[AHW24-P09] Migration Behavior of Radiocesium Derived from the Fukushima Dai-Ichi Nuclear Power Plant Accident in Natsui River and Tone River
キーワード：Radioactive Cesium, River water, Suspended solids, Fukushima Dai-ichi Nuclear Power Plant
The accident of Fukushima Dai-ichi Nuclear Power Plant due to the Tohoku earthquake, which occurred on 11 March 2011, has released a large amount of radioactive materials to the atmosphere. This accident resulted contamination of radioactive cesium (134Cs and 137Cs) on land, rivers and sea around Fukushima Prefecture. Radioactive cesium widely deposited on land and transported from watershed through river system to the ocean. In this study concentration of 134Cs and 137Cs in river water has been investigated for dissolved and particulate phase. River water sample was collected at a fixed station from the Tone River and the Natsui River at normal and high flow condition during 2018-2019. Suspended solids were separated using continuous flow centrifugation and dissolved cesium were co-precipitated using ammonium molybdophosphate (AMP) method.
The AMP precipitated and suspended solids were dried to determined radioactive cesium concentration using HPGe gamma spectrometry. Investigations of cesium concentration in the rivers have been performed to understand factors controlling transport of radiocesium during different condition. The maximum concentration of 134Cs and 137Cs at normal condition was 0.7 mBq L-1and 7.9 mBq L-1in the Tone River, and 1.1 mBq L-1and 11 mBq L-1in the Natsui River, respectively. After the rainy events and typhoon, the concentration of 134Cs and 137Cs in river water was increased. Total concentration of 134Cs after the rainy events in the Tone River and the Natsui River was 18 – 37 mBq L-1and 40 mBq L-1respectively, and concentration for 137Cs was 211 – 411 mBq L-1and 447 mBq L-1respectively. During the study period, 97-100 % of 134Cs and 137Cs was distributed by suspended solid in the Tone River and 95-100 % of 134Cs and 137Cs in the Natsui River after the rainy events. These results indicate that behavior of suspended solids is a main factor controlling variation of concentration of 134Cs and 137Cs in both rivers.
The AMP precipitated and suspended solids were dried to determined radioactive cesium concentration using HPGe gamma spectrometry. Investigations of cesium concentration in the rivers have been performed to understand factors controlling transport of radiocesium during different condition. The maximum concentration of 134Cs and 137Cs at normal condition was 0.7 mBq L-1and 7.9 mBq L-1in the Tone River, and 1.1 mBq L-1and 11 mBq L-1in the Natsui River, respectively. After the rainy events and typhoon, the concentration of 134Cs and 137Cs in river water was increased. Total concentration of 134Cs after the rainy events in the Tone River and the Natsui River was 18 – 37 mBq L-1and 40 mBq L-1respectively, and concentration for 137Cs was 211 – 411 mBq L-1and 447 mBq L-1respectively. During the study period, 97-100 % of 134Cs and 137Cs was distributed by suspended solid in the Tone River and 95-100 % of 134Cs and 137Cs in the Natsui River after the rainy events. These results indicate that behavior of suspended solids is a main factor controlling variation of concentration of 134Cs and 137Cs in both rivers.