Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
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：0.00(Nuclear Science & Technology)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.
Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*
JAEA-Review 2026-003, 173 Pages, 2026/06
JAEA-Review-2026-003.pdf:12.5MB
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 "Human resource development for research based on fuel debris study and SEEM-ology buildup" conducted in FY2024. The present study aims to buildup of "Severe Engineering Management (SEEM)-ology" that enables more rational decision-making in an uncertain and severe environment, and at the same time, to develop research personnel supporting the academic foundation of the extraction, long-term storage, treatment and disposal of fuel debris, which is a central issue in the decommissioning of 1F. Experts in different fields promote multiple research and human resource development tasks in organic collaboration. In the first fiscal year of this study, it was necessary to clarify specific research methods and set the direction in the [SEEM Fields] [Specialized Fields 1
2] and [Common Engineering Fields 13], as well as to prepare various conditions for necessary tests and analyses. It was also necessary to promote the operation of educational programs related to nuclear decommissioning and the planning of SEEM-related courses. For this reason, the purpose of this fiscal year was to obtain the prescribed results by examining specific research methods and making various preparations for conducting necessary tests, preparing various conditions, building and analyzing some measurement systems, and examining human resource development. Based on this objective, we set the performance targets and implementation methods for this fiscal year as an operational plan, implemented them as planned, and were able to achieve the targeted results in each technical field and education and human resource development activities.
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.
Luu, V. N.; Taniguchi, Yoshinori; Udagawa, Yutaka; Tasaki, Yudai; Katsuyama, Jinya
Annals of Nuclear Energy, 230, p.112114_1 - 112114_14, 2026/06
Times Cited Count：1 Percentile：90.73(Nuclear Science & Technology)Taniguchi, Yoshinori; Luu, V. N.; Tasaki, Yudai; Udagawa, Yutaka; Katsuyama, Jinya
Annals of Nuclear Energy, 231, p.112177_1 - 112177_16, 2026/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Nguyen, H. H.
Annals of Nuclear Energy, 230, p.112171_1 - 112171_13, 2026/06
Times Cited Count：1 Percentile：0.00(Nuclear Science & Technology)This study examined the effects of the moderator-to-fuel volume ratio, fuel debris shape, and the number of damaged fuel assemblies on the neutronic characteristics of a partially damaged reactor model, where the fuel assemblies at the core center melt to fuel debris while the fuel assemblies at the outer region remain intact. The investigations were conducted using the Serpent code and the JENDL-5 library. The results show that when fuel debris is surrounded by intact fuel assemblies, the k
can be classified into two groups based on the shape of the fuel debris. Conversely, in scenarios where the fuel debris is not fully encircled by intact fuel assemblies, the shape of the fuel debris has a negligible impact on the k. Additionally, the relationship between the number of neutrons entering and leaving the fuel debris determines how the shape of the fuel debris affects the k.
Yamano, Hidemasa; Matsuba, Kenichi; Sasa, Kyohei*; Kinoshita, Enki*; Morita, Koji*; Saito, Yasushi*; Ito, Kei*; Suzuki, Toru*
Dai-30-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 5 Pages, 2026/06
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：0.00(Chemistry, Analytical)
O solutionKumagai, Yuta; Kusaka, Ryoji; Takano, Masahide; Watanabe, Masayuki
Journal of Nuclear Materials, 625, p.156553_1 - 156553_7, 2026/04
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Uranium-zirconium oxide solid solution, (U, Zr)O, is a representative matrix phase found in fuel debris formed during severe nuclear reactor accidents. Understanding its chemical behavior in oxidative aqueous environments is important for evaluating the potential release of radionuclides during water contact. In this study, we investigated the reactivity of (U, Zr)O with hydrogen peroxide (HO) in pure water to assess its resistance to oxidative dissolution, because HO is the dominant oxidant produced by water radiolysis. The dissolution behavior of uranium and zirconium was monitored through repeated HO exposure experiments, and the solid phases were characterized using Raman micro-spectroscopy and X-ray diffraction. Kinetic modeling was performed to interpret experimental data. The results showed that uranium dissolution occurred initially but decreased significantly upon repeated HO exposure, while zirconium dissolution proceeded more slowly. Raman analysis revealed only minor surface changes, with limited formation of uranyl peroxide phases. The kinetic simulation reproduced the experimental trends by assuming a small fraction of redox-active surface sites. These findings suggest that the observed durability of (U, Zr)O against HO-induced oxidative dissolution is not due to the formation of a protective surface layer, but rather reflects the limited redox reactivity of most of the surface. This study provides a quantitative basis for understanding the HO-induced oxidation of (U, Zr)O in water, relevant to the long-term behavior of fuel debris.
and A
value ratios for off-site transportation of small-amount of fuel debris retrieved from the Fukushima Daiichi Nuclear Power StationSakamoto, Masahiro; Okumura, Keisuke; Kanno, Ikuo; Matsumura, Taichi; Riyana, E. S.; Terashima, Kenichi; Kaneko, Junichi*; Mizokami, Masato*; Mizokami, Shinya*
Radioisotopes, 75(S-01), p.S-001_1 - S-001_5, 2026/04
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.
Toigawa, Tomohiro; Hotoku, Shinobu; Kumagai, Yuta; Abe, Yuma*; Oyama, Kanichi*; Fukaya, Hiroyuki; Ban, Yasutoshi; Kida, Takashi; Hasegawa, Satoshi*; Nakano, Masanao*; et al.
Journal of Nuclear Science and Technology, 63(3), p.322 - 327, 2026/03
Times Cited Count：1 Percentile：46.18(Nuclear Science & Technology)The effect of temperature on hydrogen production generated from radiolysis was investigated to determine the associated implications for nuclear fuel reprocessing safety. The hydrogen yield from radiolysis of plutonium nitric acid solution was measured at temperatures up to the boiling temperature of the solution. The results showed no notable temperature dependence even under boiling conditions. The impact of solution agitation on hydrogen production was also assessed, which revealed minor differences in the hydrogen yield between static and agitated conditions at room temperature. These findings suggest that high temperatures or boiling the solution do not considerably enhance hydrogen generation, and provide crucial information for accurately modeling hydrogen risks under severe accidents.
' phase precipitation in FeCrAl alloysYamashita, Shinichiro; Abe, Yosuke; Okubo, Nariaki; Ukai, Shigeharu; Sasaki, Taisuke*
QST-M-56; QST Takasaki Annual Report 2024, P. 28, 2026/02
Pu
Am
O
Vauchy, R.; Horii, Yuta; Hirooka, Shun; Akashi, Masatoshi; Sunaoshi, Takeo*; Nakamichi, Shinya; Saito, Kosuke
Proceedings of 34th Nuclear Energy for New Europe (NENE2025) , p.232 - 238, 2026/01
Fukuda, Kodai; Shiba, Shigeki*; Iwahashi, Daiki*; Gunji, Satoshi
Journal of Nuclear Science and Technology, 14 Pages, 2026/00
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Toigawa, Tomohiro; Hotoku, Shinobu; Kumagai, Yuta; Abe, Yuma*; Oyama, Kanichi*; Fukaya, Hiroyuki; Tsubata, Yasuhiro; Ban, Yasutoshi; Kida, Takashi; Hasegawa, Satoshi*; et al.
Journal of Nuclear Science and Technology, 7 Pages, 2026/00
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)The effect of temperature on hydrogen generated from radiolysis was investigated to determine the safety implications in nuclear fuel reprocessing. Radiolytic hydrogen production poses a risk due to its flammability, especially when it accumulates in confined spaces without ventilation. Herein, generation of radiolytic hydrogen from an actual nuclear fuel-derived solution is investigated. Compared to previous studies using a plutonium nitric acid solution, this study evaluates radiolytic hydrogen yield under more realistic conditions, reflecting post-irradiation fuel composition. G-values of H are determined at multiple temperatures, and the impact of alpha, beta, and gamma radiation doses is evaluated using PHITS-based simulations. Findings from this study confirmed a reduction in hydrogen yield due to scavenging effects of high-concentration nitric acid and metal ions dissolved in the solution, and temperature dependence appeared to be minor. A weak decreasing trend of G-values with temperature under agitated conditions might be related to hydrogen consumption by palladium species.
Iguchi, Satoshi; Yoshida, Masato; Hirano, Hiroshi*; Kitamura, Akihiro
Nuclear Technology, 15 Pages, 2026/00
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)The size reduced materials resulting from the dismantling of the plutonium-contaminated gloveboxes are eventually packed into the containers as radioactive waste. Conventionally, the execution of this task has been entrusted to workers equipped with air-fed suits, a practice that carries inherent risks, including potential suit damage and inhalation hazards. Moreover, in order to mitigate these risks, the size reduced materials are covered with rags or plastic to enhance safety for workers. However, this approach entails the separation of non-flammable waste and flammable waste during the disposal process. To circumvent these issues, we have designed a glove operation compartment that enables waste handling and packing activities through glove operations instead of air-fed suits. This reduces the risks associated with air-fed suit operations and eliminates the need to cover size reduced materials with rags and plastic. The procedure involves packing the size reduced materials into metal cans, weighing the cans, and storing them in the containers. We tested these operations using the compartment's test bed and modified them through mock-up experiments to ensure feasibility. This report presents the features of the glove operation compartment, the assumed handling procedures, and the insights obtained from the test results.
Collaborative Laboratories for Advanced Decommissioning Science; The University of Osaka*
JAEA-Review 2025-040, 111 Pages, 2025/12
JAEA-Review-2025-040.pdf:22.28MB
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 FY2023, this report summarizes the research results of the "Challenge for screening of nuclear fuel debris by innovative spectral imaging and its verification by LIBS mapping" conducted in FY2023. The present study aims to develop a remote-sensing technique to identify the in-reactor materials by a combination of Hyper Spectral Imaging (HSI) and Laser Induced Breakdown Spectroscopy (LIBS). HSI analyzes spectral information of more than 100 colors, and is being applied to classify various materials. On the other hand, material composition cannot be directly evaluated by HSI. Therefore, we thought that the combination of HSI and LIBS could be an accurate and wide-ranging visualization technique. In order to demonstrate the HSI and LIBS, it is necessary to prepare standard materials that simulate in-reactor materials, and to acquire and accumulate training data on them. In this study, the University of Osaka is in charge of the preparation of standard materials and HSI data analysis, Nuclear Fuel Development (NFD) is in charge of the preparation of uranium bearing materials and HSI/LIBS measurements, and JAEA is in charge of LIBS development. On the UK side, the Univ. of Strathclyde, National Nuclear Laboratory (NNL), and Lancaster University participate in the joint research project. The compositions of the standard samples were determined from past experiments and thermodynamic calculation results. Several samples such as UO based composites and concrete were prepared. The HSI data were obtained using a hyperspectral camera installed in the NFD. For LIBS, we worked on the automatic optimization of focal distance as part of the development of remote operation technology.
Dechenaux, B.*; Brovchenko, M.*; Araki, Shohei; Gunji, Satoshi; Suyama, Kenya
Annals of Nuclear Energy, 223, p.111555_1 - 111555_11, 2025/12
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)