Input motions to equipment in a building that take into account the local response of the building must be identified to accurately evaluate the seismic response. In recent years, a 3D finite element model that can evaluate the realistic local response of a building has been used. To refine the 3D finite element model, it is important to verify its correspondence to the observed seismic behaviors.

In this study [1], we analyzed the natural frequencies and displacement diagrams of nuclear facilities from seismic observation records as the global response characteristics of the building. The vibration mode for each natural frequency was also analyzed. The target building was the High-Temperature Engineering Test Reactor (hereinafter, referred to as the “HTTR”) at the Oarai Research Institute of the Japan Atomic Energy Agency (hereinafter, referred to as the “JAEA”) and nine records were analyzed, including the record in the 2011 off-the-Pacific coast of Tohoku Earthquake (hereinafter, referred to as “3.11 main shock”), which was observed at the HTTR building [2]. This study has been conducted as part of a joint research effort between the Regulatory Standard and Research Department, Secretariat of Nuclear Regulation Authority (NRA) and JAEA.

Figure 1 shows the locations of the seismographs in the HTTR building. As an example, we analyzed the natural frequencies using transfer function of each floor to the basemat of the HTTR building during the 3.11 main shock. The frequencies at which the transfer function peaks were selected as the main natural frequencies of the HTTR building (around 4, 7, and 10Hz). We also analyzed the vibration mode at the natural frequencies using displacement diagram. The displacements were separated into rotational displacements and displacements due to building deformation, and their ratios were investigated.

In the future, we plan to create a 3D finite element model that reflects the global behavior obtained from this study and the local responses of the floors and walls. In addition, we plan to proceed with studies toward refining the 3D seismic analysis method of nuclear facilities.

Acknowledgments

In preparing this paper, we have referred to the study results of Reference [1] “Estimation of Vibration Characteristics of Nuclear Facilities Based on Seismic Observation Records, Proc. of ICONE-28, 2021” published at ICONE-28 sponsored by ASME. I would like to express my gratitude here.

References

[1] K. Yamakawa, et al., Estimation of Vibration Characteristics of Nuclear Facilities Based on Seismic Observation Records, Proc. of ICONE-28, (2021).

[2] A. Nishida, et al., Seismic Response Simulation of High-Temperature Engineering Test Reactor Building against 2011 Tohoku Earthquake, Proc. of ICONE-23, (2015)