5:15 PM - 7:15 PM
[MAG34-P04] Factor affecting for apparent Kd in rivers of the Fukushima Prefecture
Keywords:radiocaesium, stream and river water, stream and riverbed sediment, water quality, apparent Kd, Tepco Fukushima Dai-ichi Nuclear Power Stations
Due to the TEPCO Fukushima Dai-ichi Nuclear Power Stations (FDNPS) accident, approximately 10×1015 Bq of 137Cs was released into the environment (Terada et al., 2020), of which approximately 30%, or 2.7×1015 Bq, was reported to have been deposited on terrestrial environment (Onda et al., 2020). After the FDNPS accident, the solid-water distribution coefficient of the apparent Kd for 137Cs (:137Cs activity concentration in riverbed sediment/137Cs activity concentration in river water) were 1-2 orders of magnitude higher than Chernobili area (e.g. Konoplev et al., 2018). On the other hand, the apparent Kd for 137Cs in the mid-Maeda of the Maeda River in the Fukushima Prefecture on 2019-2023 were (1.74±0.3)×104-(8.66±0.2)×104 L/kg (Fukuda et al., in prepared) and these values were same order reported by IAEA TRS472 (:2.9×104 L/kg). It was observed that the interaction between river waters and sediments for 137Cs, in the Maeda River have been approaching equilibrium conditions. The Kd value is generally one of the environmental migration parameters used to assess the safety of radioactive waste. The clarification of the factor influencing variations of the Kd value contributes to evaluation of radionuclide dose assessment for medium to long time scales.
In this study, we focused on the factors affecting the apparent Kd for 137Cs between stream or river waters and sediment in the Maeda and Saruta, Takase, Ukedo rivers in Futaba and Namie Town, Fukushima Prefecture, Japan. The water phase for apparent Kdfor 137Cs is used on dissolved form (size:<0.45 μm) 137Cs activity concentrations in stream or river waters is because river waters in this study area is mainly dissolved form.
There was a significant negative correlation between the apparent Kd for 137Cs and dissolved organic carbon (DOC) concentrations (R=−0.70, p<0.02), while a positive correlation was observed between the Kd for 137Cs and NO3- concentrations (R=0.57, p<0.02) in the Maeda River. In the Saruta River, there was a significant negative correlation between the apparent Kd for 137Cs and both water temperature and Na+ and K+ concentrations (R=−0.56-−0.60, p<0.02), but not Mg2+ and Cl- concentrations (R=0.49-0.56, p<0.05). These results suggest that 137Cs migration from water to sediment is impeded by DOC in the Maeda River and water temperature in the Saruta River. In this presentation, we also reported the results in the Takse and Ukedo Rivers.
In this study, we focused on the factors affecting the apparent Kd for 137Cs between stream or river waters and sediment in the Maeda and Saruta, Takase, Ukedo rivers in Futaba and Namie Town, Fukushima Prefecture, Japan. The water phase for apparent Kdfor 137Cs is used on dissolved form (size:<0.45 μm) 137Cs activity concentrations in stream or river waters is because river waters in this study area is mainly dissolved form.
There was a significant negative correlation between the apparent Kd for 137Cs and dissolved organic carbon (DOC) concentrations (R=−0.70, p<0.02), while a positive correlation was observed between the Kd for 137Cs and NO3- concentrations (R=0.57, p<0.02) in the Maeda River. In the Saruta River, there was a significant negative correlation between the apparent Kd for 137Cs and both water temperature and Na+ and K+ concentrations (R=−0.56-−0.60, p<0.02), but not Mg2+ and Cl- concentrations (R=0.49-0.56, p<0.05). These results suggest that 137Cs migration from water to sediment is impeded by DOC in the Maeda River and water temperature in the Saruta River. In this presentation, we also reported the results in the Takse and Ukedo Rivers.