Seismic Hazard Analysis of Deeply Embedded Small Modular Reactor Structures

Abstract

Some SMRs are designed to be buried under the ground with an expectation of enhanced resistance to seismic load during an earthquake event. In such cases, a traditional approach to seismic hazard analysis used by above ground, large nuclear power plants is not applicable due to the effect of deep embedment. The reason is that the response of an embedded structure is highly affected by the dynamic Soil-Structure Interaction (SSI).There is a myth about SSI is that it is always beneficial to structural safety under earthquake loading, since the soil will decrease the natural frequency of the structure, which is likely to reduce the overall structural responses. However, the lower frequency content of seismic input to the structure may be amplified due to the effect of soil with an adverse effect on the structural safety.Unlike large nuclear power plants for which seismic-risk analysis methods and codes are well developed, a comprehensive seismic evaluation method for SMRs is not yet available. Therefore, this paper aims presents a step towards the seismic risk analysis of deeply embedded SMR structures.The paper highlights differences between the seismic analysis of traditional large NPP structure and that of deeply embedded SMR structure using a dynamic model of an SMR. To study the effect of dynamic SSI, site response spectrum at bedrock level, at the surface, and at different depths are computed and compared. Preliminary results show a large variability in seismic response depending on the type of soil. Therefore, a realistic seismic hazard analysis is necessary to demonstrate the safety of SMR structures.