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:
ssions 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 lowest-event frequencies on the F-C target and category definitions a hard-and-fast cutoff but instead should consider it in the context of other parts of the methodology described in NEI 18-04. These other considerations include the role of the integrated decisionmaking panel described in Section 5 of NEI 18-04, DID assessments, accounting for uncertainties, and assessing for potential “cliff-edge effects,” which involve a dramatic change in plant behavior caused by a small change in a plant parameter. c. NEI 18-04 describes a set of DBEHLs that will determine the design-basis seismic events and other external events that the SR SSCs will be required to withstand. When the DBEHLs are determined using NRC-approved methodologies, this approach is generally consistent with current practices and provides acceptable protection of SR SSCs. When supported by available methods, the PRA model is expected to address the full spectrum of internal events and external hazards that pose challenges to the capabilities of the plant, including external hazard levels exceeding the DBEHLs. The inclusion of external events within the BDBE category supports the overall risk-informed approach in NEI 18-04 and the DID assessments described in subsequent sections. The PRA results, including consideration of external hazards, will also validate a designer’s initial selections of DBAs and SR SSCs protected against DBEHLs, and ensure no new DBAs are introduced by external hazards. NEI 18-04 states the following: When supported by available methods, data, design and site information, and supporting guides and standards, these DBEHLs will be informed by a 7 An example is the anchor point at an event sequence frequency of 5x10-7 per plant year and total effective dose equivalent at the EAB