Model testing of radioactive contamination by 90Sr, 137Cs and 239,240Pu of water and bottom sediments in the Techa River (Southern Urals, Russia)

This paper presents results of testing models for the radioactive contamination of river water and bottom sediments by Sr-90, Cs-137 and Pu-239,Pu-240. The scenario for the model testing was based on data from the Techa River (Southern Urals, Russia), which was contaminated as a result of discharges of liquid radioactive waste into the liver. The endpoints of the scenario were model predictions of the activity concentrations of Sr-90, Cs-137 and Pu-239,Pu-240 in water and bottom sediments along the Techa River in 1996. Calculations for the Techa scenario were performed by six participant teams from France (model CASTEAUR), Italy (model MARTE), Russia (models TRANSFER-2, CASSANDRA, GIDRO-W) and Ukraine (model RIVTOX), all using different models. As a whole, the radionuclide predictions for Sr-90 in water for all considered models, Cs-137 for MARTE and TRANSFER-2, and Pu-239,Pu-240 for TRANSFER-2 and CASSANDRA can be considered sufficiently reliable, whereas the prediction for sediments should be considered cautiously. At the same time the CASTEAUR and RIVTOX models estimate the activity concentrations of Cs-137 and Pu-239,Pu-240 in water more reliably than in bottom sediments. The models MARTE (Pu-239,Pu-240) and CASSANDRA (137Cs) evaluated the activity concentrations of radionuclides in sediments with about the same agreement with observations as for water. For Sr-90 and Cs-137 the agreement between empirical data and model predictions was good, but not for all the observations of Pu-239,Pu-240 in the river water-bottom sediment system. The modelling of Pu-239,Pu-240 distribution proved difficult because, in contrast to Cs-137 and Sr-90, most of models have not been previously tested or validated for plutonium. (C) 2008 Elsevier B.V. All rights reserved.