Dispersion and accumulation of radionuclides in sediment of Urazoko Bay, (1)

Contents of 90Sr, 137Cs and 60Co in surface sediments were investigated in and around Urazoko Bay, Fukui Prefecture, where a nuclear power plant has been operating since 1969 and the waste effluent has been released into the sea. The main source of 90Sr and 137Cs was recognized to be radioactive fallout, whereas 60Co was considered to originate from the nuclear power plant. Using the 137Cs concentration as an indicator of sorption capacity of the sediment, the behaviour of 60Co was investigated. No seasonal variation was observed in the distribution pattern of 60Co/137Cs ratio and the retention of the heavy initial discharge in 1969 was considered to dominate the radionuclide level in the sediment. Correlation of 60Co/137Cs ratio in the sediment and the distance from the discharge outlet was expressed by a simple exponential function of the distance. It was suggested that the contamination is spreading out gradually to the outer region of Urazoko Bay. (auth.)