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:
terial exclusion, containment cleanliness, training, and so forth. In some cases, activities taken as part of these programs are used as compensatory measures, that is measures taken to compensate for some reduced functionality, availability, reliability, redundancy, or other feature of the plant’s design to ensure safety functions (e.g., reactor vessel inspections that provide assurance that reactor vessel failure is unlikely). Safety function is defined in NUREG-2122, “Glossary of Risk-Related Terms in Support of Risk-Informed Decisionmaking” (Ref. 28), as those functions needed to shut down the reactor, remove the residual heat, and contain any radioactive material release. A proposed licensing basis change might involve or require compensatory measures, which could include, for example, hardware (e.g., skid-mounted temporary power supplies); human actions (e.g., manual system actuation); or some combination of these measures. Such compensatory measures are often associated with temporary plant configurations. The preferred approach for accomplishing safety functions is through engineered systems. Therefore, when the proposed licensing basis change necessitates reliance on programmatic activities as compensatory measures, the licensee should justify DG-1285, Page 15 that this reliance is not excessive (i.e., not over reliant). The intent of this factor is not to preclude the use of such programs as compensatory measures but to ensure that the use of such measures does not significantly reduce the capability of the design features (e.g., hardware). 3. Preserve system redundancy, independence, and diversity commensurate with the expected frequency and consequences of challenges to the system, including consideration of uncertainty. As stated in Section C.2.1.1 above, the defense-in-depth philosophy has traditionally been applied in plant design and operation to provide multiple means to accomplish safety functions. System redundancy, independence, and