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Cs supply from rivers to coastal waters off Fukushima on the Cs behavior in seabed sedimentIkenoue, Tsubasa; Nakanishi, Takahiro; Shimadera, Hikari*; Kawamura, Hideyuki; Kondo, Akira*
E3S Web of Conferences (Internet), 530, p.02005_1 - 02005_10, 2024/05
The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) caused a radioactive contamination in seabed sediment. The Cs supply from rivers could be an important process for the long-term behavior of Cs in seabed sediment. In this study, a ten-year simulation of the Cs behavior in seabed sediment was conducted using an oceanic dispersion model combined with a prediction model of Cs behavior in land and river. In the waters north of FDNPP, the simulation results suggested that the Cs supply from rivers had a great impact on the concentrations in coastal sediment due to the initial low concentrations in seabed sediment and the large supply of Cs from rivers. In the waters near FDNPP and south of FDNPP, the simulation results suggested that the impact of the Cs supply on the temporal variation of Cs concentration in coastal sediment was relatively small due to the large initial adsorption from seawater. Overall, these results indicated that Cs supply from rivers had an impact on the spatiotemporal distribution of Cs concentrations in seabed sediment on a decadal time scale and the impact was especially great in the waters north of FDNPP.
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:13.11MBJAEA-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.
Cs in seabed sediments around the river mouth near Fukushima Daiichi Nuclear Power PlantTsuruta, Tadahiko; Harada, Hisaya*; Misono, Toshiharu; Matsuoka, Toshiyuki; Hodotsuka, Yasuyuki*
Journal of Oceanography, 73(5), p.547 - 558, 2017/10
Times Cited Count：12 Percentile：42.87(Oceanography)The seafloor topography was divided into flat and terrace seafloors based on their topographical features and seabed sediments were distributed in an area that was half a degree of the entire investigation area. The Cs inventory was several tens of kBq/m
and the grain sizes (the D50 values) were nearly constant (fine sand) on the flat seafloor. On the terrace seafloor, the Cs inventory was larger than that on the flat seafloor, and the grain size varied from silt to coarse sand. The grain size distributions appear to be influenced by the mean shear stress at the seafloor bottom, and a significant factor in the mean shear stress is thought to be the seafloor topography. Distributions of remarkably large Cs inventories, more than several thousands of kBq/m, are thought to be confined to a small area. Vertical changes in the Cs inventories suggested that the Cs inventories have significantly decreased in large areas of the shallow sea.
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Journal of the Oceanographical Society of Japan, 40, p.98 - 104, 1984/00
no abstracts in English
Ikenoue, Tsubasa
no journal, ,
We report the results of a recent simulation study by JAEA on the behavior of radiocesium (Cs) released by the Fukushima Daiichi Nuclear Power Plant accident (1F accident) near the coastal seafloor. The Cs supply from rivers could be an important process for the long-term behavior of Cs in seabed sediment. In this study, we conducted a simulation to predict the behavior of Cs in seabed sediment by combining an ocean dispersion model with a river model. Based on the simulation results, we explain the impact of Cs supply from rivers on the long-term behavior of Cs in seabed sediment.
Sawaguchi, Takuma; Miwa, Kazuji*; Shimada, Taro; Takeda, Seiji
no journal, ,
In the previous dose assessment for the radioactive waste disposal, the dissolved radionuclides leaking from the repository were assumed to flow directly into the living environment (ocean, lake, river, etc.) through natural barriers. However, based on the knowledge after the Fukushima Daiichi Nuclear Power Plant accident, it was considered that radionuclides via groundwater could sorb and desorb with soil near spring water points, and that radiocesium was mainly transferred as sorbed to suspended particles in the living environment. In this study, in order to contribute to the dose assessment for intermediate-depth disposal, we analytically understood the influence on the migration in the living environment with or without consideration of the nuclide sorption on the seabed soil during spring water inflow into a coastal zone. In addition, the effects were also evaluated for the presence or absence of the nuclide sorption/desorption on suspended particles and the particle sedimentation. As a result, the radioactivity concentrations in seabed soil and seawater immediately above the seabed were higher in the estimate that considered the sorption/desorption and the sedimentation than in the estimate that did not. These results indicate that it is important to consider the radionuclide sorption on the seabed soil and the migration of radionuclides sorbed on suspended particles in the estimation of radionuclide migration in the living environment because these phenomena could cause the increase of radionuclide concentrations in the interface layer and the seabed soil and the higher exposure due to benthic fish and shellfish ingestion, etc.
