Aerial monitoring around TEPCO's Fukushima Daiichi Nuclear Power Station and development of radiation monitoring technology for unmanned vehicle in fiscal year 2024 (Contract research)

Futemma, Akira; Ochi, Kotaro; Sasaki, Miyuki; Nakama, Shigeo; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; Matsunaga, Yuki*; Yamada, Tsutomu*; et al.

JAEA-Technology 2025-016, 253 Pages, 2026/03

JAEA-Technology-2025-016.pdf:20.16MB

Aerial Radiation Monitoring (ARM) has been used to quickly and widely measure radiation distribution caused by the TEPCO's Fukushima Daiichi Nuclear Power Station (FDNPS) accident resulted from the tsunami accompanying the Pacific coast of Tohoku Earthquake on March 11, 2011. Since the accident, As a commissioned project of the Nuclear Regulation Authority, the Japan Atomic Energy Agency (JAEA) has continuously conducted ARM around FDNPS. This report summarizes the results of the 2024 monitoring activities, evaluates temporal changes in ambient dose rates, and identifies factors contributing to these changes. A terrain-corrected analysis was applied to improve dose rates conversion accuracy, and results with and without this correction were compared. A radon-progeny discrimination method was also used to assess its impact on manned-helicopter measurements. Furthermore, development of unmanned airplane monitoring technologies was advanced to enhance the efficiency of wide-area surveys.

Investigations on distribution of radioactive substances owing to the Fukushima Daiichi Nuclear Power Station Accident in the fiscal year 2024 (Contract research)

Group for Fukushima Mapping Project

JAEA-Technology 2025-013, 206 Pages, 2026/03

JAEA-Technology-2025-013.pdf:34.64MB

This report presents results of the investigations on the distribution-mapping project of radioactive substances conducted in FY2024. Car-borne and walk surveys, a measurement using survey meters, and an unmanned helicopter survey were carried out to obtain air dose rate data on land to create their distribution maps, and temporal changes of those air dose rates were analyzed. In order to confirm the applicability of unmanned aircraft to monitoring in mountainous areas, a basic performance of unmanned aircraft was investigated in mountainous areas. Surveys on depth profile of radiocesium and in-situ measurements as for radiocesium deposition were performed. These measurement results were published on the WEB site. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated air dose rate distribution data acquired through surveys such as car-borne and walk surveys. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out. Representative life patterns that can be expected after the return to the evacuation-designated restricted area were set, and the cumulative exposure doses were evaluated for the local governments and residents in the area. Score maps to classify the importance of the measurement points were created, and the temporal changes in the score were analyzed. A system to report the tritium concentration level in seawater to the Nuclear Regulation Authority was operated, and the variation of tritium concentration before and after the discharge of ALPS treated water to the ocean was analyzed. Monitoring data in coastal area performed owing to the comprehensive radiation monitoring plan until FY2024 was analyzed.

Survey on the radioactive substance in the coastal areas near Fukushima Prefecture in FY2022

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

JAEA-Research 2025-014, 88 Pages, 2026/03

JAEA-Research-2025-014.pdf:7.52MB

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 2022 on the status of marine monitoring survey on radioactive substances. 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. From these results, we estimated the distribution and its dynamics of radioactive Cs in the sediments in the front area on the 1F.

A Strategy for selecting additional observation points when estimating radiation source distribution using LASSO regression

Yamada, Susumu; Machida, Masahiko

Nihon Oyo Suri Gakkai Rombunshi, 36(1), p.14 - 32, 2026/03

https://doi.org/10.11540/jsiamt.36.1_14

Estimating the distribution of radiation sources is crucial for the safe decommissioning of reactor buildings. LASSO regression has been applied to estimate radiation sources inside reactor buildings based on radiation measurements. However, LASSO regression requires air dose rates measured at appropriate points to produce accurate estimates. Although a strategy for adding observation points has been proposed, its effectiveness is limited depending on the model size. Therefore, we propose a new strategy that takes into account the estimated source distribution and demonstrate its effectiveness.

A Scheme to efficiently select air-dose-rate measurement positions in estimating radiation source distribution

Machida, Masahiko; Yamada, Susumu; Yoshida, Toru*; Hasegawa, Yukihiro*; Yanagi, Hideaki*; Furutachi, Naoya*

Proceedings of Waste Management Symposia 2026 (WM2026) (Internet), 15 Pages, 2026/03

Cesium sorption onto alkaline activated materials

Hagiwara, Hiroki; Takaku, Atsushi*; Sagawa, Hiroshi*; Kanno, Futoshi*; Ito, Azusa; Ando, Taichi*; Ichihara, Masatsugu*; Watanabe, Yusuke; Koarai, Kazuma; Kato, Jun; et al.

Proceedings of Waste Management Symposia 2026 (WM2026) (Internet), 7 Pages, 2026/03

Development of a high-resolution imaging camera for alpha dust and high-dose rate monitor (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*

JAEA-Review 2025-048, 56 Pages, 2026/02

JAEA-Review-2025-048.pdf:2.89MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2022, this report summarizes the research results of the "Development of a high-resolution imaging camera for alpha dust and high-dose rate monitor" conducted in FY2023. The present study aims to develop a high-resolution imaging camera for alpha dust and a high-dose rate monitor. To realize the high-resolution imaging camera for alpha dust, we have developed novel scintillation materials with emission bands of 500-800 nm. Moreover, we have prepared several materials for the camera and software. We have also developed novel scintillation materials with emission bands of 650-1,000 nm, and simulation studies have been conducted for the high-dose-rate monitor system consisting of optical fiber. In addition, we demonstrated this monitoring system, and the dose-rate dynamic range was found to be 20 mSv/h to 1 kSv/h.

Alpha ray detector developed to aid in Fukushima Daiichi nuclear reactor operations

Morishita, Yuki

Isotope News, (803), p.38 - 42, 2026/02

In this study, we developed an alpha ray imaging detector for the in-situ measurement of Pu and Np to identify alpha nuclides in real time on-site. The alpha ray imaging detector developed in this study was brought to Savannah River National Laboratory (SRNL) in the United States, where measurements were performed on actual Pu and Np oxide samples. These measurements confirmed the effectiveness of in-situ detection of Pu and Np. We also developed a detector that can directly measure alpha contamination inside pipes. We confirmed the detector's ability to distinguish between alpha and beta rays and evaluated its basic characteristics.

Development of a compact lanthanoid bromide -ray spectroscopy system with high-count-rate pulse processing and simultaneous pulse-current operation mode for in-situ non-destructive assay

Kaburagi, Masaaki; Ishii, Junya*; Kato, Masahiro*; Kamada, Kei*; Yoshino, Masano*; Shimazoe, Kenji*

Journal of Instrumentation (Internet), 21(2), p.P02051_1 - P02051_19, 2026/02

https://doi.org/10.1088/1748-0221/21/02/P02051

2025 Nuclear Data + TOMOE Project Joint Seminar Report

Suyama, Kenya

Kaku Deta Nyusu (Internet), (143), p.52 - 62, 2026/02

https://doi.org/10.3327/ndnews.143.0_52

The Seminar on Nuclear Data holds the longest history as a domestic conference on nuclear data. It has played a vital role as a forum for addressing challenges and identifying new themes in this field, bringing together participants from numerous Japanese universities, research institutions, and industry. With many students attending each session, it offers young researchers who will lead the future an opportunity to present their work and gain exposure to cutting-edge research. As announced at last year's conference, this year's event was held jointly with the ERATO Sekiguchi Three-Nucleon Force Project (TOMOE Project) as the "025 Nuclear Data + TOMOE Project Joint Seminar," aiming to leverage synergies with the latest results in nuclear physics research. While the Seminar on Nuclear Data has been reported, the practical preparation procedures have not been covered extensively in Nuclear Data News. Intended also as handover material, this article covers preparations for the event.