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:
ecific section for DID assessments. The importance of DID assessments in the NEI 18-04 methodology and the more systematic approach to performing the assessments lends itself to separate sections or a chapter in safety analysis reports (e.g., the addition of a Chapter 20, “Evaluations of Defense in Depth”). The format and content of the new chapter can follow the assessment methodology in NEI 18-04 and document IDP decisions. Safety analysis reports for operating LWRs include chapters that contain detailed descriptions of SSCs supporting safety functions. Examples include chapters on instrumentation and control systems, electrical power systems, and cooling water systems. Additional chapters in LWR safety analysis reports are dedicated to power conversion systems and systems needed to handle various forms of radioactive wastes. The various system descriptions for LWRs are appropriate, given the importance of support systems for active safety systems and the potential for support or secondary plant systems to cause a plant transient challenging the fuel cladding or other barrier to the release of radionuclides. NEI 18-04 describes a process to evaluate the risk significance of ancillary SSCs in terms of contributing to initiating events or in the mitigation of event sequences for non-LWRs. The analyses and assessments in NEI 18-04 can provide insights into the appropriate level of detail needed to describe parts of a plant outside the primary systems, which are typically described in Chapters 4, 5, and 6 of a safety analysis report. In some instances, the level of detail for ancillary plant systems in non-LWR designs can be significantly less than that provided for LWRs because of the expected use of passive safety systems and increased thermal capacities of reactor systems, which reduce sensitivities to plant upsets. A description of ancillary plant systems or the interface between the ancillary and primary plant systems should focus on any safety functions