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Mori, Masakazu; Endo, Masayuki; Seya, Manato; Hozumi, Shinsei; Sudo, Tomoyuki
JAEA-Technology 2026-002, 33 Pages, 2026/05
The Waste Treatment Facility No. 1 is equipped with an incinerator for the treatment of radioactive combustible solid waste generated from facilities at the Nuclear Science Research Institute. To obtain conformity confirmation with the New Regulatory Requirements, seismic evaluations were conducted on the facility's building and its incineration equipment. As a result, neither the building nor the equipment satisfied the required seismic standards. Therefore, seismic reinforcement work for the building and equipment was carried out from April 2018 to March 2019. This report outlines the results of seismic evaluation and design, as well as the construction process and safety management during the seismic reinforcement work.
Kuwabara, Ryota; Kagi, Takumi; Yanai, Tomohiro; Watahiki, Shunsuke
JAEA-Review 2026-002, 21 Pages, 2026/05
The JMTR (Materials Testing Reactor) nuclear facility was established and operated for the purpose of conducting irradiation experiments on reactor materials and fuels to establish domestic power reactor technology and produce radioisotopes. In the "Mid- to Long-Term Facility Management Plan" formulated by Japan Atomic Energy Agency in April 2017, JMTR was designated as a facility subject to decommissioning. In September 2019, the Agency submitted a decommissioning plan approval application to the Nuclear Regulation Authority, which was granted in March 2021. As the first step of the decommissioning plan, non-controlled area equipment removal and transportation of spent fuel elements to the United States are currently underway. The AC-1 blower, part of the JMTR reactor building ventilation system, is classified as a performance-maintenance equipment item under the decommissioning plan. Accordingly, in accordance with safety regulations, the equipment undergoes regular inspections, testing, and calibration at appropriate intervals to ensure the maintenance of necessary functions and performance for safety purposes. However, two malfunction events have occurred in the past: a grease leakage incident near the bearing on the load side of the blower fin-frame motor in 2021, and a wear confirmation incident on the blower shaft in 2024. This report summarizes the malfunction events involving bearing and shaft components of both the electric motor and blower within the performance-maintenance equipment of the decommissioning facility, JMTR, as well as the on-site repairs conducted for these problematic areas.
Risk Analysis Research Group, Nuclear Safety Research Center
JAEA-Testing 2025-007, 110 Pages, 2026/03
JAEA-Testing-2025-007.pdf:2.57MB
The Japan Atomic Energy Agency's Nuclear Safety Research Center is developing the Level 3 PRA code OSCAAR as part of its research on probabilistic risk assessment (PRA) for nuclear power plant accidents. OSCAAR is a computational code that evaluates the advection, diffusion, and deposition of radioactive materials released into the environment under various meteorological conditions, based on source terms obtained from Level 2 PRA. It can probabilistically assess the radiation doses and health effects to the public caused by these radioactive materials. OSCAAR can account for the dose reduction effects of protective measures implemented during an actual nuclear power plant accident, thereby contributing to the pre-planning of countermeasures and plans to reduce the exposure of residents near nuclear power plants during an accident. This report is a manual for users to create input files and execute the OSCAAR program.
Dei, Tatsumi; Suganuma, Kazuaki; Fujirai, Kosuke; Suzuki, Katsuo; Suzuki, Hiroshi*; Nakata, Morihiro*; Hosokawa, Hideaki*; Onose, Yuichiro*; Watanabe, Yasuhiro; Shinozaki, Shinichi; et al.
JAEA-Technology 2026-003, 27 Pages, 2026/03
JAEA-Technology-2026-003.pdf:1.3MB
Accelerator cooling-water facility cannot prevent electrolytic corrosion because the systems consist of several different kinds of metals. We have confirmed that the electrolytic corrosion certainly occurs between oxygen-free copper and carbon steel, and cannot be suppressed by the rust inhibitor used so far. We have chosen a new rust inhibitor and confirmed that the new rust inhibitor can prevent the corrosion progression of carbon steel as well as oxygen-free copper. Moreover, using the new rust inhibitor brings about saving water and the cost reduction of the inhibitors.
Tani, Riku; Inoue, Satoshi*; Mizoguchi, Takafumi*; Suda, Shoya; Nakajima, Ryota; Inoue, Hidetaka*; Kurabeishi, Nariaki*; Ouchi, Yasuhiro; Haraga, Tomoko; Shimizu, Osamu
JAEA-Technology 2025-018, 32 Pages, 2026/03
JAEA-Technology-2025-018.pdf:2.4MB
With rising summer temperatures, the number of heatstroke incidents at worksites has been increasing. Even short-term exposure to high-temperature and high-humidity environments can result in serious health hazards. In recent years, measures to prevent heatstroke in the workplace have been legally mandated, requiring employers to manage the work environment and ensure workers' health. At the JAERI Reprocessing Test Facility (JRTF), basic heatstroke prevention measures such as pre-shift health checks and strategic placement of water stations have been implemented. However, due to rising workplace temperatures and longer work durations, these conventional measures alone were considered insufficient to adequately reduce risk. This year, large spot coolers were installed, and cooling vests were introduced to improve both the work environment and individual thermal load. Data on temperature, humidity, and WBGT values were collected before and after the implementation to evaluate the effects on environmental conditions and worker comfort. This report aims to assess the effectiveness of specific countermeasures in reducing the risk of heatstroke during decommissioning work and to inform future improvements to the work environment.
Takaku, Yuhi; Sakazume, Shun; Kimura, Hideo
JAEA-Technology 2025-017, 33 Pages, 2026/03
JAEA-Technology-2025-017.pdf:2.73MB
At the Japan Atomic Energy Agency (JAEA), expectations and demand for generative AI had been increasing, particularly to improve operational efficiency and foster ideas in research and development. However, cloud-based external generative AI services such as ChatGPT typically use input data for learning, which raised security concerns and prevented handling a considerable amount of information. In addition, the required procedures and applications before use were cumbersome, making it hard to say that generative AI was widely adopted or effectively used within JAEA. To address these issues, we built a generative AI infrastructure using JAEA's existing computing resources, including its supercomputers, and open-source software. This approach kept implementation costs low while ensuring safety and ease of use. After deployment across the organization, we observed notable improvements in daily operational efficiency and a surge in interest in generative AI, leading to expanded initiatives for its utilization.
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.
Futemma, Akira; Ochi, Kotaro; Sasaki, Miyuki; Nakama, Shigeo; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; Matsunaga, Yuki*; Sanada, Yukihisa; et al.
JAEA-Technology 2025-015, 171 Pages, 2026/03
JAEA-Technology-2025-015.pdf:11.43MB
On March 11, 2011, the 2011 off the Pacific coast of Tohoku Earthquake and tsunami caused the Fukushima Daiichi Nuclear Power Station accident, releasing radioactive material. Since then, Aerial Radiation Monitoring (ARM) with manned helicopters has been used to assess radiation distribution quickly. In FY2024, the Japan Atomic Energy Agency (JAEA), under commission from the Nuclear Regulation Authority, conducted ARM around the Shimane Nuclear Power Station, producing background dose rate maps validated against ground and other data. During a nuclear emergency drill, UAV training flights complemented manned monitoring, confirming the effectiveness of real-time communication and rapid mapping. The UAV data system was developed and demonstrated for real-time analysis and multi-platform use. Skill training for multicopters was also conducted to strengthen operational capability. Additionally, joint monitoring with the U.S., France, South Korea, and Canada provided insights into international technologies and practices, emphasizing the value of information sharing. This report summarizes the results and technical challenges from these FY2024 activities, contributing to the advancement of emergency radiation monitoring.
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.
Yoshinaka, Kazuyuki
JAEA-Review 2025-063, 50 Pages, 2026/03
JAEA-Review-2025-063.pdf:3.84MB
In the decommissioning of reprocessing facilities, one of the reasons why a safe storage period is usually not set is that Pu-241 decays into Am-241, which accumulates in the process. As eighteen years have passed since the Tokai Reprocessing Plant finished its operation in 2007, it was considered during recent work that the relative proportion of Am-241 has increased compared to earlier measurements. Therefore, this trend was investigated using records of 
nuclide analyses conducted during operations. In this investigation, we focused on and discussed the relative proportion of the major nuclide, Cs-137 and Am-241. The survey confirmed that the proportion of Am-241 tended to increase in all process equipment, though the extent of the increase varied depending on the process. In operations related to spent fuel storage systems, decontaminating when moving fuel, and the solubility of Cs-137 have an effect. In recent years, there have even been cases where Am-241 accounted for 80 % to 90 % of the nuclides detected. In operations related to mechanical processes, including the shearing equipment, the increase appears to correspond to the composition of the spent fuel, and the proportion of Am-241 in all nuclides can exceed 40 % in some cases. In operations related to vitrification process, while the increase seems to correspond to the composition of the high-level radioactive waste, the proportion of Am-241 among all nuclides has not exceeded 10 % in any case. In operations related to radioactive liquid waste processes, the precipitate components at the bottom of storage tanks have an effect and Am-241 tends to be detected at a high proportion. In operations related to incineration processing of radioactive solid waste, the overall trend is thought to correspond to the type of waste handled, but relatively high proportions of Am-241 have been detected on internal walls of incinerators and similar areas.
Nuclear Science Research Institute
JAEA-Review 2025-061, 183 Pages, 2026/03
JAEA-Review-2025-061.pdf:4.01MB
Nuclear Science Research Institute (NSRI) was composed of Planning and Management Department and six departments, namely Department of Operational Safety Administration, Department of Radiation Protection, Engineering Services Department, Department of Research Reactor and Tandem Accelerator, Department of Criticality and Hot Examination Technology, and Department of Decommissioning and Waste Management, and each department manages facilities and develops related technologies to achieve the "Medium- to Long-term Plan" successfully and effectively. On November 1, NSRI unified Department of Research Reactor and Tandem Accelerator, and Department of Criticality and Hot Examination Technology, newly organized Department of Research Infrastructure Technology Development. And, Planning and Management Department was reorganized to Promotion Office. Continuously, four research centers which are Advanced Science Research Center, Nuclear Science and Engineering Center, Nuclear Engineering Research Collaboration Center and Materials Sciences Research Center, belong to NSRI. In order to contribute to future research and development, and to promote management business, this annual report summarizes information on the activities of NSRI of JFY 2024 as well as the activity on research and development carried out by Collaborative Laboratories for Advanced Decommissioning Science, Nuclear Safety Research Center and activities of Nuclear Human Resource Development Center, using facilities of NSRI.
Nonoue, Kazuki; Koda, Yuya
JAEA-Review 2025-060, 19 Pages, 2026/03
JAEA-Review-2025-060.pdf:3.22MB
"Fugen Decommissioning Engineering Center", in planning and carrying out our decommissioning technical development, organizes "Technical special committee on Fugen decommissioning" which consists of the members well-informed, aiming to make good use of Fugen as a place for technological development which is opened domestic and international, as the central place in research and development base of Fukui prefecture, and to utilize the outcome in our decommissioning to the technical development effectively. This report consists of presentation papers "The current status of Fugen decommissioning" and "Considerations of dismantling of the reactor core (including basic design report)" which are presented in the 42nd Technical Special Committee on Fugen Decommissioning.
Ningyo-toge Environmental Engineering Center
JAEA-Review 2025-059, 51 Pages, 2026/03
JAEA-Review-2025-059.pdf:6.2MB
This report outlines some main research and development activities executed by the Ningyo-toge Environmental Engineering Center in FY2024. The Center was working on the development of the nuclear fuel cycle with a focus on its frontend (i.e., uranium exploration, mining, refining, conversion, and enrichment) until 2001, and is now dismantling and removing the facilities and equipment used in the past. In addition, based on the concept of "Uranium and environmental research platform" announced in 2016, we are also working on research and development for the safe processing and disposal of uranium wastes. This research and development can be mainly divided into "Environmental research" and "Uranium waste engineering research"; the former takes advantage of the characteristics of the natural environment in Ningyo-toge, and the latter utilizes our facilities and potentials. Some works are also made on safety and its management as well as radiation effect research in terms of health physics and radiobiology. Regarding the environmental research and environmental conservation, this report describes research on the heterogeneity of groundwater in granitic mountains and the mineral immobilization of long-lived anionic nuclides. As for the uranium waste engineering research, the laser-based decontamination technique and the corrosion resistance suitable for waste package material are reported. Further, the construction of safety measures at the mill tailings ponds, the data analysis of safety information, and the environmental fate of radon are also reported. The achievements of those works have been widely presented through research papers etc.
Materials Sciences Research Center
JAEA-Review 2025-058, 175 Pages, 2026/03
JAEA-Review-2025-058.pdf:8.17MB
Fifteen neutron beam experimental instruments managed by JAEA are installed in JRR-3 (Japan Research Reactor No.3) and are available for internal use including upgrading of instruments and for external users to produce various research results. This report summarizes the progress of internal application research and technical development such as upgrading of neutron beam instruments in the fiscal years 2023 and 2024 after the restart of operation.
Kokubun, Yuji; Hosomi, Kenji; Inoue, Kazumi; Koike, Yuko; Uchiyama, Rei; Sasaki, Kazuki; Maehara, Yushi; Matsuo, Kazuki; Uesugi, Misaki; Yamashita, Daichi; et al.
JAEA-Review 2025-057, 168 Pages, 2026/03
JAEA-Review-2025-057.pdf:2.43MB
The Nuclear Fuel Cycle Engineering Laboratories conducts environmental radiation monitoring around the reprocessing plant in accordance with the "Safety Regulations for Reprocessing Plant of JAEA, Part IV: Environmental Monitoring". This report summarizes the results of environmental radiation monitoring conducted during the period from April 2024 to March 2025 and the results of dose calculations for the surrounding public due to the release of radioactive materials from the plant into the atmosphere and ocean. In the results of the above environmental radiation monitoring, several items were affected by radioactive materials emitted from the accident at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company, Incorporated (changed to Tokyo Electric Power Holdings, Inc. on April 1, 2016), which occurred in March 2011. Also included as appendices are an overview of the environmental monitoring plan, an overview of measurement methods, measurement results and their changes over time, meteorological statistics results, radioactive waste release status, and an evaluation of the data which deviated of the normal range.
Safety Division, J-PARC Center
JAEA-Review 2025-056, 145 Pages, 2026/03
JAEA-Review-2025-056.pdf:9.08MB
This annual report describes the activities on radiation safety and general safety in Japan Proton Accelerator Research Complex (J-PARC) in FY 2024. Activities on radiation safety, such as radiation control in each facility, environmental monitoring, individual monitoring, maintenance of monitoring instruments, and other activities on radiation matters, are represented. Activities on general safety, such as safety committees, meetings, lectures, trainings, and periodical checks, are described. In addition, activities on promotion of safety culture and the technological developments etc., including research activities and noteworthy safety managements on safety issues, are also summarized in each separate section.
Department of Radiation Protection, Nuclear Science Research Institute; Nuclear Facilities Management Section, Aomori Research and Development Center
JAEA-Review 2025-055, 107 Pages, 2026/03
JAEA-Review-2025-055.pdf:2.26MB
This annual report describes the activities in the 2024 fiscal year of Department of Radiation Protection at Nuclear Science Research Institute, Harima Synchrotron Radiation Radioisotope Laboratory, and Nuclear Facilities Management Section at Aomori Research and Development Center. The activities described in this report are environmental monitoring, radiation protection practices in workplaces, individual monitoring, maintenance of monitoring instruments, and research and development of radiation protection. At these institutes, the occupational exposures did not exceed the dose limits. The radioactive gaseous and liquid discharges from the facilities were well below the prescribed limits. The research and development activities in the field of radiological protection were continued.
Hirota, Noriaki
JAEA-Review 2025-054, 132 Pages, 2026/03
JAEA-Review-2025-054.pdf:14.65MB
In recent years, extending the operational lifetimes of nuclear power plants and constructing new facilities have been conducted worldwide to achieve carbon neutrality. In Japan, following the Fukushima Daiichi Nuclear Power Station accident on March 11, 2011, only light water reactors (LWRs) that meet newly established safety standards have been permitted to restart, with most restarted plants being pressurized water reactors (PWRs), which differ from the boiling water reactors (BWRs) that were utilized at the Fukushima Daiichi Nuclear Power Station. Stress corrosion cracking (SCC) poses a serious safety concern in nuclear power plants. In particular, stainless steels such as SUS304 and SUS316 are susceptible to crack initiation due to oxide films and residual stresses. Countermeasures such as alloy composition modification and laser peening, which imparts compressive residual stresses, have been attempted; however, it remains uncertain whether compressive residual stresses can be retained for long periods under high-temperature conditions. Therefore, this study focuses on grain refinement processing as a novel approach for SCC mitigation and establishes a fabrication process for grain-refined stainless steels. The influence of grain refinement on SCC crack initiation was systematically analyzed under simulated reactor environments, and the mechanisms of SCC suppression were investigated. Furthermore, a surface-localized grain refinement technique was proposed and its effectiveness in suppressing SCC was evaluated. These results indicate that this technology can significantly contribute to SCC mitigation during long-term operation of nuclear power plants and is expected to play an important role in extending the service life of structural components such as shrouds.
Integrated Support Center for Nuclear Nonproliferation, Security and Human Resource Development
JAEA-Review 2025-051, 73 Pages, 2026/03
JAEA-Review-2025-051.pdf:1.59MB
This annual report summarizes the activities of Nuclear Human Resource Development Center (NuHRDeC) of Japan Atomic Energy Agency (JAEA) in the fiscal year (FY) 2024. In FY 2024, in addition to the regular training programs at NuHRDeC, we actively organized special training courses responding to the external training needs, cooperated with universities, offered international training courses for Asian countries, and promoted activities of the Japan Nuclear Human Resource Development Network (JN-HRD.net) and the human resource development concierge. Regular domestic training programs; training courses for radioisotopes and radiation engineers, nuclear energy engineers and national qualification examinations, were conducted as scheduled in the annual plan. We also delivered training for other organizations outside the JAEA. We continued cooperative activities with universities, such as acceptance of postdoctoral researchers, and activities in line with the cooperative graduate school system, including the acceptance of students from Nuclear Professional School, the University of Tokyo. Furthermore, joint course among seven universities was successfully held by utilizing remote education system. The joint course and the intensive summer course and nuclear fuel cycle training were conducted as part of the collaboration network with universities. The Instructor Training Program (ITP) under the contract with Ministry of Education, Culture, Sports, Science and Technology, was continually offered to the ITP participating countries. As part of the ITP, the Instructor Training courses such as "Reactor Engineering Course", advanced instructor training course, and the nuclear technology seminar "Basic Radiation Knowledge for School Education" were conducted at NuHRDeC. As joint secretariat of JN-HRD.net, we steadily promoted its operation and organized various activities, including public lectures and webinars (online seminars) for the general public, as well as site visits to nuclear-related facilities for students. Regarding the human resource development concierge, we promoted human resource development concierge activities by not only responding to inquiries and consultations from inside and outside of JAEA but also planning and managing Kansai nuclear open campus, through the human resource development contact point.
Hoshino, Masato; Sasaki, Yoshifumi; Horikoshi, Hidehiko*; Tani, Kosuke*
JAEA-Review 2025-047, 122 Pages, 2026/03
JAEA-Review-2025-047.pdf:3.75MB
Horonobe Underground Research Center managed by Japan Atomic Energy Agency (JAEA) is the Japan's best environment to understand the project of geological disposal of high-level radioactive waste, because there is an Underground Research Laboratory (URL) in the center besides an exhibition facility which explains the content of research conducted in the URL. In the area of the center, there is also an exhibition facility for the full-scale model of engineered barrier system of geological disposal. JAEA takes advantage of this opportunity to conduct public hearing including questionnaire research regarding the questions, anxieties and comments by the visitors for geological disposal project. This report summarizes the result of statistical analysis of 2,830 visitors from April 2024 to January 2025.