Improvement of cesium diffusion analysis in Tokyo Bay

The object of this study is to predict the distribution of cesium deposited on the bottom of Tokyo Bay by means of the Hybrid Box Model linked with a diffusion model, released by Fukushima Daiichi Nuclear Power Plant. On the basis of the load fluxes from rivers, the distribution of concentration (separately for dis-solved cesium and small and large particulate cesium) in seawater and the mass of cesium sedimentation to the bottom of the bay were calculated by the models. Results were compared to the published observation data in order to examine the applicability of the used models. Estimated cesium concentrations in the sediment show good agreement with the observed data. From the analysis, it was estimated that 61% of the cesium inflow into the bay is deposited onto the bottom, and that 21% flow out of the bay. Cesium sedimentation is greater in the inner and middle parts of the bay, and decreases in the direction toward the bay entrance. (author)