Seismic Behavior Study of a new Isolated Structure System With Damping Supporter for Nuclear Power Plants in a Cave or Underground

Abstract

There have been heated discussions on how to reduce the earthquake response of NPPs. Generally, isolation technology is one of the most efficient methods but researches on traditional isolated structure and 3D isolated structure for NPPs, to some extent, have deficiencies. Therefore, in this paper, a new structural system which included base isolation system and lateral damping supporters for NPPs (hereinafter referred to as DISO) in a cave or underground was proposed to obtain a positive seismic response, aiming to protect the nuclear island. The motion characteristics of the system have been studied and a simplified mathematical model has been set up. The dynamic equation was deduced and solved. The theoretical analysis results that there is an optimal range of parameter β, the ratio of the damping coefficient of the additional damping support to the equivalent linear damping coefficient of isolation layer, to get a positive response of DISO system. The seismic response of the DISO structural system was analyzed and the correlation that the parameters including damping arrangement coefficient, damping index and damping coefficient have with the seismic response of the structure were discussed. The results show that the acceleration response of the DISO system decreases to minimum value with the increasing of damping coefficient, along with whiplash effect, and then increases regularly. There is a positive correlation between the damping coefficient and displacement decline rate. A case study has been completed. The numerical results show that the DISO system performs more effectively than the ISO system (refer to the traditional isolated structural system). Given that the equipment and pipelines in NPPs are sensitive to large isolation displacement, the displacement response of DISO system is less than that of the traditional isolated structural system without acceleration amplifying. Moreover, both acceleration of superstructure and displacement get decreased. And IDA-based (Incremental Dynamic Analysis) seismic fragility analysis of ISO and DISO system has been performed. DISO system has the smaller probability of failure compared with the ISO system.