BSEP-07-0035, Response to Generic Letter 2007-01, Inaccessible or Underground Power Cable Failures That Disable Accident Mitigation Systems or Cause Plant Transients

Response to Generic Letter 2007-01, Inaccessible or Underground Power Cable Failures That Disable Accident Mitigation Systems or Cause Plant Transients

ML071360062
Person / Time
Site:	Brunswick
Issue date:	05/08/2007
From:	Scarola J Progress Energy Co
To:	Document Control Desk, NRC/NRR/ADRO
References
BSEP-07-0035, GL-07-001
Download: ML071360062 (6)

Text

Progress Energy James Scarola Vice President Brunswick Nuclear Plant May 8, 2007 Progress Energy Carolinas, Inc.

SERIAL: BSEP 07-0035 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

Brunswick Steam Electric Plant, Unit Nos. 1 and 2 Docket Nos. 50-325 and 50-324/License Nos. DPR-71 and DPR-62 Response to Generic Letter 2007-01, Inaccessible or Underground Power Cable Failures That Disable Accident Mitigation Systems or Cause Plant Transients Ladies and Gentlemen:

On February 7, 2007, the NRC issued Generic Letter 2007-01, "Inaccessible or Underground Power Cable Failures That Disable Accident Mitigation Systems or Cause Plant Transients." Responses to Generic Letter 2007-01 were requested to be submitted within 90 days of the date of the letter (i.e., May 8, 2007).

The requested information is enclosed. No regulatory commitments are contained in this letter. Please refer any questions regarding this submittal to Ms. Annette H. Pope, Supervisor - Licensing/Regulatory Programs, at (910) 457-2184.

I declare, under penalty of perjury, that the foregoing is true and correct. Executed on May 8, 2007.

Sincerely, 2a,it~

James Scarola PO. Box 10429 Southport, NC 28461 T> 910.457.3698 A / -7 F> 910.457.2803

Document Control Desk BSEP 07-0035 / Page 2 WRM/wrm

Enclosure:

Response to Generic Letter 2007-01 cc (with enclosure):

U. S. Nuclear Regulatory Commission, Region II ATTN: Dr. William D. Travers, Regional Administrator Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, GA 30303-8931 U. S. Nuclear Regulatory Commission ATTN: Mr. Eugene M. DiPaolo, NRC Senior Resident Inspector 8470 River Road Southport, NC 28461-8869 U. S. Nuclear Regulatory Commission (Electronic Copy Only)

ATTN: Mr. Stewart N. Bailey (Mail Stop OWFN 8B1) 11555 Rockville Pike Rockville, MD 20852-2738 Chair - North Carolina Utilities Commission P.O. Box 29510 Raleigh, NC 27626-0510

BSEP 07-0035 Enclosure Page 1 of 4 Response to Generic Letter 2007-01 On February 7, 2007, the NRC issued Generic Letter (GL) 2007-01, "Inaccessible or Underground Power Cable Failures That Disable Accident Mitigation Systems or Cause Plant Transients." Responses to Generic Letter 2007-01 were requested to be submitted within 90 days of the date of the letter (i.e., May 8, 2007). Carolina Power & Light Company (CP&L),

now doing business as Progress Energy Carolinas, Inc., is providing responses below to the requested information for the Brunswick Steam Electric Plant (BSEP), Units 1 and 2.

Reference 1 provides guidance from Nuclear Energy Institute (NEI) for developing a response to the questions in this generic letter (GL). The preparation of these responses is consistent with the information in Reference 1.

The requested information follows.

NRC 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.

Response to Question 1 In researching the history of inaccessible or underground power cable failures at BSEP, Units 1 and 2, the following conditions were taken into account:

• Power cables only were considered o This includes distribution cables (i.e., bus, motor control center, load center feeds).

o This excludes cables for instrumentation, control, indication, etc.

" Voltage Range o Low voltage limit is 480 VAC.

o High voltage limit is 15,000 VAC.

• Failure History o Consistent with Reference 2, research starts at the beginning of automation of data recording and includes cable failures that can be searched for in electronic databases, regardless of the actual date of failure.

o In-service failures are included.

o Testing failures are included.

A review of the BSEP, Units 1 and 2 database for failures of these power cables routed in underground duct banks and conduits identified three related failures, each of which was an

BSEP 07-0035 Enclosure Page 2 of 4 in-service failure. One failure involved a low power circuitry failure and the other two involved medium voltage failures. A description of these three related failures follows.

Low Power Circuitry Failure:

There has been one in-service low power circuitry failure at BSEP.

Type: 1/c # 6 Manufacture: Commercial, Type THW Date of failure: 03/18/98 Type of service: Plant lighting, specifically High Mast lighting and Main Stack security lighting.

Voltage Class: 600 VAC Years of Service: Approximately 20 years.

Cause for Failure: Physical damage to conductor combined with water intrusion directly over the damaged area.

The 480 VAC substation SY2 branch feeder conductors supplying power to plant lighting shorted and failed due to a combination of conductor physical damage and rain water. The root cause was determined to be a short of the circuit conductors to ground and/or between multiple circuit conductors. The short circuit was attributed to physical damage of the conductor insulation.

Rain water intrusion into the manhole was directly over the area of the physical damage. The combination of the damaged conductor insulation and water dripping on the conductors was the cause of the short.

Medium Voltage Cable Failures:

There have been two in-service medium-voltage power circuitry failures at BSER The first involved the cable service from E2 to the Motor Driven Fire Pump (i.e., normal feed); the second involved the cable service from E4 to the Motor Driven Fire Pump (i.e., alternate feed). This circuitry is comprised of cabling run from separate power sources to a manual transfer switch and are continuously energized. The cable parameters are the same for each cable, as noted below.

Type: 3-1/c 4/0 shielded, 5kV Manufacture: Okonite Date of failure: 05/12/05 (normal feed) 05/18/05 (alternate feed)

Type of service: Supplied normal and alternate feeds to the Motor-Driven Fire Pump. Continuously energized.

Voltage Class: 5 kV Years of Service: Approximately 32 years.

Cause for Failures: Water treeing.

BSEP 07-0035 Enclosure Page 3 of 4 The root cause of the faulted power feed from E2 and the cable deterioration found on the power cable from E4 to the Motor-Driven Fire Pump was determined to be accelerated aging caused by a wetted environment that may have had a chemical or pre-existing flaw component. This caused the formation of water trees, or resulted in partial discharges, and subsequent electrical trees that, over a short period of time, resulted in a fault.

NRC 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).

Response to Question 2 The Brunswick Plant does not have high voltage (i.e., greater than 15 kV) inaccessible or underground power cables that support emergency diesel generators, offsite power, emergency service water, service water, component cooling water or other systems that are within the scope of 10 CFR 50.65; therefore, no inspection, testing and monitoring program has been established for high voltage cables.

The Brunswick Plant is conducting inspection, testing, and monitoring of medium-voltage cable using procedure NGG-PMB-CBL-01, "NGG Equipment Reliability Template - Medium Voltage Cable (1 kV to 15 kV)." This procedure provides recommended preventive maintenance tasks, including a testing frequency matrix and details pertaining to the specific test purpose and evolutions, to intercept aging mechanisms leading to medium voltage cable degradation and failure.

The Brunswick Plant program for predictive monitoring of the health of medium-voltage cables that are subjected to a wetted environment consists of the following:

A list of medium-voltage rated cables (5 kV) subject to a wetted environment (i.e.,

located in duct banks) has been compiled.

The wetted cables identified make up 50 medium-voltage circuits. The main service description of each circuit is identified, along with a brief discussion of the cable's function (i.e., what the circuit powers) and its service condition (i.e., whether the cable is "energized/loaded," "not energized," or "energized/not loaded").

Each of the identified circuits is comprised of two or more cable sections. The section of cable subjected to the wetted environment has been identified, along with its specific cable type (e.g., 1/c #4/0; 3/c 350 MCM; 1/c 500 MCM).

BSEP 07-0035 Enclosure Page 4 of 4 Currently, the Tan Delta testing method is used to gather data on each cable which is evaluated for a negative trend indicating degraded insulation. Cables which display a decline in insulation performance, as indicated by the test results, will be replaced.

The goal of the program is to anticipate imminent failure of medium-voltage cables located in a wetted environment and to replace those cables identified. The resulting benefit to the plant is to minimize cable failures and the resulting challenge to plant operations caused by the loss of equipment important to safety or to commercial availability.

References

1. NEI Letter from James H. Riley to Administrative Points of Contact. Guidance for Response to GL 2007-01, "Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients," March 26, 2007, ADAMS Accession Number ML070950462.

2. Letter from Michael J. Case (NRC) to James H. Riley (NEI), "Response to Nuclear Energy Institute (NEI) Letter dated March 26, 2007 - Re: Interpretation of Generic Letter (GL) 2007-01, Inaccessible or Underground Power Cable Failures That Disable Accident Mitigation Systems or Cause Plant Transients," ADAMS Accession Number ML070940311.