The radionuclide migration forecasting system in the off Shimokita region has been developed to predict the routine and accidental releases of liquid radioactive wastes during the operations of a spent nuclear fuel reprocessing plant in Aomori Prefecture, Japan. The results obtained from the case studies are as follows. (1) The calculation results following the ocean general circulation model by using the techniques of data assimilation and nesting reproduce well the flow pattern of a coastal area. (2) The results of the hypothetical release of 3H show that the concentration of 3H is about 800 times higher at maximum than the background level at the off Hiranuma region (8 km south from the release point). (3) The 137Cs concentration of the hypothetical release from the off Shimokita region is the same or less than that of the background level measured at the same area.
