Fire PRA Cable Selection (Task 3)

Task Overview

Background

This task provides instructions and technical considerations associated with identifying cables supporting those components selected in Task 2. In previous Fire PRA methods (such as EPRI FIVE and Fire PRA Implementation Guide) this task was relegated to the SSD analysis and its associated databases. This document offers a more structured set of rules for selection of cables.

Purpose

Conducting a Fire PRA in accordance with this procedure 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:

• 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 first phase of circuit analysis–selecting Fire PRA cables (Task 3). The purpose of Task 3 is to identify for all Fire PRA components the circuits/cables3 associated with the components and the routing/plant location of the identified circuits/cables. These relationships can then be used to determine the Fire PRA components potentially affected by postulated fires at different plant locations.

In most cases, it is advantageous to perform some or all of Task 9 (detailed circuit failure analysis) coincident with Task 3. The degree to which Task 3 and Task 9 are combined is highly dependent on numerous plant-specific factors. Considerations for combining the two tasks are incorporated in relevant sections of Chapter 3.

Scope

Chapter 3 provides methods and technical considerations for identifying cables to be included in the Fire PRA Cable List. This task contains the following key elements:

• Identify cables associated with Fire PRA equipment,
• Determine plant routing and location for the Fire PRA cables,
• Identify Fire PRA power supplies, and
• Correlate Fire PRA cables to Fire PRA equipment and plant locations (fire compartments and/or fire areas).

Implementation of plant-specific quality assurance and configuration control requirements that might apply to a Fire PRA is not within the scope of this task. Nor does this task address validating 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 conducted. The need to validate input source documents should be addressed as part of assembling the prerequisite information.

Related Element(s) of ASME/ANS PRA Standard, ASME-RA-Sb-2013

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

Since the publication of NUREG/CR-6850, significant research on fire-induced spurious operations has occurred. This has resulted in the publication of three EPRI/NRC reports on this subject.

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)

• NRC Memo dated June 14, 2013, Interim Technical Guidance on Fire-Induced Circuit Failure Mode Likelihood Analysis and Enclosure (ADAMS Accession Nos. ML13165A209, ML13165A214)

• NRC letter to NEI, dated December 16, 2013, Interim Technical Guidance on Fire-Induced Circuit Failure Mode Likelihood Analysis and Enclosure (ADAMS Accession Nos. ML13238A280, ML13165A214)

• NRC Memo dated February 12, 2014, Supplemental Interim Technical Guidance on Fireinduced Circuit Failure Mode Likelihood Analysis (ADAMS Accession No. ML14017A091)

• NRC letter to NEI, dated April 23, 2014, Supplemental Interim Technical Guidance on Fire-Induced Circuit Failure Mode Likelihood Analysis (ADAMS Accession No. ML14086A165)

(The memos and letters dated June 14, 2013, December 16, 2013, February 12, 2014, and April 23, 2014 referenced interim guidance until the issuance of NUREG/CR-7150, Volume 2, in May 2014. NUREG/CR-7150, Vol. 2 should be referred to as the official guidance.)

Joint Assessment of Cable Damage and Quantification of Effects from Fire (JACQUE-FIRE): Technical Resolution to Open Issues on Nuclear Power Plant Fire-Induced Circuit Failure(EPRI 3002009214 / NUREG/CR-7150 Volume 3)

Impact on EPRI 1011989 NUREG/CR-6850 Guidance

Major impacts on NUREG/CR-6850 (EPRI 1011989) guidance, include:

• The spurious operation of a three-phase AC motor due to proper polarity hot shorts on three-phase power cabling is incredible.
• The spurious operation of DC compound-wound motor due to proper polarity hot shorts in the motive/power cabling is incredible.
• The ignition of a secondary fire from an open circuited CT secondary circuit with a turns ratio of 1200:5 or less is incredible.
  • This testing is documented in NUREG/CR-7228, Open Secondary Testing of Window-Type Current Transformers
• The guidance given in Nuclear Energy Institute, NEI 00-01, Rev. 2, Appendix B.1, can be applied safely to fire safe-shutdown methodologies throughout the plant in resolving concerns associated with Multiple High-Impedance Faults (MHIFs). (Note: Appendix B.1 of NEI 00-01, Rev. 2 offers a basis for concluding that MHIFs need not be considered provided there exists breaker coordination for any circuits damaged by the fire that should previously have been assessed for the effects of MHIFs and appropriate testing and maintenance is performed).
• Spurious operation caused by shorting conductors through a surrogate ground path in ungrounded circuits as a result of fire induced damage, is a failure mode which occurred during the DESIREE-Fire testing and is referred to as “Ground Fault Equivalent Hot Short.” The probability of this failure mechanism with respect to cable-to-cable hot shorts is such that it warrants consideration for including in future testing programs and, subsequently, in analyzing post-fire safe-shutdown conditions.