Document: NRC Regulatory Guide
Document ID: 47b09be1-4bf8-45f9-a099-7fed871c09bd
Document Type: regulatory_guide
Title: Plant-Specific, Risk-Informed Decisionmaking: Inservice Testing (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2114/ML21140A055.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.175
CFR Part: 
CFR Title: 

Content:
ets Principle 4. The next section of this RG discusses one acceptable approach. PRA systematically takes credit for non-ASME OM Code components as providing support, acting as alternatives, and acting as backups to those components that are within the scope of the current ASME OM Code. Accordingly, to ensure that the proposed RI-IST program will provide an acceptable level of quality and safety, the licensee should include these additional risk-important components in its RI-IST program proposal. Specifically, the licensee’s RI-IST program should include those ASME Code Class 1, 2, and 3 and non-Code components that the licensee’s integrated decisionmaking process categorized as HSSC and thus determined to be appropriate additional candidates for the RI-IST program. Although PRAs model many of the SSCs involved in the performance of plant safety functions, other SSCs are not modeled for various reasons. However, this should not imply that nonmodeled components are not important in terms of contributions to plant risk. For example, some components are not modeled because certain initiating events may not be modeled (e.g., low-power and shutdown events, or some external events); in other cases, components may not be directly modeled because they are grouped together with events that are modeled (e.g., initiating events, operator recovery events, or within other system or function boundaries); and in some cases, components are screened out from the analysis because of their assumed inherent reliability. Failure modes may be screened out because of their insignificant contribution to risk (e.g., spurious closure of a valve). When feasible, the licensee should consider adding missing components or missing initiators or plant operating states to the PRA. When not feasible, the licensee may use information based on engineering analyses and judgment to determine whether a component should be treated as an LSSC or HSSC. One approach to combining these different pieces of