Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Mihara, Takeshi; Urano, Kenta; Udagawa, Yutaka; Kakiuchi, Kazuo
JAEA-Technology 2026-009, 15 Pages, 2026/06
JAEA-Technology-2026-009.pdf:1.15MB
Mechanical energy generated during fuel failure under reactivity-initiated accident (RIA) conditions, such as pressure pulse and water hammer, strongly depends on the fragmentation state and temperature of the fuel. When failure caused by pellet/cladding mechanical interaction (PCMI) occurs rapidly at low temperature, fission gas release drives pellet fragments to move at high velocity in water, leading to extremely efficient heat transfer between the fuel and coolant. This results in rapid vapor generation and the production of impulsive mechanical energy. These observations indicate that both the particle surface area and the highly efficient heat transfer associated with high-velocity fragment motion are key influencing factors. In the 264-2 and 264-24 experiments, test conditions were designed to simulate fuel-coolant interaction under conditions where the driving force for pellet fragment motion, which is characteristic of RIA events, is absent. In the 264-24 test, the specific surface area of the pellet particles (surface area per unit mass) was designed to exceed that of previously tested high-burnup fuels. In addition, the fuel enthalpy (thermal energy per unit mass) was set based on prior observations to conditions where significant mechanical energy generation is expected. As a result, both the pressure pulse and water hammer energies were significantly lower than those observed in high-burnup fuel failure cases, where the driving force for pellet fragment motion is considered to be present. This clearly demonstrates the critical importance of the driving force for pellet fragment motion in the generation of mechanical energy.
Fukaya, Yuji; Asano, Kazuhito; Sato, Hiroyuki; Ohashi, Hirofumi; Sakaba, Nariaki
JAEA-Review 2026-015, 10 Pages, 2026/06
JAEA-Review-2026-015.pdf:0.96MB
The Japan Atomic Energy Agency (JAEA) is developing SiC matrix fuel as a fuel to improve oxidation resistance. It is a simple manufacturing method called the slurry method, in which raw materials are dissolved in water, molded, and sintered, and are designed to pursue manufacturability in consideration of mass production. On the other hand, there is a patent in the U.S. for SiC matrix fuel, and it was expressed that there is a risk that the JAEA's SiC matrix fuel technology may infringe this patent, and it should be confirmed. In that case of infringement, it could become an obstacle to the social implementation of that technology. Therefore, in order to determine whether the SiC-based fuel for HTGR proposed by the JAEA would constitute a patent infringement against the aforementioned U.S. patent, JAEA requested a formal infringement evaluation from a major U.S. patent law firm. As a result, it was determined that the SiC-based fuel for high-temperature gas reactors proposed by the JAEA does not constitute a patent infringement against the aforementioned U.S. patent. This removed obstacles to the future deployment of the SiC matrix fuel proposed by the JAEA for high temperature gas-cooled reactors.
Engineering Services Department, Nuclear Science Research Institute
JAEA-Review 2026-011, 97 Pages, 2026/06
JAEA-Review-2026-011.pdf:4.39MB
The Engineering Services Department is in charge of operation and maintenance of utility facilities (water distribution systems, electricity supply systems, steam generation systems and drain water systems etc.) in whole of the institute. Furthermore, it also oversees the operation and maintenance of specific systems (power receiving and transforming facilities, an emergency electric power supply system, an air/liquid waste treatment system, a compressed air supply system) in nuclear reactor facilities, nuclear fuel material usage facilities and usual facilities or buildings. In addition, the department is in charge of maintenance of buildings, design and repair of electrical/mechanical equipment. This annual report describes summary of activities, operation and maintenance data and technical developments of the department carried out in JFY 2024. We hope that this report may help to future work.
Collaborative Laboratories for Advanced Decommissioning Science; Institute of Science Tokyo*
JAEA-Review 2026-007, 65 Pages, 2026/06
JAEA-Review-2026-007.pdf:4.67MB
The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), has been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") from FY2019. 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 FY2024, this report summarizes the research results of the "Development of a laser deflection-type ultrasonic wideband 3D imaging system for in-vessel visualization in high-radiation and non-visible environments" conducted in FY2024. The present study aims to maximize the safety of debris-cutting operations by enabling visualization of in-vessel structures, fuel debris shapes, and scattered particles at distances on the order of several meters, even under dusty and turbid water conditions during work. To achieve this, a compact and portable ultrasonic device suitable for mounting on robots and manipulator arms is employed to develop a laser deflection-type ultrasonic wideband 3D imaging system. In FY2024, the project carried out imaging performance evaluation and studies for the advancement and acceleration of the ultrasonic imaging system, numerical simulations, prototyping and full-scale verification of the system, radiation resistance tests, construction of a submillimeter ultrasonic ranging system, application of the ultrasonic sub-millimeter ranging system to LIBS, as well as battery-powered remote operation of the measurement system. These outcomes are summarized in this report.
Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*
JAEA-Review 2026-001, 140 Pages, 2026/06
JAEA-Review-2026-001.pdf:9.25MB
The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), has been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") from FY2019. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station (1F), 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 FY2024, this report summarizes the research results of the "Research and education for human resource development in integrated remote robot and measurement technologies for fuel debris removal" conducted in FY2024. This research aims to develop robotic technologies, sensors, and radiation measurement techniques to remotely characterize and assess the properties of fuel debris at 1F reactor, and to cultivate personnel capable of integrating these technologies into systems. Furthermore, it seeks to establish SEEM science and deploy it in actual educational settings. Achievements in FY2024 include: optimizing neutron detectors with high radiation resistance ; constructing a simulator capable of appropriately generating radiation incident events; designing and developing a rover for generating 3D volume models; building physical environments for remote operation support; examined sensor configurations for radiation distribution estimation; proposal of a multi-arm orbital structure as a transport-capable modular orbital structure; development of lightweight arms and examined interfaces for multi-view remote control systems and orbital planners; image processing methods for full-scale environmental structure modeling; investigation on image data transmission methods; development of an integrated DX platform; studies on sensor and robot modularization; development of rigid-body and elastic-body analysis methods; characterization and waste management strategies and investigation of the applicability of geopolymers as backfill materials; establishing SEEM education.
Sakurai, Takeshi; Fukushima, Masahiro
JAEA-Data/Code 2026-001, 235 Pages, 2026/06
JAEA-Data-Code-2026-001.pdf:16.46MB
Experimental data obtained in the Fast Critical Assembly (FCA) simulating a High Conversion Light Water Reactor (HCLWR) were evaluated for the criticality of assemblies XV series in the second phase of FCA-HCLWR experiments, primarily using plutonium fuel. Analysis was performed using the nuclear data libraries JENDL-4.0 and JENDL-5 and the Monte Carlo code MVP3, which calculates neutron transport using the continuous energy method. In the evaluation of criticality, a detailed uncertainty assessment was performed, taking into account the effects of uncertainties in the weight and composition of the uranium and plutonium fuel plates and simulated material plates such as moderator in the FCA. The analysis involved detailed simulations of the fuel and lattice tube structures in the FCA. The calculation results for the effective multiplication factor overestimated the experimental results by 0.4% to 0.8% using both JENDL-4.0 and JENDL-5.
Tameta, Yuito; Sano, Kyohei; Takano, Yugo*; Yamamoto, Masahiko; Nakazaki, Katsutoshi; Akiyama, Kazuki
JAEA-Technology 2026-004, 27 Pages, 2026/05
JAEA-Technology-2026-004.pdf:3.18MB
At the High Active Solid Waste Storage (HASWS) of Tokai Reprocessing Plant, high active solid waste generated from the reprocessing process is stored. In the wet cell, hull cans containing fuel cladding tubes (hulls) and end pieces are stored, along with used filters and contaminated equipment. It is being considered that utilizes a small underwater remotely operated vehicle (ROV) along with a lifter for recovering and transporting objects from the seafloor for the retrieval of the waste stored in the HASWS. Mock-up tests were conducted in FY2022 and FY2023 to verify the feasibility of retrieving waste using the ROV and the lifter. In this study, to achieve safer and more reliable waste retrieval, improvements were made to each component, including the ROV cable, waste gripping grab, lifting hook, lifter, and ROV monitoring camera, and data were collected to evaluate operational performance. For the ROV cable, attaching a float to the rear section of the ROV cable to reduce its weight facilitated forward-tilt operation and improved the ROV's attitude stability during wire-cutting. For the waste gripping grab, attaching a jig to the tips of the grab of the lifter (grabtype) enhanced the gripping stability of the hull can. For the lifting hook, setting the ring diameter of the lifter (hook-type) to 15 cm shortened the time required for grasping and improved accessibility to the hook. For the lifter, using lifters with modified internal structures enabled fine air-volume adjustment and reduced blockage of air passages, thereby improving the stability of air supply and exhaust. For the ROV monitoring camera, adding a light near the ROV monitoring camera in a dark environment ensured sufficient cell illumination and enhanced cable visibility.
Mori, Masakazu; Endo, Masayuki; Seya, Manato; Hozumi, Shinsei; Sudo, Tomoyuki
JAEA-Technology 2026-002, 33 Pages, 2026/05
JAEA-Technology-2026-002.pdf:2.01MB
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.
Fujiwara, Yusuke; Nakajima, Kunihiro; Urabe, Kohei; Nagatsuka, Kentaro; Asano, Kazuhito; Shimizu, Atsushi; Noguchi, Hiroki; Sato, Hiroyuki; Ohashi, Hirofumi; Sumita, Junya; et al.
JAEA-Technology 2026-001, 43 Pages, 2026/05
JAEA-Technology-2026-001.pdf:2.93MB
High Temperature Gas-cooled Reactors (HTGRs) have excellent safety features and can supply high-temperature heat without emitting carbon dioxide, and therefore are expected to stably produce large amounts of hydrogen to contribute carbon neutrality by 2050. The pertinent material for the "Basic Policy for GX Realization" shows the development process for the HTGR demonstrator with the goal of starting operation in the 2030s. Meanwhile, to achieve net-zero, the UK government has started the Advanced Module Reactor (AMR) Research, development and demonstration (RD&D) programme with the aim of starting operations of the HTGR demonstrator in the early 2030s. Against this background, with the aim of early deployment of HTGR technology, Japan Atomic Energy Agency (JAEA), in collaboration with the United Kingdom National Nuclear Laboratory (UKNNL), aims to demonstrate Japanese HTGR technology outside Japan and reflect the development of HTGR demonstrator in the UK to Japan. This document summarizes the results of a market survey of HTGR products and surveys of industrial infrastructure in the UK, the environment and social conditions of Hartlepool, a candidate construction site, with the aim of contributing to the design study of the HTGR demonstrator in the UK (UKJ-HTR).
Department of Decommissioning and Waste Management
JAEA-Review 2026-008, 39 Pages, 2026/05
JAEA-Review-2026-008.pdf:1.7MB
This report summarizes the activities carried out in FY2024 by the Department of Decommissioning and Waste Management (DDWM) at the Nuclear Science Research Institute (NSRI). It provides an overview of the operations and maintenance of the assigned facilities, the treatment and management of radioactive waste, decommissioning activities, and related technical development work. In FY2024, radioactive waste generated from R&D activities at NSRI was safely treated, including approximately 165 m
of combustible solid waste, 185 m of non-combustible solid waste, and 232 m of liquid waste. As of the end of FY2024, the cumulative volume of stored waste packages reached 119,601 (in 200-liter drum equivalents), representing an increase of 937 packages compared with the previous fiscal year. In addition, efforts were made to comply with the new regulatory requirements for waste management facilities. With regards to decommissioning activities, equipment removal and related work were carried out at the Japan Reprocessing Test Facility (JRTF) and the Plutonium Research Building No.1. In the field of technical development, radioactivity data were obtained from waste samples toward the establishment of waste radioactivity evaluation methods. Furthermore, at the request of the Ministry of the Environment and Tokai-mura office, JAEA conducted a demonstration project on the landfill disposal of the contaminated soil generated by the accident of the Fukushima Daiichi Nuclear Power Station.
Kuwabara, Ryota; Kagi, Takumi; Yanai, Tomohiro; Watahiki, Shunsuke
JAEA-Review 2026-002, 21 Pages, 2026/05
JAEA-Review-2026-002.pdf:2.72MB
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.
Nuclear Science and Engineering Center; NXR Development Center
JAEA-Evaluation 2026-001, 44 Pages, 2026/05
JAEA-Evaluation-2026-001.pdf:0.93MB
JAEA-Evaluation-2026-001-appendix(CD-ROM).zip:18.67MB
Japan Atomic Energy Agency (hereinafter referred to as "JAEA") consults an assessment committee, "Evaluation Committee of Research Activities for Nuclear Science and Engineering" (hereinafter referred to as "Committee") for interim evaluation of "Nuclear Science and Engineering", in accordance with "General Guideline for the Evaluation of Government Research and Development (R&D) Activities" by Cabinet Office, Government of Japan, "Guideline for Evaluation of R&D in Ministry of Education, Culture, Sports, Science and Technology" and "Regulation on Conduct for Evaluation of R&D Activities" by the JAEA. In response to the JAEA's request, the Committee evaluated research activities based on the materials prepared by JAEA. This report summarizes the results of the assessment by the Committee with the Committee report attached.
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.