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:
s options to reduce or eliminate such dependency. A key element of the DID evaluation described in NEI 18-04 is a systematic IDP review of the LBEs for non-LWRs against the layers of defense. This IDP review is necessary to evaluate the plant capabilities for DID and to identify any programmatic DID measures that may be necessary for ensuring DID adequacy. The IDP performs this review to assess important DID properties such as an appropriate balance between prevention and mitigation of LBEs, identified reliability/availability missions for SSCs serving to prevent or mitigate LBEs, effective physical and functional barriers to retain radionuclides, and ensuring measures exist to address risk-significant sources of uncertainty. Table 5-4, “Event Sequence Model Framework for Evaluating Plant Capabilities for Prevention and Mitigation of LBEs," in NEI 18-04 provides a generalized model for describing an event sequence in terms of the design features that support prevention and mitigation reflecting the above insights. This information supports the IDP review and also relates to the assessment of layers of defense—including physical barriers—that will need to be addressed within the mechanistic source term for a non-LWR design. Section 5.7 in NEI 18-04 states that the IDP’s evaluation of LBEs will determine whether additional compensatory action would be considered, depending on the risk significance of the LBE. Compensatory action can take different forms, including changes to design and operation, refinements to the PRA, revisions to the identified LBEs and safety classification of SSCs, and enhancements to the programmatic elements of DID. NEI 18-04 lists the following broad questions for the IDP to consider: • Is the selection of initiating events and event sequences reflected in the LBEs sufficiently complete? Are the uncertainties in the estimation of LBE frequency, plant response to events, mechanistic source terms, and dose well characterized? Are there