Environmental modelling of radioactive contamination of floodplains and sorlakes along the Techa and Iset rivers

The radioactive contamination of the Techa–Iset rivers downstream from the MAYAK reservoirs has been determined by measurements of 90Sr, 137Cs and transuranic elements in floodplain soils and sorlake sediments. Empirical models for the spatial distribution of the radioactive contamination in the river system were developed by fitting the data to power and exponential functions. The radionuclide inventories calculated from the models were compared with Russian data. The models applied in this study predicted higher inventories than those obtained from the Russian data in the upper reaches of the Techa; but lower inventories were predicted for the downstream part of the river. Estimation of the 90Sr inventory is encumbered with larger uncertainties than those of 137Cs and 239,240Pu because the distribution of 90Sr does not always follow simple models as do 137Cs and Pu. The contamination downstream of MAYAK of the floodplain and Techa–Iset river system was estimated to be 0.1 PBq 90Sr, 0.3 PBq 137Cs and 0.8 TBq 239,240Pu. While essentially all the 137Cs and Pu outside the MAYAK reservoir are found in the Techa river, the 90Sr contamination extends further downstream.