Estimation of total amounts of anthropogenic radionuclides in the Japan Sea

Ito, Toshimichi ; Otosaka, Shigeyoshi  ; Kawamura, Hideyuki  

The total amount of anthropogenic radionuclides - Sr, Cs and Pu - in the Japan Sea were estimated for the first time. Inventories of seawater, seabed sediment and total at each sampling site varied depending on the water depth of the sites, and the total inventories for Sr, Cs and Pu were in the range of 0.52-2.8 kBqm, 0.64-4.1 kBqm and 27-122 Bqm, respectively. Using the dependency of the seawater and seabed sediment and gridded water depth data, the total amounts in the Japan Sea were estimated to be about 1.20.4 PBq for Sr, 1.80.7 PBq for Cs and 6914 TBq for Pu, and their total was about 3.1 PBq. The amount ratio of these radionuclides (Sr : Cs : Pu) became to be 1.0 : 1.6 : 0.059 implying selective accumulation of the plutonium isotopes. This implication was supported by the balance between the existing and supplied amounts, in which the existing Sr and Cs were comparable for the supplied while the existing Pu exceeded the supplied in nearly 40 %. This work were performed using the observation data obtained through a wide-area research project, "Japan Sea Expeditions", carried out during 1997-2003 and covered the Japanese and Russian exclusive economic zones.