Document: NRC Regulatory Guide
Document ID: c7a40fcc-fc9d-4eb2-ad86-f9f5b0f04c82
Document Type: regulatory_guide
Title: Plant-Specific, Risk-Informed Decisionmaking:  Technical Specifications (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1920/ML19206A489.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.177
CFR Part: 
CFR Title: 

Content:
ffect of details about how CCFs are modeled in the PRA, and e. the effect of modeling compensatory measures in the PRA. Risk resulting from TS CT changes may be relatively insensitive to uncertainties (compared to the effect on risk from uncertainties in assumptions about plant design changes or significant changes to plant operating procedures, for example). This is because the uncertainties associated with CT changes tend to similarly affect the base case (i.e., before the change) and the changed case (i.e., with the change in place). That is, the risks result from similar causes in both cases (i.e., no new initiating transients or subsequent failure modes are likely to have been introduced by relatively minor CT changes). CT changes subject the plant to a variation in its exposure to the same type of risk, and the PRA model can predict, with relative surety based on data from operating experience, how much that risk will change based on that changed exposure. Similar results are expected for SF changes. The staff expects licensees to justify any deviations from these expectations. The effects of multiple outages may become significant during relatively large increases in CTs or SFs. In those cases, however, the Tier 2 and Tier 3 aspects of TS changes (i.e., configuration monitoring, risk predictions, and configuration control based on the risk predictions) are expected to be robust and will be relied upon to control the resulting potential for significant risk increases. Therefore, the Tier 2 and Tier 3 aspects of such TS changes should be justified as robust and adequate to control the resulting potential for significant risk increases. NUREG-1855 provides additional guidance on the treatment of uncertainties. 2.3.6 Restrictions on Dominant Risk-Significant Configurations and Compensatory Measures (Tier 2) Consistent with the key principle that changes to TS should result in only small increases in the risk to public health and safety (Principle 4 in RG 1.174),