ML071350407
| ML071350407 | |
| Person / Time | |
|---|---|
| Site: | Oconee, Mcguire, Catawba, McGuire  |
| Issue date: | 05/08/2007 |
| From: | Peterson G R Duke Energy Carolinas, Duke Power Co |
| To: | Document Control Desk, NRC/NRR/ADRO |
| References | |
| GL-07-001 | |
| Download: ML071350407 (7) | |
Text
Duke GARY R. PETERSON t aPowers Vice President McGuire Nuclear Station A Duke Energy Company Duke Power MG01 VP / 12700 Hagers Ferry Rd.Huntersville, NC 28078-9340 704 875 5333 704 875 4809 fax grpeters@duke-energy.
com May 8, 2007 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk 11555 Rockville Pike Rockville, MD 20852
Subject:
Duke Power Company LLC d/b/a Duke Energy Carolinas, LLC (Duke)Oconee Nuclear Station, Units 1, 2, and 3 Docket Nos. 50-269, 50-270, 50-287 McGuire Nuclear Station, Units 1 and 2 Docket Nos. 50-369, 50-370 Catawba Nuclear Station, Units 1 and 2 Docket Nos. 50-413, 50-414 Response to NRC Generic Letter 2007-01, Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or cause Plant Transients On February 7, 2007, the NRC issued Generic Letter (GL) 2007-01. Pursuant to 10 CFR 50.54(f), this letter and associated attachment provide Duke's 90 day response to this GL.Cables are committed to be tested in accordance with the plant life extension program commitments.
There are no additional NRC commitments beyond this existing life extension program for cables.If any questions arise or additional information is needed, please contact P. T. Vu at (704) 875-4302.Very truly yours, Gary R.eterson Attachment www.dukepower.comr U. S. Nuclear Regulatory Commission May 8, 2007 Page 2 xc: W. D. Travers, Region II Administrator U. S. Nuclear Regulatory Commission Sam Nunn Atlanta Federal Center, 23 T85 61 Forsyth St., SW Atlanta, GA 30303-8931 L. N. Olshan, Senior Project Manager (ONS)U. S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-8 G9A Rockville, MD 20852-2738 J. F. Stang, Jr., Senior Project Manager (CNS and MNS)U. S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-8 H4A Rockville, MD 20852-2738 D. W. Rich NRC Senior Resident Inspector Oconee Nuclear Station J. B. Brady NRC Senior Resident Inspector McGuire Nuclear Station A. T. Sabisch NRC Senior Resident Inspector Catawba Nuclear Station U. S. Nuclear Regulatory Commission May 8, 2007 Page 3 I affirm that I, Gary R. Peterson, am the person who subscribed my name to the foregoing, and that all the matters and facts herein are true and correct to the best of my knowledge.
Gary R. Peterson 2~ >Subscribed and Sworn to me: Lo B ?-e Date Notary Public My Commission Expires: \e 5 c Date SEAL Attachment Oconee Nuclear Station McGuire Nuclear Station Catawba Nuclear Station NRC GL 2007-01 REQUESTED INFORMATION Attachment Oconee Nuclear Station McGuire Nuclear Station Catawba Nuclear Station NRC GL 2007-01 REQUESTED INFORMATION Page 1 of 3 Question 1 Provide a history of inaccessible or underground power cable failures for all cables that are within the scope of 10 CFR 50.65 (the Maintenance Rule) and for all voltage levels. Indicate the type, manufacturer, date of failure, type of service, voltage class, years of service, and the root causes for the failure.Answer 1 A total of two (2) power cable failures were found by Duke, one at Oconee, one at McGuire, and none at Catawba. A history of these failures is provided below.The power cable failures were identified from a review of the corrective action program, work management system and licensee event reports that satisfy all of the following criteria: 0 Underground or inaccessible power cable 0 Non-connection failures* Non-excavation failures* Non-maintenance-induced failures (e.g., nail puncture)* 10 CFR 50.65 maintenance rule scope* Interpretations in NEI-to-NRC letter dated March 26, 2007 0 Response to interpretations in NRC-to-NEI letter dated April 13, 2007 These searches represent Duke's 'best-effort' to facilitate identification of power cable failures in that such data was not recorded electronically during Duke's early years (before mid-1980's) of nuclear plant operation.
History of Failures: Oconee Nuclear Station Type: Ethylene Propylene Rubber (EPR) cable insulation, semi-conductive and copper tape shielded.Manufacturer:
Okonite.Date of failure: January 10, 1980.Type of service: Normally de-energized, High Pressure Service Water Pump B, I/c-#2AWG.
Voltage class: Nominal system voltage 4160 VAC, cable rating voltage 5000 VAC.Years of service: Approximately 7 years.
Attachment Oconee Nuclear Station McGuire Nuclear Station Catawba Nuclear Station NRC GL 2007-01 REQUESTED INFORMATION Page 2 of 3 Root causes: No formal root cause was performed.
Failure was discovered during periodic DC-voltage testing of the pump motor. The feeder cable was included in the test circuit and its insulation "broke down" at a voltage above the operating level.Since the results were deemed unacceptable, the cable was replaced before the pump was placed back in service. Only a small non-degraded end portion was retained for analysis.
The investigation report indicated that the most likely contributors were excessive exposure to moisture combined with a problem on the cable jacket. Refer to Memo-to-file OS-090 dated August 19, 1980, 5KV Power Cable Incident Investigation Report B-935.McGuire Nuclear Station Type: Cable insulation type is unknown, cable is probably not shielded since it is < 5KV.Manufacturer:
Unknown due to the cable being part of the submersible pump supplied by the vendor and due to the faulted cable being discarded without recording any identification markings.Date of failure: March 29, 2006.Type of service: Normally energized, Condenser Cooling Water Bearing Cooling Water Pump B (20 HP, non-safety), no cable ID.Voltage class: Nominal system voltage 600 VAC, unknown cable rating voltage.Years of service: Approximately 20 years.Root causes: No formal root cause was performed.
Failure was discovered during post-modification functional verification testing, i.e., attempting to start and run the replaced submersible pump before placing in service. The circuit tripped immediately upon the attempt to start. The fault location (i.e., connection to the submersible pump or within the cable itself) was not documented; however, this test failure was conservatively assumed to have occurred within the motor-lead cable for the purpose of this GL 2007-01 response.
This motor-lead cable was supplied by the pump vendor, was field routed, was not described on any Duke drawing or specification, and was discarded after failure without analysis.
A spare sample of the replacement cable type was provided by Engineering and Maintenance personnel involved with the pump replacement modification.
This cable is a flat unshielded design with the following data printed on the overall black jacket: "PAIGE ELECTRIC SUBMERSIBLE PUMP CABLE #12 AWG 3/C THHN/THWN CDRS 600V (UL)". Refer to PIP M06-2189 and WO 576058.
di , Attachment Oconee Nuclear Station McGuire Nuclear Station Catawba Nuclear Station NRC GL 2007-01 REQUESTED INFORMATION Page 3 of 3 Question 2 Describe inspection, testing and monitoring programs to detect the degradation of inaccessible or underground power cables that support EDGs, offsite power, ESW, service water, component cooling water and other systems that are within the scope of 10 CFR 50.65 (the Maintenance Rule).Answer 2: Duke nuclear stations are committed to cable aging management programs including inaccessible non-EQ medium voltage cables as described in each plant's respective UFSAR Chapter 18 for license renewal. These license renewal commitments are based on the appropriate aging-stressor scope of inaccessible medium voltage (system voltage greater than 2KV) power cables exposed to significant voltage (energized at system voltage for more than twenty-five percent of the time) and exposed to standing water. This medium voltage cable wet-energized aging stressor is well defined in DOE, EPRI, IEEE, and other industry research documents as summarized in NEI Medium Voltage Underground Cable White Paper (NEI 06-05).Given Duke's low incidence of power cable failures, no additional periodic cable testing programs are being performed beyond those planned to meet the commitments associated with license renewal per Chapter 18 of each site's UFSAR. For testing convenience, some medium voltage motor cables are included in the motor preventive maintenance programs when periodic motor tests such as insulation resistance test or voltage withstand test include the feeder cable.Duke has performed cable diagnostic testing of shielded medium-voltage cable in selected cases related to the wet-energized aging stressor using 60Hz partial discharge (PD) or very low frequency (VLF) dissipation factor tests. For example, Oconee used the PD testing to successfully monitor the condition of the Keowee underground emergency power cable insulation.
On some of these cables, PD was evident at acceptable but marginal voltages above the operating level. Repeated performances of the same PD tests separated by several months found the results very repeatable with no adverse trend in inception voltage. The repeated test results were considered among many inputs in a decision to proactively replace these cables to accommodate the extended plant life.Test planning for license renewal commitments has progressed to the point where a VLF test set has recently been procured.
All Duke medium voltage cables in the scope of the committed license renewal program are insulated with EPR, known to be more resistant to water-tree growth than the other common insulation, cross-linked polyethylene (XLPE). These cables are also shielded, thus allowing each conductor's insulation to be electrically and independently tested.