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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 (nondestructive 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.
Koizumi, Mitsuo; Yogo, Akifumi*
Isotope News, (802), p.11 - 14, 2025/12
no abstracts in English
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.
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.
Ichihara, Yoshitaka*; Nakamura, Naohiro*; Nabeshima, Kunihiko*; Choi, B.; Nishida, Akemi
Nuclear Engineering and Design, 441, p.114160_1 - 114160_10, 2025/09
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)This paper evaluates the applicability of equivalent linear analysis of reinforced concrete model, which uses frequency-independent complex damping with a small computational load, to the seismic design of nuclear power plant reactor buildings. To this end, a three-dimensional finite element method analysis of the soil-structure interaction focusing on nonlinear and equivalent linear seismic behavior of the building embedded in an ideally uniform soil condition was performed for the Kashiwazaki-Kariwa Nuclear Power Plant Unit 7 reactor building. The equivalent linear analysis results correlated well with the nonlinear analysis results of the shear strain, acceleration, displacement, and acceleration response spectrum, demonstrating the effectiveness of the equivalent linear analysis method. Moreover, the equivalent linear analysis results were more conservative than those of nonlinear analysis using the material constitutive law in evaluating the shear strain of the external wall of the reactor building. From this result, equivalent linear analysis method tended to obtain a lower building stiffness than nonlinear analysis under the analysis conditions used in this paper.
Sato, Rika; Kondo, Toshiki; Umeda, Ryota; Kikuchi, Shin; Yamano, Hidemasa
Progress in Nuclear Science and Technology (Internet), 8, p.137 - 142, 2025/09
In a sodium-cooled fast reactor (SFR) coupled to thermal energy storage (TES) system, the reaction between nitrate molten salt as thermal energy storage medium and sodium (Na) as reactor coolant might occur under postulated accidental conditions. Thus, the reaction behavior of Na-nitrate molten salt is one of the important phenomena in terms of safety assessment of the SFR with TES system. In this study, reaction experiments on Na-solar salt were performed. It was found that Na-solar salt reaction occurred after the NaNO
-KNO eutectic melting. Based on the measured reaction temperature, the kinetic parameters and rate constant were obtained and compared with the sodium-water reaction. From the results of kinetic analysis, it could be assumed that Na-solar salt reaction occurs in the time frame of the accident such as the failure of heat transfer tube of sodium-molten salt heat exchanger.
Yamamoto, Masahiko; Horigome, Kazushi; Goto, Yuichi; Taguchi, Shigeo; Kuno, Takehiko
Progress in Nuclear Science and Technology (Internet), 8, p.387 - 392, 2025/09
Flush-out of Tokai Reprocessing Plant was completed in February, 2024 for the preparation of process decontamination. Since remaining nuclear materials were contained in main process, purpose of the activities was to recover nuclear materials by transferring them to the highly radioactive liquid waste storage tank and converting uranium solution into uranium trioxide, and to rinse all related processes with nitric acid and water. During this activity, analysis of U and Pu was conducted for nuclear material control and accountancy. Appropriate analytical methods such as isotope dilution mass spectrometry, gravimetric method, spectrophotometry and alpha-ray counting methods were selected depending on the status of flush-out. Also, gamma-ray emitted nuclides in rinsing solution were detected by highly purified germanium detector. This paper describes analysis and its results related to flush-out activities of decommissioning in reprocessing plant.
Collaborative Laboratories for Advanced Decommissioning Science; Institute of Science Tokyo*
JAEA-Review 2025-010, 62 Pages, 2025/08
JAEA-Review-2025-010.pdf:3.63MB
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 FY2021, this report summarizes the research results of the "Fuel debris criticality analysis technology using non-contact measurement method" conducted from FY2021 to FY2023. The purpose of research was to improve the fuel debris criticality analysis technology using non-contact measurement method by the development of the fuel debris criticality characteristics measurement system and the multi-region integral kinetic analysis code. It was performed by Institute of Science Tokyo, Tokyo City University, National Institute of Advanced Industrial Science and Technology, and Nagaoka University of Technology. We developed the fuel debris criticality characteristics measurement system which has a two layer structure surrounding a canister containing fuel debris fragments with 
He proportional counters. The operational validation and performance evaluation were performed on the developed detector system. We have demonstrated the feasibility and accuracy of measuring the amount of fissile material and water content. MIK2.0-MVP code, which can calculate fission reaction rate attributed to both prompt and delayed neutrons and also can take the movement of fuel debris into calculation, was developed. After parallelizing the tally process of C
(
) function, MIK2.0-MVP code will be applicable to weakly coupled reactors which include moving fuel debris particles if a supercomputer will be used for the tally process of C() function and if the coupling of MIK2.0-MVP code with MPS will be weak.
Motegi, Kosuke; Matsumoto, Toshinori; Shiotsu, Hiroyuki
Proceedings of 21st International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-21) (Internet), 10 Pages, 2025/08
Collaborative Laboratories for Advanced Decommissioning Science; Fukushima University*
JAEA-Review 2025-002, 108 Pages, 2025/07
JAEA-Review-2025-002.pdf:5.25MB
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 FY2019, this report summarizes the research results of the "Development of methodology combining chemical analysis technology with informatics technology to understand perspectives property of debris and tie-up style human resource development" conducted from FY2019 to FY2023. The present study aims to Goal of this study is to implement a research plan relate to a development of combinational technology of new chemical analysis with informatics, and the aim is to develop new system for whole image estimation system using small quantities of information. Conducting the collaboration study with JAEA researchers (tie-up style) make connect to the development of human resource from master's course student to post-doctoral researchers who are progress in the local-based and/or many academics fields research. We are in progress to grow international-minded human resources.
Hamdani, A.; Soma, Shu; Abe, Satoshi; Shibamoto, Yasuteru
Progress in Nuclear Energy, 185, p.105771_1 - 105771_13, 2025/07
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*
JAEA-Review 2024-064, 118 Pages, 2025/06
JAEA-Review-2024-064.pdf:6.73MB
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 FY2019, this report summarizes the research results of the "Development of extremely small amount analysis technology for fuel debris analysis" conducted from FY2019 to FY2023. Understanding the properties of fuel debris is necessary for handling, criticality control, storage control, etc. A key technique is the chemical analysis of actinide nuclides. We developed sample pretreatment technology and separation / analysis process required for chemical analysis. The purpose of this study is to streamline future planned fuel debris analysis. To promote 1F decommissioning, we will train human resources through on-the-job training. In particular, we applied the extremely small amount analysis (ICP-MS/MS), which has recently been successful in the fields of analytical chemistry and radiochemistry, to the nuclear field. This method allows high-accuracy analysis without pretreatment to isolate the nuclide to be measured. The separation pretreatment can be skipped and a rapid analysis process can be established.
Yanagisawa, Hiroshi; Motome, Yuiko
JAEA-Research 2025-001, 99 Pages, 2025/06
JAEA-Research-2025-001.pdf:1.98MB
The detailed computational models for nuclear criticality analyses on the first startup cores of NSRR (Nuclear Safety Research Reactor), which is categorized as a TRIGA-ACPR (Annular Core Pulse Reactor), were created for the purposes of deeper understandings of safety inspection data on the neutron absorber rod worths of reactivity and improvement of determination technique of the reactivity worths. The uncertainties in effective neutron multiplication factor (k
) propagated from errors in the geometry, material, and operation data for the present models were evaluated in detail by using the MVP version 3 code with the latest Japanese nuclear data library, JENDL-5, and the previous versions of JENDL libraries. As a result, the overall uncertainties in k for the present models were evaluated to be in the range of 0.0027 to 0.0029 
k. It is expected that the present models will be utilized as the benchmark on k for TRIGA-ACPR. Moreover, it is confirmed that the overall uncertainties were sufficiently smaller than the values of absorber rod worths determined in NSRR. Thus, it is also considered that the present models are applicable to further analyses on the absorber rod worths in NSRR.
Takeda, Takeshi
JAEA-Data/Code 2025-005, 106 Pages, 2025/06
JAEA-Data-Code-2025-005.pdf:2.93MB
JAEA has been creating input data for pressurized water reactor (PWR) analysis with RELAP5/MOD3.3 code, mainly based on design information for the four-loop PWR's Tsuruga Power Station Unit-2 as the reference reactor of the Large Scale Test Facility (LSTF). The cold leg large-break loss-of-coolant accident (LBLOCA) calculation in the flamework of the BEMUSE program is cited as a representative OECD/NEA activity related to the PWR analysis. The new regulatory requirements for PWRs in Japan include the event of loss of recirculation functions from emergency core cooling system (ECCS) in the cold leg LBLOCA. This event should be evaluated the effectiveness of measures against severe core damage. The input data for this study were made preparations to analyze the PWR LBLOCA, which is one of the design basis accidents that should be postulated in the safety design. This report describes the main features of the input data for the PWR LBLOCA analysis. The PWR model comprised a reactor vessel, pressurizer (PZR), hot legs, steam generators (SGs), SG secondary-side system, crossover legs, cold legs, and ECCS. A four-loop PWR was simulated by two loops in the LBLOCA calculation. Specifically, loop-A attached with the PZR corresponded to three loops, and loop-B mounted with the break was equal to one loop. The nodalization schemes of the PWR components were referred to those of the LSTF components. Moreover, interpretations were added to the main input data for the PWR LBLOCA analysis, and further information such as the basis for determining the input data was provided. In addition, transient analysis was performed employing the prepared input data for the loss of ECCS recirculation functions event. The present transient analysis was confirmed to be appropriate generally by comparing with the calculation in the previous study using the RELAP5/MOD3.3 code. Furthermore, sensitivity analyses were executed exploiting the RELAP5/MOD3.3 code to clarify the effects of a discharge coefficient through the break and water injection flow rate of the alternative recirculation on the fuel rod cladding surface temperature. This report explains the results of the sensitivity analyses within the defined ranges, which complement some of the content of the previous study's calculation for the loss of ECCS recirculation functions event.
Sugita, Yutaka; Ono, Hirokazu; Beese, S.*; Pan, P.*; Kim, M.*; Lee, C.*; Jove-Colon, C.*; Lopez, C. M.*; Liang, S.-Y.*
Geomechanics for Energy and the Environment, 42, p.100668_1 - 100668_21, 2025/06
Times Cited Count：1 Percentile：67.60(Energy & Fuels)The international cooperative project DECOVALEX 2023 focused on the Horonobe EBS experiment in the Task D, which was undertaken to study, using numerical analyses, the thermo-hydro-mechanical (or thermo-hydro) interactions in bentonite based engineered barriers. One full-scale in-situ experiment and four laboratory experiments, largely complementary, were selected for modelling. The Horonobe EBS experiment is a temperature-controlled non-isothermal experiment combined with artificial groundwater injection. The Horonobe EBS experiment consists of the heating and cooling phases. Six research teams performed the THM or TH (depended on research team approach) numerical analyses using a variety of computer codes, formulations and constitutive laws.
Auh, Y. H.*; Neal, N. N.*; Arole, K.*; Regis, N. A.*; Nguyen, T.*; Ogawa, Shuichi*; Tsuda, Yasutaka; Yoshigoe, Akitaka; Radovic, M.*; Green, M. J.*; et al.
ACS Applied Materials & Interfaces, 17(21), p.31392 - 31402, 2025/05
Times Cited Count：0 Percentile：0.00(Nanoscience & Nanotechnology)Fukuda, Kodai; Obara, Toru*; Suyama, Kenya
Nuclear Technology, 211(5), p.963 - 973, 2025/05
Times Cited Count：1 Percentile：35.03(Nuclear Science & Technology)Guembou Shouop, C. J.; Tsuchiya, Harufumi
Nuclear Instruments and Methods in Physics Research A, 1072, p.170189_1 - 170189_14, 2025/03
Times Cited Count：2 Percentile：59.21(Instruments & Instrumentation)Okazaki, Nobuo*; Hattori, Takanori
CROSS Reports (Internet), 3, p.001_1 - 001_8, 2025/02
There have been requests for remote analysis of measured data at the BL11 PLANET beamline in the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC), but a system to perform this analysis on a regular basis has not been established. In order to meet this demand, a system for remote analysis was established using NoMachine, which is widely used as a remote desktop connection environment. This system is built on the cloud, and users can analyze data from anywhere with an Internet environment by using the NoMachine client.
