Effect of radioactive cesium-rich microparticles on radioactive cesium concentration and distribution coefficient in rivers flowing through the watersheds with different contaminated condition in Fukushima

Tatsuno, Takahiro*; Waki, Hiromichi*; Kakuma, Minato*; Nihei, Naoto*; Takase, Tsugiko*; Wada, Toshihiro*; Yoshimura, Kazuya; Nakanishi, Takahiro; Ote, Nobuhito*

Journal of Environmental Management, 329, p.116983_1 - 116983_13, 2023/03

https://doi.org/10.1016/j.jenvman.2022.116983

Dynamics of radiocesium in coastal areas following river flood

Misono, Toshiharu; Nakanishi, Takahiro; Shiribiki, Takehiko; Nagao, Seiya*; Ochiai, Shinya*; Sanada, Yukihisa; Tsuruta, Tadahiko

Gekkan Kaiyo, 54(11), p.558 - 561, 2022/11

Sediment traps were set up around estuaries and in coastal areas to collect sinking particles at the time of river discharge. Around the estuary, changes in radiocesium concentration and mass flux of sinking particles linked to the discharge of radiocesium from the river were observed.

Geochemical and grain composition analysis of embankment and debris flow deposits in the Izusan area, Atami City, Shizuoka Prefecture, central Japan

Kitamura, Akihisa*; Okazaki, Sota*; Kondo, Mitsuru*; Watanabe, Takahiro; Nakanishi, Toshimichi*; Hori, Rie*; Ikeda, Masayuki*; Ichimura, Koji; Nakagawa, Yuki; Mori, Hideki*

Shizuoka Daigaku Chikyu Kagaku Kenkyu Hokoku, (49), p.73 - 86, 2022/07

https://doi.org/10.51053/shizuoka.49.0_73

On July 3 2021, a debris flow caused by a landslide from a landfill occurred along the Aizome River in the Izusan area of Atami City, Shizuoka. In this study, debris flow deposits and soil samples were characterized in terms of their sedimentology and geochemically analyzed.

Remobilisation of radiocaesium from bottom sediments to water column in reservoirs in Fukushima, Japan

Funaki, Hironori; Tsuji, Hideki*; Nakanishi, Takahiro; Yoshimura, Kazuya; Sakuma, Kazuyuki; Hayashi, Seiji*

Science of the Total Environment, 812, p.152534_1 - 152534_10, 2022/03

https://doi.org/10.1016/j.scitotenv.2021.152534

Reservoir sediments generally act as a sink for radionuclides derived from nuclear accidents, but under anaerobic conditions, several radionuclides remobilise in bioavailable form from sediment to water columns, which may contribute to a long-term contamination in aquatic products. This study systematically investigated the Cs activities between sediment and pore water, which is a direct evidence of the remobilisation of bioavailable Cs from sediments, in two highly contaminated reservoirs affected by the Fukushima Dai-ichi Nuclear Power Plant accident. Our results strongly indicate a competitive ion exchange process between Cs and NH via a highly selective interaction with the frayed edges sites of phyllosilicate minerals to be the major reason for the variability of the Kd values between sediment and pore water, even in the Fukushima case.

Visualization of radiocesium distribution in surface layer of seafloor around Fukushima Daiichi Nuclear Power Plant

Sanada, Yukihisa; Urabe, Yoshimi*; Misono, Toshiharu; Shiribiki, Takehiko; Nakanishi, Takahiro; Watanabe, Yusuke; Tsuruta, Tadahiko

Scientific Reports (Internet), 11(1), p.23175_1 - 23175_13, 2021/11

https://doi.org/10.1038/s41598-021-02646-9

After the accident at the Fukushima Daiichi Nuclear Power Station (FDNPP) on March 15, 2011, a large amount of volatile radionuclides were released into the atmosphere and hydrosphere. Monitoring of radioactive cesium in sediments is important for assessing the behavior and effects of radioactive cesium in the environment. In this study, the distribution of radioactive cesium in the superficial deposits around FDNPP was visualized as a radioactive cesium map using regular survey data from a towed gamma-ray detection system.

Dynamics of radioactive cesium in coastal area linked with river discharge

Misono, Toshiharu; Tsuruta, Tadahiko; Shiribiki, Takehiko; Nakanishi, Takahiro; Nagao, Seiya*; Ochiai, Shinya*; Sanada, Yukihisa

Journal of Coastal Research, 114(SI), p.315 - 319, 2021/10

https://doi.org/10.2112/JCR-SI114-064.1

For understanding future radioactive Cs dynamics and its distribution in the coastal area of Fukushima Prefecture, it is important to evaluate the supply of radioactive Cs from river discharge. Especially particulate radioactive Cs supplied in floods might have a significant impact on the coastal area. However, there are few studies on the dynamics of particulate radioactive Cs at the coastal area linked with rivers at the flood event. As a result of measuring the Cs concentration of the sinking particles collected by the sediment trap, at the observation point installed in front of the river, the Cs concentration collected immediately after the typhoon Bualoi (October 25th) was about higher than before the typhoon. However, the Cs concentration of the sinking particles collected two days after the typhoon was almost the same as before the typhoon. The impact of rivers on coastal areas during torrential rain stuck is extremely limited.

Summary of radioactive Cs dynamics studies in coastal areas and assessment of river impacts

Misono, Toshiharu; Tsuruta, Tadahiko; Nakanishi, Takahiro; Sanada, Yukihisa

Global Environmental Research (Internet), 24(2), p.137 - 144, 2021/06

http://www.airies.or.jp/ebook/Global_Environmental_Research_Vol.24No.2.pdf

A large amount of radioactive material was released into the environment following the 2011 Great East Japan earthquake. Nine years have passed since this accident, and the radioactive concentration in the seabed sediments has decreased. However, the influence of rivers causes coastal areas to be dynamic. The Japan Atomic Energy Agency has conducted studies at the mouth of the Ukedo River. Here, we review previous studies and evaluate the radioactive Cs supplied by rivers using a sediment trap. In this study, a mooring system consisting of a sediment trap was installed in the Ukedo River estuary near the Fukushima Daiichi Nuclear Power Plant from February 2017 to November 2017. A calculation of the annual Cs flux estimated from the obtained contribution rates indicates that the contribution of resuspension to the flux was over 60% during this period. Therefore, this study shows that the mobilization of radioactive Cs in the coastal area is primarily due to resuspension.

Leaching characteristics of Cs for forest floor affected by the Fukushima nuclear accident; A Litterbag experiment

Sakuma, Kazuyuki; Yoshimura, Kazuya; Nakanishi, Takahiro

Chemosphere, 264, p.128480_1 - 128480_9, 2021/02

https://doi.org/10.1016/j.chemosphere.2020.128480

We investigated characteristic of dissolved Cs leaching from litters collected at a coniforest needle and a deciduous broadleaf forests using litterbags at upstream area of Ohta River in Fukushima. Each leaf type of litters was collected into 36 litterbags, respectively, and installed each forest floor in June and December, 2017. Triplicate samples were collected at each forest floor and readily transported to the laboratory in August, December, 2017 and March, May, August, December, 2018. Samples were put in buckets and soaked in purified water. We took leaching water samples from the buckets at 20 min, 140 min, 1 day after soaking litter samples in the water. These samples were analysed about Cs activity. The main results were that the deciduous broadleaf litter showed much higher leaching ratio of dissolved Cs (0.81-6.6%) than that of the coniferous needle litter (0.13-2.0%). A multi-regression analysis of Cs leaching ratios were conducted against antecedent mean precipitation and temperature, and accumulated temperature during the litterbag experiments. The model can reproduce observed Cs leaching ratios (R = 0.61-0.99).

Survey on the radioactive substance in the coastal areas near Fukushima Prefecture in FY2019 (Contract research)

Misono, Toshiharu; Tsuruta, Tadahiko; Nakanishi, Takahiro; Sanada, Yukihisa; Shiribiki, Takehiko; Miyamoto, Kenji*; Urabe, Yoshimi*

JAEA-Research 2020-008, 166 Pages, 2020/10

JAEA-Research-2020-008.pdf:13.11MB
JAEA-Research-2020-008(errata).pdf:0.92MB

After the accident at TEPCO Fukushima Daiichi Nuclear Power Station (1F), marine monitoring survey on radioactive substances have been conducted with financially supported by the Nuclear Regulatory Agency from FY2019. Results obtain in the project in FY2019 are presented in this report. Based on scientific grounds, the concept necessary for "progress of sea area monitoring" was arranged for the future medium- to long-term investigation of radiocesium concentrations. As basic information of survey frequency revise, a seabed topography and sediment distribution survey was conducted, and an attempt was made to understand the relationship between the seabed topography and the grain size distribution of bottom sediment. A columnar core sample was collected in the coastal area and analyzed for radioactive cesium concentration. In order to understand the dynamics of radioactive cesium contained in suspended matter flowing in from a river, suspended solids was collected using a sediment trap and the concentration of radioactive cesium was measured. We re-analyzed the towed monitoring data that had been implemented since 2013, and tried to improve the accuracy of the radioactive cesium distribution estimation map in the coastal area.

Radiocesium distribution in the sediments of the Odaka River estuary, Fukushima, Japan

Hagiwara, Hiroki; Nakanishi, Takahiro; Konishi, Hiromi*; Tsuruta, Tadahiko; Misono, Toshiharu; Fujiwara, Kenso; Kitamura, Akihiro

Journal of Environmental Radioactivity, 220-221, p.106294_1 - 106294_9, 2020/09

https://doi.org/10.1016/j.jenvrad.2020.106294