A computational study of dose coefficients for 239Pu

This paper presents the results of a computational study of dose coefficients for 239Pu. The procedure involved solutions of complete compartmental models that describe the biokinetic behaviour of inhaled plutonium aerosols in the human body. Two complete compartmental models were constructed by integrating the respiratory tract and gastro-intestinal (GI) tract models through the transfer compartment, namely, blood, with the two-biokinetic models of plutonium - the new and old given in ICRP publications 67 and 30 respectively. The solutions of the models were obtained by solving the related first order differential equations with constant coefficients. For this purpose a computer method based on an algorithm that uses matrix algebra was adapted from the published literature. The computed values of dose coefficients for 239Pu were found to match very well with those given: (a) by ICRP in its publication 68 for the new biokinetic model and (b) by LUDEP 2.05 for the old biokinetic model, and thus validated the computational procedure employed. Interestingly, the use of more realistic new biokinetic model of plutonium, which involves recycling, yielded results similar to those of the old (ICRP-30) model. The investigations of the dependence of dose coefficients for 239Pu on transfer rates given in the complete compartmental models brought out their relative insensitivity to the magnitudes of transfer coefficients in the new as well as old biokinetic models. The variations in the dose coefficient values for the default transfer rates modified by factors 2 and 4 respectively, were mostly found to be well within ±20% except for a few of the parameters: (a) in the respiratory tract model for both Types (M and S) of plutonium and (b) in the biokinetic model for Type M plutonium. These findings have ramifications in individual specific dose assessments. (author)