ML071570255
| ML071570255 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 06/01/2007 |
| From: | Miskiewicz D Progress Energy Carolinas |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| FAQ 06-0017, Rev 2, NEI 04-02 | |
| Download: ML071570255 (3) | |
Text
FAQ Number 06-0017 FAQ Revision 2 FAQ Title Ignition Source Counting Guidance for High Energy Arching Faults Page 1 of 3 faq 06-0017 - rev 2.doc Plant: Harris Date:June 1, 2007 Contact: Dave Miskiewicz Phone:919.546.7588 Email:David.Miskiewicz@pgnmail.com Distribution: (NEI Internal Use) 805 TF FPWG FPRATF RIRWG BWROG PWROG Purpose of FAQ:
Clarification/enhancement of Ignition Source counting guidance for High Energy Arcing Faults (HEAF) in NUREG/CR-6850, supporting NFPA-805 Fire PRA application.
Is this Interpretation of guidance? Yes / No Proposed new guidance not in NEI 04-02? Yes / No Details: NEI 04-02 guidance needing interpretation (include section, paragraph, and line numbers as applicable):
New attachment on interpretation issues Circumstances requiring guidance interpretation or new guidance:
The guidance provided in NUREG/CR-6850 for Ta sk 6, Fire Ignition Frequency (Section 6.5.6, Bin 16), states:
Bin 16 - High-Energy Arcing Faults (Plant-Wide Components): High-energy arcing faults are associated with switchgear and load centers. Switchyard transformers and isolation phase buses are not part of this bin. For this bin, similar to electrical cabinets, the vertical segments of the switchgear and load centers should be counted. Additionally, to cover potential explosive failure of oil filled transformers (those transformers that are associated with 4.16 or 6.9kV switchgear and lower voltage load centers) may be included in vertical segment counts of the switchgear.
Pilot discussions and benchmarking of NUREG/CR-6850 for Task 6, Fire Ignition Frequency, has shown inconsistency in the treatment of High Energy Arcing Faults (Bin 16).
Strict interpretation of the guidance is that the HEAF count should mimic the electrical cabinet counts for switchgear and load centers. The application of such a counting method is expected to result in reported High Energy Arcing Fault (HEAF) frequency values for an individual plant being inconsistent with i ndustry experience. The industry experience and consequently the HEAF frequency is based on 3 events occurring on medium voltage FAQ Number 06-0017 FAQ Revision 2 FAQ Title Ignition Source Counting Guidance for High Energy Arching Faults Page 2 of 3 faq 06-0017 - rev 2.doc switchgears and 1/2 event occurring on a 480 VAC Load Center. Because of the relative numbers of switchgears and load centers at an individual plant, it is expected that the resultant frequency may be inappropriately skewed. There is a concern that the occurrence of a HEAF frequency distribution that departs significantly from the 3 to 1/2 ratio would cause results to be challenged.
There is a need to resolve these issues to prevent future rework and to reduce burden associated with uncertainty treatment. This topic has impact on the NFPA-805 pilots, non-pilots and other users of NUREG/CR-6850.
Detail contentious points if licensee and NRC have not reached consensus on the facts and circumstances:
Potentially relevant existing FAQ numbers:
This guidance is specific to the characteriz ation of electrical cab inets for Bin 16 HEAF determination. The characterization and counting of electrical cabinets for Bin 15 determination is addressed by FAQ 06-0016.
FAQ 07-0035 addresses counting Bus Duct for HEAF. Response Section:
Proposed resolution of FAQ and the basis for the proposal:
Split fire ignition frequency Bin 16, HEAF, into two bins; namely, "16a - HEAF for low-voltage panels (480-1000V)" and "16b - HEAF for medium-voltage panels (greater than 1000V)." For each bin, the method of panel counting would remain consistent with the guidance for Bin 15 (see FAQ 06-0016). Additionally, MCCs with molded-case circuit breakers should not be counted as HEAF sources unless it is associated with switchgear that is used to directly operate equipment such as load centers.
The net result is a re-partitioning of the "higher-consequence" HEAF events between low and medium-to-high voltage equipment in accordance with the event data. The revised fire frequencies for these two new bins are as follows:
16a: HEAF for Low-Voltage Panels (480 - 1000V)
Mean = 4.8E-04 Variance = 1.4E-03 5% Lower Bound = 1.6E-05 50% (Median) = 2.0E-04 95% Upper Bound = 1.5E-03 16b: HEAF for Medium-Voltage Panels (greater than 1000V) Mean = 1.4E-03 FAQ Number 06-0017 FAQ Revision 2 FAQ Title Ignition Source Counting Guidance for High Energy Arching Faults Page 3 of 3 faq 06-0017 - rev 2.doc Variance = 1.2E-02 5% Lower Bound = 3.8E-05 50% (Median) = 6.2E-04 95% Upper Bound = 4.1E-03
Basis: This FAQ revision includes the respons e proposed by the NRC and the NUREG/CR-6850 writing team.
If appropriate, provide proposed rewording of guidance for inclusion in the next Revision: