Document: NUREG-0800
Document ID: 6d95bc89-e14a-4d87-bf91-1d1760c2aff8
Document Type: srp
Title: FOUNDATIONS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1235/ML12353A388.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.8.5
CFR Part: 
CFR Title: 

Content:
NCE CRITERIA 1. Revised SRP Section 3.8.5 II.4 “Design and Analysis Procedures” item B, to include enhanced guidance to evaluate sliding and overturning stability. The technical rationale for this change is as follows. The conservatism in the SRP pseudo-static approach for demonstrating the factors of safety for sliding and overturning stability has led to difficulties when performing such analyses for generic plant designs where higher seismic loads are defined and a range of soil profiles are typically considered. Therefore, it is reasonable to utilize more realistic analytical methods which reduce some of the conservatisms inherent in the static type stability evaluation methods. Several recent DC applicants have resorted to more complex analytical methods to reduce the conservatisms inherent in the static approach. These methods rely on time history analyses using three directions of statistically-independent seismic loadings that are applied simultaneously. This approach eliminates the static analysis assumption that the maximum vertical and maximum horizontal demand forces occur at the same time. The oscillatory nature of the response in a seismic time history analysis may demonstrate that the specified factors of safety are maintained at each instant in time. If the linear time history analysis indicates that some sliding and uplift may occur, then a nonlinear time history analysis can be performed to include these effects. To provide guidance about the staff’s expectations when performing the time history evaluations discussed above, the guidance in SRP Section 3.8.5 was enhanced to address several issues: (1) since there is no single value to be used for the seismic demand, how the FOS should be calculated in the evaluation, (2) for nonlinear analysis, how many time histories should be considered and how should the results from each of the time histories be evaluated, (3) the adequacy of the mathematical model, (4) 3.8.5-25 Draft Revision 4 - December