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Okuda, Yukihiko; Nishida, Akemi
Transactions of the 28th International Conference on Structural Mechanics in Reactor Technology (SMiRT28) (Internet), 10 Pages, 2025/08
no abstracts in English
Nishida, Akemi; Choi, B.; Kang, Z.; Shiomi, Tadahiko; Iigaki, Kazuhiko; Yamakawa, Koki*
Transactions of the 28th International Conference on Structural Mechanics in Reactor Technology (SMiRT28) (Internet), 10 Pages, 2025/08
Our research and development are aimed at improving the accuracy of the three-dimensional seismic analysis of nuclear buildings to better understand their three-dimensional seismic behavior in response to enhanced regulatory requirements on impact assessment against external events such as earthquakes. In 2019, we constructed a large-scale observation system for the High Temperature Engineering Test Reactor (HTTR) building of the Japan Atomic Energy Agency (JAEA) in collaboration with the Nuclear Regulation Authority (NRA) and JAEA. Since then, we also conducted several excitation tests by the ACROSS system and obtained observation record at many accelerometers using the observation system. These records are important since the excitation source is clearly defined unlike earthquake's uncertain transmission pathway. In this paper, we focus mainly on the vibration characteristics of the entire building and report on these observation records and the characteristics, such as the dominant frequencies and corresponding three-dimensional deformation modes.
Yamakawa, Koki*; Hiramatsu, Masako*; Moritani, Hiroshi*; Iiba, Masanori*; Nishida, Akemi; Shiomi, Tadahiko; Choi, B.; Iigaki, Kazuhiko
Transactions of the 28th International Conference on Structural Mechanics in Reactor Technology (SMiRT28) (Internet), 9 Pages, 2025/08
To understand the three-dimensional seismic behavior of nuclear buildings, the Nuclear Regulation Authority (NRA) and the Japan Atomic Energy Agency (JAEA) have been conducting research and development aimed at improving the accuracy of three-dimensional seismic analysis methods for nuclear buildings. A large-scale observation system was constructed in the High Temperature engineering Test Reactor (HTTR) building of JAEA, enabling seismic observation and artificial wave excitation. Using this system, vibration characteristics of the HTTR building have been analyzed based on both seismic observation records and analyses using a three-dimensional seismic analysis model of the HTTR building. This paper reports on the vibration characteristics of the HTTR building obtained from the analysis of seismic observation records, as well as on the improvements made to the three-dimensional finite element model and the results of simulation analyses using artificial waves. In particular, this paper presents the results of an analysis of the Fourier spectral ratio at the first floor of the HTTR building based on seismic records, and discusses the dominant frequencies and acceleration modes of the superstructure.
Choi, B.; Nishida, Akemi; Tsutsumi, Hideaki*; Takada, Tsuyoshi
Transactions of the 28th International Conference on Structural Mechanics in Reactor Technology (SMiRT28) (Internet), 10 Pages, 2025/08
One of the key lessons learned from the Fukushima Daiichi Nuclear Power Plant accident is the necessity of developing a probabilistic risk assessment (PRA) method that considers multiple external hazards (multi-hazards), such as earthquakes and tsunamis. In this study, we organized classification concepts for multi-hazards that could lead to significant disasters. A classification method for multi-hazard scenarios was developed based on causal relationships (dependent or independent) and temporal relationships (simultaneous or time-lagged occurrence). Furthermore, we examined modeling approaches for multi-hazard scenarios using the developed classification method. The modeling considered elements such as hazard curves, hazard intensity, hazard frequency, time, and event duration, and these were defined in terms of conditional probability density functions. This paper reports application examples of multi-hazard evaluation under hypothetical site and analysis conditions, focusing on representative scenarios such as earthquake-tornado and earthquake-tsunami combinations, based on the multi-hazard classification method developed in previous studies.
Watakabe, Tomoyoshi; Yamano, Hidemasa; Futagami, Satoshi
Transactions of the 28th International Conference on Structural Mechanics in Reactor Technology (SMiRT28) (Internet), 10 Pages, 2025/08
The fragility evaluation method of the RV in the SFR has been developed for both failure mode buckling and fatigue. The past studies showed the fragility using the RV of a loop-type SFR: radius R / thickness t is about 100. Recently, Japan Atomic Energy Agency together with Japanese industrial partners has been conducting a pool-type SFR design. The fragility of the pool-type RV has never been evaluated by the proposed method, which is based on the fatigue failure mode instead of the buckling. To investigate the basic behaviour of the pool-type RV under excessive seismic loading, this report investigated the fragility by using a simple cylindrical model with a wall thickness close to the design of the pool-type RV: R/t is 200, as the first trial.
Satoda, Akira*; Matsukawa, Keisuke*; Guo, Z. H.*; Choi, B.; Nishida, Akemi
Transactions of the 28th International Conference on Structural Mechanics in Reactor Technology (SMiRT28) (Internet), 10 Pages, 2025/08
In order to contribute to the seismic safety assessment of nuclear power plants and other industrial facilities against large earthquakes, it is an important issue to realistically capture the seismic behavior of plant structures and enable practical response analyses. Among the structural features that significantly influence seismic behavior, joints play a particularly critical role. In the case of steel pipe support structures (hereafter referred to as pipe racks), the joints connecting members (hereafter referred to as joints) have conventionally been modeled by empirical approaches, often idealized as pinned or rigid, leading to conservative evaluations. The final objective of this study is to develop a joint modeling method that reproduces more realistic behavior by utilizing three-dimensional detailed models of joints. To date, using the developed three-dimensional detailed analysis techniques, we have evaluated realistic semi-rigid stiffness of joints in both elastic and elasto-plastic ranges, proposed simplified joint models, and reported the obtained results. Furthermore, three-dimensional detailed analyses of an entire pipe rack including joints have been conducted, demonstrating the possibility of simultaneously capturing both the global seismic response of the pipe rack and the local joint behavior. In this paper, the simplified joint model proposed in previous studies is applied to the pipe rack joints modeled with conventional beam elements used in design practice, and the analysis results are compared with those of the detailed three-dimensional analysis. The findings are organized to clarify the differences and applicability. This enables improvement in the accuracy of practical seismic response analysis methods using beam elements. By applying the obtained results to the modeling of joints in steel structures of plant facilities, more rational seismic safety assessments of nuclear facilities and other plant structures can be expected.