Reconstruction of time changes in radiocesium concentrations in the river of the Fukushima Dai-ichi NPP contaminated area based on its depth distribution in dam reservoir's bottom sediments

• Published in: Environmental research Vol. 206; p. 112307
• Main Authors: Konoplev, Alexei, Wakiyama, Yoshifumi, Wada, Toshihiro, Ivanov, Maxim, Komissarov, Mikhail, Nanba, Kenji
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 15.04.2022
• Subjects: Cesium Radioisotopes; Dam reservoir; Dissolved; Fukushima; Fukushima Nuclear Accident; Japan; Nuclear Power Plants; Particulate; Radiation Monitoring; Radiocesium; River; Rivers; Water Pollutants, Radioactive - analysis; Japan; Dam reservoir; Particulate; MEXT; Dissolved; IAEA; HPGe; Fukushima; River; FDNPP; Radiocesium; NPP
• DOI: 10.1016/j.envres.2021.112307
• ISSN: 0013-9351

Radionuclide depth distribution in bottom sediments in deep-water zones of dam reservoirs, where no sediment mixing occurs, can be used to reconstruct time changes in particulate activity concentrations of radionuclides strongly bound to bottom sediments. This approach was used to analyze the 137Cs concentration profile in a bottom sediment core collected from Ogaki dam reservoir on the Ukedo River in the Fukushima Dai-ichi nuclear power plant contaminated zone in October 2019. The derived 137Cs particulate concentrations provided a basis for estimating the dissolved concentration and its temporal trend in the Ukedo River, using the mean value of the apparent 137Cs distribution coefficient. The reconstructed particulate and dissolved 137Cs concentrations and their temporal trends are consistent with monitoring data. The annual mean particulate and dissolved 137Cs wash-off ratios were also calculated for the period of eight years after the accident. Interestingly, the particulate 137Cs wash-off ratios for the Ukedo River at Ogaki dam were found to be similar to those for the Pripyat River at Chernobyl in the same time period after the accident, while the dissolved 137Cs wash-off ratios in the Ukedo River were an order of magnitude lower than the corresponding values in the Pripyat River. Both the particulate and dissolved 137Cs wash-off ratios in the Ukedo River declined faster during the first eight years after the FDNPP accident than predicted by the diffusional model, most likely, due to greater natural attenuation and, to some extent, remediation measures implemented on the catchments in Fukushima. •137Cs depth profile in bottom sediments can be taken as representing radionuclide dynamics in river.•Reconstructed 137Cs concentrations in Ukedo River are consistent with monitoring data.•137Cs wash-off ratios in Fukushima tend to decrease faster than in Chernobyl.