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Cs) on the coastal seafloor near the Fukushima Daiichi Nuclear Power Plant inferred from radiocesium distributions in long coresNakanishi, Takahiro; Tsuruta, Tadahiko; Misono, Toshiharu; Shiribiki, Takehiko; Urabe, Yoshimi*; Sanada, Yukihisa
Journal of Coastal Research, 116(SI), p.161 - 165, 2024/01
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.
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.
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.
Cs concentrations in coastal sediments off FukushimaSuzuki, Shotaro*; Amano, Yosuke*; Enomoto, Masahiro*; Matsumoto, Akira*; Morioka, Yoshiaki*; Sakuma, Kazuyuki; Tsuruta, Tadahiko; Kaeriyama, Hideki*; Miura, Hikaru*; Tsumune, Daisuke*; et al.
Science of the Total Environment, 831, p.154670_1 - 154670_15, 2022/07
Times Cited Count：2 Percentile：29.93(Environmental Sciences)Misono, Toshiharu; Nakanishi, Takahiro; Tsuruta, Tadahiko; Shiribiki, Takehiko; Sanada, Yukihisa
Marine Pollution Bulletin, 178, p.113597_1 - 113597_9, 2022/05
Times Cited Count：3 Percentile：59.35(Environmental Sciences)It is essential to evaluate secondary migration caused by riverine input and resuspension from seabed sediments to estimate the future distribution of radioactive cesium (Cs) in the coastal area off Fukushima Prefecture. In particular, the inflow from rivers cannot be ignored because most of the Cs inflow from rivers is deposited on the coast without elute into seawater. Two mooring systems were installed near the Ukedo River's mouth (Fukushima Prefecture) from February 2017 to February 2018. The first contained a sediment trap system, collecting sinking particles during the period. The second comprised a turbidity sensor and a current sensor. The contribution of resuspension and inflow from the river to the mass flux was quantitatively evaluated using multiple regression equations. The results showed that resuspension caused 79%-83% of secondary Cs migration in nearshore areas, whereas the influence of riverine Cs input on the sediment was only 7% per year.
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.
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
Times Cited Count：2 Percentile：13.39(Multidisciplinary Sciences)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.
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
Times Cited Count：2 Percentile：17.67(Environmental Sciences)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.
Tsuruta, Tadahiko; Shiribiki, Takehiko; Misono, Toshiharu; Nakanishi, Takahiro; Sanada, Yukihisa; Urabe, Yoshimi*
Journal of Coastal Research, 114(SI), p.320 - 324, 2021/10
Times Cited Count：0 Percentile：0.01(Environmental Sciences)no abstracts in English
Misono, Toshiharu; Tsuruta, Tadahiko; Nakanishi, Takahiro; Sanada, Yukihisa
Global Environmental Research (Internet), 24(2), p.137 - 144, 2021/06
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.
Otosaka, Shigeyoshi*; Kambayashi, Shota*; Fukuda, Miho*; Tsuruta, Tadahiko; Misono, Toshiharu; Suzuki, Takashi; Aono, Tatsuo*
Environmental Science & Technology, 54(21), p.13778 - 13785, 2020/11
Times Cited Count：12 Percentile：54.1(Engineering, Environmental)Concentrations of Cs in seawater, seabed sediment, and pore water collected from the area around Fukushima were investigated from 2015 to 2018, and the potential of coastal sediments to supply radiocesium to the bottom environment was evaluated. The Cs concentration in the pore water ranged from 33 to 1934 mBq L
and was 10-40 times higher than that in the overlying water (seawater overlying within 30 cm on the seabed). At most stations, the Cs concentrations in the overlying water and the pore water were approximately proportional to those in the sediment. The conditional partition coefficient between pore water and sediment was 0.9-14
10
L kg, independent of the year of sampling. These results indicated that an equilibrium of Cs between pore water and sediment has established in a relatively short period, and Cs in the pore water is gradually exported to seawater near the seabed. A simple box model estimation based on these results showed that the Cs in the sediment was decreased by about 6% per year by desorption/diffusion of Cs from the seabed.
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.
Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.
JAEA-Research 2020-007, 249 Pages, 2020/10
JAEA-Research-2020-007.pdf:15.83MB
The accident of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, Japan Atomic Energy Agency (JAEA) has been conducting "Long-term Assessment of Transport of Radioactive Contaminants in the Environment of Fukushima" concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.
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
Times Cited Count：0 Percentile：0(Environmental Sciences)Kubo, Taiki*; Matsuda, Norihiro*; Kashiwaya, Koki*; Koike, Katsuaki*; Ishibashi, Masayuki; Tsuruta, Tadahiko; Matsuoka, Toshiyuki; Sasao, Eiji; Lanyon, G. W.*
Engineering Geology, 259, p.105163_1 - 105163_15, 2019/09
Times Cited Count：11 Percentile：54.53(Engineering, Geological)Rock matrix permeability is mainly controlled by microcracks. This study aims to identify the factors influencing the permeability of the Toki granite, central Japan. Permeability of core samples, measured by a gas permeameter, largely increases in the fault and fracture zones. Although a significant correlation is identified between permeability and P-wave velocity, this correlation is enhanced by classifying the samples into two groups by the Mn/Fe concentration ratio. Thus, lithofacies is another control factor for permeability due to the difference in mineral composition. Moreover, permeability shows significant negative and positive correlations with Si and Ca concentrations, respectively. These concentrations are probably affected by dissolution of silicate minerals and calcite generation in the hydrothermal alteration process. Therefore, a combination of hydrothermal alteration and strong faulting are the predominant processes for controlling permeability.
Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.
JAEA-Research 2019-002, 235 Pages, 2019/08
JAEA-Research-2019-002.pdf:21.04MB
The accident of the Fukushima Daiichi Nuclear Power Station (hereinafter referred to 1F), Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, JAEA has been conducting Long-term Environmental Dynamics Research concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.
Tsuruta, Tadahiko; Niizato, Tadafumi; Nakanishi, Takahiro; Dohi, Terumi; Nakama, Shigeo; Funaki, Hironori; Misono, Toshiharu; Oyama, Takuya; Kurikami, Hiroshi; Hayashi, Seiji*; et al.
JAEA-Review 2017-018, 86 Pages, 2017/10
JAEA-Review-2017-018.pdf:17.58MB
Since the accidents at Fukushima Daiichi Nuclear Power Plant following the Tohoku Region Pacific Coast Earthquake on March 11th, 2011, Fukushima Environmental Safety Center has carried out research on natural mobilization of radionuclide (especially radiocesium) and future forecast from forest to water system and surrounding residential areas. The report summarizes the latest results that have been accumulated from each study field, of our agency together with the other related research organizations. The contents of the report is to be used as evidence-based information for the QA-styled pages in the website of JAEA Sector of Fukushima Research and Development at the time of next renewal.
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：11 Percentile：44.95(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.
Kurikami, Hiroshi; Niizato, Tadafumi; Tsuruta, Tadahiko; Kato, Tomoko; Kitamura, Akihiro; Kanno, Mitsuhiro*; Kurosawa, Naohiro*
JAEA-Research 2016-020, 50 Pages, 2017/01
JAEA-Research-2016-020.pdf:6.02MB
In this report, we developed a compartment model of radionuclide migration in environment based on exposure pathways in a river basin scale and performed a preliminary calculation. The results showed good agreement with some measurement, although the comparison of bed sediment, transportation to outer sea and to agricultural products with the measurement was not enough. We continue to validate the model.
Tsuruta, Tadahiko; Sasao, Eiji
Oyo Chishitsu, 56(6), p.298 - 307, 2016/02
Japan Atomic Agency (JAEA) are performing Mizunami Underground Research Laboratory project (MIU project), which is a broad scientific study of the deep geological environment as a basis of research and development for geological disposal of nuclear wastes. Geological investigations, reflection seismic surveys, borehole drilling, etc., are carried out to understand the distribution and properties of important geological structures (permeable fractures, faults, etc). This report summarizes specifications and data characteristic of geological mapping on the shafts and gallery wall, and describes contributions to developments of geological model based on the results of geological mapping.
