Coupling analysis of the seismic systems in nuclear power plants

Facilities in nuclear power plants are complicated systems consisting of structures, piping systems, equipments and components (SSCs). Seismic designs and analyses for Seismic Category I facilities are carried out as an important procedure to ensure the safety of nuclear power plants under SSE design basis accidents. In order to perform the seismic analyses for complex SSC systems more comprehensively, reliably and thoroughly, the most effective and consistent manner is to suitably resolve the total seismic system into several main and sub systems. Starting from the basic principles of vibrations, where the main and sub systems are simplified as a two-degree-of-freedom system, this paper deduces the decoupling conditions for the main and sub systems and verifies the basis of decoupling conditions proposed in the Standard Review Plan 3.7.2. The requirements are presented for the decoupling of sub systems from the coupled system. Conclusions drawn in this paper provide the engineers of seismic design and analysis, as well as safety reviewers, with an important criterion for their designs, analyses and reviews. (authors)