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Zou, Z.*; Morita, Koji*; Ishida, Shinya; Yamano, Hidemasa
International Communications in Heat and Mass Transfer, 180, Part 2, p.112532_1 - 112532_22, 2026/11
Times Cited Count：0Collaborative Laboratories for Advanced Decommissioning Science; Tokai National Higher Education and Research System*
JAEA-Review 2026-018, 141 Pages, 2026/09
JAEA-Review-2026-018.pdf:14.13MB
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 FY2023, this report summarizes the research results of the "Pilot study on thermal, physico-chemical, and mechanical behavior of concrete to understand the failure behavior of Fukushima Daiichi Nuclear Power Station reactor pressure vessel pedestals" conducted in FY2024. The present study aims to examine the mechanism of the collapse of only concrete with rebar remaining in the pedestal in the containment vessel (PCV) of 1F. In verifying concrete-specific factors, (1) high-temperature heating experiments were conducted on cement paste, aggregates, and their mixtures to obtain heating behavior. Phase composition changes and melting behavior under high-temperature conditions were analyzed using thermodynamic phase equilibrium calculations, and a numerical analysis method to reproduce water absorption behavior after high-temperature exposure was developed. In addition, (2) exposure experiments simulating the temperature and water injection history of the pedestal were conducted, and time-dependent expansion after heating and expansion behavior induced by water supply were evaluated. In the verification of special external environmental factors, (1) thermal conditions of concrete in the PCV during debris accumulation were evaluated by heat transfer analysis based on accident scenarios. In addition, (2) concrete collapse behavior with and without water vapor was evaluated by small-scale high-temperature holding tests, and concrete damage behavior due to reactions with simulated fuel debris was evaluated by high-temperature reaction tests.
Wakai, Takashi; Ando, Masanori; Okajima, Satoshi; Toyota, Kodai; Ishigami, Katsuo*; Onuma, Terumitsu*; Takahashi, Ryoya*; Asayama, Tai
Nihon Kikai Gakkai Rombunshu (Internet), 92(961), p.26-00004_1 - 26-00004_12, 2026/09
This paper describes current efforts within the Japan Atomic Energy Agency to develop a new materials surveillance technology for sodium-cooled fast reactors that aims at raising the confidence levels in operating reactors' structural integrity to the ones which could otherwise be achieved only by a vast amount of long-term material test data that needs decades to accumulate. The technology would allow for monitoring on-going materials degradation processes in an actual reactor, namely fatigue and creep-fatigue, by inserting a newly developed specimen for this purpose into the reactor and establishing procedures to observe and evaluate the specimen to get desired information such as the extent of degradation and residual life. To establish the test procedure, a passive creep-fatigue test model was developed in the framework of the "Civil Nuclear Energy Research and Development Working Group (CNWG)", a collaboration agreement between the US and Japan, and a demonstration test was performed under cyclic thermal loads using an electric furnace. Temperature conditions had been determined based on finite element analyses. As a result, the test specimen failed by several hundred thermal cycles. Macroscopic inspection of the specimen after the test showed the test had been performed successfully without buckling. Fracture surface observations suggested that the failure caused probably by fatigue or creep-fatigue.
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.
Ishida, Reiya; Aoki, Emi; Sonobe, Hiroshi; Oto, Tsutomu; Kimura, Akihiro
JAEA-Review 2026-019, 50 Pages, 2026/07
JAEA-Review-2026-019.pdf:5.3MB
Subsequent to a leakage incident in October 2012 involving the SFC waste liquid transfer piping in the C Trench, additional leakage incidents occurred in the No. 4 drainage system piping and the SFC waste resin transfer piping. Furthermore, leakage incidents occurred in the tank yard, including seepage at welded joints in the waste liquid piping, as well as leakage from the waste liquid tanks. Since these incidents, the transfer of liquid waste from the hot laboratory facility to the JMTR tank yard has been suspended. Currently, as the waste liquid piping in the JMTR tank yard and the waste liquid tanks receiving liquid waste from the hot laboratory have been replaced and in sound condition, a plans is being developed to resume liquid waste transfer. To confirm the integrity of the waste liquid piping system, which runs from the hot laboratory through the C Trench to the tank yard, radiographic testing (hereafter referred to as "RT") of the pipe welds will be conducted. As it has been confirmed that the waste liquid piping is wrapped with asbestos-containing thermal insulation materials, these materials will be removed from the piping prior to RT. During this removal work, it is essential to comply with applicable laws and regulations and to ensure worker safety. This report summarizes the plan for removal of asbestos-containing thermal insulation materials in radiation controlled areas in order to minimize asbestos-related risks, as well as the procedures for the removal work and the methods for storage management.
Harada, Masahide
JPS Conference Proceedings (Internet), 45, p.011042_1 - 011042_6, 2026/06
At Materials and Life science Facility (MLF) in J-PARC, 3 GeV and 1MW proton beam induces a carbon target and a mercury target to provide muon beam and neutron beam, respectively. The first target station of MLF, "TS1", started to operate from 2008 and stably operates with nearby 1MW as of April 2024. As an upgrade of MLF, the second target station, "TS2", is being planned. TS2 is located near TS1 and the proton beam line to TS2 is divided at halfway to the TS1 proton beam line. Total proton beam power supplied by accelerators increases to 1.5MW. Although the repetition rate is still 25Hz, 1 of 3 pulses are transported to TS2, resulting in 8.3Hz and 0.5MW of proton beam to TS2. TS2 has a tungsten rotating target to provide both neutron and muon, and moderators to provide much higher neutron brightness by adopting higher current density of proton beam, a closer moderator position to the target, a flatter moderator and so on. Beryllium and Iron are chosen as reflector materials. The rotating target cooled by helium gas is also expected to increase neutron and muon intensities with a coexistence of them. Details of TS2 plan are summarized in Ref. In order to provide high intensity neutrons, optimization studies of TS2 were performed by the simulation code PHITS and MCNP. Finally, the coupled moderator of TS2 can provide 4 times higher intensity than that of TS1. If smaller height of moderator is chosen, brightness increases to 8 times compared with TS1. Decoupled moderators of TS2 also provide 3 time higher than that of TS1. A fixed solid target case was also compared.
Takei, Hayanori
JPS Conference Proceedings (Internet), 45, p.011175_1 - 011175_7, 2026/06
The Japan Atomic Energy Agency is working on the research and development of an accelerator-driven nuclear transmutation system (ADS) for transmuting minor actinides. This system is a combination of a subcritical nuclear reactor and a high-power superconducting proton linear accelerator (JADS-linac). One of the challenges in developing the JADS-linac is to reduce the number of beam trips. Until now, the beam trip frequency of the JADS-linac has been estimated from the operation data of the J-PARC linac, which uses the normal-conducting acceleration (NC) cavities. Recently, data on beam trips in the superconducting acceleration (SRF) cavities of the Spallation Neutron Source of the Oak Ridge National Laboratory (SNS) have been published. These data are important for the estimation of the beam trip frequency of the JADS-linac. Rather, the SNS data are more appropriate than the J-PARC data, because the JADS-linac uses the SRF cavities. On the other hand, the calculation methods in the published data for the NC cavities of J-PARC and the SRF cavities of SNS are different, so it is not possible to simply compare the two. In this study, the mean time between beam trips (MTBT) of the J-PARC NC cavity and the SNS SRF cavity are compared using the same condition. Specifically, the MTBT of the acceleration cavities connected to a single klystron system was calculated and compared. As a result, the MTBT of the SNS SRF cavity was 5.0 and 8.8 times longer than that of the J-PARC NC cavity for 
and 
h, respectively, where 
is the beam trip duration.
Zr(n, 
)
Zr and 
Zr(n, )
Zr reactions at JRR-3Nakamura, Shoji; Kimura, Atsushi; Endo, Shunsuke; Rovira Leveroni, G.; Shibahara, Yuji*
Journal of Nuclear Science and Technology, 63(6), p.653 - 666, 2026/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Nakamura, Shoji; Shibahara, Yuji*; Kimura, Atsushi; Endo, Shunsuke; Rovira Leveroni, G.
KURNS Progress Report 2025, P. 101, 2026/06
no abstracts in English
Fukuda, Kodai; Obara, Toru*
Nuclear Technology, 212(6), p.1567 - 1578, 2026/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Ha, H.*; Kim, J.*; Gu, G. H.*; Harjo, S.; Gong, W.; Hong, S.-J.*; Kim, H. S.*
Materials Characterization, 234, p.116086_1 - 116086_12, 2026/04
Times Cited Count：2 Percentile：90.58(Materials Science, Multidisciplinary)Ebihara, Kenichi; Yamaguchi, Masatake; Itakura, Mitsuhiro
Metallurgical and Materials Transactions A, 57(4), p.1480 - 1489, 2026/04
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Hydrogen (H) embrittlement is an important issue for steel. The experimental thermal desorption spectra of H from an iron sample containing H-enhanced strain-induced vacancies (Vs) were successfully reproduced by revising a previous numerical model. In the revised model, we adopted concentration variables for Vs and V clusters, which are distinguished by the number of trapped H atoms. This revision eliminated the assumption of V and V cluster migration, required in the original model. Simulation results of the revised model revealed that the spike-like desorption on the peak attributed to Vs and V clusters in the spectra simulated by the original model was an artifact caused by the assumption. In addition, it was suggested that V clusters can exist other than Vs in the specimens after deformation with H charging. It is considered that the revised model is a useful framework for studying Vs and V clusters under H-affected conditions.
Tada, Kenichi; Kondo, Ryoichi; Kamiya, Tomohiro; Fukuda, Takanari; Fukuda, Kodai; Ono, Ayako; Nagaya, Yasunobu; Yoshida, Hiroyuki
Proceedings of International Conference on the Physics of Reactors (PHYSOR 2026) (Internet), 8 Pages, 2026/04
High-fidelity multi-physics simulations are important for the verification of core design codes. JAEA is developing a high-fidelity multi-physics platform JAMPAN to couple many single-physics codes. This paper demonstrates the BWR whole core neutronics and thermal-hydraulics coupling simulation using the continuous energy Monte Carlo calculation code MVP and the three-field subchannel code NASCA. The initial loading core of Peach Bottom Unit 2 obtained from the OECD/NEA Peach Bottom turbine trip benchmark was used for the BWR core calculations. The k-effective value and the axial fission rate distribution in each assembly converged in about 20 seconds (10 iterations) from the initial state. The axial fission rate distribution in each assembly is physically reasonable. These calculation results indicate that JAMPAN appropriately couples the neutronics and thermal-hydraulics calculations for the BWR whole core geometry.
Sakakibara, Ryotaro*; Terasawa, Tomoo; Kawauchi, Taizo*; Fukutani, Katsuyuki; Ito, Takahiro*; Norimatsu, Wataru*
Small Methods, 10(8), p.e01889_1 - e01889_12, 2026/04
Times Cited Count：1 Percentile：70.18(Chemistry, Physical)Terasawa, Tomoo; Katsube, Daiki*; Yano, Masahiro; Ozawa, Takahiro*; Tsuda, Yasutaka; Yoshigoe, Akitaka; Asaoka, Hidehito; Suzuki, Seiya
Chemistry of Materials, 38(6), p.2933 - 2945, 2026/03
Times Cited Count：0 Percentile：0.00(Chemistry, Physical)Ahn, S. Y.*; Kim, E. S.*; Jeong, S. G.*; Harjo, S.; Kawasaki, Takuro; Gong, W.; Kim, H.-J.*; Hong, S.-J.*; Hong, S. I.*; Kwon, H.*; et al.
Materials Science & Engineering A, 955, p.149839_1 - 149839_18, 2026/03
Times Cited Count：3 Percentile：93.72(Nanoscience & Nanotechnology)
neutron diffraction at cryogenic temperaturesYamashita, Takayuki*; Harjo, S.; Gong, W.; Kawasaki, Takuro; Morito, Shigekazu*; Morooka, Satoshi; Fujii, Hidetoshi*; Tomota, Yo*
Journal of Alloys and Compounds, 1056, p.186668_1 - 186668_11, 2026/02
Times Cited Count：0 Percentile：0.00(Chemistry, Physical) 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.
Zhu, L.*; Dong, W.*; Naeem, M.*; Kong, H.*; Hu, C.*; Fan, Z.*; Gong, W.; Harjo, S.; Lan, S.*; Wu, Y.*; et al.
Acta Materialia, 303, p.121734_1 - 121734_10, 2026/01
Times Cited Count：8 Percentile：69.61(Materials Science, Multidisciplinary)