0CAN050701, Response to Generic Letter 2007-01, Inaccessible or Underground Power Cable Failures That Disable Accident Mitigation Systems or Cause Plant Transients
| ML071350241 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 05/07/2007 |
| From: | Mitchell T Entergy Operations |
| To: | Document Control Desk, NRC/NRR/ADRO |
| References | |
| 0CAN050701, GL-07-001 | |
| Download: ML071350241 (6) | |
Text
ar Entergy Operations, Inc.
~
1
~i,,v.1448 SR. 333 Russellville, AR 72802 Tel 479-858-3110 Timothy G. Mitchell Vice President, Operations ANO OCAN050701 May 7, 2007 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Response to Generic Letter 2007-01 Arkansas Nuclear One - Units I and 2 Docket Nos. 50-313 and 50-368 License Nos. DPR-51 and NPF-6
References:
- 1. NRC Generic Letter 2007-01, dated February 7, 2007 "Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients" (0CNA020707)
- 2. NEI letter from J. H. Riley to Administrative Points of Contact, dated March 16, 2007 "Guidance for Response to Generic Letter (GL) 2007-01"
- 3. NRC Letter from Michael J. Case, to J. H. Riley dated April 13, 2007, "Response to Nuclear Energy Institute (NEI) Letter Dated March 26, 2007 - Re: Interpretation of GL 2007-01, Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients"
Dear Sir or Madam:
Per reference 1, the NRC issued GL 2007-01 to request facilities to submit the following information to the NRC within 90 days of the date of the generic letter:
(1) Provide a history of inaccessible or underground power cable failures for all cables that are within the scope of 1 OCFR50.65 (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.
(2) Describe inspection, testing and monitoring programs to detect the degradation of inaccessible or underground power cables that support emergency diesel generators, offsite power, essential service water, service water, component cooling water, and other systems that are within the scope of I OCFR50.65 (the maintenance rule).
OCAN050701 Page 2 The response to Question 1 is provided in the attachment to this letter. In researching plant records for the requested information, Entergy used the NEI and NRC guidance provided in references 2 and 3 to clarify the population of cables of interest. Data bases researched included plant condition reporting system, plant data management system, and the maintenance rule database. To date, Arkansas Nuclear One (ANO) has experienced five cable failures within the scope of the GL.
In response to Question 2, ANO inspection, testing, and monitoring practices presently include visual cable inspection during routine operations, periodic meggering of cables and connected equipment associated with maintenance activities, and periodic inspection of manholes for dewatering. The ANO corrective action program is used to determine root cause and extent of conditions where deemed necessary and would be the mechanism for determining the need for and extent of any increased cable monitoring.
No new commitments are identified in this submittal. If you have any questions or require additional information, please contact Ms. Natalie Mosher at (479) 858-4635.
The requested information is being provided pursuant the requirements of 1 OCFR50.54(f). I declare under the penalty of perjury that the foregoing information is true and correct. Executed on May 7, 2007.
Sincerely, TGM/nbm Attachment cc:
Dr. Bruce S. Mallett Regional Administrator U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Ms. Farideh E. Saba Mail Stop O-8B1 Washington, DC 20555-0001
Attachment to 0CAN050701 History of Inaccessible or Underground Power Cable Failures Within the Scope of 1 OCFR50.65 for ANO
Attachment to 0CAN050701 Page 1 of 3 History of Inaccessible or Underground Power Cable Failures within the Scope of 10CFR50.65 for ANO Cable Type Voltage Class Manufacturer Date of Failure!
Type of Service Root Cause' Service (Yrs.)
250 Million 5 kV cable Anaconda 05/06/93 (15 yrs) 2P-4A (ANO-2 Indeterminate. Independent Circular Mils rating (original installation in service water test lab concluded that there (MCM) Black 1978) pump) was no direct evidence for Ethylene 4160 VAC Normally energized.
the cause of the fault. Other Propylene nominal service Cable ID:
than the fault site, the Rubber (EPR)
R2A302A, B, C remainder of the cable was (shielded) electrically sound.
250 MCM Black 5 kV cable General Cable 11/10/95 (21 yrs)
P-4C (ANO-1 Indeterminate. First failure EPR (shielded) rating Corporation (original installation in service water occurred between the pump 1974) pump) and manhole #3. Just this 4160 VAC Normally energized.
section of cable was nominal service Cable ID: GPA402A replaced. Independent lab (now identified as testing revealed no exact GPA402B, C, D cause for the failure, and after cable testing of the cable at replacement and locations other than the fault splice in manhole site revealed above average
- 3) breakdown level for cable of this vintage, indicating that the failure was an isolated incident.
- I
Attachment to 0CAN050701 Page 2 of 3 Cable Type Voltage Class Manufacturer Date of Failure/
Type of Service Root Cause
- Service (Yrs.)
250 MCM Black 5 kV cable General Cable 10/10/99 (25 yrs)
P-4C (ANO-1 Indeterminate. Second EPR (shielded) rating Corporation (original installation in service water failure occurred between the 1974) pump) breaker and manhole #3.
4160 VAC Normally energized. Just this section of cable was nominal service Cable ID: GPA402A replaced. Independent lab (now identified as testing (using different lab
- GPA402B1, C1, D1 than previous failure) after cable indicated that the failure was replacement) most likely due to voids or water treeing; however, due to the dark color of the insulation (Black EPR), a conclusive inspection for water treeing was unable to be performed.
250 MCM Black 5 kV cable General Cable 01/27/01 (27 yrs)
P-6A (electric fire Trouble shooting revealed a EPR (shielded) rating Corporation (original installation in water pump) tear in the cable jacket at the 1974)
Normally energized.
fault site, indicating that it 4160 VAC Cable ID: Al 14A was most likely due to nominal service (now identified as damage that occurred during A114A1, B1, C1 the original cable pull.
after cable replacement)
Attachment to 0CAN050701 Page 3 of 3
, 1 Cable Type Voltage Class Manufacturer Date of Failure/
Type of Service Root Cause
- Service (Yrs.)
250 MCM Black 5 kV cable Anaconda 02/05/03 (25 yrs) 2P-4C (ANO-2 No formal failure analysis EPR (shielded) rating (original installation in service water was performed. Since this 1978) pump) was the fifth failure of 4160 VAC Normally energized.
underground cables, an nominal service Cable ID:
adverse trend condition G2A402A, B, C report (CR) was written to address the failures.
- The adverse trend CR (CR-ANO-C-2003-00067) was written concurrently with the fifth failure of underground cables in a 10-year period. As shown in the table, the exact cause of these failures was indeterminate, but the most probable cause is now believed to be water treeing. The failed underground cables at ANO had black EPR insulation and therefore, could not be microscopically inspected for water treeing. (The water treeing test requires a cable sample to be boiled until translucent to allow for inspection, and black EPR insulation doesn't turn translucent). It is now known that black EPR insulation is made using carbon black which has a tendency to pull in moisture making it more susceptible to water treeing.
The corrective action plan from this adverse trend CR replaced all remaining black EPR insulated underground safety-related 4160 VAC power cables at ANO with red EPR insulated cables that contain no carbon black. EPRI Report 1003664, Medium-Voltage Cables in Nuclear Plant Applications - State of Industry and Condition Monitoring, dated October 2003, provides more information on the water treeing phenomenon.