Analysis of oceanic dispersal of Cs derived from Fukushima Dai-ichi Nuclear Power Plant using the short-term emergency assessment system of marine environmental radioactivity

Ikenoue, Tsubasa  ; Kawamura, Hideyuki  ; Kamidaira, Yuki   

In this study, we analyzed the characteristics and trends of oceanic dispersal of Cs by performing the oceanic dispersion simulations using past oceanographic data received on the Short-Term Emergency Assessment system of Marine Environmental Radioactivity (STEAMER) developed at JAEA. Oceanic dispersion simulations in 1461 cases were carried out in the northwestern Pacific Ocean for 60 days from every day between 2015 and 2018. It was assumed that Cs was released into the ocean from the Fukushima Dai-ichi Nuclear Power Plant. In all calculation cases, the maximum concentration in 30 days at each computational grid (maximum concentration distribution) was calculated. Cs in the ocean surface in winter tended to be not dispersed so much. In the ocean surface, the seasonal variation was greater than the annual variation though the maximum concentration distributions have little annual variation. The average of the maximum concentration distribution in all calculation cases was inclined to be high from the coast of Fukushima to the offshore (140E-145E) and near the Kuroshio Extension.