Abstract
Deposition of 134Cs, 137Cs and other fallout nuclides was observed at PNC O-arai Engineering Center in May 1986 after Chernobyl accident. The fallout radionuclides, especially 90Sr and 137Cs in lake water, sediments and fish have been measured in Lake Hinuma located 2km north-west of the Center since 1986 in order to investigate migration behavior of these nuclides in lake ecosystem. In August 1986, the 137Cs in sediments was irregularly distributed at each sampling point in Lake Hinuma. It was different from distributions of 239, 240Pu and 241Am, which showed that concentrations at center of the lake were higher than that near the shore in 1986. Horizontal distributions of 137Cs in sediments then shifted to similar distribution of 239, 240Pu by 1989. The 137Cs concentrations in sediment showed a tendency to increase slightly in 1987 and 1988 and then to decrease. An apparent half-life of 137Cs in sediment was derived from field data as approximately 3 years. Distribution coefficient (Kd) for 90Sr in sediments, a ratio of the concentration of 90Sr in dry sediment to that in water, was approximately 90(l/kg) as 50% value in cumulative probability distribution of observed KdS. Concentration Factors (CFs) for 90Sr were from 4 to 45(l/kg) in edible parts of fishes (Haze, Ugui and Wakasagi).
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