05000339/LER-2007-002

LER-2007-002, Virginia Electric and Power Company
North Anna Power Station
P. 0. Box 402
Mineral, Virginia 23117
June 29, 2007
U. S. Nuclear Regulatory Commission Serial No.: 07-0280A
Attention: Document Control Desk NAPS: JHL
Washington, D. C. 20555-0001 Docket No.: 50-339
License No.: NPF-7
Dear Sirs:
Pursuant to 10CFR50.73, Virginia Electric and Power Company hereby submits the
following Licensee Event Report applicable to North Anna Power Station Unit 2.
Report No. 50-339/2007-002-01
This report has been reviewed by the Station Nuclear Safety and Operating Committee
and will be forwarded to the Management Safety Review Committee for its review.
Sincerely,
D. G. Stoddard, Site Vice President
North Anna Power Station
Enclosure
Commitments contained in this letter: None
cc: United States Nuclear Regulatory Commission
Region II
Sam Nunn Atlanta Federal Center
61 Forsyth Street, SW, Suite 23T85
Atlanta, Georgia 30303-8931
Mr. J. T. Reece
NRC Senior Resident Inspector
North Anna Power Station
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSIOP APPROVED BY OMB NO. 3150-0104 EXPIRES: 6/30/2007
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1. FACILITY NAME 2.'DOCKET NUMBER 3. PAGE
NORTH ANNA POWER STATION , UNIT 2 05000 339 1 OF 4
4. TITLE
Automatic Start of 2H EDG on Loss of "B" Reserve Station Service Transformer Due To Cable Fault

Document Numbersequentia Revmonth Day Year Year Month Day Year
Event date:	03-07-2007
Report date:	06-29-2007
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
3392007002R01 - NRC Website

FACILITY NAME (1) DOCKET LER NUMBER (6) PAGE (3) 1.0 DESCRIPTION OF THE EVENT On March 7, 2007, at 0305 hours0.00353 days <br />0.0847 hours <br />5.042989e-4 weeks <br />1.160525e-4 months <br />, with North Anna Unit 2 operating at 100% power (Mode 1), Control Room Operations personnel received several annunciators (EIIS Component ANN) simultaneously that indicated that the "B" Reserve Station Service Transformer (RSST) (EIIS System EA, Component XFMR) tripped and locked out. The Unit 2 "H" Emergency Diesel Generator (EDG) (EIIS System EK, Component DG) automatically started on a Degraded Voltage/Under Voltage signal due to the loss of the "B" RSST.

Operations personnel entered appropriate abnormal procedures and stabilized the plant.

Condition "A" of Technical Specification (TS) 3.8.1 was entered due to the inoperable RSST. The Unit 2 "H" EDG loaded onto the Unit 2 "H" emergency bus (EIIS System EB, Component BU) as designed.

An 8-hour Non-Emergency Report was made to the NRC at 0611 hours0.00707 days <br />0.17 hours <br />0.00101 weeks <br />2.324855e-4 months <br />, in accordance with 10 CFR 50.72 (b)(3)(iv)(A), for an event that results in valid actuation of an EDG. On March 7, 2007, at 1929 hours0.0223 days <br />0.536 hours <br />0.00319 weeks <br />7.339845e-4 months <br />, the power sources were realigned and the Unit 2 "H" EDG was shutdown and placed in automatic clearing Condition "A" of TS 3.8.1.

2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS North Anna utilizes three RSSTs to supply offsite power to the four emergency busses (EIIS Component BUS) and as a backup supply for the six station services busses. The "B" RSST is the normal supply of the 2H emergency bus and 1G bus and a backup supply for the 1B and 2B station service busses.

There were no nuclear safety consequences as a result of this event since the Unit 2 "H" EDG started as designed and re-energized the emergency bus. Also, the Unit 2 "J" EDG and "2J" emergency bus remained operable. The Unit 1 "G" bus automatically transferred to the "C" RSST. Therefore, the health and safety of the public were not affected at any time during the event. This event is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A) for an event that resulted in the automatic actuation of an EDG.

3.0 CAUSE The trip and lockout of the "B" RSST were caused by a fault on one of the "B" phase cables (EIIS Component CBL) associated with the low side on the "B" RSST. The root cause of the event was damage during original construction installation that resulted in a hole in the cable jacket allowing moisture intrusion, which resulted in corrosion and then breakage of the zinc shield tape.

The faulted section of the cable was shipped to the manufacturer where it was subjected to laboratory examination and dissection. The examination determined FACILITY NAME (1) DOCKET LER NUMBER (6) PAGE (3) that the cable jacket must have had a hole in it, which resulted in the zinc tape shield corroding. With the zinc tape shield corroded, subsequent movement of the cable led to the tape breaking. The zinc tape shield original overlap had also separated due to movement and the vertical run. With the zinc tape shield broken and separated, this led to an electrical discontinuity (gap) in the shield. There was then a potential difference across the gap that resulted in current flow. The current flowed across material contaminated with water and corrosion products, leading to the underlying dacron fabric and insulation degrading. The insulation degradation reached the threshold where the normal cable voltage resulted in a conductor to ground short, failing the cable.

4.0 IMMEDIATE CORRECTIVE ACTION(S) Operations personnel entered appropriate abnormal procedures and stabilized the plant.

Operations personnel entered Condition "A" of Technical Specification (TS) 3.8.1 due to the inoperable RSST. On March 7, 2007, at 1929 hours0.0223 days <br />0.536 hours <br />0.00319 weeks <br />7.339845e-4 months <br />, the power sources were realigned and the Unit 2 "H" EDG was shutdown and placed in automatic. This allowed clearing Condition "A" of TS 3.8.1.

5.0 ADDITIONAL CORRECTIVE ACTIONS A temporary modification was implemented to remove the failed portion of the "B" RSST cable from service. The "B" RSST was returned to operable.

Part of the failed "B" phase cable was replaced, including the entire South side Turbine Building vertical run and the temporary modification was cleared.

An inspection was performed on the "B" phase cables adjacent to the failure location to ensure there was no damage that could affect the shield or interior of the cables. No problems were identified.

An inspection of the "B" RSST cables identified missing tie-wraps. The missing tie-wraps on the "B" RSST cables were replaced.

An inspection was performed on the RSST cables, at the vertical grip locations, on the south side of the Turbine Building for damage. No problems were identified.

6.0 ACTIONS TO PREVENT RECURRENCE Additional corrective actions are being tracked in the Corrective Action Program and will be implemented as required.

FACILITY NAME (1) DOCKET LER NUMBER (6) 7.0 SIMILAR EVENTS Licensee Event Report No. 50-339/1990-002-00, dated August 30, 1990, documents the automatic start of the Unit 2 "H" EDG due to failure of the "B" RSST.

8.0 ADDITIONAL INFORMATION At the time of this event, North Anna Unit 1 was operating at 100 percent power. The Unit 1 "G" bus automatically transferred to the "C" RSST, therefore, Unit 1 was not affected by this event.

Component Information Manufacturer: Kerite Component: 2000 kcmil 5kV copper shielded cable Model No.: HTK 90 degree C, EPR insulation with CSPE jacket