Document: NUREG-0800
Document ID: 32179098-f78d-4852-9c29-1e5e3abb2705
Document Type: srp
Title: RISK-INFORMED DECISION MAKING:  TECHNICAL SPECIFICATIONS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0703/ML070380228.pdf
Revision Date: 2023-06
Chapter: 16
Section ID: 16.1
CFR Part: 
CFR Title: 

Content:
s, plant response and safety margins are evaluated by assumptions intended to be conservative. National standards and engineering considerations like defense-in-depth attributes and the single-failure criterion also influence plant design and operation. Margins and defenses for these considerations may be affected by the proposed TS change and, therefore, should be re-evaluated for a requested TS change. In this reevaluation, the impact of the proposed TS change on affected equipment functionality, reliability, and availability is determined. The engineering evaluation should assess whether the proposed TS change is consistent with the defense-in-depth philosophy and maintains sufficient safety margins. The reviewers should confirm whether the acceptance criteria of subsection II of this SRP section are met as to the principles of defense in depth and safety margins. B. Probabilistic Engineering Evaluation (i) Risk Evaluation for AOTs. The staff has a three-tiered approach to evaluate the risk of proposed TS AOT changes. Tier 1 evaluates the impact on plant risk of the proposed TS change as expressed by the change in CDF (ªCDF), the ICCDP, and, where appropriate, the changes in LERF (ª LERF) and the ICLERP. Tier 2 evaluates the process for addressing potentially high-risk configurations if equipment in addition to that affected by the change were taken out of service simultaneously or if other risk-significant operational factors like concurrent system or equipment testing also were involved. The objective of this part of the review is to ensure that appropriate restrictions on dominant risk-significant configurations of the change are in place. Tier 3 evaluates the overall configuration risk management program for whether adequate programs and procedures are in place to compensate for other configurations of lower probability but nonetheless risk-significant from maintenance and other operational activities. If the Tier 2 evaluation demonstrates, with reasonable