DCL-07-053, 90-day Response to NRC Generic Letter 2007-01, Inaccessible or Underground Power Cable Failures That Disable Accident Mitigation Systems or Cause Plant Transients.
| ML071290050 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 05/02/2007 |
| From: | Jacobs D Pacific Gas & Electric Co |
| To: | Document Control Desk, NRC/NRR/ADRO |
| References | |
| DCL-07-053, GL-07-001, OL-DPR-80, OL-DPR-82 | |
| Download: ML071290050 (7) | |
Text
Pacific Gas SElectric and Company Donna Jacobs Diablo Canyon Power Plant Vice President P. 0. Box 56 Nuclear Services Avila Beach, CA 93424 805.545.4600 May 2, 2007 Fax: 805.545.4234 PG&E Letter DCL-07-053 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk 11555 Rockville Pike Rockville, MD 20852 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 and 2 90-day Response to NRC Generic Letter 2007-01, "Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients" Pursuant to 10 CFR 50.54(f), this letter provides the Pacific Gas and Electric Company (PG&E) 90-day response to NRC Generic Letter 2007-01, "Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients," dated February 7, 2007. The generic letter requests licensees to provide a history of inaccessible or underground power cable failures, and to describe inspection, testing, and monitoring programs to detect the degradation of inaccessible or underground power cables for cables within the scope of 10 CFR 50.65.
PG&E's response is provided in the enclosure.
PG&E makes no regulatory commitments (as defined by NEI 99-04) in this letter.
This letter includes no revisions to existing regulatory commitments.
If you have questions regarding this response, please contact Mr. Stan Ketelsen at (805) 545-4720.
I state under penalty of perjury that the foregoing is true and correct.
Executed on May 2, 2007.
Don 4 Jacobs A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway e Comanche Peak
- Diablo Canyon
- Palo Verde
- South Texas Project
- Wolf Creek
5 Document Control Desk PG&E Letter DCL-07-053 a May 2, 2007 Page 2 mjrm/4557 cc: Terry W. Jackson, Senior Resident Inspector Bruce S. Mallett, Region IV Sandra Shewry, Director, California Department of Health Services Diablo Distribution cc/enc: Alan B. Wang, NRR A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
- South Texas Project e Wolf Creek
Enclosure PG&E Letter DCL-07-053 Response to Requested Information of NRC Generic Letter 2007-01, Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients Below is the Pacific Gas and Electric Company (PG&E) response to the information requested in NRC Generic Letter 2007-01, "Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients," dated February 7, 2007. The generic letter's requested information is shown in italics, followed by PG&E's response.
NRC Requested Information Item (1):
Provide a history of inaccessible or undergroundpower 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.
PG&E Response (1):
Research into inaccessible or underground power cable failures at Diablo Canyon Power Plant (DCPP) revealed 10 failures in power cables within the scope of 10 CFR 50.65. Table 1 below contains the information requested as well as additional information on the types of failures, components supported, and cable identifiers.
For most of the cable failures listed in Table 1, no definitive evidence was found to determine a root cause for the failure. However, water was found present in most cases. PG&E suspects that water may have been a contributing factor, and limiting or eliminating the wet environment would remove a possible degradation mechanism.
After the analysis of the component cooling water motor 2-3 cable failure found the root cause to be a discrete contaminant particle within the cable insulation, PG&E established a cable replacement program as a corrective action to replace all safety-related medium voltage cables and other critical non safety-related medium voltage cables with more modern cables during refueling outages. DCPP has completed more than 50 percent of these replacements.
NRC Requested Information Item (2):
Describe inspection, testing and monitoring programs to detect the degradation of inaccessible or undergroundpower cables that support EDGs, offsite power,
[emergency service water] ESW, service water, component cooling water and othersystems that are within the scope of 10 CFR 50.65 (the Maintenance Rule).
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Enclosure PG&E Letter DCL-07-053 PG&E Response (2):
Testing:
PG&E periodically performs direct current hi-pot testing on medium voltage cables during the overhaul or maintenance of the equipment they feed.
DCPP uses a high resistance ground system for the 4kV and 12kV systems, and an ungrounded system for the low voltage (480V and under) system. Medium voltage and low voltage degraded cables typically fail to ground rather than phase to phase. In an ungrounded or high resistance ground system, a single ground fault will bring in a ground alarm alerting operators of a problem, providing time for operator actions. Additionally, surveillance test procedures performed periodically on safety-related equipment demonstrate that the cables are functional.
Pull Box Inspections:
PG&E performs inspections on a periodic basis to eliminate or minimize wet conditions known to impact cable degradation rates. DCPP has the following recurring preventive maintenance activities and inspections in place to mitigate the potential for cable degradation:
" Bimonthly inspection and dewatering of outdoor electrical pull boxes located between the turbine building and the intake structure (inspections may be deferred if weather conditions do not warrant inspection, but have to be performed a minimum of four times per year). Pull boxes are checked for standing water and if water is found, it is pumped out, and corrective action is initiated to investigate the cause of the standing water.
" Yearly verification that pull boxes and manholes, sump pumps, alarms, and drains are functional.
" Once per cycle inspection of the pull boxes at the intake structure to verify that they are dry, and the drainage system is functional.
In addition, PG&E inspects and dewaters a limited number of the non-safety related electrical pull boxes that are known to have moisture problems during the rainy season (those without drain pipes or sump pumps). These pull boxes are inspected and pumped out monthly during the rainy season.
Conduit Inspections:
Although the pull box inspection and dewatering program has been effective in keeping the pull boxes dry, PG&E discovered in the process of cable 2
Enclosure PG&E Letter DCL-07-053 replacements that water was present in some dips in the conduits subjecting the cables to long term wetting. A new underground conduit inspection program is being implemented for DCPP to inspect the duct bank underground conduits suspected of containing water. This inspection will look for the presence of water, and will remove any water that is found. Any conduits found to contain water will be monitored to verify that the water does not return.
In addition to the current inspection, testing, and maintenance practices, DCPP continues to stay informed of new technologies, and will evaluate the new technologies for implementation as additional information becomes available.
These could include such techniques as partial discharge testing, very low frequency, dissipation factor, etc.
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Enclosure PG&E Letter DCL-07-053 Table 1. DCPP Cable Failure Data Zb "0
-. C A0 0 00 0 0 00
- .C 0 C A-C 4,
.0 00 A 0 00 0 00.
00 00.
0 C ~00 (~ '~-
0~V
-~
0 I.M.9
.0.0 I?RY 00 C. o ~. -
1 Inservice EPR Yes Okonite 10/29/1989 Energized ASW 2-2 G06H00 4kV 5kV 16 Unknown Black 1 2 Inservice EPR Yes Okonite 5/3/1992 Energized MCC 14D D08H00 4kV 5kV 17 Unknown Black (Note 4) (Note 1) 3 Hi-pot EPR Yes Okonite 10/31/1992 Energized ASW 1-2 G06H00 4kV 5kV 17 Unknown Black 4 Inservice EPR Yes Okonite 2/5/1993 Energized CWP 1-1 D05V00 12kV 15kV 21 Chemical Black Attack 5 Inservice EPR Yes Okonite 3/12/1993 Energized CWP 1-2 E05V00 12kV 15kV 22 Chemical Black Attack 6 Inservice EPR Yes Okonite 10/25/1995 Energized MCC 15D D06HOO 4kV 5kV 23 Unknown Black I (Note 4) 7 Hi-pot EPR Yes Okonite 4/16/1996 Energized MCC 24E E06HOO 4kV 5kV 24 Unknown Black I (Note 4) (Note 1) 8 Inservice EPR Yes Okonite 6/12/1997 Energized MCC 14D D08H00 4kV 5kV 25 Unknown Black I (Note 4) (Note 1) 9 Inservice EPR Yes Okonite 8/18/2002 Energized CCW 2-3 H12H00 4kV 5kV 29 Insulation Black Contaminant (Note 3) 10 Hi-pot EPR Yes Okonite 2/22/2003 Energized MCC 24E E06H00 4kV 5kV 30 Unknown Black I I (Note 4) (Note 1) 4
Enclosure PG&E Letter DCL-07-053 Table 1 Notes:
Note 1: These circuits failed twice as the cables were only partially replaced to remove the failed section the first time.
Subsequently the remaining portion of the original cable failed, and the circuits were then replaced entirely.
Note 2: In all cases, except failure No. 9, water was present in the pull boxes/conduits.
Note 3: This cable was evaluated by Altran Solutions Inc. for failure analysis and the root cause was found to be due to a discrete contaminant particle within the cable insulation. The underground duct bank conduit was found to be dry. There was no bulk degradation of the dielectric properties of this cable, and no evidence of chemical attack or water damage on this cable.
Note 4: 480 VAC motor control center (MCC).
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