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:
rt the conclusion that no significant degradation will occur. RG 1.175, Page 18 b. Consider the effects of enhanced testing to the extent needed to substantiate the change. Other issues that should be addressed in the quantification of the change in risk include the following: a. The impact of the IST change on the frequency of event initiators (those already included in the PRA and those screened out because of low frequency) should be determined. For applications of an RI-IST program, potentially significant initiators include valve failure that could lead to interfacing system loss-of-coolant accidents or to other sequences that fail the containment isolation function. b. The impact of the implementation of the proposed RI-IST program on the CCF contributions of affected component(s) should be addressed either by the use of sensitivity studies or by the use of qualitative assessments that show that the CCF contribution would not become significant under the proposed RI-IST program (e.g., by use of phased implementation, staggered testing, and monitoring for common-cause effects). c. Justification of IST relaxations should not be based on credit for post-accident recovery of failed components (repair or ad-hoc manual actions, such as manually forcing stuck valves to open). However, credit may be taken for proceduralized implementation of alternative success strategies. For each human action that compensates for an increase in basic event probability as a result of IST relaxation, the human action should be feasible and proceduralized, including appropriate operator training, to ensure performance of the human action at the level credited in the quantification. d. The failure rates and probabilities used for components affected by implementation of the proposed RI-IST program should appropriately consider both plant-specific and generic data. The licensee should determine whether individual components affected by the change are performing more poorly than the