Performance Evaluation of Floating Seismic Isolation System

Abstract Floating-type nuclear plants have been studied and in some cases deployed as marine systems. Although horizontal components of seismic waves may be naturally isolated from the floating plant due to little transfer of shear forces in water, the vertical component can propagate through water to the plant from the seafloor in what is called a “seaquake” phenomenon. The concept of a Floating Seismic Isolation System (FSIS) has been proposed by the authors. The FSIS is a unique seismic isolation mechanism having a number of cavities and orifices embedded in the bottom of the floating structure. The cavity is designed to reduce the peak vibration response of the structure to vertical seismic input, whereas the orifice is used to add damping for residual vibration reduction. The demonstration test to verify the seismic isolation performance of FSIS has been completed on the 3D Full-Scale Earthquake Testing Facility called “E-Defense” in Japan. The test model is a 1/15 scale mockup down-sized by similarity from an FSIS-paired small module reactor (SMR) plant design for floating in a pool. The peak acceleration input is up to 1.3G horizontally and 1.0G vertically, and three sets of frequency response spectra must be determined from the most significant earthquakes recorded in Japan. This paper presents a post-test analysis of the measurements and evaluation of the seismic isolation potential of the FSIS. The results presented herein support that the FSIS can reduce seismic responses of a floating nuclear reactor plant by substantial levels in horizontal and vertical directions.