Document: NRC Regulatory Guide
Document ID: 82659041-98b0-4721-b25d-c4fb2ea394d0
Document Type: regulatory_guide
Title: An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1635/ML16358A153.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.174
CFR Part: 
CFR Title: 

Content:
, activities such as maintenance, testing, inspection, and qualification) was based. During the design process, plant response and associated safety margins are evaluated using assumptions of physical properties and operating characteristics that are intended to be conservative. Consideration of national standards, the defense-in-depth philosophy, and the single-failure criterion constitute additional engineering considerations that also influence plant design and operation. A licensee’s proposed licensing basis change might affect safety margins and defenses incorporated into the current plant design and operation; therefore, the licensee should reevaluate the safety margins and layers of defense to support the proposed change. As part of this evaluation, the impact of the proposed licensing basis change on the functional capability, reliability, and availability of affected equipment should be determined. The plant’s licensing basis is the reference point for judging whether a proposed licensing basis change adversely affects safety margins or defense-in-depth. Sections C.2.1.1 and C.2.1.2 below provide guidance on assessing whether implementation of the proposed licensing basis change maintains adequate safety margins and consistency with the defense-in-depth philosophy. DG-1285, Page 13 2.1.1 Defense-in-Depth The engineering evaluation should demonstrate whether the implementation of the proposed licensing basis change is consistent with the defense-in-depth philosophy. In this regard, the intent of this key principle of risk-informed decisionmaking is to ensure that any impact of the proposed licensing basis change on defense-in-depth is fully understood and addressed and that consistency with the defense-in-depth philosophy is maintained. The intent is not to prevent changes in the way defense-in-depth is achieved. The licensee should fully understand how the proposed licensing basis change impacts plant design and operation from both risk and traditional