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:
so used to improve test strategies, and not just to relax testing requirements. This is discussed more in Sections III.A.2 and III.A.3 under the review of program scope and strategy. In evaluating the impact from changes to the [ST program, reviewers should determine that the change is consistent with the defense in depth philosophy. Accounting for defense in depth is an effective way to compensate for uncertainties in equipment and human performance. In some cases, risk analysis can help quantify the range of uncertainty; however, there will remain areas of relatively large uncertainty or areas not covered by the risk analysis. Therefore, where a comprehensive risk quantification is not, or cannot be done, traditional defense in depth considerations should be used or maintained to account for uncertainties. Review guidelines for defense in depth considerations is provided in SRP Chapter 19. For IST changes, defense in depth is preserved if, for example: * The risk analysis shows that a reasonable balance is maintained between prevention of core damage, prevention of containment failure, and consequence mitigation. * System redundancy, independence, and diversity are maintained commensurate with the expected frequency and consequences of challenges to the system. The effects on system redundancy, independence, and diversity from potential common cause failures 3.9.7-22 Rev. 0 -August 1998 that could result from IST changes are addressed as part of the risk quantification and/or as part of the implementation and monitoring strategies associated with the IST change. Credit taken for operator actions to compensate for relaxations in IST are justified and these actions are backed up by licensee commitment (e.g., training, plant procedures, etc.). Credit is not taken for non-proceduralized actions (e.g. for the recovery of failed components). This ensures that the change preserves defenses against human errors. Another element of the integrated decisionmaking is the