Document: NUREG-0800
Document ID: 4e1d86bd-74a5-4678-8bc0-ffce3ba28ea0
Document Type: srp
Title: RISK-INFORMED INSERVICE TESTING
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0428/ML042880272.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.9.7
CFR Part: 
CFR Title: 

Content:
the change in risk include the following: * 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 in RI-IST, potentially significant initiators include valve failure that could lead to interfacing system loss-of-coolant accidents (LOCAs) or to other sequences that fail the containment isolation function. * The effect of common cause failures should be addressed either by the use of sensitivity studies or by the use of qualitative assessments that shows that CCF contribution would not become significant under the proposed IST requirements (e.g., use of phased implementation, staggered testing, and monitoring for common cause effects). * 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 a basic event probability increasing as a result of IST relaxation, there should be a licensee commitment to ensure performance of the function at the level credited in the quantification. Excessively low human failure probabilities should be adequately justified and there should be adequate training programs, personnel practices, plant policies, etc. to ensure continued licensee performance at that level. * The failure rates and probabilities used for components affected by the proposed change in IST 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 average associated with their class; the licensee should avoid relaxing IST for those components to the point that the unavailability of the poor performers would be appreciably worse than that