Mid- to long-term radiocesium wash-off from contaminated catchments at Chernobyl and Fukushima

We analyzed mid- to long-term Cs-137 wash-off from the catchments contaminated due to the Chernobyl accident in 1986 and the Fukushima Dai-ichi Nuclear Power Plant accident in 2011. A semi-empirical diffusional model for radionuclide wash-off is proposed to enable estimation of the dissolved and particulate Cs-137 wash-off ratios for the Chernobyl and Fukushima contaminated catchments; the differences in the wash-off characteristics for these two regions are explained and their long-term trends predicted. The model is based on the premise that the catchment topsoil layer is the source of sediments in the rivers, and the radionuclide concentration in the topsoil can be described by a simple diffusion equation. The particulate Cs-137 wash-off ratios for the Fukushima contaminated catchments appear to be comparable or slightly lower than those for Chernobyl. The dissolved Cs-137 wash-off ratios for Fukushima catchments are at least an order of magnitude lower than those for Chernobyl, mainly due to an order of magnitude difference in the Cs-137 distribution coefficients for the Fukushima and Chernobyl rivers. The proposed semi-empirical diffusional model for radionuclide wash-off satisfactorily describes the temporal trends in the Cs-137 wash-off characteristics for both the Chernobyl and Fukushima cases, and can be used as a tool for predicting Cs-137 wash-off after a nuclear accident. (C) 2020 The Author(s). Published by Elsevier Ltd.