5:15 PM - 6:45 PM
[MAG34-P08] Estimation of riverine export Cesium-137 fluxes to the marine environment
Keywords:Fukushima Daiichi Nuclear Power Plant, radioactive cesium, river
Due to the Fukushima Daiichi Nuclear Power Plant (FDNPP) accidents in March 2011, Cs-137 were introduced into the marine environment. The Cs-137 concentration in ocean water near the FDNPP has stayed around 0.01-0.1 (Bq/L) from 2013 to 2023. This level hasn't returned to pre-accident levels (0.001-0.002 Bq/L), indicating a persistent high state of two orders of magnitude. The continued high Cs-137 concentration in Fukushima coastal waters, even 12 years after the accident, are attributed to both direct discharge from the FDNPP and river input.
This study analyzed the river input using Cs-137 concentration data from rivers and river water flow rates. Both dissolved Cs-137 and particulate Cs-137 were examined. It was observed that particulate Cs-137 dissolves from the particles into the ocean due to an increase in competing ions when it enters the marine environment. To calculate the total influx, we included both dissolved Cs-137 and the dissolved portion from particulate Cs-137. We assumed a dissolution rate of 3-30% for particulate Cs-137 entering ocean from rivers. Furthermore, we analyzed recent Cs-137 concentration data in river water and compared it with information from global fallout from nuclear testing and the Chernobyl accident to understand temporal changes. We examined various trends in river Cs-137 concentrations, drawing on measurements taken over a 12-year period from the accident until 2023 in Fukushima. Additionally, we compared the direct discharge of Cs-137 with the river input and explored the relationship between Cs-137 concentration fluctuations in the marine environment.
Estimates of river inputs indicated that the input of the dissolved Cs-137 significantly decreased about one year after the accident and has continued to decline gradually since. On the other hand, the particulate Cs-137 is presumed to have reached a state of long-term equilibrium, like findings from previous studies on Eurasian rivers affected by global fallout from atmospheric nuclear testing and the Chornobyl accident (Smith et al., 2004), indicating a stabilization. Therefore, considering the dissolution of particulate Cs-137, the input of Cs-137 into the ocean, even years after the accident, could potentially reach levels comparable to those seen during the one year after the accident when river flow was high. Additionally, river input, considering particulate dissolution, has surpassed direct discharge from the FDNPP, which is believed to have decreased recently. However, the input of dissolved Cs-137 from rivers alone is still about an order of magnitude lower than direct discharge, underscoring the potentially significant impact of particulate dissolution on future inputs. Furthermore, while the combined inflow from both direct and river sources has decreased over time, there's a suggestion of a changing ratio between direct and river inflow.
This study analyzed the river input using Cs-137 concentration data from rivers and river water flow rates. Both dissolved Cs-137 and particulate Cs-137 were examined. It was observed that particulate Cs-137 dissolves from the particles into the ocean due to an increase in competing ions when it enters the marine environment. To calculate the total influx, we included both dissolved Cs-137 and the dissolved portion from particulate Cs-137. We assumed a dissolution rate of 3-30% for particulate Cs-137 entering ocean from rivers. Furthermore, we analyzed recent Cs-137 concentration data in river water and compared it with information from global fallout from nuclear testing and the Chernobyl accident to understand temporal changes. We examined various trends in river Cs-137 concentrations, drawing on measurements taken over a 12-year period from the accident until 2023 in Fukushima. Additionally, we compared the direct discharge of Cs-137 with the river input and explored the relationship between Cs-137 concentration fluctuations in the marine environment.
Estimates of river inputs indicated that the input of the dissolved Cs-137 significantly decreased about one year after the accident and has continued to decline gradually since. On the other hand, the particulate Cs-137 is presumed to have reached a state of long-term equilibrium, like findings from previous studies on Eurasian rivers affected by global fallout from atmospheric nuclear testing and the Chornobyl accident (Smith et al., 2004), indicating a stabilization. Therefore, considering the dissolution of particulate Cs-137, the input of Cs-137 into the ocean, even years after the accident, could potentially reach levels comparable to those seen during the one year after the accident when river flow was high. Additionally, river input, considering particulate dissolution, has surpassed direct discharge from the FDNPP, which is believed to have decreased recently. However, the input of dissolved Cs-137 from rivers alone is still about an order of magnitude lower than direct discharge, underscoring the potentially significant impact of particulate dissolution on future inputs. Furthermore, while the combined inflow from both direct and river sources has decreased over time, there's a suggestion of a changing ratio between direct and river inflow.