# Seismic Response Analysis of Buried Nuclear Power Plant Structures in Non-Bedrock Sites
## 1 Introduction
[PERSON] and others [13; 14] focused on the new CAP1400 nuclear island structure for nuclear engineering, establishing an integrated finite element model for the shielding and auxiliary building structures. They conducted vibration table experiments for nuclear plant structures on non-bedrock sites, examining the seismic response of nuclear island structures on geotechnical sites with varying shear wave velocities. Their findings indicate that site conditions and soil-structure interaction analysis should be considered when assessing the seismic response of nuclear plant structures. [PERSON] et al. [15] addressed the influence of soil stiffness, structure-soil-structure interaction (SSSI), and backfill soil stiffness. When comparing seismic responses between flexible and rigid soils, a significant reduction in the maximum absolute acceleration values was obtained for flexible soils. Additionally, under rigid soil conditions, the maximum horizontal acceleration was significantly amplified with height. [PERSON] et al. [16] investigated the dynamic response of nuclear structures under SSSI (soil-structure-site interaction), developing a numerical model of double nuclear structures under SSSI. Their comparative study on the dynamic responses of nuclear structures under SSI and SSSI revealed that the presence of a single nuclear plant has a limited optimizing effect on the seismic response of an adjacent nuclear plant, such as reducing displacement responses. Additionally, the effects of SSSI are influenced not only by soil properties but also by the direction of seismic motion. Currently, research on the seismic performance of nuclear structures with periodic foundations in non-bedrock sites is incomplete. Through extensive numerical simulations and actual case analyses, this method can be used to more accurately assess the uncertainty of nuclear power plant structure responses under earthquakes, offer new insights for re liability analysis in seismic design, and effectively address the limitations of traditional deterministic analysis methods. In addition, previous studies mostly focused on traditional large-scale nuclear island structures with surface exposure. Today, through the design of soil-embedded reactor buildings, embedded nuclear island structures have performed well in enhancing their resistance to extreme external events (such as aircraft impacts, tornadoes, etc.) and have become a key research direction for the next generation of nuclear safety systems. The seismic response mechanism of embedded nuclear facilities is very different from that of traditional ground structures. Due to their underground structural characteristics, their structural behavior is more influenced by the deformation of the surrounding soil, resembling typical underground structures. Research has shown that site conditions significantly affect the seismic response of underground structures. However, current studies mainly focus on areas such as subway stations and tunnels. For new compact embedded nuclear island structures, current research mainly focuses on the influence of site shear wave velocity (Vs) on structural response modes, while there are few studies on the influence of the embedded depth of a structure on seismic performance. Numerous studies on pile-nuclear island structures and pile-raft-nuclear island structures on soft soil sites [17; 18; 19; 20; 21; 22; 23] also positively contribute to understanding the nuclear power response mode of soft soil sites. But these studies focus on traditional large-scale surface nuclear island structures. The new buried nuclear power plant discussed in this paper is a small modular reactor with the main structure located underground and configured as an underground box structure. The structural morphology indicates that its dynamic behavior is closer to that of underground structures, significantly differing from traditional large-scale ground nuclear island structures. Unlike aboveground structures, the seismic response of underground structures is dictated by surrounding soil deformation.