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Journal Articles

Development of a practical tritiated water monitor to supervise the discharge of treated water from Fukushima Daiichi Nuclear Power Plant

Sanada, Yukihisa; Oshikiri, Keisuke*; Kanno, Marina*; Abe, Tomohisa

Nuclear Instruments and Methods in Physics Research A, 1062, p.169208_1 - 169208_7, 2024/05

As part of the decommissioning work at the Fukushima Daiichi Nuclear Power Plant (FDNPP), the release of stored treated water began in 2023. In this study, we developed a practical tritium monitor to continuously monitor the concentration of tritiated water, as confirmed by batch sampling measurements at the FDNPP. The monitor is arranged with a flow cell detector comprising inexpensive plastic scintillator pellets and incorporating simultaneous measurements by three detectors, a veto detector, and lead shielding to reduce the influence of environmental $$gamma$$-rays. The system reached a detection limit of 911 Bq L-1 with a measurement time of 30 min, which is lower than the discharge standard for tritiated water of 1,500 Bq L-1. The system can also qualitatively distinguish the presence of disturbances due to interfering radionuclides other than tritium or background radiation using the $$beta$$-ray spectrum.

JAEA Reports

Radiation monitoring via manned helicopter around the nuclear power station in the fiscal year 2022 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Nagakubo, Azusa; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; Matsunaga, Yuki*; Akutsu, Yuichiro*; Arai, Yoshinori*; et al.

JAEA-Technology 2023-027, 146 Pages, 2024/03

JAEA-Technology-2023-027.pdf:18.12MB

By the accident at Tokyo Electric Power Company's (TEPCO's) Fukushima Daiichi Nuclear Power Station (FDNPS), caused by tsunami triggered by the 2011 off the Pacific coast of Tohoku Earthquake, a large amount of radioactive material was released into the surrounding environment. After the accident, Airborne Radiation Monitoring (ARM) via manned helicopter has been applied as a method to quickly and extensively measure the distribution of radiation. Japan Atomic Energy Agency (JAEA) has continuously conducted ARM via manned helicopter around FDNPS. In this report, we summarize the results of the ARM around FDNPS in the fiscal year 2022, evaluate the changes of ambient dose rates and other parameters based on the comparison to the past ARM results, and discuss the causes of such changes. In order to contribute to improve the accuracy of ambient dose rate conversion, we analyzed the ARM data taking into account undulating topography, and evaluated the effect of this method. Furthermore, the effect of radon progenies in the air on the ARM was evaluated by applying the discrimination method to the measurement results.

JAEA Reports

Background radiation monitoring via manned helicopter and development of technology for radiation monitoring via unmanned airplane for application of nuclear emergency response technique in the fiscal year 2022 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Sasaki, Miyuki; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; Matsunaga, Yuki*; Akutsu, Yuichiro*; Arai, Yoshinori*; et al.

JAEA-Technology 2023-026, 161 Pages, 2024/03

JAEA-Technology-2023-026.pdf:14.66MB

By the accident at Tokyo Electric Power Company's (TEPCO's) Fukushima Daiichi Nuclear Power Station (FDNPS), caused by tsunami triggered by the 2011 off the Pacific coast of Tohoku Earthquake, a large amount of radioactive material was released into the surrounding environment. After the accident, Airborne Radiation Monitoring (ARM) via manned helicopter has been utilized as a method to quickly and extensively measure radiation distribution surrounding FDNPS. In order to utilize ARM and to promptly provide the results during a nuclear emergency, information on background radiation levels, topographical features, and controlled airspace surrounding nationwide nuclear facilities have been prepared in advance. In the fiscal year 2022, we conducted ARM around the Mihama Nuclear Power Station of Kansai Electric Power Company (KEPCO), the Tsuruga Power Station of Japan Atomic Power Company (JAPC), and the Ikata Power Station of Shikoku Electric Power Company (YONDEN), and prepared information on background radiation doses and controlled airspace. In addition, we have developed an aerial radiation detection system via unmanned airplane, which is expected to be an alternative to ARM, during a nuclear emergency. This report summarizes the results and technical issues identified.

Journal Articles

Initial deposition of radioactive materials due to the Fukushima Daiichi Nuclear Power Station accident and airborne monitoring of radiation

Torii, Tatsuo; Sanada, Yukihisa

Introduction to Environmental Radioactivity, p.31 - 54, 2024/02

no abstracts in English

Journal Articles

Behavior of radiocesium ($$^{137}$$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

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.

Journal Articles

Application of USV to marine monitoring after Fukushima Daiichi Nuclear Power Plant Accident and its applicability as a nuclear disaster prevention tool

Sanada, Yukihisa; Misono, Toshiharu; Shiribiki, Takehiko*

Kaiyo Riko Gakkai-Shi, 27(2), p.37 - 44, 2023/12

This paper summarizes the general situation of marine monitoring conducted after the Fukushima Daiichi Nuclear Power Plant accident, the experience of development and operation of USVs, and the possibility of applying unmanned vessels as a tool for nuclear disaster prevention in the future. 0.01 Bq/L or less for seawater and 10 Bq/L or less for seabed soil. Operational tests of three USVs have been continuously conducted for use in such environmental radiation monitoring. Development of these UAVs is underway with a view to utilizing them for seawater sampling, direct measurement of the seafloor soil surface layer, and seafloor soil sampling, depending on their performance. It is necessary to promote the development of USVs for future nuclear power plant accidents.

Journal Articles

Visual analysis of air dose rate maps

Takahashi, Shigeo*; Sakurai, Daisuke*; Nagao, Fumiya; Kurikami, Hiroshi; Sanada, Yukihisa

Shimyureshon, 42(2), p.68 - 75, 2023/06

This paper introduces a case in which scientific knowledge on understanding the deposition process of radionuclides and evaluating the dose rate reduction due to decontamination work was obtained through visual analysis based on data on the spatio-temporal distribution of air dose rates accumulated through radiation monitoring after the accident. We will discuss the prospects for future efforts to effectively obtain important knowledge that will assist in the planning of policies for reconstruction from the nuclear power plant accident in the future.

JAEA Reports

Research on atmospheric radioactivity concentration in the specified reconstruction and revitalization base (FY2018-FY2021)

Abe, Tomohisa; Funaki, Hironori; Yoshimura, Kazuya; Shiribiki, Natsu*; Sanada, Yukihisa

JAEA-Data/Code 2023-001, 38 Pages, 2023/05

JAEA-Data-Code-2023-001.pdf:3.04MB
JAEA-Data-Code-2023-001-appendix(CD-ROM).zip:32.02MB

In this study, commissioned by the Cabinet Office, we conducted a survey on radioactive materials in atmospheric dust in three municipalities (Futaba Town, Okuma Town, and Tomioka Town) in Fukushima Prefecture to contribute to the assessment of internal exposure in the Specified Reconstruction and Revitalization Base (SRRB). Air dust samplers were installed in the targeted municipalities to investigate the atmospheric $$^{137}$$Cs concentrations and to evaluate internal exposure doses based on measured value. This report summarizes the results of measurements between 2018 and 2021. A database of information on internal exposure dose assessment results based on atmospheric radioactivity concentrations and actual measurements, and meteorological observation data was compiled.

Journal Articles

Purposeful adaptive sampling of integrated air dose rate maps for visual analysis

Takahashi, Shigeo*; Kurikami, Hiroshi; Sanada, Yukihisa; Sakurai, Daisuke*

ERAN FY2022 Annual Report (Internet), 1 Pages, 2023/04

This study aims to establish a highly accurate evaluation technique for decontamination effects through multilateral and quantitative evaluation of decontamination effects. The applicability of the visual analysis technique was confirmed through a trial analysis.

Journal Articles

Evaluation of external dose exposure of workers during house demolition and dose reduction work in a difficult-to-return zone

Sanada, Yukihisa; Tokiyoshi, Masanori*; Nishiyama, Kyohei*; Sato, Rina; Yoshimura, Kazuya; Funaki, Hironori; Abe, Tomohisa; Ishida, Mutsushi*; Nagamine, Haruo*; Fujisaka, Motoyuki*

Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 22(2), p.87 - 96, 2023/04

Since the accident at the Fukushima Daiichi Nuclear Power Plant, many decontamination works have been carried out, but it is difficult to say that much data on workers' exposure has necessarily been analyzed in detail. In this paper, based on the GPS location information carried by the workers together with their personal dosimeters, the air dose rate in the work area and the characteristics of each type of work were analyzed. The results showed that more than 50% of the measured actual doses were more than twice the median planned dose calculated from the air dose rate and actual working hours. Furthermore, as a result of the analysis by work type, it was found that the exposure doses of demolition workers tended to be high, and that this was due to the fact that most of the work was carried out before the work was carried out to reduce the dose at the work site. In addition, when the conversion from air dose to effective dose was taken into account, there were many cases of underestimation where the planned values were lower than the measured values, and it is considered important for management to set appropriate working factor.

Journal Articles

Radiation distribution around Fukushima Daiichi Nuclear Power Station decade after the accident

Sanada, Yukihisa; Sasaki, Miyuki; Kurikami, Hiroshi; Mikami, Satoshi

Journal of Nuclear Fuel Cycle and Waste Technology, 21(1), p.95 - 114, 2023/03

During the decades after the Fukushima Daiichi Nuclear Power Station (FDNPS) accident, ambient dose rates have markedly decreased when compared to those at the early state of the accident. Government projects have been continuously conducted by surveying the ambient dose rate and radiocesium distributions. Airborne surveys using crewed helicopters and unmanned aerial vehicles (UAVs) are the best methods for obtaining an overall picture of the distribution. However, ground-based surveys are required for accurate measurements near the population. The differences between these methods include the knowledge of the post depositional behavior of radionuclides in land use. The survey results form the basis for policy decisions such as lifting evacuation zones, decontamination, and other countermeasures. These surveys contain crucial findings regarding post-accident responses. This paper reviews the survey methods of government projects and current situation around the FDNPS. The visualization methods and databases of ambient dose rates are also reviewed to provide information to the population.

Journal Articles

External exposure assessment in the Fukushima accident area for governmental policy planning in Japan, 2; Matters to be attended for assessments of external exposure

Yoshimura, Kazuya; Sanada, Yukihisa; Sato, Rina; Nakayama, Mariko*; Tsubokura, Masaharu*

Journal of Radiation Research (Internet), 64(2), p.203 - 209, 2023/03

 Times Cited Count:0 Percentile:0.01(Biology)

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, individual exposure doses to residents have been assessed by many municipalities, governments and research institutes. Various methods including measurements with personal dosimeters and simulations have been used for this evaluation depending on purposes, but the information of assessments and methods has not been systematically organized. A comprehensive review of the knowledge and experiences of individual exposure doses assessments accumulated so far and understanding the characteristics of the assessment methods will be very useful for radiation protection and risk communication, following to governmental policy planning. We reviewed the efforts made by the Japanese government and research institutes to assess radiation doses to residents after the FDNPS accident in Part1. On the other hand, each method of assessing individual exposure doses includes uncertainties and points to be considered for the appropriate assessment. These knowledge and experiences are important for the assessment implementation and applying the assessment results to the governmental policy planning, and are summarized in Part2 of this article.

JAEA Reports

Background radiation monitoring via manned helicopter for application of technique of nuclear emergency response in the fiscal year 2021 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Sasaki, Miyuki; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; Matsunaga, Yuki*; Akutsu, Yuichiro*; Hokama, Tomonori; et al.

JAEA-Technology 2022-028, 127 Pages, 2023/02

JAEA-Technology-2022-028.pdf:15.21MB

A large amount of radioactive material was released by the nuclear disaster of Fukushima Daiichi Nuclear Power Station (FDNPS), Tokyo Electric Power Company, caused by the Great East Japan Earthquake and the following tsunami on March 11, 2011. After the nuclear disaster, airborne radiation monitoring via manned helicopter has been utilized to grasp rapidly and widely the distribution of the radioactive materials surrounding FDNPS. We prepare the data of background radiation dose, geomorphic characteristics and the controlled airspace surrounding nuclear facilities of the whole country in order to make effective use of the monitoring technique as a way of emergency radiation monitoring and supply the results during an accident of a facility. This report has summarized the knowledge noted above achieved by the aerial radiation monitoring around Ohi and Takahama nuclear power stations. In addition, the examination's progress aimed at introducing airborne radiation monitoring via an unmanned plane during a nuclear disaster and the technical issues are summarized in this report.

JAEA Reports

Radiation monitoring via manned helicopter around the Nuclear Power Station in the fiscal year 2021 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Nagakubo, Azusa; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; Matsunaga, Yuki*; Akutsu, Yuichiro*; Urabe, Yoshimi*; et al.

JAEA-Technology 2022-027, 148 Pages, 2023/02

JAEA-Technology-2022-027.pdf:19.64MB

By the nuclear disaster of Fukushima Daiichi Nuclear Power Station (FDNPS), Tokyo Electric Power Company (TEPCO), caused by the Great East Japan Earthquake and the following tsunami on March 11, 2011, a large amount of radioactive material was released from the FDNPS. After the nuclear disaster, airborne radiation monitoring via manned helicopter has been conducted around FDNPS. The results of the airborne radiation monitoring and the evaluation for temporal change of dose rate in the fiscal 2021 were summarized in this report. Analysis considering topographical effects was applied to the result of the airborne monitoring to improve the accuracy of the conventional method. In addition, technique for discriminating gamma rays from the ground and those from the airborne Rn-progenies was also utilized to evaluate their effect on airborne radiation monitoring.

JAEA Reports

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.

JAEA Reports

Individual exposure dose assessment of residents for lifting of evacuation orders (Contract research)

Sato, Rina; Sanada, Yukihisa; Yoshimura, Kazuya; Nakayama, Mariko*

JAEA-Review 2022-055, 42 Pages, 2023/01

JAEA-Review-2022-055.pdf:1.31MB

The evacuation order zones established after the accident at the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Station have been reorganized according to the decrease in ambient dose equivalent rates and the decontamination progress. It has been decided to decontaminate the difficult-to-return zones and lift the evacuation order depending on the evacuee's intention of returning to the areas over the course of the 2020s. In order to consider the future of individual exposure dose assessment for residents for lifting of the evacuation orders, the methods and characteristics of the assessment that have been conducted after the accident using personal dosimeter measurements and simulations were systematically reviewed. This report summarized the results of the review.

Journal Articles

External exposure assessment in the Fukushima accident area for governmental policy planning in Japan, 1; Methodologies for personal dosimetry applied after the accident

Sanada, Yukihisa; Yoshimura, Kazuya; Sato, Rina; Nakayama, Mariko*; Tsubokura, Masaharu*

Journal of Radiation Research (Internet), 64(1), p.2 - 10, 2023/01

 Times Cited Count:0 Percentile:0.06(Biology)

The evacuation orderareas established due to the accident at the Tokyo Electric Power Company Holdings' (TEPCO) Fukushima Daiichi Nuclear Power Plant (FDNPP) have been reorganized according to the decrease in ambient dose rates and the decontamination progress. The Japanese government decided to decontaminate the difficult-to-return areas and lift the evacuation order by 2030. This radiation protection strategy can be optimized by examining emergency exposure situations to date and the existing exposure after the accident. This article reviews the methods that can determine the individual radiation doses of residents who should return to their homes when the evacuation order is lifted in the specific reconstruction reproduction base area and the difficult-to-return areas outside this base area and summarizes the points to be considered when implementing these methods. In Part 1 of this article, we review the efforts made by the Japanese government and research institutes to assess radiation doses to residents after the FDNPP accident.

Journal Articles

Basic study on tritium monitor using plastic scintillator for treated water discharge at Fukushima Daiichi Nuclear Power Plant

Sanada, Yukihisa; Abe, Tomohisa; Sasaki, Miyuki; Kanno, Marina*; Yamada, Tsutomu*; Nakasone, Takamasa*; Miyazaki, Nobuyuki*; Oshikiri, Keisuke*; Watabe, Hiroshi*

Journal of Nuclear Science and Technology, 10 Pages, 2023/00

The "treated water" from which the main radioactive materials were removed contains tritium, and stakeholders in Japan have been debating how to treat it. The amount of treated water stored in the facility has reached its limit, and the Japanese government has decided that the treatment method will be to discharge the water into the ocean by FY 2023 (FY: Fiscal Year). The present research developed a simple and practical tritium monitor for the Fukushima Daiichi Nuclear Power Station (FDNPS) tritiated water release. A simple and practical tritium monitor was developed for FDNPS tritiated water release based on thin plastic scintillator sheets. The developed devices were calibrated using standard tritium solutions and a method for calculating the minimum detectable activity. Fifteen 0.25 mm-thick scintillators can be placed in the 0.26 L flow cell where the sample water is fed, yielding an active surface area of 3,200 mm$$^{2}$$. The efficiency of tritiated water with full water is 0.000035 cps Bq$$^{-1}$$. The minimum detectable activity under simple shielding conditions was 7,800 Bq L$$^{-1}$$ (Measurement time was 3,600 s).

Journal Articles

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.

Journal Articles

Estimation of the effect of GNSS positioning errors on the dose rate calculation concerning aerial radiation monitoring

Mori, Airi; Seguchi, Eisaku*; Futemma, Akira; Iwai, Takeyuki*; Sanada, Yukihisa

Journal of Instrumentation (Internet), 17(10), p.P10015_1 - P10015_11, 2022/10

 Times Cited Count:0 Percentile:0(Instruments & Instrumentation)

303 (Records 1-20 displayed on this page)