Design and analysis of a three-dimensional seismic isolation device for small modular reactor building

Seismic isolation in nuclear power plant (NPP) buildings has been infrequently applied using a rubber-based horizontal seismic isolation system (SIS) without vertical isolation under a peak ground acceleration (PGA) of 0.3 g as the seismic design requirement. For NPP buildings with seismic design requirements of PGA 0.5 g or greater, vertical seismic isolation has become an essential requirement to ensure the seismic protection of the systems, structures, and components (SSCs) inside the NPP, necessitating the development of feasible devices for a three-dimensional seismic isolation system (3D SIS). This study suggests a feasible device design for a 3D SIS capable of supporting a NuScale small modular reactor (SMR) building with a vertical load of 266,000 tf under a PGA seismic design requirement of 0.5 g. The performance of the designed 3D SIS in providing vertical and horizontal seismic isolation for the building is numerically examined. The proposed 3D SIS comprises 133 modularized 3D seismic isolation devices (3D SIDs) each with a vertical load capacity of 2000 tf, and dimensions of 3500 mm × 3500 mm, delivering natural frequencies of 1 and 0.3 Hz in vertical and horizontal directions, respectively. Viscous or friction damping devices are integrated into the 3D SID, designed to achieve vertical and horizontal damping ratios of at least 0.4 and 0.1, respectively, to reduce the peak acceleration response of the isolated target building to less than 0.3 g under the seismic input of 0.5 g PGA on the ground. The performance of the 3D SIS, constructed with the designed 3D SIDs for a target building, is validated through a full 3D numerical transient response analysis using ANSYS.