PNO-III-12-001, Byron Unit 2 Restarts After a Loss of Offsite Power and Declaring a Notice of Unusual Event
| ML12038A272 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 02/07/2012 |
| From: | Bruce Bartlett, Eric Duncan NRC/RGN-III |
| To: | |
| References | |
| PNO-III-12-001 | |
| Download: ML12038A272 (2) | |
PRELIMINARY NOTIFICATION - REGION III February 7, 2012 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE - PNO-III-12-001 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. Some of the information may not yet be fully verified or evaluated by the Region III staff.
Facility Licensee Emergency Classification Byron Unit 2 X Notification of Unusual Event Exelon Generation Company, LLC Alert Byron, Illinois Site Area Emergency Docket: 50-455 General Emergency License: NPF-66 Not Applicable
SUBJECT:
BYRON UNIT 2 RESTARTS AFTER A LOSS OF OFFSITE POWER AND DECLARING A NOTICE OF UNUSUAL EVENT DESCRIPTION:
At 10:18 a.m. (CST) on January 30, 2012, the licensee declared a Notice of Unusual Event at Byron Unit 2 due to a loss of offsite power. The reactor automatically shut down in response to the offsite power loss. The licensee subsequently restored offsite power to safety systems. The Notice of Unusual Event was then terminated at 8:00 p.m. (CST) on January 31, 2012.
The NRC began a Special Inspection on January 31, 2012, to review the circumstances surrounding the loss of offsite power that led to the Unit 2 shutdown. The results of the Special Inspection will be documented in a publically available inspection report.
The licensee completed extensive troubleshooting of the affected equipment to determine the cause of the problem that resulted in the loss of offsite power. A broken cable insulator in the switchyard was identified as the direct cause of the problem and was subsequently replaced.
NRC inspectors monitored the troubleshooting, testing, and repair activities, and reviewed the licensees corrective actions for restart and found them appropriate. On February 6, at 8:15 a.m., the licensee restarted the Unit 2 reactor and synchronized the unit to the offsite electrical distribution grid at 2:31 p.m.
During power ascension, operators at the plant failed to maintain steam generator level properly which resulted in a feedwater transient. In response to the transient, the licensee manually tripped the reactor. All safety systems responded as expected and the plant was stabilized with decay heat removal provided by the auxiliary feedwater system via the main condenser. Steam was not released from the plant for cooling. The NRC resident inspector responded to the site and closely monitored licensee actions to stabilize the plant.
The licensee provided training to the operators on this event and increased management oversight in the control room. The licensee restarted the reactor on February 7 at 5:39 a.m. and synchronized the unit to the offsite grid at 12:02 p.m. The resident inspector monitored the reactor restart in the control room. No issue was identified with this startup activity.
Unit 1 was unaffected by the event and continues to operate at 100 percent power.
The information presented herein has been discussed with the licensee, and is current as of February 7 at 3:00 p.m.
ADAMS Accession Number ML12038A272 CONTACT: Eric Duncan Bruce Bartlett 630-829-9620 815-234-5451 eric.duncan@nrc.gov bruce.bartlett@nrc.gov