other model parameter values and (2) the results support the dose coefficients (Sv Bq ^-1 intake) derived by ICRP for ingestion of ²³⁹Pu and ²⁴¹Am by adult members of the public.