[3J09-12] Fukushima 2

[3J11] Investigation on distribution of radioactive substances in Fukushima

(11) Factors and long-term changes in Cs-137 concentrations in river-bottom sediments in Fukushima Prefecture

*Naoyuki Wada¹, Yuichi Onda¹ (1. Univ. of Tsukuba)

Keywords:Cs-137, River-bottom sediment, Suspended sediment, Distribution coefficient

The Fukushima Daiichi nuclear power plant accident in 2011 released large amounts of radioactive material, which was quickly deposited by rainfall. There have been few studies of Cs-137 in river-bottom sediments. In this study, we used long-term monitoring data collected by the Ministry of the Environment to show trends in the concentration of Cs-137 They found that the concentration would increase rapidly about a year. The rapid decrease was found to last 1-2 years longer than in the suspended sediment. One of the reasons for this difference is that high concentrations of sediment from upstream were deposited. It was also suggested that the Kd values changed due to ionic competition caused by the prolonged contact with the pore water.