PNO-II-11-003, B, Preliminary Notification of Event or Unusual Occurrence
| ML111230070 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 05/02/2011 |
| From: | Brian Bonser NRC/RGN-II/DRS/PSB1 |
| To: | |
| References | |
| PNO-II-11-003B | |
| Download: ML111230070 (1) | |
May 2, 2011 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE - PNO-II-11-003B This preliminary notification constitutes EARLY notice of events of possible safety or public interest significance. The information is as initially received without verification or evaluation, and is basically all that is known by Region II staff (Atlanta, Georgia) on this date.
Facility: Licensee Emergency Classification:
Tennessee Valley Authority Notification of Unusual Event Browns Ferry Units 1, 2, and 3 Alert Site Area Emergency Docket Numbers: 50-259, 260 and 50-296 General Emergency License Numbers: DPR- 33, DPR-52 and DPR-68 Not Applicable
SUBJECT:
NOTIFICATION OF UNUSUAL EVENT DUE TO LOSS OF OFFSITE POWER (UPDATE)
At 6:21 p.m. EDT, on April 27, 2011, NRC entered the Monitoring Mode due to the Browns Ferry Nuclear Plant declaring a Notification of Unusual Event at 6:01 p.m. EDT. The emergency was declared due to a loss of normal and alternate supply voltage to all 4KV shutdown boards for greater than 15 minutes and at least two Diesel Generators supplying power to 4KV shutdown boards. The loss of AC power was due to damage from storms and a tornado moving through the area. All three units automatically shut down with no significant complications. Seven of the plants eight back-up diesel generators started and powered emergency busses and are currently operating. The diesel that did not start was out of service for maintenance and was subsequently returned to service.
TVA has placed all three units in Mode 4, cold shutdown. There are presently two sources (161 KV buses) of reliable offsite power available to the site. All shutdown electrical loads are being supplied by off-site power.
All the diesel generators are secured. Six diesels are considered operable and two are available, but not operable. TVAs efforts to restore the 500 KV buses are continuing and are expected to take several days to complete. There have been no radioactive releases above regulatory limits.
After the restoration of reliable offsite power the licensee exited the NOUE at 8:50 CDT on May 2, 2011. The NRC has closely monitored these activities, including direct onsite observation. The NRC exited Monitoring Mode at 10:33 p.m., EDT for this incident.
CONTACT: Brian Bonser 404-997-4653