Modelling of circulation and dispersion of radioactive pollutants in the Japan Sea

A large amount of radioactive waste was deposited in the Japan Sea, at a de pth of about 3 000 m by the former Soviet Union. Research was carried out t o determine to what extent the surface waters could be contaminated by poss ible leakage from the dumped containers. A three-dimensional, non-linear, b aroclinic model was used to determine the circulation and pollutant dispers ion. The computations were carried out in the diagnostic mode, taking into account data on winter and summer temperature and salinity distribution. Th ermohaline forcing due to strong temperatures and salinity gradients is the main forcing factor influencing the bottom circulation. Wind forcing and t he inflow/outflow surface currents were also taken into account. The simula ted velocity fields show relatively good agreement with observed surface cu rrents and with some measurements of bottom currents. The simulated hydrody namic field is in visibly closer agreement with the observed surface circul ation when topographic stress is taken into account. After the release of r adionuclides at the sea bottom, the first very small contamination would re ach the surface layers after 3 years. The maximum concentrations of about 1 0(-3) Bq .m(-3) would be attained after 30 years. But everywhere the predic ted radionuclide concentrations would be about two orders of magnitude smal ler than the background values, caused by global fallout from nuclear weapo ns tests. Therefore, it will be impossible to determine the effect of leaka ge of wastes from the dumping sites over the present background levels. (C) 2000 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.