Soil Structure Interaction Analysis of a Deeply Embedded Reactor Silo

This paper reviews the seismic soil structure interaction (SSI) analysis performed for the Modular High Temperature Gas-cooled Reactor (MHTGR). The large depth to diameter ratio of the silo requires proper modeling of embedment and silo flexibility when evaluating the response of the structure to seismic loads. The carputer program SASSI was used to perform the three dimensional SSI analysis in order to take full advantage of embedment in reducing seismic response. Acceleration response spectra were computed for three soil sites at various points in the silo walls and internal vessels. The results demonstrated the effectiveness of embedment in reducing the seismic response. In general, the lowest silo and vessel accelerations occurred in the softest site where the SSI effects are the most pronounced. For a rock site, embedment eliminated the problem faced by structures founded at grade of amplification at the structure's fundamental modes.