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:
er, the reviewer is expected to look for evidence that the licensee has considered the effects of IST changes on initiating events that were analyzed in the PRA and those that were previously screened out from the analysis to determine whether these events can become more important as a result of the IST change. However, if a licensee argues for a relaxation in testing frequency and/or method based on the adverse risk effects of testing, the reviewer should review the calculational basis, especially if other plants of the same type have not drawn similar conclusions. Common Cause Failures (CCFs): The reviewer should check to confirm that the impact of the IST change on potential CCFs has been considered in the PRA. It is important that the selection of common component groups was performed correctly to ensure that important common cause failure groups were not omitted. As a minimum, the CCF groups should include: redundant standby pumps; redundant MOVs and air-operated valves (AOVs) that change state; redundant check valves; and any other components that change state in order to support IST component operability. Changes to CCF probabilities could result from increases in the individual component failure probabilities, or could occur as a result of an increase in the CCF model parameters (e.g., beta factors, multiple Greek letter factors. etc.) If credit is taken for improved testing or staggered testing, reviewers should check that licensees have established that performance monitoring is capable of detecting CCF before multiple failures are allowed to occur subsequent to an actual system challenge. Human Reliability Analysis (HRA): The IST-specific aspects of HRA include errors related to testing, and quantification of compensating human actions. Errors related to testing are those that leave equipment unavailable until the condition is discovered during a subsequent test or until the equipment is demanded (i.e., a restoration error). Reviewers should verify that