Document: NRC Regulatory Guide
Document ID: 47b09be1-4bf8-45f9-a099-7fed871c09bd
Document Type: regulatory_guide
Title: Plant-Specific, Risk-Informed Decisionmaking: Inservice Testing (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2114/ML21140A055.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.175
CFR Part: 
CFR Title: 

Content:
c component test intervals as part of the licensee’s RI-IST program submittal). However, licensees will need to submit alternative requests to use the RI-IST program in future 120- month IST program intervals. 2.2 Perform Engineering Evaluation The licensee should consider the appropriateness of qualitative and quantitative analyses, as well as analyses using traditional engineering approaches and those techniques associated with the use of PRA findings. Areas to be evaluated from this viewpoint include the potential effect of the proposed RI-IST program on defense-in-depth attributes and safety margins. In addition, defense-in-depth and safety margin should also be evaluated, as feasible, using risk techniques (e.g., PRA). 2.2.1 Defense-in-Depth Evaluation RG 1.174 provides guidance on how to evaluate the impact of a proposed licensing-basis change on defense-in-depth to ensure that any impact is fully understood and addressed and that consistency with the defense-in-depth philosophy is maintained. The guidance in RG 1.174 should be used to evaluate the impact of a proposed RI-IST change on defense-in-depth to determine whether consistency with the defense-in-depth philosophy is maintained. Defense-in-depth is an element of the NRC’s safety philosophy that employs successive compensatory measures to prevent accidents or mitigate damage if a malfunction, accident, or naturally RG 1.175, Page 12 caused event occurs at a nuclear facility. The defense-in-depth philosophy has traditionally been applied in plant design and operation to provide multiple means to accomplish safety functions and prevent the release of radioactive material. It has been and continues to be an effective way to account for uncertainties in equipment and human performance and, in particular, to account for the potential for unknown and unforeseen failure mechanisms or phenomena that, because they are unknown or unforeseen, are not reflected in either the PRA or deterministic engineering