JpGU-AGU Joint Meeting 2020

Presentation information

[J] Oral

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

[M-AG44] Dynamics of radionuclides emitted from Fukushima Dai-ichi Nuclear Power Plant in the environment

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

[MAG44-09] Mass balance and long term behavior of fluxes of 137Cs derived from the TEPCO FNPP1 accident among atmosphere, land and ocean

*Michio Aoyama1 (1.Center for Research in Isotopes and Environmental Dynamic, Faculty of Life and Environmental Sciences, University of Tsukuba)

Keywords:137Cs, flux, river , resuspension, decontamination

The consensus values of total atmospheric release of 137Cs from FNPP1 accident is 15-21 PBq, it for atmospheric deposition of 137Cs on land is 3-6 PBq, it for atmospheric deposition of 137Cs on the North Pacific is 12-15 PBq, it for direct discharge of 137Cs to ocean is 3-6 PBq and it for total inventory of 137Cs in the North Pacific is 15-18 PBq (Aoyama et al., 2019). Regarding with fluxes from domain to domain for several years after the accident, the amount of 137Cs transported by the rivers in the south of Pacific coast of Tohoku region to the ocean might be 40 TBq (Aoyama et al., in revise) which is corresponding to less than 1.3 % of deposited 137Cs on land. In terms of annual flux of 137Cs, it was estimated to be10–12 TBq year-1 in 2011-2012 by 14 rivers around FNPP1 including particulate form and dissolved form (Kitamura et al., 2014) and ca. 0.9 TBq year-1 for particulate form and dissolved form and 0.04 TBq for dissolved form only in Dec. 2016 (Tsumune et al., 2020). In October and November 2019, 137Cs activity concentrations in surface water off Tohoku region were reported to be 10-20 Bq m-3 by governmental monitoring after floods by the Typhoon Hagibis in October 2019. Preliminary results of integration of 137Cs for coastal region off Miyagi, Fukushima and Ibaraki prefectures, of which size was 200 km x 20 km, showed that flux from land to ocean in this region by floods might be ca. 0.1 TBq per this typhoon event. This might one tenth of annual flux by the rivers. For resuspension, the annual deposition of 137Cs at Okuma during the period from 2014 to 2018 means that 4 TBq year-1 to 10 TBq year-1 should be amount of resuspension from land to atmosphere and this amount correspond to 0.1 % to 0.3 % of total deposition of 137Cs on land in Japan. The 137Cs activity concentration at 56N canal in 2016-2018 correspond to 137Cs discharge of 0.73 TBq year-1 to 1.0 TBq year-1 from FNPP1 site to open water. As a result of decontamination works, 134 TBq of 137Cs was removed from surface soil until February 2019 which correspond to 4 % of deposited 137Cs on land in Japan (Aoyama et al., in revise). The integrated amount of FNPP1 derived 137Cs that entered the Sea of Japan, SOJ, until 2017 was 0.27 ± 0.02 PBq, which is 6.4 % of the estimated total amount of FNPP1-derived 137Cs in the STMW in the North Pacific. The integrated amount of FNPP1-derived 137Cs that returned to the North Pacific Ocean through the Tsugaru Strait from SOJ was 0.11 ± 0.01 PBq, 42 % of the total amount of FNPP1-derived 137Cs transported to the SOJ ( Inomata et al., 2020)