[M-AG24] 福島原発事故により放出された放射性核種の環境動態

[MAG24-P10] ダム湖における降雨時の土砂・セシウム137の挙動に対する感度解析

*操上 広志¹、北村 哲浩¹ (1.国立研究開発法人日本原子力研究開発機構)

キーワード：福島第一原子力発電所、ダム湖、感度解析、FLESCOT、セシウム、土砂

Investigations and simulations are important to understand sediment and radioactive cesium migration in reservoirs contaminated by the accident at the Fukushima Dai-ichi Nuclear Power Plant. In the previous study, we presented one- and two-dimensional simulations of sediment and radioactive cesium migration in the Ogaki Dam reservoir located in the middle reach of the Ukedo River and found that the reservoir played an important role to delay and buffer the movement of radioactive cesium in heavy rainfall events and that the buffer effect depended on particle sizes of suspended sediment and the water level in the reservoir. In this study, to understand the sensitivity of intensity and duration of flood events to discharges of sediment and radioactive cesium during flood events, we performed sensitivity analyses by using the FLESCOT code, a three-dimensional finite volume model developed by the Pacific Northwest National Laboratory. It considers turbulent water flow and transports of multi-size sediment and radioactive cesium both in dissolved and particulate forms. The results showed that the discharge proportions depended on sediment size, event intensity and event duration. The proportions of sediment/¹³⁷Cs discharges increase, as event duration is shorter/heavier. The silt component is a main carrier of radioactive cesium in larger events, while the clay-sorbed and dissolved forms are dominant in smaller events. In heavier events, resuspention of bed sediment took place.