Multi-periods conditional mean spectrum for ground motion selection in seismic analysis of nuclear power plant structures

Constructing an accurate target spectrum that reflects the dynamic characteristics of all components is critical for the Probabilistic Safety Assessment (PSA) of nuclear power systems, as it links seismic hazard to structural response. Current methods often yield conservative estimates of structural responses, leading to excessive conservatism in seismic design. Furthermore, the Conditional Mean Spectrum (CMS) is limited by its reliance on a single conditioning period, restricting its ability to provide suitable ground motions for complex structures with multiple vibration periods. To address these limitations, this study introduces the Multi-Period Conditional Mean Spectrum (MPCMS) as a target spectrum for the dynamic analysis of nuclear power structures. This method incorporates the dynamic properties of individual structural components to establish an appropriate target spectrum for ground motion selection. The MPCMS effectively integrates the dynamic characteristics of various structural components by constraining spectral values at periods other than the primary conditioning period. Compared to current methods, the MPCMS reduces the calculated failure probabilities for nuclear power structures by 11.2–19.2 %, thereby mitigating inherent conservatism. These findings provide a valuable reference for the PSA of nuclear power systems.