PNNL

Abstract

Predictions of four risk assessment models, RESRAD, PRESTO, MMSOILS, and MEPAS, for a test scenario involving the migration of a single rapidly transforming radionuclide, Sr-90, and a persistent long transformation-chained radionuclide, U-234 and its progeny, in ground water are compared. All four models make comparable predictions for the flume centerline concentrations of the primary contaminants in the aquifer, for up to a distance of about 300 m for the source. MEPAS, MMSOILS, and RESRAD make similar predictions for the transfer profiles in the aquifer. There are considerable differences in the predictions of the four models for the temporal concentration profiles of he progeny in the aquifer. The profiles differ in shape, magnitude, = of the peak and in width; these differences are due to the simplifying assumptions made by each of the models