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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)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.
Soma, Yasutaka; Komatsu, Atsushi; Igarashi, Takahiro
Corrosion Science, 265, p.113182_1 - 113182_13, 2026/06
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Oshima, Masumi*; Hayakawa, Takehito*; Asai, Masato; Goto, Jun*; Shinohara, Hirofumi*
Nihon Genshiryoku Gakkai-Shi ATOMO
, 68(6), p.361 - 365, 2026/06
We have developed an innovative method named "spectral determination method (SDM method)" to analyze radiation spectra containing a number of radioactive isotopes with better accuracy than that of conventional analysis methods. We applied this method to 
-ray spectra measured with Ge detectors or scintillation detectors, 
-particle spectra measured with liquid scintillation counters, and - coincidence spectra. Furthermore, we found that the accuracy of the analysis results was much improved by unifying all these spectra and applying the SDM method to those unified spectra.
Fukuda, Kodai; Obara, Toru*
Nuclear Technology, 212(6), p.1567 - 1578, 2026/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Takubo, Yusaku*; Takayama, Yusuke*; Sugita, Yutaka; Ogoshi, Minori; Ishida, Keisuke*
Environmental Earth Sciences, 85(9), p.229_1 - 229_19, 2026/05
Times Cited Count：0 Percentile：0.00(Environmental Sciences)Yanagisawa, Kayo; Matsueda, Makoto; Oka, Toshitaka; Kitatsuji, Yoshihiro
Journal of Radioanalytical and Nuclear Chemistry, 335(3), p.2091 - 2100, 2026/03
Times Cited Count：0 Percentile：0.00(Chemistry, Analytical)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.
Hamdani, A.; Soma, Shu; Abe, Satoshi; Shibamoto, Yasuteru
Nuclear Engineering and Technology, 9 Pages, 2026/00
Kitatani, Hikari; Ozone, Kenji; Nakata, Hisakazu
JAEA-Technology 2025-011, 57 Pages, 2025/12
JAEA-Technology-2025-011.pdf:5.32MB
Japan Atomic Energy Agency is responsible for near-surface disposal of research-related low-level radioactive waste and is considering two types of facilities: trench and concrete-pit. In safety assessment of such facilities, dose evaluation requires data on infiltration water. Evaluating infiltration involves uncertainties due to waste conditions and disposal environment. Therefore, in this report, a reference model was established based on the conceptual design conditions of near-surface disposal facilities, and leachate from the facilities was estimated by groundwater flow analysis, using applications by prior operators as reference and reflecting the latest knowledge for safety assessment. This allowed evaluation of how the hydraulic conductivity of each facility layer and surrounding soil affects leachate. Specifically, the 2D FEM groundwater flow code MIG2DF was used: trench facilities were evaluated assuming cover degradation, and concrete-pit facilities assuming salt effects in waste packages. Results showed that in trench facilities, deterioration of clay hydraulic conductivity increased inflow to the waste layer, especially when drainage layer conductivity decreased, as horizontal flow paths failed and infiltration into clay was promoted. In concrete-pit facilities, clay fracturing increased local flow and water through the waste layer. These results quantitatively demonstrate how changes in hydraulic conductivity of each layer affect leachate, providing useful insights for scenario development in safety assessment and for facility management.
Saijo, Tomoaki; Shimazaki, Yosuke; Ishihara, Masahiro
JAEA-Technology 2025-010, 126 Pages, 2025/12
JAEA-Technology-2025-010.pdf:12.52MB
During the operation of the High Temperature Engineering Test Reactor (HTTR), thermal stress is generated in the graphite components. In addition, graphite exhibits dimensional shrinkage and creep deformation under neutron irradiation. As a result, residual stress remains in the graphite components during reactor shutdown. Therefore, in the design of the HTTR core graphite structures, stress analyses of the graphite components have previously been performed using the finite element analysis code VIENUS. In the HTTR, the graphite components are exposed to a wide range of temperature, from approximately 400
C to 1200C, depending on their location. Consequently, irradiation-induced behaviors such as material property changes and irradiation shrinkage vary among the graphite components. On the other hand, since VIENUS code evaluates stress based on thermal fluid and heat conduction analysis results, it is not suitable for parametric studies. In this study, the influence of irradiation behavior on the stress behavior of graphite components in the wide temperature range (400C to 1200C) was analyzed using simplified viscoelastic evaluation model, consisting of two beam elements, to conduct efficient parametric studies. Operational stress exhibits two distinct patterns depending on whether the irradiation temperature is below or above 800C, due to irradiation shrinkage. Residual stress approaches the thermal stress, preventing excessive increase even when irradiation shrinkage is large. Moreover good agreement in stress behavior trends was observed between the stress analysis results by the simplified viscoelastic evaluation model and VIENUS code. These results indicate that the simplified viscoelastic evaluation model is beneficial in simulating stress behavior.
Yoneyama, Kai; Nitta, Ayako; Tanaka, Yasuyuki; Kodaka, Noriyasu; Kikuchi, Riku; Sakano, Takuma; Furuse, Takahiro; Sato, Soichi; Sambongi, Mitsuru; Tanaka, Kosuke
JAEA-Technology 2025-008, 44 Pages, 2025/12
JAEA-Technology-2025-008.pdf:4.3MB
At the TEPCO's Fukushima Daiichi Nuclear Power Station (1F), an investigation inside the reactors has been carried out. In order to safely carry out the decommissioning work such as fuel debris retrieval and building demolition, it is important to estimate the contamination in primary containment vessel for control the decommissioning planning and the worker radiation exposure levels. Therefore, the analysis of the deposit inside the penetration for the 1F Unit 2 primary containment vessel ("X-6 penetration") was performed to clarify the components and activity. The smears from the deposit were used for the analysis. Non-destructive analysis such as gamma-ray spectrometry, X-ray Fluorescence (XRF) and Scanning Electron Microscope-Energy dispersive X-ray spectroscopy (SEM-EDX) for the smear-samples were performed to determine the gamma-nuclides and the morphology of elements in the deposit. Furthermore, in order to evaluate the nuclides and nuclide composition of the deposit in detail, the smear-samples were dissolved and the quantitative analysis of gamma-nuclides, Sr-90, alpha-nuclides in the dissolved solution were conducted. The results (non-destructive analysis and quantitative analysis) were compared with the results of samples collected at different locations in the X-6 penetration in 2020. In the gamma-ray spectrometry as non-destructive analysis where the smears were analyzed directly, Co-60, Sb-125, Cs-134, Cs-137, Eu-154, Eu-155 and Am-241 were detected. In XRF results, Fe originating from construction material was detected as a major element and small amount of U and Zr originating from the fuel and fuel cladding were also detected. In SEM-EDX results, O and Fe were found as a major element of the deposit and U particles coexisting with Fe, Si, Cr, Ni and Zr were also found. These results were consistent with the SEM-EDX results of the samples collected in 2020. In radioactivity analysis, quantitative values for gamma-nuclides (Co-60, Sb-125, Cs-134, Cs-137, Eu-154, Eu-155), Sr-90, Pu-238, Pu-239+240, Am-241, Cm-244, U-235 and U-238 were obtained. Using the results, the ratios of radioactivity based on Cs-137 and U-238 were calculated. Both sets of the ratios were compared to the calculated value of the Unit 2 fuel composition from ORIGEN.
Aoyagi, Kazuhei; Tamura, Tomonori; Ozaki, Yusuke; Ishii, Eiichi; Motoshima, Takayuki*; Sugawara, Kentaro*
Dai-51-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu(Internet), p.119 - 124, 2025/12
In a high-level radioactive waste disposal, it is important to understand the extent of the Excavation Damaged Zone (EDZ) because it can be one of the factors to determine whether disposal galleries or pits can be excavated or not in the design or construction phases. In this study, we performed a hydro-mechanical coupling analysis to simulate the three-dimensional excavation of the twin galleries which were excavated at a depth of 500 m in the Horonobe Underground Research Laboratory. The analysis revealed that the EDZ was developed 1.5-2.0 m from the gallery wall. The stress acting on the shotcrete was within the ultimate limit state. Based on these results, we estimated that the stability of the twin galleries will be maintained, despite the relatively large extent of the EDZ.
Koizumi, Mitsuo; Yogo, Akifumi*
Isotope News, (802), p.11 - 14, 2025/12
no abstracts in English
Nakamura, Yuki*; Kojima, Yoshihiro*; Yamashita, Takuya; Shimomura, Kenta; Mizokami, Shinya
Journal of Nuclear Science and Technology, 62(12), p.1226 - 1230, 2025/12
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Collaborative Laboratories for Advanced Decommissioning Science; Tokai National Higher Education and Research System*
JAEA-Review 2025-023, 63 Pages, 2025/11
JAEA-Review-2025-023.pdf:5.74MB
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 and evaluation of a real-time 3D positioning embedded system combining wireless UWB and camera image analysis" conducted in FY2023. The present study aims to realize an embedded system that combines two of the latest popular technologies, "wireless UWB (Ultra Width Band)" and "multi-camera object recognition" with the goal of simple real-time 3D positioning with less than 10 cm accuracy by a human or robot for measuring air doses in nuclear reactor buildings. In this research, Gifu Univ. and National Institute of Technology, Fukushima College have developed an embedded system with camera shooting function, camera analysis function, and wireless communication function, in order to realize real-time 3D positioning based on the analysis of camera images by using these multiple devices. The Univ. of Tokyo and LocationMind Inc. will apply UWB real-time positioning technology to the inside of nuclear reactor buildings and attempt to develop technology to improve stability. Nagoya Univ. will be in charge of verifying wireless UWB stability from the hardware side by using electromagnetic wave absorbing materials. The radiation resistance evaluation will be conducted in cooperation with the JAEA and National Institute of Technology, Fukushima College.
Wada, Kazuma*; Kazama, Hiroyuki*; Abe, Chikage*; Onishi, Takashi; Yamamoto, Masahiko; Taguchi, Shigeo; Kuno, Takehiko; Maeda, Koji; Idemitsu, Kazuya*; Suzuki, Tatsuya*
Journal of Radioanalytical and Nuclear Chemistry, 334(11), p.8961 - 8968, 2025/11
Times Cited Count：0 Percentile：0.00(Chemistry, Analytical)The feasibility of using commercially available polyvinylpolypyrrolidone (PVPP) as a pretreatment for mass spectrometry to separate actinides was investigated. Uranium, thorium, and plutonium were used as actinides in the study. Adsorption data for An(IV) and An(VI) were obtained by adsorption experiments in nitric acid. In addition, An(III)/An(IV)/An(VI) mutual separation was successfully performed by a column separation method using PVPP. Furthermore, the elution efficiency of U(VI) was improved by the introduction of carbonate ions. This method may be applicable as a mutual separation for actinide mass spectrometry.
Onoda, Yuichi; Uchita, Masato*; Tokizaki, Minako*; Okazaki, Hitoshi*
Nuclear Technology, 211(11), p.2812 - 2831, 2025/11
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Collaborative Laboratories for Advanced Decommissioning Science; University of Fukui*
JAEA-Review 2025-007, 120 Pages, 2025/09
JAEA-Review-2025-007.pdf:8.13MB
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 FY2021, this report summarizes the research results of the "Clarification of debris formation conditions on the basis of the sampling data and experimental study using simulated fuel debris and reinforcement of the analytical results of severe accident scenario" conducted from FY2021 to FY2023. The present study aims to clarify the debris formation mechanism and utilize the results to refine the accident scenario. In the backward analysis of oxide debris formation, we prepared simulated fuel particles by the aerodynamic levitation method and ejection of melted oxides from a tungsten pipe with a small hole and summarized the relationship between preparation conditions and the properties of the particles. We also demonstrated the formation of simulated fuel debris obtained by the sampling in 1F and clarified the difference between the experimental results and thermodynamic calculation. From the estimation of mixing, melting and solidified states of metallic debris, it was found that the formation of thin reaction layer suppresses the damage of SUS in spite of Zr content around 1000 C, and we quantify the elution rate of B
C and Zircaloy to the melted SUS. We extended reaction rate data between various pressure vessel with SUS and Zr and welding parts and suggested reaction rate equation for large scale experiment. We also estimated the failure behavior of lower plenum of pressure vessel and outflow behavior of melt. Furthermore, we estimated transition behavior of Uranium melt to metallic debris melt in the re-melting process of predropped metallic debris. As the experimental techniques in the future, we prepared the semi-melted debris from oxide and metals and analyzed the reaction products and discussed the formation of simulated debris with a small amount of uranium oxide using a CCIM furnace and the aerodynamic levitation method.
Matsushita, Kentaro; Ezure, Toshiki; Fujisaki, Tatsuya*; Nakamine, Yoshiaki*; Imai, Yasutomo*; Tanaka, Masaaki
Nihon Kikai Gakkai 2025-Nendo Nenji Taikai Koen Rombunshu (Internet), 5 Pages, 2025/09
In the design of sodium-cooled fast reactors (SFRs), it is important to evaluate the transition behavior of non-condensable gas entrained into the primary coolant system due to cover gas entrainment and dissolution. In this study, trajectories of non-condensable gas bubbles in the cold plenum of the pool-type SFR evaluated by three-dimensional CFD analyses applying Discrete Phase Model. As the result of sensitivity analyses regarding bubble radius flowing into the cold plenum, it was clarified that the release rate of bubbles showed an increase according to the increase of bubble radius and an asymptotic increasing behavior in the large bubble radius cases.
