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

¹ Japan Atomic Energy Agency, 2-4 Shirakata, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
² Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan

^* Corresponding author: ikenoue.tsubasa@jaea.go.jp

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.