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:
an and mechanical failures so that no single layer, no matter how robust, is exclusively relied upon. Defense in depth includes the use of access controls, physical barriers, redundant and diverse key safety functions, and emergency response measures. DG-1353, Page 18 Figure 5-2, “Framework for Establishing DID Adequacy,” in NEI 18-04 depicts a framework to establish DID for non-LWRs that includes probabilistic and deterministic assessment techniques using a combination of plant capabilities and programmatic controls. Plant capability defense in depth generally relates to hardware and design, and is provided by ensuring that SSCs are able to prevent and mitigate events, defend against common cause failures, include conservative design margins, and provide barriers to the release of radionuclides. Programmatic defense in depth includes measures to increase confidence in SSC performance during operation and throughout the life of a plant (e.g., quality assurance, testing, maintenance, and configuration control), operational procedures and training, and preparedness for emergency plan protective actions. The methodology in NEI 18-04 calls for non-LWR designers to perform evaluations based on several established approaches to DID to assess a reactor design and determine if additional measures are appropriate to address an over-reliance on specific SSCs or to address uncertainties. One element of NEI 18-04 related to assessing DID is adapted from a process defined in IAEA standards and guidance, such as IAEA Specific Safety Requirements No. SSR-2/1, “Safety of Nuclear Power Plants: Design.” This approach includes evaluating each LBE to identify the DID attributes incorporated into the design to prevent and mitigate accident sequences and to ensure that the DID attributes reflect adequate SSC reliability and capability. Figure 5-3, “Framework for Evaluating LBEs Using Layers of Defense Concept Adapted from IAEA,” in NEI 18-04, depicts this element of the DID