Document: NUREG-0800
Document ID: 22eb178a-5190-4317-b1e3-239da15df8c5
Document Type: srp
Title: Ground Motion Response Spectra.  In this subsection, the staff reviews the
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0707/ML070730593.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.5.2.6
CFR Part: 
CFR Title: 

Content:
applicant's procedure to determine the GMRS. If the applicant uses the reference probability approach, the GMRS are considered acceptable if they meet Regulatory Position 4 and Appendix F of Regulatory Guide 1.165. If the applicant uses the performance-based approach, the GMRS are considered acceptable if they meet Regulatory Position 5 of Regulatory Guide 1.208. The staff also reviews the method used to determine the vertical GMRS. Vertical response spectra are developed by combining the appropriate horizontal response spectra and the most recent V/H ratios for either CEUS or WUS sites. Appropriate V/H ratios should be determined from the most recent ground motion attenuation models. However, as there are currently no CEUS attenuation models that predict vertical motions, appropriate V/H ratios for CEUS sites should be developed in accordance with Regulatory Position 5 of Regulatory Guide 1.208. To meet the requirements in 10 CFR 100.23, the horizontal and vertical GMRS are determined in the free field on the ground surface. For sites with soil layers near the 2.5.2-10 Revision 4 - March 2007 surface that will be completely excavated to expose competent material, the GMRS is specified on an outcrop or a hypothetical outcrop that will exist after excavation. Motions at this hypothetical outcrop should be developed as a free surface motion, not as an in-column motion. Although the definition of competent material is not mandated by regulation, a number of reactor designs have specified a shear wave velocity of 1000 fps as the definition of competent material. When the GMRS are determined as free- field outcrop motions on the uppermost in-situ competent material, only the effects of the materials below this elevation are included in the site response analysis. The time duration and number of cycles of strong ground motion are required for analysis and design of many plant components. The adequacy of the time history for structural analysis is reviewed under SRP