Monitoring of low-level radioactive liquid effluent in Tokai reprocessing plant

Mizutani, Tomoko ; Koarashi, Jun   ; Takeishi, Minoru 

Tokai reprocessing plant (TRP) has discharged low-level liquid-wastes to the Pacific Ocean since the start of its operation in 1977. We have performed the liquid effluent monitoring to realize an appropriate radioactive discharge control. Comparing simple and rapid analytical methods with labor-intensive radiochemical analyses demonstrated that the gross-alpha and gross-beta activities agreed well with the total activities of plutonium (Pu) isotopes and major beta-emitters (e.g. Sr and Cs), respectively. The records of the radioactive liquid discharge from the TRP showed that the normalized releases of all nuclides, except for H, were three or four orders of magnitude lower than those from the oversea reprocessing plants. This was probably due to the installation of multi-stage evaporators in the liquid waste treatment process in 1980. Plutonium radioactivity ratios (Pu/Pu) of the liquid effluents were determined to be 1.3-3.7, while those of the seabed sediment samples collected around the discharge point were 0.003-0.059, indicating no remarkable accumulation of Pu in the regional aquatic environment. The annual public doses were estimated to be less than 0.2 Sv y from the aquatic pathway. Thus, we concluded that there were no significant radiological effects on the aquatic environment and the public during the past 30-year operation of the TRP.