Long-term variation of Cs concentration due to the Fukushima Daiichi Nuclear Power Plant accident

Kawamura, Hideyuki  ; Kobayashi, Takuya ; Furuno, Akiko   ; Usui, Norihisa*; Kamachi, Masafumi*

In this study, we conducted numerical experiments on oceanic dispersion of Cs discharged from the Fukushima Daiichi Nuclear Power Plant (FNPP1) in the North Pacific. A oceanic dispersion model (SEA-GEARN) based on difference equations was used in order to clarify surface dispersion as well as intermediate dispersion of Cs. We used reanalysis data calculated by a three-dimensional variational data assimilation system (MOVE) developed at Meteorological Research Institute, Japan Meteorological Agency. It was suggested that highly polluted water discharged from the FNPP1 was efficiently diluted by meso-scale eddies in the Kuroshio extension region. Simultaneously, these meso-scale eddies played an important role to carry Cs into the intermediate layer in the Kuroshio extension region. The directly discharged Cs was fundamentally carried eastward and it attained at approximately 165W in August, 2012.