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Integrated watershed modeling for simulation of spatiotemporal redistribution of post-fallout radionuclides: Application in radiocesium fate and transport processes derived from the Fukushima accidents

Mori, Koji, Tada, Kazuhiro, Tawara, Yasuhiro, Ohno, Koichi, Asami, Mari, Kosaka, Koji, Tosaka, Hiroyuki
Environmental modelling & software 2015 v.72 pp. 126-146
accidents, aquifers, basins, cesium, computer software, hydrologic models, nuclear power, power plants, radionuclides, sediments, simulation models, surface water, suspended sediment, watersheds
Simulation of the watershed-scale fate and transport of radionuclides is required in order to predict the consequences of contamination redistribution. Integrated watershed modeling is a suitable technique for this task, but it requires fully coupled investigation of radionuclide behavior in surface water, suspended sediment and subsurface aquifers. We developed a novel simulator for computing the spatiotemporal redistribution of fallout radionuclides in watersheds. The simulator was applied to an actual reservoir basin contaminated by fallout radionuclides from the Fukushima Dai-Ichi Nuclear Power Plant accident in 2011. As a result, the simulated 137Cs concentration in bottom sediment showed a reasonably close match with the measurement data. The distribution coefficient of 137Cs consistent with the latest measurement data was identified as being at least 400,000 L/kg, and it was estimated that more than 90% of the total 137Cs distributed in the fallout remains in the catchment area.