Document: NUREG-0800
Document ID: e32f0820-4e33-476e-aa36-4ca8c2c64af0
Document Type: srp
Title: Use of Probabilistic Risk Assessment in Plant-Specific, Risk-Informed Decisionmaking:
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0119/ML011940192.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
-RF are above the guideline values (i.e., 10. and 10' per reactor year) Review of Combined Change Requests In assessing combined change requests, reviewers should evaluate the acceptability of each of the individual changes with respect to the defense-in-depth and safety margin guidelines discussed in Section 111.2.1 of this SRP chapter. In addition, reviewers should evaluate the overall risk impact of the combined changes using the guidelines discussed in Section 111.2.2 of this SRP chapter. In evaluating the overall (i.e., combined) risk impact, reviewers should take into account the relationship between the individual changes. For example, in combined change requests for which individual changes that increase risk are compensated for by other changes that decrease risk, reviewers should evaluate and understand the major contributors to both the risk increase and risk decrease, including the analysis assumptions and uncertainties from each contributor that might affect the decision process. Combining risk impacts from the individual contributors is prudent when the contributors are closely related in terms of analysis assumptions and uncertainty. Contributors could also be related if they impact on the same plant functions, for example. Conversely, for contributors that are not closely related, risk impacts from each change should be evaluated on an individual basis. Finally, combined changes should not trade many small risk decreases for a large risk increase (i.e., create a new significant contributor to risk). It is expected that implementation of combined change requests will improve, or at least maintain, the overall plant risk profile. A desirable risk profile is one in which no contributors are overly dominant. Therefore, proposed changes should not create or exacerbate a risk imbalance either in terms of dominant plant elements (SSCs or operator actions) or accident sequences. SRP 19-26 Develop Implementation and Monitorincq Strategies Implementation and