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3 rod bundle simulating BWR subchannels at elevated pressure conditionsWada, Yuki; Shibamoto, Yasuteru; Hibiki, Takashi*
International Communications in Heat and Mass Transfer, 179, Part 3, p.112282_1 - 112282_22, 2026/10
Times Cited Count：0 Percentile：0.00(Thermodynamics)Nguyen, T.-B.; Hirose, Yoshiyasu; Satou, Akira; Abe, Satoshi; Shibamoto, Yasuteru; Okawa, Tomio*
Nuclear Engineering and Design, 457, p.115036_1 - 115036_20, 2026/10
Times Cited Count：1 Percentile：0.00(Nuclear Science & Technology)Uesawa, Shinichiro; Maeshima, Takahiro*; Okada, Makoto*; Tomita, Hirobumi*; Tate, Naofumi*; Aoki, Kunitomo*; Hiramatsu, Natsuki*; Ono, Koji*; Yoshida, Hiroyuki
Konsoryu Shimpojiumu 2026 Koen Rombunshu (Internet), 2 Pages, 2026/08
To use detailed two-phase flow simulations as an alternative or complement to large-scale mockup experiments, quantitative validation of instantaneous and local gas-liquid interfacial information is required in addition to flow-regime reproducibility. However, conventional wire-mesh sensors (WMSs) cannot measure void fraction distributions at a spatial resolution finer than the wire-crossing interval. To overcome this limitation, we are developing a technique to estimate high accurate, high-resolution void fraction distributions from WMS signals by combining WMS measurements, detailed two-phase flow simulations, electrostatic field analysis, and generative AI. This presentation reports on the development status of a Pix2Pix-based model and its application to experimentally obtain WMS signals in a 33 rod-bundle channel.
Collaborative Laboratories for Advanced Decommissioning Science; The University of Osaka*
JAEA-Review 2026-009, 81 Pages, 2026/07
JAEA-Review-2026-009.pdf:5.42MB
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 radiation resistant laser scanner and 3D modeling method using AI and image processing" conducted in FY2024. This research focuses on developing a radiation-resistant 3D laser scanner and technologies to enhance the quality of point cloud data. A new scanner system was designed with a laser scanning head composed only of radiation-tolerant electrical and mechanical components, excluding semiconductors, and a control unit placed remotely in a low-radiation zone. The system aims to enable stable scanning in high-radiation environments. Its performance will be evaluated in comparison with commercial scanners. To address the sparsity of acquired point clouds, we are developing two complementary systems: one uses machine learning to complete and enhance point clouds through processes such as denoising, normalization, and interpolation; the other uses photogrammetry to reconstruct 3D data from image sets and integrate it with scanner-derived data. In FY2024, (1) Optical and electronic circuits were designed and assembled, and waveform collection and analysis software was developed to prepare for scanner detection efficiency evaluation. (2) A point cloud completion system incorporating AI was implemented, and methods for point cloud densification and completion were investigated. (3) A processing environment and workflow were established to integrate point clouds with photogrammetry, and 3D surface models were constructed. (4) Efficient scanning strategies under high-radiation conditions were analyzed, and a methodology for accuracy evaluation was studied. (5) The project was advanced through close coordination among research components and related institutions.
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.
Ta(n,
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Ta reactionKawamura, Shiori*; Endo, Shunsuke; Iwamoto, Osamu; Iwamoto, Nobuyuki; Kimura, Atsushi; Kitaguchi, Masaaki*; Nakamura, Shoji; Okudaira, Takuya*; Rovira Leveroni, G.; Shimizu, Hirohiko*
JPS Conference Proceedings (Internet), 45, p.011069_1 - 011069_7, 2026/06
La(n,)
La reactionEndo, Shunsuke; Fujioka, Hiroyuki*; Goto, Yu*; Ino, Takashi*; Iwamoto, Osamu; Iwamoto, Nobuyuki; Kawamura, Shiori*; Kimura, Atsushi; Kitaguchi, Masaaki*; Kobayashi, Ryuju; et al.
JPS Conference Proceedings (Internet), 45, p.011056_1 - 011056_8, 2026/06
8 pin bundleLiong, C.*; Endo, Tomohiro*; Tada, Kenichi; Yamamoto, Akio*
Proceedings of International Conference on the Physics of Reactors (PHYSOR 2026) (Internet), 8 Pages, 2026/04
A Deep Neural Network (DNN) is applied to predicting pin-wise coolant void and temperature distributions in a BWR 88 bundle for the neutronics/thermal-hydraulics multi-physics coupling simulation. The calculation results, obtained through precise neutronics and thermal-hydraulics simulations on a Boiling Water Reactor (BWR) 88 bundle under with and without control blade conditions, serve as the training data for the DNN model. In the DNN model, the pin-wise coolant void fraction and temperature radial distributions at the lower axial mesh, and the pin power radial distribution at the current axial mesh, are used to predict the coolant void fraction and temperature radial distributions at the current axial mesh. The DNN model makes accurate predictions for void fraction and temperature distributions at the no control blade case, although slight biases are observed in the control blade insertion case.
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.
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.
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.
Yamazaki, Takumi*; Ishitani, Yugo*; Nakada, Katsuyuki*; Sasaki, Tomoyuki*; Endo, Yasushi*; Takanashi, Koki; Seki, Takeshi*
Journal of Applied Physics, 138(23), p.233905_1 - 233905_11, 2025/12
Times Cited Count：1 Percentile：0.00(Physics, Applied)Takahashi, Tone; Mochimaru, Takanori*; Koizumi, Mitsuo; Yoshimi, Yuki*; Yamanishi, Hirokuni*; Wakabayashi, Genichiro*; Ito, Fumiaki*
JAEA-Review 2025-039, 34 Pages, 2025/11
JAEA-Review-2025-039.pdf:2.18MB
To prevent acts of terrorism involving nuclear or radioactive materials at major public events, it is required to have surveillance technologies that either prevent these materials from being brought in or detect quickly if somebody brings them in secretly. Setting radiation gate monitors to survey pedestrians and vehicles is one of the effective methods. However, considering the possibility of individuals bypassing these monitors, complementary technologies are needed to continuously survey areas inside the gates. To survey extensive areas, radiation mapping is effective. By using multiple detectors and aggregating the data, the survey becomes much more efficient. We have developed mobile detectors capable of simultaneously measuring location data and radiation levels outdoors, with the ability to aggregate measurement results via a network and immediately visualize them on a map. For indoor environments, we have developed a technology that integrates radiation measurement results with environmental mapping created using SLAM (Simultaneous Localization and Mapping) to produce 3D maps of the surveyed areas. Additionally, we have been working on the development of a source search technology using a fast neutron detector to quickly detect neutron sources, including nuclear materials. In this report, we describe a concept of the wide area survey system and report technology development results so far.
Yanagisawa, Hiroshi; Motome, Yuiko
JAEA-Research 2025-010, 197 Pages, 2025/11
JAEA-Research-2025-010.pdf:3.5MBJAEA-Research-2025-010(errata).pdf:0.38MB
For understandings of nuclear criticality risks of TRIGA fuel rods and review of safety measures for handling them, nuclear criticality characteristics for infinite and finite heterogeneous lattice systems composed of the NSRR fuel rods were re-evaluated with the use of a detailed computational model for the fuel rod. The MVP version 3 code was used with the JENDL libraries including the latest version, JENDL-5, for the re-evaluation. As the criticality characteristics, variations of neutron multiplication factors of the infinite and water-reflected finite systems were examined in detail with parameters of the lattice pitch and density of moderator water. From the results of the re-evaluated criticality characteristics, the minimum critical number of fuel rods for the water-reflected hexagonal shaped lattice system was obtained to be 46.8 
0.2 using the JENDL-5 library. Moreover, the attainability of criticality without the water as moderator and reflector was examined because the zirconium hydride moderator and graphite reflector are equipped with the TRIGA fuel rod. It was found that the criticality is possible to be attained by 115.7 0.6 of the number of fuel rods, which is the smaller number of fuel rods than loaded in the NSRR standard core, even though no water exists.
Zhang, H.*; Umehara, Yutaro*; Horiguchi, Naoki; Yoshida, Hiroyuki; Eto, Atsuro*; Mori, Shoji*
Energy, 335, p.138090_1 - 138090_18, 2025/10
Times Cited Count：0 Percentile：0.00(Thermodynamics)Nuclear power is a key low-carbon energy source for a carbon-neutral future. In boiling water reactors (BWRs), steam-water annular flow near fuel rods is crucial for reactor safety, but its high-temperature, high-pressure conditions (285
C, 7 MPa) make direct measurement challenges. To address this, we used an HFC134a-ethanol system at lower conditions (40C, 0.7 MPa) to simulate BWR annular flow. Using a high-speed camera and the constant electric current method, we analyzed liquid-film characteristics, wave velocity and frequency. We also examined surface tension and interfacial shear stress effects. Furthermore, we proposed a new correlation for base film thickness.
Taniguchi, Yoshinori; Urano, Kenta; Mihara, Takeshi; Udagawa, Yutaka; Kakiuchi, Kazuo; Katsuyama, Jinya
Proceedings of TopFuel 2025; Nuclear Reactor Fuel Performance Conference (Internet), p.1292 - 1301, 2025/10
Engineering Services Department, Nuclear Science Research Institute
JAEA-Review 2025-018, 83 Pages, 2025/09
JAEA-Review-2025-018.pdf:4.99MB
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. And also is in charge of 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 2023. We hope that this report may help to future work.
Hf(n,)
Hf reaction measurementKawamura, Shiori*; Endo, Shunsuke; Iwamoto, Osamu; Iwamoto, Nobuyuki; Kimura, Atsushi; Kitaguchi, Masaaki*; Nakamura, Shoji; Okudaira, Takuya*; Rovira Leveroni, G.; Shimizu, Hirohiko*; et al.
EPJ Web of Conferences, 329, p.05002_1 - 05002_3, 2025/06
Times Cited Count：0 Percentile：0.00(Physics, Nuclear)no abstracts in English
