Japan Geoscience Union Meeting 2022

Presentation information

[J] Poster

M (Multidisciplinary and Interdisciplinary) » M-AG Applied Geosciences

[M-AG39] Radioisotope migration: New development for dynamics study of radionuclides from 1F NPP accident

Tue. May 31, 2022 11:00 AM - 1:00 PM Online Poster Zoom Room (33) (Ch.33)

convener:Daisuke Tsumune(Central Research Institute of Electric Power Industry), convener:Yuichi Onda(Center for Research on Isotopes and Environmental Dynamics, University of Tsukuba), convener:Yoshio Takahashi(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo), convener:Akira Kirishima(Tohoku University), Chairperson:Daisuke Tsumune(Central Research Institute of Electric Power Industry), Yuichi Onda(Center for Research on Isotopes and Environmental Dynamics, University of Tsukuba)

11:00 AM - 1:00 PM

[MAG39-P01] Riverine 137Cs dynamics during high-flow events in the Niida River basin

*Yoshifumi Wakiyama1, Takuya Niida2, Hyoe Takata1, Keisuke Taniguchi3, Kazuki Fujita4, Alexei Konoplev1, Yuichi Onda5 (1.Institute of Environmental Radioacitivity, Fukushima Universiy, 2.KANSO TECHNOS, CO. LTD., 3.National Institute of Technology, Tsuyama College, 4.Fukushima Prefectural Centre for Environmental Creation, 5.Center for Research in Isotope and Environmental Dynamics, University of Tsukuba)

Keywords:137Cs, Catchment, Desorption, Typhoon

Majority of terrestrial 137Cs is transported from river basins to ocean during high-flow events triggered by rainstorms. Recent studies have revealed substantial impacts of riverine 137Cs flux on its behavior in ocean during typhoon events, underlying importance of better understanding of riverine 137Cs dynamics. A comparative study on riverine 137Cs dynamics in the coastal contaminated catchments suggested dependency of 137Cs dynamics on rainfall properties and on catchment characteristics, such as spatial pattern of 137Cs inventory and land use composition. Further inter-catchment comparison will lead us to achieve better understanding of 137Cs dynamics. This study presents temporal variations in riverine 137Cs concentration at four sites and quantified 137Cs flux at one site in the Niida river basin during high-flow events occurred in 2016 and 2017.
Study sites were Sakegawa-bashi (SK), Haramachi (HR), Notegami-kita (NT) and Warabi-daira (WR) in the Niida River basins. Respective catchment area on SK, HR, NT, WR were 29, 103, 206, 259 km2. Respective mean 137Cs inventory on SK, HR, NT, WR were 1420, 790, 850, 740 kBq m-2. River water samples were collected for 5-6 times during typhoon events in 16-17 August 2016 and 22-23 October 2017. Dissolved 137Cs concentration (Csdis: Bq L-1) and 137Cs concentration in suspended sediment (CsSS: Bq kg-1) were measured. Based on the concentrations and hydrological data, 137Cs fluxes were calculated for HR. SS samples collected at HR in peak water discharge phase were further analyzed for desorption with seawater to estimate potential quantity of 137Cs desorbed from SSs into ocean.
Mean CsSS ranged from 5900 to 21000 Bq kg-1, and mean Csdis from 11 to 34 Bq L-1. The concentrations depended on catchment mean 137Cs inventory. Temporal variations in CsSS appeared to differ between upstream and downstream sites; peaked in peak water discharge phase at SK and HR whereas declined throughout events at NT and WR. These tendencies suggest reflections of spatial patterns of 137Cs inventory in the catchments to the variations. Although we have not found any explainable feature for variations in Csdis by inter-catchment and -event comparisons, it declined and elevated in all events without monotonous trends. 137Cs fluxes at HR in the events in 2016 and 207 were 60 and 55 GBq, respectively. They accounted for 0.034 and 0.031% of total deposited 137Cs in the catchment. Desorption ratio of 137Cs, obtained by 1-day shaking experiment of SS in seawater, were 3.6% for 2016 and 5.3% for 2017. By multiplying these ratios by correspondent particulate 137Cs fluxes, potential quantity of 137Cs desorbed from SSs into ocean in 2016 and 2017 events were estimated as 0.21 and 0.28 GBq, respectively. These quantities 15 and 3.6 times higher than correspondent dissolved 137Cs fluxes. Further analyses, such as evaluation of decontamination impacts and inter-catchment comparisons of 137Cs fluxes, are required for better understanding.