Seismic Review of Retrofit Effect by Base Isolation of Load Center Cabinet in Operating Nuclear Plants

This paper aims to examine the validity of applying individual seismic isolation technologies to small facilities or equipment, such as safety-related cabinets within domestic operating nuclear power plants, to enhance their seismic performance. Generally, applying seismic isolation technology to older nuclear power plant buildings poses significant technical and cost burdens. Therefore, a recent approach has been to first check the seismic performance of major equipment with high safety importance through probabilistic seismic analysis and select those with insufficient performance to improve their seismic capabilities. In this paper, among the equipment requiring seismic performance improvement, we focus on applying device isolation to Load Center (LC) cabinets and analyze the effectiveness of seismic performance enhancement against beyond design basis earthquakes (BDBE). To achieve this, we first conduct modal analysis through finite element modeling of the target equipment and then model it as a concentrated mass type with similar dynamic characteristics. We calculate the maximum response under BDBE by applying fixed conditions and two types of isolation conditions. Furthermore, we validate the analytical results through a 3D shaking table test on a physical model equipped with small seismic isolation bearings developed in previous studies. As a result, it is confirmed that applying seismic isolation technology individually to safety-critical equipment, such as Load Center cabinets, can also be a viable alternative for improving seismic performance.