Generation of artificial earthquake time histories and power spectral density for seismic analysis of nuclear power plants

Regulatory Guide (RG) 1.60 presents the response spectra for the seismic design of nuclear power plants. New reactor designs necessitate Modified Design Response Spectra (MDRS), extending the high-frequency range from Design Response Spectra (DRS) in RG 1.60. This paper explores the generation procedure of artificial earthquake time histories conforming to acceptable criteria outlined in SRP Section 3.7.1 for MDRS. The process involves defining MDRS, generating artificial time histories, calculating Power Spectral Density (PSD), and producing Artificial Earthquake Ground Motions (AEGMs). Modified spectra broaden the high-frequency range and increase acceleration values at specific frequencies. For AEGM generation, two Approaches are explored using P-CARES and in-house code. Generated AEGMs satisfy the criteria outlined in SRP Section 3.7.1, ensuring compatibility with target response spectra. Additionally, seismic analyses of a nuclear power plant model, both with or without a base isolator, are conducted, and the results of the structural response using the seismic ground motion produced through the two Approaches are compared. The seismic response of the nuclear power plant model based on Approach 1 is somewhat higher than that based on Approach 2. The accelerations of the structure with the base isolator are significantly reduced compared to the structure without the base isolator.