PNNL

Abstract

Two major areas of emphasis in the BIOMASS (Biosphere Modelling and Assessment Methods) programme were the improvement of the accuracy of model predictions and the improvement of modelling procedures within the general area of environmental assessment. Theme 2 of BIOMASS, Environmental Releases, focused specifically on issues of dose reconstruction and remediation assessment. Within Theme 2, the Dose Reconstruction Working Group was concerned with the evaluation of the reliability of methods and models used for dose reconstruction for specific individuals and members of specific population subgroups. The Dose Reconstruction Working Group of BIOMASS carried out model testing exercises. The present paper describes the first one, which was based on an accidental release of 131I from the Hanford Purex Chemical Separations Plant in the northwestern United States in September 1963 (BIOMASS, 1999). The scenario made use of monitoring data originally collected during the two months following the release (Soldat, 1965) and further evaluated as part of the Hanford Environmental Dose Reconstruction (HEDR) project in the 1990s (Farris et al., 1994). Radioiodine releases are important for many radiation accidents, and because data on the results of these releases are often incomplete, models for estimating 131I transport and exposure are essential in dose reconstruction efforts. The Hanford scenario therefore provided a valuable opportunity to intercompare modelling approaches and model predictions among several assessors, to compare model predictions with data, and to identify the most important sources of bias and uncertainty in the model results.