Potential remobilization of 137Cs, 60Co, 99Tc and 90Sr from contaminated Mayak sediments river and estuary environments

Following 50 years of nuclear production at Mayak PA, sediments in storage reservoirs are significantly contaminated. Dam failure or flooding could potentially transport large amounts of sediments, via rivers, to the Ob estuary and Kara Sea. The objectives of this work were to investigate fresh and seawater remobilization of (CS)-C-137, (CO)-C-60, Tc-99, and (90-) Sr from contaminated Reservoir 10 sediments. Sediments were extracted sequentially using synthetic Techa freshwater, seawater, and chemical reagents with increasing dissolution powers. Cs-137 and Sr-90 freshwater distribution coefficients (apparent Kd) agreed quite well with published values; values for Tc-99 were higher and values for Co-60 were lower than expected, In seawater, mean apparent Kd values decreased by 94, 77, 48, and 73% ( (137)cs, Co-60, 99 Tc, and Sr-90, respectively), indicating increased radionuclide mobility. Remobilization in seawater was 5, 15, 1, and 23% of total activities (i.e., releases of 165, 11, 0.3, and 170 kBq kg(-1) d.w.) for Cs-137, Co-60, Tc-99, and Sr-90, respectively. Cs-137 and Tc-99 were strongly bound to sediments (60% and 80%, respectively). Co-60 and Sr-90 were more mobile (70% reversibly bound), In conclusion, Mayak Reservoir sediments could potentially contaminate the Ob estuary due to remobilization of sediment-held radionuclides upon contact with seawater.