Behavior of radiocesium (Cs) on the coastal seafloor near the Fukushima Daiichi Nuclear Power Plant inferred from radiocesium distributions in long cores

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

Journal of Coastal Research, 116(SI), p.161 - 165, 2024/01

https://doi.org/10.2112/JCR-SI116-033.1

Continuous data of Cs-137 concentration in surface seabed sediment around the Fukushima Daiichi Nuclear Power Plant (FDNPP) from 2012 to 2022 was compiled and its temporal change was fitted by exponential function. In general, Cs-137 concentrations were gradually declining with time. However, at some monitoring points in shallow region, long half-lives and/or large deviations of Cs-137 concentrations were noticed. To gain insight into cesium dynamics in shallow seafloor, long sediment cores were collected at shallow region near the FDNPP, and the vertical profiles of Cs-137 concentration and particle size distribution were determined. At the beach, Cs-137 concentration and particle size distribution were very homogenized from several tens of cm to more than 1 m deep, probably due to strong vertical mixing by wind waves and tides. Therefore, beach sediments have significant Cs-137 reserves in deeper layers at present. It was suggested that the Cs-137 supply from deep layers as well as the land area might suppress the decline of surface Cs-137 concentration in this area. At sampling points located at the bases of cliffs and depressions at the offshore zone, the vertical distributions of Cs-137 concentration were highly heterogeneous, showing the particle size dependency. Moreover, Cs-137 profiles obtained at the same point for several years were quite different. Therefore, it might cause the large fluctuation of Cs-137 concentration at surface sediment over time.

Simulation study on H behavior in the Fukushima coastal region; Comparison of influences of discharges from the Fukushima Daiichi and rivers

Sakuma, Kazuyuki; Yamada, Susumu; Machida, Masahiko; Kurikami, Hiroshi; Misono, Toshiharu; Nakanishi, Takahiro; Iijima, Kazuki

Marine Pollution Bulletin, 192, p.115054_1 - 115054_10, 2023/07

https://doi.org/10.1016/j.marpolbul.2023.115054

Survey on the radioactive substance in the coastal areas near Fukushima Prefecture in FY2021

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

JAEA-Research 2022-010, 134 Pages, 2023/02

JAEA-Research-2022-010.pdf:8.45MB

An accident occurred at the TEPCO's Fukushima Daiichi Nuclear Power Station (1F) in 2011 and a large amount of radioactive materials were deposited around the 1F. Japan Atomic Energy Agency has continued to conduct research on the dynamics of radioactive materials after the accident. This report summarizes the results of the survey conducted in FY 2021 on the status of marine monitoring survey on radioactive substances. Furthermore, a seabed topography and sediments distribution survey was conducted in the coastal area off the Mano River from the Ohta River to understand the topography and sediment distribution. Furthermore, in order to evaluate the inflow of radioactive Cs from the river, the horizontal distribution of the radioactive Cs concentration on the surface sediment in front of the rivers was measured. As basic information on the effects of radioactive materials on marine products, the distribution status of fish was investigated. In addition, a demonstration test of water sampling and sediment sampling was conducted using an unmanned observation vessel. From these results, we estimated the distribution and its dynamics of radioactive Cs in the sediments in the front area on the 1F.

Neutron reflectivity study on the suppression of interfacial water accumulation between a polypropylene thin film and Si substrate using a silane-coupling agent

Shimokita, Keisuke*; Yamamoto, Katsuhiro*; Miyata, Noboru*; Arima-Osonoi, Hiroshi*; Nakanishi, Yohei*; Takenaka, Mikihito*; Shibata, Motoki*; Yamada, Norifumi*; Seto, Hideki*; Aoki, Hiroyuki; et al.

Langmuir, 38(41), p.12457 - 12465, 2022/10

https://doi.org/10.1021/acs.langmuir.2c01599

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.

Dispersive XAFS Study on the Laser-Induced Reduction of a Rh ion complex; Presence of a Rh Intermediate in Direct Photoreduction

Saeki, Morihisa*; Matsumura, Daiju; Nakanishi, Ryuzo*; Yomogida, Takumi; Tsuji, Takuya; Saito, Hiroyuki*; Oba, Hironori*

Journal of Physical Chemistry C, 126(12), p.5607 - 5616, 2022/03

https://doi.org/10.1021/acs.jpcc.1c10160

The reaction mechanism of the direct photoreduction of a Rh ion complex to a Rh species induced by pulsed ultraviolet laser irradiation was studied using dispersive X-ray absorption fine structure (DXAFS) spectroscopy. The time-resolved X-ray absorption near edge structure (XANES) showed the absence of isosbestic points and suggested that more than two Rh species contribute toward the direct photoreduction of Rh. Analysis of the time-resolved XANES data by singular value deposition showed that the direct photoreduction involves three Rh species. Multivariate curve resolution by alternating least-squares analysis (MCR-ALS) of the time-resolved XANES data gave pure spectra and concentration profiles of the three Rh species. The Rh species were assigned to Rh, Rh, and Rh species based on the features of the pure XANES spectra. The concentration profiles suggested that the direct photoreduction proceeds in the order of Rh Rh Rh. A reaction mechanism, which was proposed involving photoreductions of Rh and Rh, photoinduced autocatalytic reductions of Rh and Rh, and photooxidation of Rh, well reproduced the concentration profiles of three Rh species.

Survey on the radioactive substance in the coastal areas near Fukushima Prefecture in FY2020 (Contract research)

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

JAEA-Research 2021-004, 214 Pages, 2021/11

JAEA-Research-2021-004.pdf:12.76MB

After the accident of TEPCO's Fukushima Daiichi Nuclear Power Station (1F), the project of marine monitoring survey on radioactive substances have been conducted by the contract research from the Nuclear Regulatory Agency in FY2020. Results obtain in the project are presented in this report. Based on the monitoring results of radioactive substances of seawater and sediments, we suggested the evaluation method for optimizing the survey points and frequency, and examined the proper monitoring method on marine monitoring. In addition, core samples were collected at 70 points at the coast of Fukushima Prefecture to reveal the accumulation of radioactive Cs in the sediments. Furthermore, in order to evaluate the inflow of radioactive Cs from the river, sediment traps were installed at the coastal area to collect sinking sediment, and the horizontal distribution of the radioactive Cs concentration on the surface sediment in front of the rivers was measured. We carried out the revaluation of the towed radiation monitoring data conducted from 2013 to 2018, taking into account the natural radionuclides, and improved the radioactive Cs distribution map in the coastal sediments. In addition, a seabed topography and sediments distribution survey was conducted in the silt band area off the 1F to understand the topography and sediment distribution. From these results, we estimated the distribution and its dynamics of radioactive Cs in the sediments in the front area on the 1F.

Impact of extreme typhoon events on the fluvial discharge of particulate radiocesium in Fukushima Prefecture

Nakanishi, Takahiro; Oyama, Takuya; Hagiwara, Hiroki; Sakuma, Kazuyuki

Journal of Coastal Research, 114(SI), p.310 - 314, 2021/10

https://doi.org/10.2112/JCR-SI114-063.1

The two huge typhoons in 2019, Hagibis and Bualoi, caused enormous flood damage to Fukushima. On the basis of field observations over 6 years in Ukedo River near the Fukushima Nuclear Power Plant, sediment and Cs discharges from the river catchment were quantitatively evaluated. Approximately 90% of annual sediment and Cs discharges in 2019 was occupied during the typhoons Hagibis and Bualoi events. This sediment discharge was almost twice than the discharge during the largest ever flood event since the Fukushima nuclear accident, caused by typhoon Etau in September 2015. However, Cs discharge during Hagibis and Bualoi events was two-thirds that of Etau event, because the particulate Cs concentration in river water decreased during the observation period. Moreover, Cs discharge during two typhoon events in 2019 accounted for only 0.1% of the catchment Cs deposition and the impact of radiocesium to the coastal area was extremely limited.

Vertical profiles of radioactive Cs distributions and temporal changes in seabed sediments near river mouth in coastal area of Fukushima Prefecture

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

Journal of Coastal Research, 114(SI), p.320 - 324, 2021/10

https://doi.org/10.2112/JCR-SI114-065.1

no abstracts in English

Factors affecting Cs concentrations in river water under base-flow conditions near the Fukushima Dai-ichi Nuclear Power Plant

Nakanishi, Takahiro; Funaki, Hironori; Sakuma, Kazuyuki

Journal of Radioanalytical and Nuclear Chemistry, 328(3), p.1243 - 1251, 2021/06

https://doi.org/10.1007/s10967-021-07735-7

To confirm factors affecting Cs concentration in river water after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, this study conducted monthly observations of nine rivers near the FDNPP from April 2017 to March 2018 under base-flow conditions. The annual mean dissolved and particulate Cs concentrations correlated well with the mean Cs deposition in the catchment. The normalized Cs concentrations in both phases by dividing by the mean Cs deposition in the catchment showed significant negative correlations with the Cs deposition ratio for forests. The inflow from the downstream plain areas increased the Cs concentrations near the FDNPP.