05000424/LER-2013-001
| Vogtle Electric Generating Plant - Unit 1 | |
| Event date: | 11-27-2013 |
|---|---|
| Report date: | 01-16-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4242013001R00 - NRC Website | |
CONTINUATION SHEET
— 'I. FACILITY NAME 2., DocKEr ----,...-- S. LER NUMBER 3. PAGE Vogt% Electric Generating Plant — Unit 1 05000-424 2013 - 01 00 1
A. REQUIREMENT FOR REPORT
This report is required per 10 CFR50.73(a)(2)(i)(B) based on the Train A 125 VDC Source being inoperable for a duration greater than the allowed out of service time of Technical Specification LCO 3.8.4.
B. UNIT STATUS AT TIME OF EVENT
Mode 1, 100% power
C. DESCRIPTION OF EVENT
On November 27, 2013, an internal wiring discrepancy was discovered on Class 1 E battery charger 1AD1CB following the trip of the battery charger AC input breaker. Each battery charger is equipped with two rectifier bridges, a master and a slave rectifier bridge. The wiring discrepancy affected the slave rectifier bridge and prevented the battery charger from performing all required functions of LCO 3.8.4, DC Sources - Operating. Subsequent investigation determined the wiring discrepancy was the result of rolled electrical leads on the slave rectifier bridge performed by the manufacturer prior to shipping. The manufacturer rolled the leads to ensure proper rectifier operation but did not notify Southern Nuclear Operating Company (SNC) to update affected design drawings.
During the battery charger receipt inspection, SNC personnel identified that the as-built configuration did not match the design drawings and actions were taken to correct the as-built condition to match design drawings. This wiring discrepancy did not initially result in a degradation that prevented the battery charger from providing proper output float and equalizing voltage during subsequent maintenance testing. A review of the operating history of the battery charger determined the charger was operating in a degraded but operable condition until the slave rectifier degraded to a point that resulted in an overvoitage trip of the battery charger AC input breaker.
Subsequent review of battery charger maintenance activities determined that on September 30, 2013 the remaining redundant operable battery charger was removed from service for maintenance activities for approximately 14.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. LCO 3.8.4, DC Sources — Operating requires restoration of the inoperable DC source within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> or entry into Mode 3 within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and entry into Mode 5 within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. Although the degraded charger was able to maintain battery terminal voltage within limits under minimal loading condition, the DC source was inoperable for a time greater than allowed by Technical Specification.
All other safety-related battery chargers were inspected to confirm proper master and slave rectifier operation. No other issues were identified and this is considered to be an isolated event.
1. FACILITY-FLAME - 2. DOCKET 6, LER NUMBER.
05000-424 NUMBER NUMBER 2013 - 01 - 00
1. PAGE
The direct cause of the event was a wiring error on the battery charger slave rectifier bridge, with failure to properly address the wiring error upon discovery during the receipt inspection and a less than adequate functional test prior to placing the battery charger in service.
E. SAFETY ASSESSMENT
This event was evaluated using the internal events Probabilistic Risk Assessment model and the Incremental Core Damage Probability was determined to be less than 1E-06; therefore, this event is of very low safety significance. The Class 1 E batteries are rated for 2.75 hours8.680556e-4 days <br />0.0208 hours <br />1.240079e-4 weeks <br />2.85375e-5 months <br /> of continuous operation under full load, accident conditions. The redundant, operable battery charger, once the loss of DC source was identified, was returned to service in less than 45 minutes. Therefore under accident conditions an operable DC source could have been established in a timely manner.
F. CORRECTIVE ACTION
The functional test procedure for installation of future battery chargers and the battery charger calibration procedures will include adequate checks for proper rectifier operation. In addition, engineering personnel have been briefed on this event including consequences and lessons learned.
G. ADDITIONAL INFORMATION
1) Failed Components:
AMETEK 125 VDC Battery Charger 2) Previous Similar Events:
None 3) Energy Industry Identification System Code:
[E..1] DC Power Systems, Class 1 E 4) Other Systems Affected:
None 5) Commitment Information:
This report does not create any commitments.
NRC FORM 3541A