Long-lived radionuclides in sea sediments around Kashiwazaki-Kariwa nuclear power station

Natural and artificial radionuclide concentrations in sea sediments around Kashiwazaki-Kariwa nuclear power station have been investigated with respect to the particle size distributions and the ignition losses during assay. Plutonium concentrations around the south and north discharge area, ranged from 0.054 to 0.24 Bq·kg-1 (average 0.145) and 0.15 to 0.25 Bq·kg-1 (average 0.213), respectively. Plutonium concentrations were significantly related to erosion and accumulation processes of sediments in both south and north discharges. Additionally, the ratios of 239Pu to 240Pu were evaluated with ICP-MS to determine the origin of the Pu-isotopes. Uranium-238, 232Th and 40K were found in concentration range of 7.3–67, 12–100 and 260–560 Bq·kg-1 with mean concentrations of 20, 29 and 390 Bq·kg-1, respectively. It is assumed that the relatively high concentrations of the natural radionuclides such as U and Th are due to the presence of minerals (the south discharge regions). On the basis of these results, the origin of the Pu-isotopes was assumed to be derived from fallout of the past atmospheric nuclear tests.