Distribution of Pu isotopes in marine sediments in the Pacific 30 km off Fukushima after the Fukushima Daiichi nuclear power plant accident

Abstract

Copyright © 2012 by The Geochemical Society of Japan. in seawater in the immediate vicinity of the Fukushima DNPP (TEPCO, 2011). From the analysis of 131I/137Cs activity ratios, Tsumune et al. (2012) found that the direct release of radioactive liquid wastes into the ocean started on March 26, 2011, and the direct release from the plant site contributed more to the measured 137Cs concentration than atmospheric deposition did. Using a regional ocean model, they further estimated that from March 26 to the end of May, the total amount of 137Cs directly released was 3.5 ± 0.7 PBq. In May–June, 2011, accident-released 134Cs and 137Cs were already being observed in coastal seawater along the Northern Sanriku coast and Tsugaru Strait, 250–450 km north of the Fukushima DNPP (Inoue et al., 2012). Honda et al. (2012) studied the distribution of 134Cs and 137Cs in surface seawater in the western North Pacific one month after the accident and found that accident-released radionuclides were distributed widely in the western North Pacific. The 137Cs observed there was transported not only by diffusion and advection of seawater but also via the atmosphere as an aerosol after the accident. Honda et al. (2012) estimated the deposition of 137Cs into the sea surface via the atmosphere was 0.18 PBq, which is smaller than the deposition of ca. 5 PBq estimated by Kawamura et al. (2011) using a numerical simulation. Distribution of Pu isotopes in marine sediments in the Pacific 30 km off Fukushima after the Fukushima Daiichi nuclear power plant accident