Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
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.