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:
rovide an indication, in numerical terms, of what is considered acceptable. As such, the numerical values associated with defining the regions in Figures III-1 and III-2 are approximate values used to indicate the changes that are generally acceptable. Furthermore, the state of knowledge (or epistemic) uncertainties associated with PRA calculations preclude a definitive decision (based purely on the numerical results) with respect to which region a given application belongs. The intent in making the comparison of the PRA results with the acceptance guidelines is to demonstrate with reasonable assurance that the proposal fulfills Principle 4 (discussed in Subsection II of this SRP section). The assessment of whether this has been demonstrated must be made on the basis of an understanding of the contributors to the PRA results and on the impacts of the uncertainties (both those that are explicitly accounted for in the results and those that are not). This is a somewhat subjective process; therefore, in order to complete the assessment, reviewers must carefully document the reasoning behind the decisions. As discussed in Regulatory Guide 1.174, PRA values can be affected by particular modeling assumptions that are a response to the uncertainty regarding how to correctly model the plant response following an initiating event. Thus, it is important that uncertainties in the PRA results 19.2-20 June 2007 be taken into account in assessing the risk impact and in the risk-informed decisionmaking process to demonstrate the robustness of the results. The scope of the required uncertainty analysis is a function of the role that the quantification results play in the decision and on the significance of the calculated change. The general approach to accounting for uncertainty is discussed in Regulatory Guide 1.174, Section 2.2.5. In that discussion, uncertainties are categorized as parameter, model, and completeness uncertainties. In assessing analysis of uncertainties,