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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, 61(5), p.693 - 702, 2024/05

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

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).

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

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.

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.

Journal Articles

Improvement of training data for dose rate distribution using an artificial neural network

Sasaki, Miyuki; Sanada, Yukihisa

Journal of Advanced Simulation in Science and Engineering (Internet), 9(1), p.30 - 39, 2022/01

This study presents the evaluation results of the validity of the visualization map of the ambient dose rate at 1 m above the ground level using an artificial neural network. The dose rate map created using the artificial neural network-based method is found to reproduce ground-based survey results better than conventional methods. Suggested to improve the validity of the airborne radiation survey visualization, applying the color data obtained using a photogrammetry system is a new experience.

Journal Articles

Analysis of radiation measurement data using AI

Sasaki, Miyuki

Isotope News, (778), p.2 - 5, 2021/12

no abstracts in English

Journal Articles

Visual analysis of geospatial multivariate data for investigating radioactive deposition processes

Takahashi, Shigeo*; Sakurai, Daisuke*; Sasaki, Miyuki; Miyamura, Hiroko; Sanada, Yukihisa

Visual Computer, 37(12), p.3039 - 3050, 2021/12

 Times Cited Count:0 Percentile:0.01(Computer Science, Software Engineering)

The Fukushima nuclear accident in 2011 raised awareness on the importance of radioactive deposition processes, especially for proposing aerosol measures against possible air pollution. However, identifying these types of processes is often difficult due to complicated terrains. This paper presents an application study for identifying radioactive deposition processes by taking advantage of visual interaction with topographic data. The idea is to visually investigate the correspondence of the spatial positions to the air dose rate along with relevant attributes. This is accomplished by composing scatterplots of pairwise attributes, onto which we project terrain areas to interactively find specific patterns of such attributes. We applied our approach to the analysis of air dose rate distribution data around the Fukushima nuclear plant after the accident. Our visualization technique clearly distinguished contamination areas derived from different deposition processes, and thus is useful for elucidation of the deposition process.

JAEA Reports

Background radiation monitoring using manned helicopter for application of technique of nuclear emergency response in the fiscal year 2020 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Sasaki, Miyuki; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Sato, Kazuhiko*; Haginoya, Masashi*; Matsunaga, Yuki*; Kikuchi, Hikaru*; et al.

JAEA-Technology 2021-020, 138 Pages, 2021/11

JAEA-Technology-2021-020.pdf:17.11MB

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 is summarized that the knowledge as noted above achieved by the aerial radiation monitoring around Tsuruga and Mihama nuclear power station, research reactors in Kindai University Atomic Energy Research Institute and Institute for Integrated Radiation and Nuclear Science, Kyoto University. In addition, examination's progress aimed at introduction of airborne radiation monitoring via unmanned plane during nuclear disaster and the technical issues are summarized in this report.

Journal Articles

New method for visualizing the dose rate distribution around the Fukushima Daiichi Nuclear Power Plant using artificial neural networks

Sasaki, Miyuki; Sanada, Yukihisa; Katengeza, E. W.*; Yamamoto, Akio*

Scientific Reports (Internet), 11, p.1857_1 - 1857_11, 2021/01

 Times Cited Count:13 Percentile:67.48(Multidisciplinary Sciences)

This study proposed a new method to visualize the ambient dose rate distribution using artificial neural networks from the results of airborne radiation monitoring. The method used airborne radiation monitoring conducted around Fukushima Daiichi Nuclear Power Plant by an unmanned aerial vehicle. A lot of survey data which had obtained in the past was used as training data for building a network. The reliability of the artificial neural network method was evaluated by comparison with the ground-based survey data. The dose rate map that was created by the artificial neural networks method reproduced the ground-based survey results better than traditional methods.

Journal Articles

Evaluation of decreasing trend in air dose rate and ecological half-life within an 80 km range from Fukushima Dai-ichi Nuclear Power Plant, using car-borne survey data measured by KURAMA systems up to 2018

Ando, Masaki; Sasaki, Miyuki; Saito, Kimiaki

Journal of Nuclear Science and Technology, 57(12), p.1319 - 1330, 2020/12

 Times Cited Count:4 Percentile:43.68(Nuclear Science & Technology)

Air dose rates measured by car-borne surveys within 80 km range of Fukushima Dai-ichi Nuclear Power Plant using KURAMA systems from 2011 up to 2018 were analyzed, and decreasing trends and ecological half-life were evaluated. The decreasing speed of air dose rates became 0.08 over a period of seven years, indicating a much more rapid decrease than estimated by the physical decay of radiocesium (0.3). The fast components of the ecological half-lives evaluated in entire the evacuation order area were about 2 to 3 y, and were considerably larger than those outside the evacuation order area (0.4 to 0.5 y). To model the acceleration in the decrease of air dose rates observed in evacuation order areas, we modified the bi-exponential curve formula of ecological half-life and introduced the two-group model. The fast decreasing components of the ecological half-life evaluated using the two-group model after 2013 were 0.5 to 1 y, and were much shorter than those up to 2013, at 2 to 3 y.

Journal Articles

Application of the forest shielding factor to the maximum-likelihood expectation maximization method for airborne radiation monitoring

Sasaki, Miyuki; Sanada, Yukihisa; Yamamoto, Akio*

Radiation Protection Dosimetry, 184(3-4), p.400 - 404, 2019/10

 Times Cited Count:3 Percentile:30.79(Environmental Sciences)

The maximum-likelihood expectation maximization (ML-EM) method is expected to improve the accuracy of airborne radiation monitoring using an unmanned aerial vehicle. The accuracy of the ML-EM method depends on various parameters, including detector efficiency, attenuation factor, and shielding factor. In this study, we evaluate the shielding factor of trees based on several field radiation measurements. From the actual measurement, the shielding factors were well correlated with the heights of the trees. The evaluated shielding factors were applied to the ML-EM method in conjunction with the measured data obtained from above the Fukushima forest. Compared with the conventional methods used for calculating the dose rate, the proposed method is found to be more reliable.

Journal Articles

Student and Young researcher's view of research on health physics and environment science

Miwa, Kazuji; Terasaka, Yuta; Ochi, Kotaro; Futemma, Akira; Sasaki, Miyuki; Hirouchi, Jun

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 61(9), p.687 - 691, 2019/09

This report summarizes the contents of the session of the Health Physics and Environment Science Division, which was held in Atomic Energy Society of Japan 2019 Spring Meeting. In this session, six students and young researchers who engaged in the field of nuclear energy and radiation gave a lecture about health physics and environmental science research through their expertise. After the all presentations end, we took discussion time about the issues and future development in this field with all attendees. In this report, we summarized each lecture outline and discussion contents.

JAEA Reports

Applied research for the establishment of radiation monitoring and evaluation of exposure dose of residence at the zone designated for reconstruction and recovery

Funaki, Hironori; Takahara, Shogo; Sasaki, Miyuki; Yoshimura, Kazuya; Nakama, Shigeo; Sanada, Yukihisa

JAEA-Research 2018-016, 48 Pages, 2019/03

JAEA-Research-2018-016.pdf:29.73MB

Cabinet Office Nuclear Emergency Response Headquarters starts to consider radiation protection in the "specific reconstruction reproduction base area" of which evacuation order will be lifted by 2023. It is essential to grab the present situations of radiation contamination and evaluate exposure dose in the area to realize the plan. Many surveys have evaluated the distributions of air dose rate and exposure dose has been estimated based on the results since the Fukushima Daiichi Nuclear Power Plant accident. Nevertheless, more detailed information on exposure is needed for the areas because its radiation level is relatively high. That is also to help make prudent evaluation plan. This study aimed to evaluate the detailed contamination situation there and estimate exposure dose with considering areal circumstances. Investigations were carried out for (1) airborne survey of air dose rate using an unmanned helicopter (2) evaluation of airborne radiocesium and (3) estimation of external/internal effective doses for typical activity patterns assumed. Additionally, we applied new methods for the airborne survey to evaluate exposure dose. Our study showed a detailed three-dimensional map of air dose rate and clarified the distribution pattern in the areas. Results of effective dose estimation suggested that the internal effective dose due to inhalation accounts for less than 1% of the external effective dose.

Journal Articles

Comparison of the Fukushima radioactive mapping by two different aerial radiation monitoring systems

Kim, B.-J.*; Sasaki, Miyuki; Sanada, Yukihisa

Progress in Nuclear Science and Technology (Internet), 6, p.130 - 133, 2019/01

Journal Articles

Comparison of airborne and ground-based tools used for radiation measurement in the environment

Ochi, Kotaro; Sasaki, Miyuki; Ishida, Mutsushi*; Sanada, Yukihisa

Progress in Nuclear Science and Technology (Internet), 6, p.103 - 107, 2019/01

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, a large amount of radionuclides was spread out all over the world. In our previous study, we developed the aerial radiation monitoring technique using unmanned helicopter for investigating the dose rate derived deposited radionuclides over wide area. In addition, many monitoring techniques were developed for investigating the local distribution of radionuclides using unmanned aerial vehicle, handheld instrument and car within small area. Distinction of these methods depends on desirable position resolution of dose rate. However, the comparison method of the measurement result between different methods is not established. In this study, we attempted to evaluate the some methods of airborne and ground radiation measurement in same extended farm.

Journal Articles

Development of analysis method for airborne radiation monitoring using the inverse problem solutions

Sasaki, Miyuki; Ishizaki, Azusa; Sanada, Yukihisa

Progress in Nuclear Science and Technology (Internet), 6, p.63 - 67, 2019/01

Since the accident at Fukushima Daiichi Nuclear Power Station (FDNPS), some unmanned vehicles (UAVs) are applied to airborne radiation measurement in around FDNPS. In conventional analysis methods, count rate that is obtained in the sky is converted to air dose rate at 1 m above the ground (agl.) under following premises. (1) Topography under the UAV is a plane (plane source model). (2) The air dose rate at 1 m agl. under the UAV is constant inside approximately 10 m radius. (3) Relationship of altitude and count rate is exponential correlation. Therefore, it is difficult that dose rate by airborne radiation measurement is precisely measured at the mountains and uneven place of dose rate by the conventional method. In this study, Maximum Likelihood-Expectation Maximization (ML-EM) method which is used in the medical radiation such as Positron Emission Tomography (PET) is attempted to apply to environmental radiation measurement using UAV.

Journal Articles

Evaluation of ecological half-life of dose rate based on airborne radiation monitoring following the Fukushima Dai-ichi Nuclear Power Plant accident

Sanada, Yukihisa; Urabe, Yoshimi*; Sasaki, Miyuki; Ochi, Kotaro; Torii, Tatsuo

Journal of Environmental Radioactivity, 192, p.417 - 425, 2018/12

 Times Cited Count:27 Percentile:68.75(Environmental Sciences)

Journal Articles

Estimation of the vertical distribution of radiocesium in soil on the basis of the characteristics of $$gamma$$-ray spectra obtained via aerial radiation monitoring using an unmanned helicopter

Ochi, Kotaro; Sasaki, Miyuki; Ishida, Mutsushi*; Hamamoto, Shoichiro*; Nishimura, Taku*; Sanada, Yukihisa

International Journal of Environmental Research and Public Health, 14(8), p.926_1 - 926_14, 2017/08

 Times Cited Count:4 Percentile:22.30(Environmental Sciences)

After the Fukushima Daiichi Nuclear Power Plant accident, the vertical distribution of radiocesium in soil has been investigated to better understand the behavior of radiocesium in the environment. The typical method used for measuring the vertical distribution of radiocesium is troublesome because it requires collection and measurement of the activity of soil samples. In this study, we established a method of estimating the vertical distribution of radiocesium by focusing on the characteristics of $$gamma$$-ray spectra obtained via aerial radiation monitoring using an unmanned helicopter. In this method, the change in the ratio of direct $$gamma$$ rays to scattered $$gamma$$ rays at various depths in the soil was utilized to quantify the vertical distribution of radiocesium. The results show a positive correlation between the abovementioned and the actual vertical distributions of radiocesium measured in the soil samples.

JAEA Reports

Radiation monitoring using manned helicopter around the Nuclear Power Station in the fiscal year 2015 (Contract research)

Sanada, Yukihisa; Munakata, Masahiro; Mori, Airi; Ishizaki, Azusa; Shimada, Kazumasa; Hirouchi, Jun; Nishizawa, Yukiyasu; Urabe, Yoshimi; Nakanishi, Chika*; Yamada, Tsutomu*; et al.

JAEA-Research 2016-016, 131 Pages, 2016/10

JAEA-Research-2016-016.pdf:20.59MB

By the nuclear disaster of Fukushima Daiichi Nuclear Power Station (FDNPS), Tokyo Electric Power Company (TEPCO), caused by the East Japan earthquake and the following tsunami occurred on March 11, 2011, a large amount of radioactive materials was released from the NPS. After the nuclear disaster, airborne radiation monitoring using manned helicopter was conducted around FDNPS. In addition, background dose rate monitoring was conducted around Sendai Nuclear Power Station. These results of the aerial radiation monitoring using the manned helicopter in the fiscal 2015 were summarized in the report.

Patent

放射線検出器及び放射線の入射方位推定方法

眞田 幸尚; 佐々木 美雪

鳥居 建男*

JP, 2021-176290  Patent licensing information

【課題】放射線の入射方向を検出することができ、かつ、安価に小型軽量化を図ることが可能な放射線検出器を提供する。 【解決手段】放射線検出器1は、放射線を検出し、フラクタル構造を形成するように配列された複数の放射線センサ10と、隣り合う放射線センサ10の間を埋める放射線遮蔽材20と、を備える。

61 (Records 1-20 displayed on this page)