ESTIMATING INTERNAL DOSE DUE TO INGESTION OF RADIONUCLIDES FROM NEVADA TEST SITE FALLOUT

The U.S. Department of Energy initiated the Radiation Exposure Review Project to provide a critical reexamination of radiation doses to peop le resulting from testing nuclear devices at the Nevada Test Site. One part of this effort focused on the dose resulting from the ingestion of contaminated food. The PATHWAY radionuclide transport model was dev eloped to provide estimates of food concentrations for 20 radionuclide s for each of 86 test events and 15 agricultural scenarios. These resu lts were then used as input to the Human Ingestion model to provide do se estimates for individuals and populations in 9 western states. The model considered the life-style and age of the people, and accounted f or the transport of milk between locations. Estimates of uncertainty w ere provided for all doses using Monte Carlo simulation techniques. Pr opagation of uncertainty between the PATHWAY model and the Human Inges tion model required the development of special strategies to ensure th at the inherent correlations between concentrations of the radionuclid es in foods were handled properly. In addition, the size of the input data base (60 megabytes), the number of cases to consider (over 30,000 ), and the number of Monte Carlo simulations (over 6 million) required the development of efficient and reliable methods of data access and storage while running simulations concurrently on up to 14 UNIX workst ations. The problems encountered in this effort are likely to be typic al of any dose reconstruction involving geographically heterogeneous e nvironmental conditions. This paper documents the methods used to disa ggregate the system to achieve computation efficiency, the methods use d to propagate uncertainty through the model system, and the technique s used to manage data in a distributed computing environment. The radi onuclide- and age-specific dose factors used in the analysis are also provided.