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JAEA Reports

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.

JAEA Reports

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima (FY2018) (Translated document)

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.

Journal Articles

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

 Times Cited Count:0 Percentile:100(Environmental Sciences)

Journal Articles

Rapid tritium analysis for marine products in the coastal area of Fukushima

Kuwata, Haruka*; Misono, Toshiharu; Fujiwara, Kenso; Takeishi, Minoru; Manabe, Sachi*; Kitamura, Akihiro

Radiation Environment and Medicine, 9(1), p.28 - 34, 2020/02

The analysis of tritium in aquatic biota is one of the most important research areas in Fukushima. The conventional method for measuring the concentration of tritium consists of complicated pretreatment procedures and requires skillful techniques as well as a significant amount of time. Consequently, there are only a few reports on tritium monitoring data in marine products from the coast of Fukushima. In this study, we measured the Tissue Free Water Tritium (TFWT) and Organically Bound Tritium (OBT) in flounders collected from the coast of Fukushima to examine the impacts of the nuclear accident on aquatic biota. The study was done for a period of 4 years; from 2015 to 2018. The conventional method of analysis was firstly used, after which the method was modified by improving the freeze-drying and combustion water recovery processes. Results from both methods show that the most of the concentrations of the TFWT and OBT in the flounder were below the detection or quantitative limit. The effect of the nuclear accident on humans, through internal exposure, was also examined and found to be negligible. Although some uncertainties exist due to the short cut of the processes, the modified version could be considered an effective and practical approximate method.

JAEA Reports

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima (FY2018)

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.

JAEA Reports

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima; As a part of dissemination of evidence-based information

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.

Journal Articles

Horizontal and vertical distributions of $$^{137}$$Cs in seabed sediments around the river mouth near Fukushima Daiichi Nuclear Power Plant

Tsuruta, Tadahiko; Harada, Hisaya*; Misono, Toshiharu; Matsuoka, Toshiyuki; Hodotsuka, Yasuyuki*

Journal of Oceanography, 73(5), p.547 - 558, 2017/10

 Times Cited Count:4 Percentile:59.26(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 $$^{137}$$Cs inventory was several tens of kBq/m$$^{2}$$ and the grain sizes (the D50 values) were nearly constant (fine sand) on the flat seafloor. On the terrace seafloor, the $$^{137}$$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 $$^{137}$$Cs inventories, more than several thousands of kBq/m$$^{2}$$, are thought to be confined to a small area. Vertical changes in the $$^{137}$$Cs inventories suggested that the $$^{137}$$Cs inventories have significantly decreased in large areas of the shallow sea.

Journal Articles

Activities for the environmental recovery from the Fukushima Daiichi Nuclear Power Plant accident by JAEA

Tsuruta, Tadahiko; Harada, Hisaya; Misono, Toshiharu; Iijima, Kazuki

Enganiki Gakkai-Shi, 28(3), p.2 - 6, 2015/12

no abstracts in English

Oral presentation

Distribution of sediments and current property in the coastal sea of Fukushima Prefecture

Tsuruta, Tadahiko; Harada, Hisaya; Misono, Toshiharu

no journal, , 

no abstracts in English

Oral presentation

Oral presentation

Relationship between SSflux and sediment distribution in the Fukushima coastal area

Misono, Toshiharu; Tsuruta, Tadahiko; Harada, Hisaya

no journal, , 

no abstracts in English

Oral presentation

Oral presentation

Characteristic of mineral assemblage of seabed sediments off the Fukushima coast

Tsuruta, Tadahiko; Harada, Hisaya*; Misono, Toshiharu

no journal, , 

no abstracts in English

Oral presentation

Study on the dynamics of radioactive cesium using sediment trap in the coastal area of Fukushima Prefecture

Misono, Toshiharu; Tsuruta, Tadahiko; Namikawa, Mitsuo

no journal, , 

no abstracts in English

Oral presentation

Simplification of oxygen combustion process in OBT analysis

Fujiwara, Kenso; Kuwata, Haruka*; Misono, Toshiharu; Iijima, Kazuki

no journal, , 

Since various radionuclides including tritium was released into the ocean by the Fukushima Dai-ichi Nuclear Power Station accident, transfer of those to marine products has been concerned. In case of tritium, Organically Bound Tritium (OBT) was considered to be relatively important for the transfer due to its longer biological half-life. However, huge sequential treatment processes and a few weeks are needed to measure the concentration of each type of tritium. Therefore, simplification of the processes and reduction of the duration were required for the purpose of rapid analysis and obtaining more data on environmental monitoring.

Oral presentation

Development of rapid analysis method of organically bound tritium

Fujiwara, Kenso; Kuwata, Haruka*; Misono, Toshiharu; Kitamura, Akihiro

no journal, , 

Since various radionuclides including tritium was released into the ocean by the Fukushima Dai-ichi Nuclear Power Station accident, transfer of those to marine products has been concerned. In case of tritium, Organically Bound Tritium (OBT) was considered to be relatively important for the transfer due to its longer biological half-life. However, analysis of organically bound tritium (OBT), which is one of beta-emitting radionuclides, requires complicated pretreatment and takes a long time conventionally. Therefore, in this method, the time per combustion could be shortened compared to the conventional method by reviewing the combustion process in the analysis of OBT. As a result of comparing the amount and composition of water recovered after combustion, almost no difference between the two methods was observed. The analysis results of tritium in tissue free water (TFWT) and OBT in the conventional method are all below the lower limit of detection, Both TFWT and OBT were at the nSv level even if internal exposure was evaluated using these values.

Oral presentation

Factors affecting radiocesium concentration in sediment off Fukushima; Lateral transport of suspended particles

Otosaka, Shigeyoshi*; Suzuki, Takashi; Tsuruta, Tadahiko; Misono, Toshiharu; Mino, Yoshihisa*; Sukigara, Chiho*; Ito, Yukari*; Shirai, Kotaro*; Sugihara, Naoko*

no journal, , 

In order to clarify the transport process of suspended radiocesium from the coast to the offshore area, which is one of the processes that change the concentration of radiocesium in sediments off Fukushima, a time-series sediment trap was deployed from October 2017 to June 2018 at a station located in southeast of the Fukushima Daiichi Nuclear Power Plant. Sinking particles of 39 periods were collected by this experiment. $$^{137}$$Cs was detected from sinking particles throughout the observation period, and the concentration showed clear seasonal variation. The maximum $$^{137}$$Cs concentration was an order of magnitude higher than that in the surface sediment (0-1 cm layer) at the station. On the other hand, the observed annual sinking flux of $$^{137}$$Cs was less than 1% of the $$^{137}$$Cs inventory in the seabed column. From these results, it can be concluded that the transport of $$^{137}$$Cs-bound particles from the coastal area has a relatively small effect of changing the abundance of radiocesium in sediments.

Oral presentation

Understanding of the behavior of radioactive cesium in front of rivers during typhoons

Misono, Toshiharu; Tsuruta, Tadahiko; Nakanishi, Takahiro

no journal, , 

Radioactive cesium was released into the environment and deposited extensively by the accident of Fukushima Daiichi Nuclear Power Plant. In the coastal area, it is necessary to understand the behavior of radioactive cesium supplied with the suspended solids from the river at the time of typhoon. In this study, sediment trap system and a water quality system, were installed in front of major rivers on the coast of Fukushima Prefecture, and sinking particles and water quality data were collected continuously. As a result, it was suggested that most of the radioactive cesium settled in front of the river, and the supply of radioactive cesium to the offshore was limited.

Oral presentation

Simplified oxygen combustion process in OBT analysis

Fujiwara, Kenso; Kuwata, Haruka*; Misono, Toshiharu; Kitamura, Akihiro

no journal, , 

Generally, when tritium is produced or released in the environment, it is required to confirm the behavior of organically bound tritium (OBT) due to its longer biological half-life. However, sequential treatment processes are needed to measure the concentration of each type of tritium and it takes a month for measurement of Tissue Free Water Tritium (TFWT) and a few weeks for measurement of OBT. Therefore, simplification of the processes and reduction of the duration were required for the purpose of rapid analysis and obtaining more data on environmental monitoring, especially in case of accident that requires emergency response. We are applying the analytical system composed of the TFWT separation process by means of freeze-drying and the OBT separation process by means of oxygen combustion vessel. In the TFWT separation process, a heater was attached to the outside of the freeze-dried cell, and freeze-drying and heating-drying were continuously performed quickly. The system has been improved that 90% TFWT was removed by freeze-drying and 10% TFWT was removed by heating drying. Then, the freeze-dried samples were divided for reducing the sample volume of one batch. Since the time of freeze-drying depends on the size of the sample, it could be shortened to about 3 days by dividing the sample into four. It successfully leads to reduction of measurement duration, from 14 days to 3 days. And in order to prevent isotope exchange, freeze- drying and heating-drying were performed inside the evacuated cell. In the OBT separation process, the pretreatment time was shortened by reducing the amount of combustion, and the value of detection limit was evaluated. When measured by the above-mentioned method, the tritium concentration of fish samples in Fukushima was below detection limit (several Bq/kg) and committed effective dose was very small (under 10$$^{-5}$$ mSv).

Oral presentation

Simplification of tritium analysis in seafood

Kuwata, Haruka*; Misono, Toshiharu; Terashima, Motoki; Fujiwara, Kenso; Kitamura, Akihiro

no journal, , 

Simplification of the processes and reduction of the duration were required for the purpose of rapid analysis and obtaining more data on environmental monitoring at the accident for emergency response. We are applying the analytical system composed of the TFWT separation process by means of freeze-drying and the OBT separation process by means of oxygen combustion vessel.

22 (Records 1-20 displayed on this page)