Document: NRC Regulatory Guide
Document ID: b3da4d67-03d8-4f52-b04b-8e76d142c857
Document Type: regulatory_guide
Title: Guidance for a Technology-Inclusive, Risk-Informed, and Performance-Based Methodology to Inform the Licensing Basis and Content of Applications for Licenses, Certifications, and Approvals for Non-Light Water Reactors + HISTORY - HISTORY 05/2019 – Issued DG-1353 , Proposed Revision 0
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1831/ML18312A242.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.233
CFR Part: 
CFR Title: 

Content:
events are failures of SSCs themselves, in which case the reliability of the SSC in question serves to limit the initiating event frequency. In other cases, the initiating events represent challenges to the SSC in question, in which case the reliability of the SSC to perform a safety function in response to the initiating event needs to be considered. Finally, in some cases the challenge to the SSC in question is defined by the combination of an initiating event and combinations of successes and failures of other SSCs in response to the initiating event. All of these cases are included in the PRA and represent the set of challenges presented to a specific SSC. Figure 4-1, “SSC Function Safety Classification Process,” and Figure 4-2, “Definition of Risk Significant and Safety Significant SSCs,” in NEI 18-04 depict the SSC safety classification process. The process includes a review of each of the LBEs, including those in the AOO, DBE, and BDBE regions, to determine the function of each SSC in the prevention and mitigation of the LBE. Risk-significant SSCs are those with an important role in controlling the frequencies and consequences of LBEs relative to the F-C target or in meeting the cumulative risk metrics. An SSC that is determined to be important for DID as discussed in Section 5 of NEI 18-04 and the subsequent section of this RG is included within the broader category of safety-significant SSCs, even if the SSC is not otherwise found to be risk significant. A designer would classify a safety function as a “required safety function” if that function is needed to keep the frequency or consequence of a DBE below the F-C target using realistic assumptions, or the consequences of a DBA below the reference values included in NRC regulations using conservative assumptions. The safety classification categories used in NEI 18-048 for non-LWRs are defined as follows: • safety related: o SSCs selected by the reactor designer from the SSCs that are