2020 年 24 巻 2 号 p. 137-144
A large amount of radioactive Cs was released into the environment from the Fukushima Daiichi nuclear power plant (FDNPP) following the 2011 Great East Japan Earthquake. Nine years have passed since this accident, and the radioactive Cs concentration in seabed sediments has decreased. The behavior of radioactive Cs in coastal areas, however, is complicated due to the influence of rivers, waves and so on. The Japan Atomic Energy Agency has conducted several studies at the mouth of the Ukedo River. Here, we review previous studies and evaluate the impact of the radioactive Cs supplied by rivers using a sediment trap. In this study, a mooring system consisting of a sediment trap was installed in the Ukedo River estuary near the FDNPP in 2017. The results showed 137Cs flux in winter accounting for 60% of the annual flux. This suggests that mobilization of radioactive Cs in the coastal area is primarily due to resuspension and not river discharge.
