It is difficult at present to verify the distribution of radioactivities and to estimate their accumulation trends only from the results of environmental monitoring because of quite low level of effluent from nuclear power plants. Therefore, a mathematical model was developed to support the environmental monitoring as well as to predict the accumulation trends of radioactivities discharged into the environment. Then the model was simulated by applying on the behavior of
60Co released from the nuclear power station located in the coast of Uchiura Bay, a part of Wakasa Bay.
The mathematical expression is composed of an estimation model for distribution of current velocities based on the results of field observations, a diffusion equation including the terms of advection, diffusion, appearance and disappearance, and a box model applied for some reaches. Adsorption on sediment and effect of scavenging are also taken into consideration. Details of the model are described in this paper and the validity is checked and discussed. The results of verification draw the conclusions as follows:
(1) On the concentration of
60Co in the sediment only detectable near the discharge point, the values estimated and observed were agreed within a factor of three.
(2) It was estimated that the half amount of
60Co released during 8yr after 1974 is accumulated in the bay sediment, whereas the other is lost away from the bay.
(3) The results of calculation showing no increase of accumulation at 1982 suggest nonprogressive accumulation in the future.
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