Document: NUREG-0800
Document ID: b9816943-ef18-4be4-aafd-035aa1feda4e
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/ML1331/ML13316C066.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. Following the site response analysis to determine the ground motion at the free surface, the applicant should calculate a frequency-dependent design factor using the uniform hazard soil surface motions corresponding to the 10-4 and 10-5 MAPE. The design factor is then applied to the soil response motion at the MAPE of 10-4, and the horizontal performance-based site- specific GMRS is determined. RG 1.208 and American Society of Civil Engineers (ASCE)/Software Engineering Institute (SEI) Standard 43-05 describe the development of the performance-based motion in detail. The performance-based site-specific GMRS are considered acceptable if they meet Regulatory Position 5 of RG 1.208. The staff also reviews the method used to determine the vertical GMRS. For near surface site elevations, vertical response spectra are developed by combining the appropriate horizontal response spectra and the appropriate vertical and horizontal (V/H) spectral ratios for either CEUS or WUS sites obtained from the available empirical database. 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 RG 1.208. For deeper site elevations, V/H ratios for the deep soil profile need to be developed and the methodology used is reviewed on a case-by-case basis. 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 surface that will be completely excavated to expose competent material, the GMRS are specified on an outcrop or a hypothetical outcrop that will exist after excavation. Motions at the hypothetical outcrop should be developed as a free surface motion, not as an in- column motion. Although the definition