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Li, X.; Yamaji, Akifumi*; Sato, Ikken*; Yamashita, Takuya
Annals of Nuclear Energy, 214, p.111217_1 - 111217_13, 2025/05
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Yamada, Takeshi*; Li, X.; Yamashita, Takuya; Yamaji, Akifumi*
Proceedings of 31st International Conference on Nuclear Engineering (ICONE31) (Internet), 10 Pages, 2024/11
In this study, a new crust model is being developed to analyze MCCI, which involves continuous concrete ablation with presence of the crust layer between the corium and the concrete walls, which may gradually move with the slow concrete wall ablation process over long time. The new crust model must enable accumulation of physical displacement of the crust particle over long time (i.e., enable physical creeping) while preventing accumulation of numerical displacement of the crust particles over long time (i.e., preventing numerical creeping), Hence, in the new crust model, the PS has been effectively disabled for the crust particles. Qualitative validity of such numerical modeling was confirmed through some trial analyses of VULCANO-VBS test using a set of tentative calculation conditions and parameters, which should be carefully revised for future quantitative discussions including validation of the analysis results with experimental results.
Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*
JAEA-Review 2022-010, 155 Pages, 2022/06
JAEA-Review-2022-010.pdf:9.78MB
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 FY2020. 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 FY2018, this report summarizes the research results of the "Development of the technology for preventing radioactive particles' dispersion during the fuel debris retrieval" conducted from FY2018 to FY2021 (this contract was extended to FY2021). Since the final year of this proposal was FY2021, the results for four fiscal years were summarized. The present study aims to clarify the behavior of microparticles in gas and liquid phases in order to steadily confine radioactive microparticles during fuel debris retrieval in Fukushima Daiichi Nuclear Power Station, TEPCO. As measures to prevent dispersion of microparticles, (1) a method to suppress the dispersion with minimum amount of water utilizing water spray etc., and (2) a method to suppress the dispersion by solidifying fuel debris were evaluated by experiments and simulation. The applicability of these methods to the actual plants was also evaluated.
Yoshikawa, Shinji; Yamaji, Akifumi*
JAEA-Research 2021-006, 52 Pages, 2021/09
JAEA-Research-2021-006.pdf:3.89MB
In Fukushima Daiichi Nuclear Power Station (referred to as "FDNPS" hereafter) unit2 and unit3, failure of the reactor pressure vessel (RPV) and relocation of some core materials (CRD piping elements and upper tie plate, etc.) to the pedestal region have been confirmed. In boiling water reactors (BWRs), complicated core support structures and control rod drive mechanisms are installed in the RPV lower head and its upper and lower regions, so that the relocation behavior of core materials to pedestal region is expected to be also complicated. The Moving Particle Semi-implicit (MPS) method is expected to be effective in overviewing the relocation behavior of core materials in complicated RPV lower structure of BWRs, because of its Lagrangian nature in tracking complex interfaces. In this study, for the purpose of RPV ablation analysis of FDNPS unit2 and unit3, rigid body model, parallelization method and improved calculation time step control method were developed in FY 2019 and improvement of pressure boundary condition treatment, stabilization of rigid body model, and calculation cost reduction of debris bed melting simulation were achieved in FY2020. These improvements enabled sensitivity analyses of melting, relocation and re-distribution behavior of deposited solid debris in RPV lower head on various cases, within practical calculation cost. As a result of the analyses of FDNPS unit2 and unit3, it was revealed that aspect (particles/ingots) and distribution (degree of stratification) of solidified debris in lower plenum have a great impact on the elapsed time of the following debris reheat and partial melting and on molten pool formation process, further influencing RPV lower head failure behavior and fuel debris discharging behavior.
Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*
JAEA-Review 2019-037, 90 Pages, 2020/03
JAEA-Review-2019-037.pdf:7.0MB
JAEA/CLADS, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. 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 FY2018, this report summarizes the research results of the "Development of Technology to Prevent Scattering of Radioactive Materials in Fuel Debris Retrieval". The objective of the present study is to clarify the behavior of microparticles in gas and liquid phases in order to steadily confine radioactive microparticles at the time of debris retrieval in Fukushima Daiichi Nuclear Power Station. In addition, as measures to prevent scattering, we will evaluate and develop methods by experiments and simulation as to; (1) a method to suppress the scattering with minimum amount of water utilizing water spray etc., and (2) a method to suppress the scattering by solidifying fuel debris.
Li, X.; Sato, Ikken; Yamaji, Akifumi*; Duan, G.*
Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 8 Pages, 2018/07
Molten corium-concrete interaction (MCCI) is an important ex-vessel phenomenon that could happen during the late phase of a hypothetical severe accident in a light water reactor. In the present study, a three-dimensional (3-D) numerical study has been performed to simulate COMET-L3 test carried out by KIT with a stratified molten pool configuration of simulant materials with improved MPS method. The heat transfer between corium/crust/concrete was modeled with heat conduction between particles. Moreover, the potential influence of the siliceous aggregates was also investigated by setting up two different case studies since there was previous study indicating that siliceous aggregates in siliceous concrete might contribute to different axial and radial concrete ablation rates. The simulation results have indicated that metal melt as corium in MCCI can have completely different characteristics regarding concrete ablation pattern from that of oxidic corium, which needs to be taken into consideration when assessing the containment melt-through time in severe accident management.
Watanabe, Tadashi; Hirano, Masashi;
Journal of Nuclear Science and Technology, 30(10), p.1078 - 1083, 1993/10
Times Cited Count：1 Percentile：18.62(Nuclear Science & Technology)no abstracts in English
; Abe, Yutaka; Onuki, Akira; Murao, Yoshio
JAERI-M 90-122, 36 Pages, 1990/08
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