ESTIMATION OF RADIONUCLIDES CONCENTRATIONS IN THE OCEAN AT THE HYPOTHETICAL SUBMERGENCE OF FRESH MOX FUEL PACKAGE

Under INF code and IAEA standard, radioactive materials in Type B package are transported safely on the sea. To gain the supplementary public acceptance for these transports, environmental impact assessments have been made by assuming that a Type B package might be sunk into the sea. A method of the assessment consists of the estimation of release rates of radionuclide from a package, simulation of radionuclide concentration both in coastal and global areas, and dose assessment for the public. We summarized the radiological impact at the submergence of Type B packages, such as spent fuel (SF), PuO2 powder, high level wastes (HLW) and fresh mixed oxide (MOX) fuel in coastal areas. The evaluated dose equivalents by radiation exposure to the public for all materials were far below the limit of the ICRP recommendation (1mSv year-1). These assessments had a lot of uncertainties especially in the simulation of radionuclide concentration therefore the results might be overestimated. We developed more realistic methods to simulate both in coastal and global areas to explain the evaluated results of the impacts to the public in an efficient manner. General circulation models for the Japan Sea and for the world ocean were employed at coastal and global areas respectively. It is impossible to validate the method directly because no accident with release of radionuclide in the ocean has occurred. Therefore we simulated background radionuclide concentrations by fallouts (137Cs and 239,240Pu) to validate the methods. Fallouts were input into ocean by nuclear weapon test since 1945 and mainly in 1960s. And their concentrations in the ocean have been measured to keep monitoring the artificial contaminations now. Observed database is useful to compare with simulated results in both coastal and global areas. Simulated results were in good agreement with observation. And then, we simulated radionuclides concentrations at the hypothetical release from the submerged Type B package in the Japan Sea and global ocean. Simulated concentrations in the coastal and global areas were quite smaller than the background concentration by the fallouts.