Document: NRC Regulatory Guide
Document ID: db0c5d18-2d27-4720-8935-40b402e52f9a
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:
atent cancer fatality risk. Important roles for the PRA in NEI 18-04 include the evaluation of the aggregate or plant-level acceptance criteria and identification of risk-significant LBEs. As shown in Figure 3-4, “Use of the F-C Target to Define Risk-Significant LBEs,” NEI 18-04 defines risk-significant LBEs as those with frequencies and consequences within 1 percent of the F-C target, with site boundary doses exceeding 2.5 mrem. To consider the effects of uncertainties, the applicant should use the upper 95th percentile DG-1353, Page 13 estimates of both frequency and dose. The use of the 1-percent metric is consistent with the approach to defining risk-significant accident sequences in various PRA standards. The 2.5-mrem cutoff is reasonable given it is approximately 10 percent of the dose that an average person at the site boundary would receive in 30 days from background radiation. NEI 18-04 also notes that risk importance measures such as risk reduction worth can be used to gain additional insights into the significance of particular events and SSCs. C.1 Staff Position: NEI 18-04 provides an acceptable method for identifying and categorizing events, with the following clarifications: a. The staff emphasizes the cautions in NEI 18-04 that the F-C target figure does not depict acceptance criteria or actual regulatory limits. The anchor points used for the F-C target figure are expressed in different units, timescales, and distances than those used in NRC regulations to provide common measures for the evaluations included in the methodology.7 The F-C target provides a reasonable approach for use within a broader, integrated approach to determine risk significance, support SSC classification, and confirm the adequacy of DID. b. The F-C target and related discussions in NEI 18-04 include an upper bound event sequence frequency (i.e., 95th percentile) of 5×10-7/plant-year to define the lower range of BDBEs. Applicants should not consider this demarcation of