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:
e 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 assurance, that there are no risk-significant configurations for the subject equipment, the application of 16.1-12 Revision 1 - March 2007 Tier 3 may not be necessary to the proposed AOT. Although defense in depth is protected to some degree by most current TSs, the three-tiered approach to the evaluation of risk-informed TS modifications addressed in the following subsection adds assurance that defense in depth will not be impacted significantly by such changes to the licensing basis. (1) Tier 1: PRA Capability and Insights. The first tier evaluates the impact of the proposed TS change on CDF, ICCDP, and, where appropriate, on LERF and ICLERP. Two aspects must be considered, (a) the validity of the PRA and (b) the PRA insights and findings. The depth of the staff review at this stage depends on the extent to which the licensee demonstrates that its PRA is valid for assessing the proposed TS changes and overall impact on plant risk. (2) Tier 2: Avoidance of Risk-Significant Plant Configurations for TS AOT Changes. The licensee's assessment also should provide reasonable assurance that risk-significant plant equipment outage configurations will not occur when specific plant equipment is out of service after the proposed TS AOT change. An effective assessment evaluates equipment according to its contribution to plant risk (or safety) while the equipment affected by the proposed AOT change is out of service. Evaluation of such combinations of equipment out of service against the Tier 1 ICCDP acceptance guideline is one appropriate method of identifying risk-significant configurations. With plant equipment risk contribution evaluated, the licensee can assess whether TS or procedure enhancements are required to avoid risk-significant situations. In addition, compensatory