05000280/LER-2013-001
| Surry Power Station, Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| 2802013001R00 - NRC Website | |
1.0 DESCRIPTION OF THE EVENT On December 6, 2012, at 11:15, with Unit 1 at 100 percent and Unit 2 at 98 percent power, the scheduled performance of the emergency diesel generator (EDG) 3 [El IS-EK-GEN] monthly start test found the incoming voltage meter indicated the generator output voltage was off scale high. Normal voltage output is expected to be between 4000 VAC and 4400 VAC. An estimate of the generator output voltage was 5600 VAC. Following an unsuccessful attempt to lower voltage, the stop pushbuttons were depressed and EDG 3 was secured at 11:37.
During visual inspection of the EDG 3'remote excitation cabinet, a lead in the voltage regulator circuit was found not connected/landed in its expected location.
The lead is associated with the control room motor operated potentiometer and is in series with the voltage regulator feedback control magnetic amplifiers. With the lead detached, the voltage regulator had no feedback or control to lower or regulate voltage. The lead connection is a flat blade inserted into a blade receptacle. An inspection of the detached lead showed no indication of damage, and the female connection showed no signs of spring. The lead was reconnected, and the tightness of the connection was verified.
Near the end of the shutdown sequence, personnel within the EDG room reported an acrid odor coming from the EDG remote excitation panel. After the EDG shutdown, small wisps of smoke were visible emanating from the panel vent.
Thermography of the cabinet exterior identified increased temperature in the area of the generator output potential transformers, which supply excitation current to the generator field during operation. The cabinet was opened and inspected, and components subjected to the elevated voltage were tested with no damage identified.
The last successful run of EDG 3 prior to this event was on November 3, 2012 for the emergency bus logic test. During the logic test, a data acquisition system (DAS) was installed in the remote excitation cabinet with the test leads secured to internal wiring to ensure the test leads would remain secure for the diesel run.
Following the successful test and EDG 3 run, the DAS leads were removed from the cabinet. An evaluation determined the voltage regulator circuit lead was most probably detached during the removal of the DAS after logic testing, and that EDG 3 would not have been able to perform its function with the lead detached.
As a result of the prior operability evaluation, EDG 3 was assumed to be inoperable from November 3, 2012 until December 7, 2012, exceeding Technical Specification 3.16 limiting condition of operation of seven days for one of two EDGs. Therefore, this report is being submitted pursuant to 10CFR50.73(a)(2)(i)(B), any operation or condition prohibited by the plant's Technical Specifications.