Pu distribution in seawater in the near coastal area off Fukushima after the Fukushima Daiichi Nuclear Power Plant accident

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released large amount of radionuclides into the marine environment. Compared with the fission products, data on the distributions of Pu in the marine environment of the western North Pacific after the accident is limited. To better understand the Pu contamination in the marine environment after the accident, for the first time, we determined Pu isotope ratio (²⁴⁰Pu/²³⁹Pu) in addition to ^239+240Pu activity in seawater collected in the near coastal area (mostly within the 30 km zone) off the FDNPP site. The ^239+240Pu activities were 4.16-5.52 mBq/m³ and the ²⁴⁰Pu/²³⁹Pu atom ratios varied from 0.221 to 0.295. These values were compared with the baseline data for Pu distribution in the near coast seawaters before the FDNPP accident (2008-2010). The results suggested that there is no significant Pu contamination in seawater in the near coastal area off the FDNPP site from the accident two years after the accident. (author)