Document: NRC Regulatory Guide
Document ID: a5ee4c78-1135-4bb6-8d54-e974a3402f87
Document Type: regulatory_guide
Title: An Approach for Plant-Specific, Risk-Informed Decisionmaking: Graded Quality Assurance
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1221/ML12216A017.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.176
CFR Part: 
CFR Title: 

Content:
ord for future licensee evaluations and for NRC inspections should cover all high safety-significant system functions, all system components that support the high safety-significant functions, and all external system support functions required by any component. The licensee is to be able to describe technically how each issue was addressed and resolved. Here are some examples that illustrate areas of potential concern regarding the accuracy and completeness of this information. One component can directly support another system's function. For example, some contain- ment sump recirculation valves are nominally assigned to the low-pressure injection system but directly support containment spray by providing the recirculation flow path. Some instrumentation can belong to one system but provide signals used in other systems, or be used by the operators as a basis for proceduralized or unproceduralized actions. Instrumentation used to actuate and control system and plant functions needs careful attention if grading of instrumenta- tion is contemplated. Component failures could lead to an initiating event such as loss of feedwater or loss of component cooling water. Components whose failure could cause an initiating event should be identified in the matrix as being necessary to support the normal operation function (e.g., air- operated feedwater control valves are required to support feedwater at power). Well organized and detailed information is also needed to systematically propagate safety categoriza- tion through successive tiers of support systems not modeled in the PRA. If systems are not graded in a top- down sequence, it is particularly important that the evaluation should include a traceable record of the previously assumed categorization of upper-tiered functions requiring support from other systems. Eventually, the categorization of all support functions should be consistent, e.g., the safety significance of the functions requiring support in the upper-tiered