5:15 PM - 7:15 PM
[MAG34-P03] Numerical Simulation of the Transfer of Radiocaesium in a River
Keywords:River, 1-D Finite element method simulation, Cs-137
The accident at the Fukushima Daiichi Nuclear Power Plant of the Tokyo Electric Power Company in March 2011 released radioactive nuclides such as Cs-137 into the environment. Since cesium is strongly adsorbed by soil particles, much of the released Cs-137 remains in terrestrial areas such as forests. It was thought that this could flow into rivers due to rainfall and, as a result, move into residential areas. For these reasons, it became important to understand the dynamics of Cs-137 in rivers.
In this study, we conducted a numerical simulation of the behavior of Cs-137 in the Hirose River, which flows through the Nakadori region of Fukushima Prefecture. Using the actual measurement data obtained from five observation points on the main stream of the Hirose River and four observation points on major tributaries, we applied the TODAM model, which is a type of one-dimensional finite element method model, and obtained results that reproduced the actual measurement data for flow rate, suspended sediment concentration, suspended and dissolved Cs concentration well.
In this study, in addition to the four tributaries with observation points, seven relatively large tributaries were added to the calculation section. The discharge from these tributaries was established by reproducing the flow rate, suspended sediment concentration, and dissolved and suspended Cs-137 concentrations at three verification points on the main river. The inflow from the tributaries located upstream was set to be high, while the inflow from the tributaries located downstream was set to be low. This was consistent with the distribution of the measured precipitation. It was also estimated that water with a high dissolved Cs-137 concentration of about 20 mBq/L flowed into the tributary located upstream before the water level began to rise. This was consistent with the phenomenon seen in mountain streams that flow out of forests immediately after the start of rainfall.
In this study, we conducted a numerical simulation of the behavior of Cs-137 in the Hirose River, which flows through the Nakadori region of Fukushima Prefecture. Using the actual measurement data obtained from five observation points on the main stream of the Hirose River and four observation points on major tributaries, we applied the TODAM model, which is a type of one-dimensional finite element method model, and obtained results that reproduced the actual measurement data for flow rate, suspended sediment concentration, suspended and dissolved Cs concentration well.
In this study, in addition to the four tributaries with observation points, seven relatively large tributaries were added to the calculation section. The discharge from these tributaries was established by reproducing the flow rate, suspended sediment concentration, and dissolved and suspended Cs-137 concentrations at three verification points on the main river. The inflow from the tributaries located upstream was set to be high, while the inflow from the tributaries located downstream was set to be low. This was consistent with the distribution of the measured precipitation. It was also estimated that water with a high dissolved Cs-137 concentration of about 20 mBq/L flowed into the tributary located upstream before the water level began to rise. This was consistent with the phenomenon seen in mountain streams that flow out of forests immediately after the start of rainfall.