BYRON UNIT 2 RESTARTS AFTER A LOSS OF OFFSITE POWER AND DECLARING A NOTICE OF UNUSUAL EVENT
At 10:18 a.m. (CST) on January 30, 2011, 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 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 licensee’s 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.
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