Detailed Circuit Failure Analysis (Task 9)
Contents
Task Overview
Background
This task provides an approach and technical considerations for identifying how the failure of specific cables will impact the components included in the Fire PRA plant response model.
Purpose
Conducting a Fire PRA in accordance with this methodology necessitates an analysis of fire-induced circuit failures beyond that typically conducted during original Fire PRAs. The circuit analysis elements of the project are conducted in three distinct phases:
- Fire PRA cable selection (Task 3)
- Detailed circuit failure analysis (Task 9), and
- Circuit failure mode likelihood analysis (Task 10).
This chapter provides methods and instructions for conducting the second phase of circuit analysis–detailed circuit failure analysis (Task 9). The purpose of Task 9 is to conduct a more detailed analysis of circuit operation and functionality to determine equipment responses to specific cable failure modes. These relationships are then used to further refine the original cable selection by screening out cables that cannot prevent a component from completing its credited function. The output of this task supports the quantitative screening process under Task 7.
As discussed in Chapter 3, in most cases it is advantageous to perform some aspects of Task 9 along with the basic cable selection process of Chapter 3. Analysts are encouraged to screen out early in the cable selection/analysis process those cables that are readily identifiable as not posing a risk to the credited PRA function. A full and complete detailed circuit failure analysis can be time consuming and resource intensive. Accordingly, this level of analysis should be reserved for cases in which the quantitative screening demonstrates a clear need and advantage to fully developing a circuit’s failure modes and response to fire-induced cable failures. Ultimately, each plant will need to find the most efficient balance point with respect to how much detailed circuit analysis is conducted coincident with the cable section.
Scope
Chapter 9 provides methods and technical considerations for identifying the potential response of circuits and equipment to specific cable failure modes associated with fire-induced cable damage. This task contains the following key elements:
- Determine the component response to postulated conductor/cable failure modes, and
- Screen out cables that do not impact the ability of a component to complete its credited function.
This task does not address implementation of plant-specific quality assurance and configuration control requirements that might apply to a Fire PRA. Nor is it intended that this procedure validate the accuracy of plant-specific data extracted from plant drawings, documents, or databases. Each plant should follow appropriate quality assurance, administrative, and configuration control procedures applicable to the work being conducted. The need to validate input source documents should be addressed as part of assembling the prerequisite information in Step 1.
Related Element of ASME/ANS PRA Standard
Cable Selection and Location (CS)
Related EPRI 1011989 NUREG/CR-6850 Appendices
Appendix B, Appendix for Chapter 3, Example
Appendix I, Appendix for Chapter 9, Examples of Components Circuits Analysis
Supplemental Guidance
Refer to Task 3 for discussion on supplemental information related to cable selection/circuit analysis (including detailed circuit analysis).
