Evaluation of the impact of the 137Cs supply from rivers to coastal waters off Fukushima on the 137Cs behavior in seabed sediment

Abstract

The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) caused a radioactive contamination in seabed sediment. The 137Cs supply from rivers could be an important process for the long-term behavior of 137Cs in seabed sediment. In this study, a ten-year simulation of the 137Cs behavior in seabed sediment was conducted using an oceanic dispersion model combined with a prediction model of 137Cs behavior in land and river. In the waters north of FDNPP, the simulation results suggested that the 137Cs supply from rivers had a great impact on the concentrations in coastal sediment due to the initial low concentrations in seabed sediment and the large supply of 137Cs from rivers. In the waters near FDNPP and south of FDNPP, the simulation results suggested that the impact of the 137Cs supply on the temporal variation of 137Cs concentration in coastal sediment was relatively small due to the large initial adsorption from seawater. Overall, these results indicated that 137Cs supply from rivers had an impact on the spatiotemporal distribution of 137Cs concentrations in seabed sediment on a decadal time scale and the impact was especially great in the waters north of FDNPP.