estimated ratio at NTS is only about 100. The designation of lungs and bone as critical organs was based on radiation dose calculations which showed these two organs receiving the highest dose, after 70 years, of all organs for which radiation dose criteria have been established by the International Commission on Radiological Protection (ICRP). The calculated dose to lymph nodes was higher but ICRP has not established dose criteria for lymph nodes. The results of these dose calculations are shown in Figure 2 (Martin and Bloom, 1977). Table 1. Fractions of 739Pu in Bone, Liver, or Kidney Due to Chronic Ingegtjon and Inhalation for a Period of 50 Years Fraction Due Fraction Due 1 0.0005 0.9995 10 0.0053 0.9947 100°? 0.0506 0.9494 200 0.0964 0.9036 400 0.1758 0.8242 1000 0.3478 0.6522 Ingestion/Inhalation (a) (b) to Ingestion to Inhalation Estimated burdens based on ICRP Publications 2 and 19. Estimated ratio at the Nevada Test Site. The previous calculations are subject to considerable uncertainty due to variations in source term and parameters in the models. These variations result from uncertainties in sampling, measuring, and interpreting plutonium levels in laboratory experiments and in the environment. A detailed analysis of the effects of all these variations would be a prohibitively large task. Fortunately, this is not necessary since it has been shown that the most significant effects of these variations are directed toward the inhalation pathway and the radiation dose to lungs and bone. This report examines these parts of the model by developing simplified equations that are valid for periods of exposure greater than about 19 years and exploring the effects of these variations on this simpler model. 516