Document: NUREG-0800
Document ID: ac43f632-9db1-4857-9f56-bfba45965456
Document Type: srp
Title: * These are modifications to a plant’s design, operations, or other activities that require NRC approval. These modifica
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0232/ML023250195.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19
CFR Part: 
CFR Title: 

Content:
nding 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. • 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 Section III.2.1.3 regarding the need to maintain the LB. The thrust of the guidance in the present section 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 SRP 19-12 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 affected by the application) will provide useful information to help in the reviewers’ decisionmaking. As an example, in evaluating available safety margins, reviewers should consider the risk profile of the plant. If a proposed LB change creates or exacerbates a situation where risk is dominated by a few elements (SSCs or human actions) or a few accident sequences, the reviewers should carefully evaluate the modeling of these elements or sequences including the modeling of uncertainties. Reviewers should consider the results from the analysis of uncertainty when determining the acceptability of the reduction in margin from the proposed change. In demonstrating available safety margins, licensees will in some cases