Abstract
In order to assess the concentrations of radioactive substances in river basins contaminated by such substances released through the Fukushima Daiichi nuclear power plant accident in March 2011, a watershed model was developed. The model, improved on the basis of the AIST-SHANEL software, can estimate indexes such as the river water concentration and deposition amount of radioactive cesium in river basins after the accident using a submodel for estimating suspended solids and the radioactive cesium load in runoff water. In this study, we carried out some case studies by applying the model to the Abukuma River basin. Two major results were obtained. The model was valid for the estimation of the concentration of radioactive cesium, and the radioactive cesium load in the runoff water was quite low. In particular, for cesium 137, its natural elimination rate is low owing to its long half-life. As a result, the deposition amount of radioactive cesium in river basins would only negligibly decrease. Therefore, we suggest a need for the comprehensive examination of all measures of reducing radioactive cesium including decontamination. The model is useful for evaluating the temporal-spatial concentrations of and the impact of control policies for radioactive substances in river basins associated with nuclear accidents.
