Circuit Failure Mode Likelihood Analysis (Task 10)

Task Overview

Background

This task considers the relative likelihood of various circuit failure modes. This added level of resolution may be a desired option for those fire scenarios that are significant contributors to the risk. The methodology provided in this document benefits from the knowledge gained from the tests performed in response to the circuit failure issue.

Purpose

Conducting a Fire PRA in accordance with this methodology necessitates an analysis of fireinduced circuit failures beyond that typically conducted during original Fire PRAs. The circuit analysis elements of the project are conducted in three distinct phases:

1. Fire PRA cable selection (Task 3),
2. Detailed circuit failure analysis (Task 9), and
3. Circuit failure mode likelihood analysis (Task 10).

This task provides methods and instructions for conducting the third phase of circuit analysis – circuit failure mode likelihood analysis for Fire PRA cables. Task 10 estimates the probability of hot short cable failure modes of interest, which in turn can be correlated to specific component failure modes. As discussed in Section 3.3.2 of Volume 1, the methods and techniques for deriving circuit failure mode probability estimates are based on limited data and experience. Consequently, this area of analysis is not yet a mature technology, and undoubtedly further advances and refinements will come with time. Nonetheless, the methods and techniques presented in this chapter represent the current state of knowledge and provide a reasonable approach for establishing first-order circuit failure mode probability estimates, albeit with relatively high uncertainty tolerances.

Scope

Chapter 10 provides methods and technical considerations for assigning probability estimates to specific cable failure modes associated with fire-induced cable damage.

This task does not address the implementation of plant-specific quality assurance or configuration control requirements that might apply to a Fire PRA. Nor is it intended to 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(s) of ASME/ANS PRA Standard, ASME-RA-Sb-2013

Circuit Failures (CF)

Related EPRI 1011989 NUREG/CR-6850 Appendices

Appendix J, Appendix for Chapter 10, Technical Basis for Circuit Failure Mode Likelihood Equations

Appendix K, Appendix for Chapter 10, Examples of Component Circuit Failure Mode Likelihood Analyses

Supplemental Guidance

Since the publication of NUREG/CR-6850, significant research on fire-induced spurious operations has occurred. EPRI 3002001989 / NUREG/CR-7150 Volume II revises a significant portion of Task 10 of EPRI 1011989 / NUREG/CR-6850.

Joint Assessment of Cable Damage and Quantification of Effects from Fire (JACQUE-FIRE): Phenomena Identification and Ranking Table (PIRT) Exercise for Nuclear Power Plant Fire-Induced Electrical Circuit Failure (EPRI 1026424 / NUREG/CR-7150 Volume 1)

This report documents a Phenomena Identification and Ranking Table (PIRT) exercise on fire-induced electrical circuit failures that may occur in nuclear power plants as a result of fire damage to cables. The results and conclusions of the PIRT panel are a primary input to the follow on PRA Expert Panel documented in Volume 2.

Joint Assessment of Cable Damage and Quantification of Effects from Fire (JACQUE-FIRE): Expert Elicitation Exercise for Nuclear Power Plant Fire-Induced Electrical Circuit Failure (EPRI 3002001989 / NUREG/CR-7150 Volume 2)

This report documents the results of the PRA panel's expert elicitation that is used to develop the conditional probabilities of hot-short induced spurious operation & duration of various control circuit configurations.

The information in this report revises a significant portion of Task 10 of NUREG/CR-6850. The results are presented such that the bounding values can be applied based on a minimum set of parameters, and more specific values can be applied if more rigors are used to define the circuit configuration and conditions. Unfortunately, the application is not a simple update of the numbers. The use of Option #2 (Computational Probability Estimates) as a technical approach for calculating spurious operation likelihood has been eliminated

The following tables in EPRI 3002001989 / NUREG/CR-7150 Volume 2 summarize the results for both spurious operation and duration of control circuits:

• Failure Mode Probability Estimation Tables
  • Table 4-1 - Conditional Probability of Spurious Operation: SOV Single Break-Control Circuits
  • Table 4-3 - Conditional Probability of Spurious Operation: MOV Single Break Control Circuits
  • Table 4-4 - Conditional Probability of Spurious Operation: Ungrounded DC Control Circuits for Medium Voltage Circuit Breaker
  • Table 5-1 - Conditional Probability of Spurious Operation: Double Break Control Circuits for Ungrounded AC (w/ individual CPTs) Base Case – SOV
  • Table 5-2 - Conditional Probability of Spurious Operation: Double Break Control Circuits
  • Table 5-3 - Conditional Probability of Spurious Operation: Double Break Control Circuits for Ungrounded AC (w/ individual CPTs) Motor-Operated Valve
  • Table 5-4 - Conditional Probability of Spurious Operation: Double Break Control Circuits Ungrounded DC (or Ungrounded Distributed AC)

• Spurious Operation Duration Tables or Probability Distributions
  • Table 6-3 - Tabulated Spurious Operation Duration Conditional Probability Values for AC and DC Control Circuits