# Seismic Response Analysis of Buried Nuclear Power Plant Structures in Non-Bedrock Sites
## 1 Introduction  
As of December 2024, according to the World Nuclear Association [1], the global nuclear power grid-connected capacity reached 396 GW, there were 439 grid-connected nuclear island structures, the capacity under construction was 71.8 GW, and there were 66 nuclear island structures under construction. The scale of nuclear power occupies an important position in the global energy structure. From the perspective of distribution area, Asia, Europe, and North America are regions with relatively concentrated nuclear power installed capacity. It is observed that more than 90% of the world's nuclear facilities are located on coastal bedrock sites. The geological conditions in these areas are stable, providing a solid foundation for the safe operation of nuclear island structures. A series of statistical data strongly demonstrates that China's nuclear power industry is experiencing a trend of rapid growth. So far, China's nuclear power installed capacity has continued to rise, and its proportion in the energy structure has increased day by day. However, it cannot be ignored that most of the current domestic nuclear island structures are located in coastal areas. However, the available resources of coastal bedrock sites are gradually decreasing. With the increasing scarcity of available space in coastal regions, future nuclear power construction sites in China are expected to move towards inland non-bedrock locations. Due to the significant water resource demands for nuclear power facility operations, inland nuclear island structures are frequently situated near rivers and lakes, which generallyexhibit non-bedrock geological characteristics. Numerous studies [2; 3; 4; 5; 6; 7; 8; 9] indicate that in the seismic design of nuclear power structures, the acceleration and floor response spectra of the structures are critical points of focus. Therefore, investigating the seismic response patterns of acceleration and floor spectra for new types of nuclear power structures, along with methods for reducing seismic response, has become one of the key research priorities in the field of nuclear power structures. Numerous standards and design documents [10; 11; 12] indicate that fixed foundation analysis is applicable when the shear wave velocity reaches 2400 m/s, eliminating the need to consider soil-structure interaction (SSI) effects. However, the situation is quite different in non-bedrock sites. Given the complexity of such sites, SSI effects may significantly influence the safety of nuclear power plant structures. Thus, to ensure the safety and stability of these structures in non-bedrock sites, SSI effects must be thoroughly considered during the engineering design and construction process. Targeted strategies should be formulated in all aspects, including in geological surveys, structural design, and construction, to effectively respond to the challenges brought by non-bedrock sites and ensure the safe operation of nuclear island structures. However, with the growth of global energy demand and the decreasing number of available coastal site resources, the construction sites of nuclear island structures in the future are expected to shift more to inland non-bedrock areas. The site conditions in these inland areas are more complex than those in coastal bedrock sites. There are many uncertainties in foundation stability and soil characteristics, and the engineering challenges brought about by this are particularly prominent. It has been established that when the average shear wave speed of a structure's foundation exceeds 2400 m/s, or when the stiffness of the foundation is more than twice that of the superstructure [10], the interaction between the foundation and structure can be disregarded. In all other cases, the soil-structure interaction (SSI) must be considered. This interaction is particularly critical in the seismic analysis of nuclear safety structures built on non-bedrock foundations. Recently, substantial progress has been made in theoretical research [13; 14; 15; 16] on nuclear structure control.