Seismic analysis and evaluation of the base isolation system in AP1000 NI under SSE loading

Safety and integrity of NPP must be ensured during the plant life in any design conditions, particularly, in the event of a severe earthquake. Base isolation as a popular and powerful technology can drastically reduce the seismic response of the structure and prevent the structure from damage. The objective of this paper is to numerically investigate the dynamic response of the AP1000 Nuclear Island (NI) building with and without isolators under a typical safe shutdown earthquake (SSE). By the help of a sophisticated detailed three-dimensional finite element model of the Nuclear Island, the different design solutions are compared in terms of acceleration and relative displacement. The decreasing amplitude ratio (DAR) obtained in the calculations highlights the effectiveness of the isolation system in mitigating the seismic response of the nuclear island of AP1000. Acceleration floor response spectra (carried out from both isolated and non-isolated seismic analysis) are herein also presented and compared in order to validate the isolation technology effectiveness. The obtained numerical results highlight the drastic reduction of considered floor accelerations as the base isolation major effect. The connection of pipelines and design criteria of isolators presently recommended for the stability of isolated building are also validated and verified to highlight the feasibility and safety of the base isolation system. In addition, seismic gap, expansion joint and horizontal fail safe system are also recommended to apply in the isolated structure. (C) 2014 Elsevier B.V. All rights reserved.