Document: NRC Regulatory Guide
Document ID: 239cc7c1-f2cb-46cc-945d-8009db28aa6c
Document Type: regulatory_guide
Title: General Site Suitability Criteria for Nuclear Power Stations + HISTORY - HISTORY 12/2023 – DG-4034 , Proposed Revision 4 12/2011 – DG-4021 , Proposed Revision 3 02/1995 – DG-4004, Second Proposed Revision 2 11/1992 – DG-4003, Proposed Revision 2 (Rev. 4)
Source: NRC Regulatory Guide Division 4
Source URL: https://www.nrc.gov/docs/ML2312/ML23123A090.pdf
Revision Date: 2023-10
Chapter: 
Section ID: RG-4.7
CFR Part: 
CFR Title: 

Content:
as applicable. A simpler design with relatively coarse assumptions might require less accounting for uncertainty at the cost of design margin (e.g., through the use of more conservative assumptions). Conversely, a finely refined analysis can be used to capture design margin (with an associated lower margin between the analysis and acceptance criteria) at the cost of quantifying the uncertainty and justifying how the analysis meets the applicable NRC requirements. The need to provide assurances that safety functions will be fulfilled, and uncertainties are addressed is reflected in requirements such as 10 CFR 50.43(e), which requires demonstration of safety feature performance by analysis, appropriate test programs, experience, or a combination of all three. If not captured directly by conservatism in the analyses, uncertainties should be established, where applicable, and quantified if possible. Subjectivity in establishing these uncertainties is ideally avoided through the use of quantitative tools that address uncertainties such as a probabilistic risk assessment or consideration of experimental or dataset uncertainty. However, use of a hazard assessment coupled with provisions of defense in depth (multiple means of satisfying a safety function to reduce or eliminate the likelihood of phenomena) can satisfactorily address phenomenological uncertainties. A-4. Defense in Depth Defense in depth involves using multiple independent and redundant layers of defense to compensate for potential failures so that no single layer, no matter how robust, is relied on exclusively. More specifically, when evaluating defense in depth for the siting analysis, no single feature should be relied on exclusively for performance of a safety function. The consideration of defense in depth as part of developing a source term for use in the siting analyses for non-LWRs is difficult to quantify and is somewhat narrower than the full defense in depth concept referred to elsewhere, such as