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:
fense in depth. An important qualitative overall guideline is that two or more independent plant design or operational features be provided to meet the layer-specific guidelines for each LBE. Any SSCs required to meet this guideline, as determined by the IDP, would be regarded as performing a safety function necessary for adequacy of plant capability DID. Such SSCs, if classified as risk significant, would already be classified as safety significant. If one of the plant features used to meet the need for multiple means to ensure DID involves the use of SSCs that are neither SR nor risk significant, the IDP would classify the SSC as safety significant and NSRST because it performs a function required for DID adequacy. Special treatment requirements for NSRST SSCs include the setting of performance requirements for SSC reliability, availability, and capability and any other treatments the IDP responsible for evaluating the adequacy of DID deems necessary. A non-LWR designer using the methodology described in NEI 18-04 evaluates the adequacy of plant capability DID by focusing on the completeness, resiliency, and robustness of the plant design. The designer assesses the design with respect to all hazards, responding to identified initiating events, and the availability of independent levels of protection in the design for preventing and mitigating the progression of event sequences. The process encourages the use of redundant and diverse means across the collective layers of defense to achieve the needed levels of protection sufficient to address different threats to public health and safety. Additionally, the plant capability DID adequacy evaluation examines whether any single feature is excessively relied on to achieve public safety objectives, and, if so, identifies 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