Radioactive materials released into the sea by the March 2011 accident at the Fukushima Daiichi Nuclear Power Station had reached a spot in the Pacific Ocean about 3,200 km east of the coast of Fukushima Prefecture, a recent study has found.
Researchers, including those from the government’s Meteorological Research Institute and the Atmosphere and Ocean Research Institute at the University of Tokyo, will present the findings at a meeting of the Atomic Energy Society of Japan opening today in Higashihiroshima city in Hiroshima Prefecture.
Radioactive materials originating in the Tokyo Electric Power Co plant on the Pacific coast started to sink below the sea surface earlier this year and are likely to move southward in the future carried by deep-water currents, the study found.
The team collected seawater from about 300 spots in the northern Pacific from April last year through June.
They confirmed a cesium concentration of 10 Becquerels per tonne of seawater, or 5-10 times higher than the pre-crisis level, last December on the ocean surface about 2,500 km east of Fukushima.
The team also confirmed the presence of radioactive materials on the surface about 3,200 km east of the prefecture in March.
While the cesium concentration on the surface roughly came down to the pre-disaster level in June, a high concentration of about 9 Becquerels per tonne of seawater was confirmed at a depth of 300-400 meters in an area about 2,000 km east of the prefecture.
“Radioactive cesium started to sink from around January this year,” Michio Aoyama, a senior scientist at the meteorological institute said.
“It is likely that it will move southward in the future on sea currents that are different from those near the surface.”