Document: NUREG-0800
Document ID: 7916b088-fb90-4163-84fe-027bd315bcc5
Document Type: srp
Title: REVIEW OF RISK INFORMATION USED TO SUPPORT PERMANENT PLANT-
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0717/ML071700658.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.2
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CFR Title: 

Content:
2 Safety Margins In the determination of the design performance characteristics of a system, safety margin represents an allowance for uncertainty in SSC performance. Current safety analysis practices incorporate consideration of margin in most areas. As examples, many engineering standards, licensing analyses, and technical specifications take margin into account. Incorporating margin can result in over-designing of components, incorporation of extra systems or system trains, or in conservative operating requirements for systems and components. Therefore, some licensee applications will seek to reduce this margin in some areas. Such reductions should appropriately reflect the current understanding of existing uncertainties and the potential impact of the proposed change. Therefore, in evaluating a proposed change request, reviewers should establish that the proposal fulfills the following guidelines: • The proposal meets established engineering codes and standards or NRC-approved alternatives, or deviations are justified. 19.2-11 June 2007 • The proposal meets the safety analysis acceptance criteria in the LB, or proposed revisions provide sufficient margin to account for uncertainty in the analysis and data. Clearly, these guidelines are closely related to the guidance provided in Subsection III.2.1.3 of this SRP section regarding the need to maintain the LB. The thrust of the guidance in this subsection is to sensitize reviewers to the implications of relaxing the margin when evaluating the acceptability of changes to the LB. The level of justification required for changes in margin should depend on how much uncertainty is associated with the performance parameter in question, the availability of alternatives to compensate for adverse performance, and the consequences of functional failure of the affected elements. Therefore, the results derived from risk evaluations and the associated analysis of uncertainties (especially in the analysis areas and models