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Journal Articles

Impact of fluvial discharge on $$^{137}$$Cs in the ocean following the Fukushima Daiichi Nuclear Power Station accident

Tsumune, Daisuke*; Tsubono, Takaki*; Misumi, Kazuhiro*; Sakuma, Kazuyuki; Onda, Yuichi*

Pure and Applied Chemistry, 16 Pages, 2024/00

https://doi.org/10.1515/pac-2023-0902
 Times Cited Count：1 Percentile：68.06(Chemistry, Multidisciplinary)

Twelve years after the Fukushima Daiichi Nuclear Power Station (F1NPS) accident, $$^{137}$$Cs activity concentrations have not yet decreased to pre-accident levels because of direct release from the site and fluvial discharges of $$^{137}$$Cs deposited on land. It is necessary to consider dispersion processes in the coastal area to understand the impact of multiple river discharges and direct release. To achieve this goal, we carried out oceanic dispersion simulations that considered direct release and fluvial discharges and compared the results with the annual averages of observed data. We assumed that particulate $$^{137}$$Cs discharged from rivers to the ocean quickly resuspended and re-leached after coagulation and precipitation and that all of the $$^{137}$$Cs were dispersed. The reproducibility of results was improved by considering fluvial discharges of particulate $$^{137}$$Cs at all sites between 2013 and 2016, except near the F1NPS. In other words, particulate $$^{137}$$Cs discharged from rivers was found to influence the results of ocean surface activity concentrations within a relatively short period of time. The impact of direct release was dominant for the observed $$^{137}$$Cs activity concentrations adjacent to the F1NPS, which was used to estimate direct releases.

Journal Articles

First isolation and analysis of caesium-bearing microparticles from marine samples in the Pacific coastal area near Fukushima Prefecture

Miura, Hikaru*; Ishimaru, Takashi*; Ito, Yukari*; Kuribara, Yuichi; Otosaka, Shigeyoshi*; Sakaguchi, Aya*; Misumi, Kazuhiro*; Tsumune, Daisuke*; Kubo, Atsushi*; Higaki, Shogo*; et al.

Scientific Reports (Internet), 11, p.5664_1 - 5664_11, 2021/03

https://doi.org/10.1038/s41598-021-85085-w
 Times Cited Count：15 Percentile：66.31(Multidisciplinary Sciences)

For the first time, we isolated and investigated seven CsMPs (radioactive caesium-bearing microparticles) from marine particulate matter and sediment. From the elemental composition, the $$^{134}$$Cs/$$^{137}$$Cs activity ratio, and the $$^{137}$$Cs activity per unit volume results, we inferred that the five CsMPs collected from particulate matter were emitted from Unit 2 of the FDNPP, whereas the two CsMPs collected from marine sediment were possibly emitted from Unit 3. The presence of CsMPs can cause overestimation of the solid-water distribution coefficient of Cs in marine sediments and particulate matter and a high apparent radiocaesium concentration factor for marine biota. CsMPs emitted from Unit 2, which were collected from the estuary of a river that flowed through a highly contaminated area, may have been deposited on land and then transported by the river. By contrast, CsMPs emitted from Unit 3 were possibly transported eastward by the wind and deposited directly onto the ocean surface.

Journal Articles

Factors controlling the spatiotemporal variation of $$^{137}$$Cs in seabed sediment off the Fukushima coast; Implications from numerical simulations

Misumi, Kazuhiro*; Tsumune, Daisuke*; Tsubono, Takaki*; Tateda, Yutaka*; Aoyama, Michio*; Kobayashi, Takuya; Hirose, Katsumi*

Journal of Environmental Radioactivity, 136, p.218 - 228, 2014/10

https://doi.org/10.1016/j.jenvrad.2014.06.004
 Times Cited Count：24 Percentile：55.43(Environmental Sciences)

Major controls on spatiotemporal variations of $$^{137}$$Cs activity in seabed sediments derived from the Fukushima Dai-ichi Nuclear Power Plant accident during the first year after the accident were investigated by using numerical simulations. The model successfully reproduced major features of the observed spatiotemporal variations of $$^{137}$$Cs activity in sediments. The spatial pattern of $$^{137}$$Cs in sediments, which mainly reflected the history of $$^{137}$$Cs activity in the bottom water overlying the sediment and the sediment particle size distribution, became established during the first several months after the accident. Taking $$^{137}$$Cs activities in sediments in the coastal area and in the vicinity of the power plant into account, increased the simulated total inventory of $$^{137}$$Cs in sediments off the Fukushima coast to a value on the order of 10$$^{14}$$ Bq.

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