Is Soil-structure-interaction Analysis of Isolated Reactor Buildings Needed?

Current federal regulations in the United States require soil-structure-interaction (SSI) analysis for the design of conventionally founded large light water reactors, unless they are founded on very hard rock. Such reactors are typically massive and stiff, which are two key ingredients for significant SSI on soil sites. Advanced small modular and micro-reactors are one or more orders of magnitude lighter and smaller than their GW-scale predecessors. This reduction in physical scale, coupled with seismic isolation, which adds base flexibility, may effectively eliminate SSI and the need for such analysis. This paper explores the importance of SSI for isolated reactors through simulating the seismic response of an archetype advanced reactor building for multiple isolation systems, soil domains, seismic inputs, and intensities of shaking. The results presented here show that SSI effects are insignificant for this seismically isolated advanced reactor and that its design can proceed using surface free-field representations of ground shaking. Companion results for other reactor buildings, seismic isolation systems, soil domains, and seismic inputs, to be presented later, support this recommendation.