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:
n the risk ranking of SSCs from a pre-solved cutset equation, the following apply: < The truncation criterion is sufficiently low to ensure stable results, that is, the magnitude of the CDF or release frequency will not change as a result of lower truncation limits, and the grouping of SSCs into risk categories will not be affected. < The components affected by the application are, for the most part, not truncated out of the model. In cases where they are, a qualitative assessment can demonstrate the reasons why they are unimportant to risk. 19.2-59 June 2007 A.10 Modeling of Containment Response and Changes in Large Early Release Frequency a. Areas of Review The purpose of this section is to provide guidance for use in reviewing the licensee’s evaluation of changes in LERF stemming from proposed changes to the plant’s design or operations. In general, only a subset of CDF sequences will be affected by a change. Whether or not this subset contributes significantly to LERF depends on several plant-specific characteristics. This section focuses on the characteristics that strongly affect LERF and identifies review approaches based on these characteristics. It also provides guidance to help reviewers identify the major items related to functional plant capability that directly affect the potential for large early release, to direct reviewers in establishing whether the proposed changes can affect this capability, and to determine whether the licensee has appropriately addressed these items in estimating changes in LERF. b. Review Guidance and Procedures There are several ways in which a change to the plant’s design or operation can significantly alter LERF, including those that: • Change the frequency of containment bypass sequences (e.g., steam generator tube ruptures and interfacing system LOCAs). • Change the frequency of core damage sequences that pose severe challenges to containment (e.g., sequences resulting in elevated reactor coolant system (RCS)