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Shi, W.*; Machida, Masahiko; Okamoto, Koji*; Luo, X.*; Feng, W.*; Liu, X.*
Reliability Engineering & System Safety, 272, Part1, p.112538_1 - 112538_18, 2026/08
The reliability of emergency response in severe nuclear accidents critically depends on robust real-time monitoring of radioactive source distributions. However, this safety function is challenged by physical constraints that create monitoring blind spots and by the inadequacy of static methods in tracking dynamic releases. To enhance the reliability and robustness of source term estimation, this study proposes a dynamic reconstruction framework based on LASSO regression with temporal regularization. A sliding-window time-penalty mechanism is introduced, imposing 
-norm constraints on inter-step source variations to ensure physical continuity. The contribution matrix and measurement vector are normalized to counteract biases from radiation shielding and time-varying intensities. Validation using a two-room model with internal shielding, with PHITS Monte Carlo simulation, demonstrates accurate reconstruction of dynamic sources from remote measurements. Temporal regularization enhances situational awareness by suppressing spatial aliasing: at sliding-window width 
(no regularization), hotspot locations fluctuate significantly, with quantitative mean absolute error fluctuations at around 
, whereas 
yields improved spatial consistency and the fluctuation quantities decrease to the 
range. Comparative analysis identifies 
as optimal in balancing accuracy and computational cost. This work establishes a more reliable pathway for dynamic hazard assessment, enabling accurate localization and intensity tracking under challenging conditions. The proposed framework provides a decision-support tool enhancing the resilience and safety of emergency management in nuclear facilities.
Abe, Takumi; Suzuki, Taiga*; Okamura, Tomohiro*; Nakase, Masahiko*
Annals of Nuclear Energy, 232, p.112224_1 - 112224_7, 2026/07
Times Cited Count：0 Percentile：0.00Kreinder, B.; Cox, I.*; Grzywacz, R.*; Nishio, Katsuhisa; 24 of others*
Nuclear Instruments and Methods in Physics Research A, 1085, p.171298_1 - 171298_7, 2026/05
Times Cited Count：0 Percentile：0.00(Instruments & Instrumentation)Batsaikhan, M.; Oba, Hironori*; Karino, Takahiro; Akaoka, Katsuaki; Wakaida, Ikuo*; Iwata, Yoshihiro; Sakamoto, Kan*
Journal of Analytical Atomic Spectrometry, 41(4), p.1324 - 1335, 2026/04
Times Cited Count：0 Percentile：0.00Risk 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.
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.
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.
Matsui, Tetsuya; Shimodaira, Masaki; Yamaguchi, Yoshihito; Toyama, Takeshi; Katsuyama, Jinya
JAEA-Research 2025-017, 41 Pages, 2026/03
JAEA-Research-2025-017.pdf:4.52MB
The JAEA Safety Research Center has been conducting fundamental research on advanced inspection and structural integrity assessment technologies since FY2024, including the development of a machine-learning-based ultrasonic flaw detection method using an ultrasonic simulator. To assess the simulator's applicability, phased array ultrasonic testing (PAUT) results produced by the simulator were compared with actual measurement data. Due to limited publicly available datasets, an intergranular crack in the pressurizer spray line piping of Kansai Electric Power Co. Inc.'s Ohi Nuclear Power Station Unit 3 was selected as the reference case. PAUT linear scanning analysis at a 45
incident angle detected the crack's corner and edge echoes. Strong columnar-crystal propagation echoes were also observed within the weld metal, with their intensity showing dependence on the symmetric axis angle. Analysis at a 31 incident angle similarly identified strong columnar-crystal propagation echoes, which connected to the crack's corner echoes and propagated into the weld region. These results align with actual measurements, indicating that the observed weld-metal echoes are likely attributable to columnar-crystal propagation.
Okamoto, Naritoshi; Komeno, Akira; Seya, Atsumasa; Inaba, Hideki*; Terakado, Shinichi*; Higuchi, Masashi*
JAEA-Data/Code 2025-022, 497 Pages, 2026/03
JAEA-Data-Code-2025-022.pdf:18.06MB
The Plutonium Fuel Third Development Laboratory of the Nuclear Fuel Cycle Engineering Laboratories has applied for a change of use permit (hereinafter referred to as "license") for plutonium fuel facilities. For the criticality safety design of gloveboxes and equipment/instruments handling mixed oxide (MOX), various criticality calculation codes are used. The most recent employs the 3D Monte Carlo calculation code KENO-V.a embedded in the SCALE 4.4 code system, along with the 27-group ENDF/B-IV neutron cross-section library. SCALE 4.4 was released by the Oak Ridge National Laboratory (ORNL) in the US in 1998, and has now been in use for 27 years. ORNL has continuously improved its functionality, with SCALE 6.3.2 released in 2024. When designing and constructing new MOX fuel facilities, it is desirable to obtain a license using criticality calculation codes based on the latest knowledge. However, it is necessary to verify that these codes have sufficient reliability. Therefore, in 2018, benchmark calculations were performed using the 252-group ENDF/B-VII.1 neutron cross-section library (v7-252n) for two versions of the criticality calculation sequences KENO-V.a and KENO-VI from SCALE 6.2.3, based on past criticality experimental setups. The estimated critical-limiting multiplication factor was calculated. The results indicate that these codes can be used with sufficient confidence for criticality safety design of MOX fuel facilities.
Konno, Chikara
JAEA-Data/Code 2025-019, 70 Pages, 2026/03
JAEA-Data-Code-2025-019.pdf:4.47MB
AMPX format libraries were produced from the evaluated nuclear data library JENDL-5 to make JENDL-5 usable in the US nuclear safety analysis code systems SCALE6.2 and SCALE6.3, which are widely used in Japan. The produced libraries are an AMPX continuous energy library, AMPX multigroup libraries and AMPX covariance libraries. This report explains in detail how to produce the libraries and describes test calculation results for verification of the AMPX libraries.
Guerinoni, E.*; Ueda, Yuki; Motokawa, Ryuhei; Zemb, T.*; Pellet-Rostaing, S.*; Dourdain, S.*
Langmuir, 42(12), p.8313 - 8321, 2026/03
-ray beam measurementsOmer, M.; Shizuma, Toshiyuki*; Koizumi, Mitsuo; Taira, Yoshitaka*; Zen, H.*; Ogaki, Hideaki*; Hajima, Ryoichi*
Radiation Physics and Chemistry, 240, p.113467_1 - 113467_8, 2026/03
Times Cited Count：0 Percentile：0.00(Chemistry, Physical)Kawazu, Ryohei
JAEA-Technology 2025-014, 48 Pages, 2026/02
JAEA-Technology-2025-014.pdf:2.19MB
The Japan Atomic Energy Agency (JAEA) conducts research and development in various fields related to nuclear energy as a comprehensive research and development organization for nuclear power. Computational science and technology are utilized in many of these research and development activities. The supercomputer system HPE SGI8600 (hereinafter referred to as the "supercomputer") was introduced in December 2020 as critical infrastructure to meet the increasing computational demands driven by advancements in technologies such as digital twins, machine learning, and big data processing. It has become indispensable for promoting research and development at JAEA. Improving the efficiency of job operations and program waiting times (hereinafter referred to as "job waiting times") on the supercomputer, which is an essential infrastructure supporting JAEA's computational science and technology, is useful for enhancing research and development efficiency. This report presents the results of the investigation into the changes in job waiting times following the integration of queue classes, which was implemented in fiscal year 2022 to efficiently utilize computational resources. It summarizes the process from the analysis of the supercomputer's usage information to the improvements made for the integration of queue classes and the improvement of job waiting times.
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.
Risk Analysis Research Group, Nuclear Safety Research Center
JAEA-Data/Code 2025-015, 68 Pages, 2026/02
JAEA-Data-Code-2025-015.pdf:2.82MB
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 preplanning of countermeasures and plans to reduce the exposure of residents near nuclear power plants during an accident. This report is a manual explaining the analysis model used in OSCAAR code version 2.0.
scintillation detection system for simple non-destructive measurements (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development ProjectCollaborative Laboratories for Advanced Decommissioning Science; Tohoku University*
JAEA-Review 2025-046, 70 Pages, 2026/01
JAEA-Review-2025-046.pdf:5.46MB
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 (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 FY2023, this report summarizes the research results of the "Development of an innovative n/ scintillation detection system for simple non-destructive measurements" conducted in FY2023. At 1F, removal of fuel debris from the primary containment vessel (PCV) is scheduled for FY2023, and a phased expansion of the removal scale is being considered in the future. As a solution to the above problem, this study will develop an innovative scintillation radiation detection system for screening and continuous monitoring during target sample removal. To develop a remote measurement system that contributes to in-vessel investigations for decommissioning of nuclear facilities such as 1F. More specifically, we will develop vertically integrated research into the following elemental technologies: (1) development of innovative high-performance scintillation materials for thermal neutron / gamma-ray discrimination (Tohoku University), (2) downsizing of censer and signal processing system (the University of Tokyo), (3) construction and characterization of various radiation fields (National Institute of Advanced Industrial Science and Technology), and (4) development of a simple non-destructive measurement system and hot cell demonstration test (JAEA). By vertically integrating elemental technologies, R&D on each research item planned in FY2023 was conducted to develop a detector that can discriminate gamma-ray and neutron radiation in environments exceeding 10 Gy/h and simultaneously identify the dose rate and nuclide of each in PCVs and in each acceptance cell.
HPC Technology Promotion Office, Center for Computational Science & e-Systems
JAEA-Review 2025-044, 140 Pages, 2026/01
JAEA-Review-2025-044.pdf:8.77MB
Japan Atomic Energy Agency (JAEA) conducts research and development (R&D) in various fields related to nuclear power as a comprehensive institution of nuclear energy R&Ds, and utilizes computational science and technology in many activities. Over the past 10 years or so, the publication of papers utilizing computational science and technology at JAEA has accounted for about 20 percent of the total publications each fiscal year. The supercomputer system of JAEA has become an important infrastructure to support computational science and technology. In FY2024, the system was utilized in R&D activities that were prioritized in the Fourth Medium- to Long-Term Plan, including contributing to carbon neutrality through the development of innovative technologies for improving safety, creating innovation by promoting diverse R&D related to nuclear science and technology, promoting R&D in response to the accident at TEPCO's Fukushima Daiichi Nuclear Power Station, steadily implementing technological developments for the treatment and disposal of high-level radioactive waste, and supporting nuclear safety regulatory administration and nuclear disaster prevention by promoting safety research for these purposes. This report presents a great number of R&D results accomplished by using the system in FY2024, as well as user support, operational records and overviews of the system, and so on.
Qin, T. Y.*; Hu, F. F.*; Xu, P. G.; Zhang, R.*; Su, Y. H.; Ao, N.*; Li, Z. W.*; Shinohara, Takenao; Shobu, Takahisa; Wu, S. C.*
International Journal of Fatigue, 202, p.109233_1 - 109233_16, 2026/01
Times Cited Count：3 Percentile：76.65(Engineering, Mechanical)Maruyama, Shuhei; Yamamoto, Akio*; Endo, Tomohiro*
Journal of Nuclear Science and Technology, 63(1), p.31 - 44, 2026/01
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Shi, W.*; Machida, Masahiko; Yamada, Susumu; Okamoto, Koji*
Measurement, 258(Part D), p.119444_1 - 119444_15, 2026/01
Times Cited Count：1 Percentile：48.69(Engineering, Multidisciplinary)