GENERATING SEISMIC DESIGN BASIS SPECTRA FOR US NUCLEAR ENERGY FACILITIES

Regulatory Guide RG 1.208 references ASCE/SEI 43-05 to define ground motion response spectra (GMRS) for the seismic design of safety-related structures, systems, and components (SSCs) in nuclear power plants. Subsequent seismic analysis per ASCE/SEI 4 and SSC design per ASCE/SEI 43, and the materials standards referenced therein, are expected to deliver a target performance goal (TPG). Standard ANS 2.26 provides the basis for assigning a seismic design category (SDC) to an SSC. Each SDC is characterized by a TPG. The definitions of the GMRS and the design response spectra (DRS) per ASCE/SEI 43-05 for nuclear facilities are identical. In 2021, ASCE/SEI 43-05 was re-issued as 43-19, which provides a different process for developing DRS. The computation of a DRS per ASCE/SEI 43-19 utilizes a scale factor (SF), calculated at each spectral period used to define the DRS. The value of the SF is a function of the seismic hazard data for the site, soil type, and SDC of the SSC. This paper presents values for the SFs for SDCs 3, 4, and 5, eight sites of nuclear energy facilities across the United States, and near-surface geology of both soft rock and stiff soil. The consideration of multiple sites, two soil classes, and three SDCs provides a wide range of seismic hazard characteristics for the generation of the SFs. Based on the reported SFs, a value of 0.5 is recommended for all SDCs, soil types, and spectral periods to simplify hazard and design calculations for SSCs in nuclear facilities in the US, which is the major technical contribution of this paper. The appendix to this paper enables a comparison of DRS calculated using ASCE/SEI 43-05 and 43-19 for three SDCs, eight sites, and two soil classes, and shows that although the process has changed, the DRS are the same.