05000219/LER-2009-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. N/A N/A | |
| Event date: | 02-01-2009 |
|---|---|
| Report date: | 03-31-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2192009001R00 - NRC Website | |
Plant Condition Prior to Event Event Date: February 1, 2009 Event Time: 2156 Unit 1 Mode: Power Operation Power Level: 100%
Description of Event
Note: Energy Industry Identification System (EIIS) codes are identified in the following text in brackets as [XX].
On February 1, 2009 the Oyster Creek Generating Station was operating at 100% reactor power, 661 Megawatts Electric. Oyster Creek had been online for 56 days following the 1F17 Forced Outage on the M1A transformer failure on November 28, 2008.
At 2156 hours0.025 days <br />0.599 hours <br />0.00356 weeks <br />8.20358e-4 months <br />, Oyster Creek's main generator [GEN] tripped due to the actuation of the 230kV bus section differential relay [87] due to the failure of the M1A main power transformer [XFMR]. This caused a load reject SCRAM that automatically shut down the reactor [RCT]. The transformer failure led to the declaration of an Unusual Event at 2211 hours0.0256 days <br />0.614 hours <br />0.00366 weeks <br />8.412855e-4 months <br />, based on a fire lasting greater than 15 minutes affecting the M1A transformer. As required, the Shift Emergency Director completed immediate notifications. The deluge system actuated as expected and off-site fire responders were called in to assist. The fire was extinguished at 2227 hours0.0258 days <br />0.619 hours <br />0.00368 weeks <br />8.473735e-4 months <br /> and the Unusual Event was terminated at 2337 hours0.027 days <br />0.649 hours <br />0.00386 weeks <br />8.892285e-4 months <br /> on February 1, 2009.
Analysis of Event:
A review of the grid disturbance report provided by Jersey Central Power & Light and the digital fault recorder in the switchyard showed that there were no abnormalities in the grid on or before the time of failure. However, the digital protective relay system data, differential current and voltage data, visual inspections, and post failure test indicate that the failure occurred at the B' phase high voltage (HV) bushing of the M1A transformer.
The plant responded as designed and operator action was prompt and appropriate. The transient was within the design basis of the plant and had no nuclear safety significance.
After the fire on the M-1A transformer was extinguished, an immediate visual inspection showed that a catastrophic failure of the 'B' HV bushing had occurred. Upon further inspections-after the 'B' HV bushing was removed from the transformer, there was evidence that there had been a phase-to-ground fault on the 'B' HV bushing main conductor and that it had faulted to ground through the ground sleeve of the bushing. This fault occurred about 10.5 inches below the bushing-mounting flange and approx three inches above the current transformers internal to the housing of the 'B' phase bushing.,
Cause of Event:
A catastrophic failure of the 'B' HV bushing on M1A Main Power Transformer led to a reactor automatic shutdown due to a load reject SCRAM.
Corrective Actions:
The M1A Main Transformer was replaced with a transformer obtained from another Exelon generating station.
The long-term corrective action is to replace both main transformers (M1A and M1B) with new units during the next refueling outage, scheduled for the fourth quarter of 2010.
Previous Occurrences
This is the second failure of a main power transformer at Oyster Creek in less than three months, however, the November 28, 2008 M1A failure resulted from a 'B' phase internal winding fault unrelated to this most recent failure.
Component Failure Data
Component: M1A Main Transformer (325 MVA) Manufacturer: GE (Rewind 1989-90 by GE Philadelphia) Serial No.# D577931 Cause: High Voltage Bushing Failure