PNO-I-12-005, Oyster Creek Reactor Shutdown and Unusual Event Due to a Loss of Offsite Power and Shutdown Greater than 72 Hours

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PNO-I-12-005 - Oyster Creek Reactor Shutdown and Unusual Event Due to a Loss of Offsite Power and Shutdown Greater than 72 Hours
ML12214A163
Person / Time
Site: Oyster Creek
Issue date: 07/31/2012
From: Hunegs G
NRC/RGN-I/DRP/PB6
To:
HUNEGS, GK
References
PNO-I-12-005
Download: ML12214A163 (3)


Date: July 31, 2012 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE -- PNO-I-12-005 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 the Region I staff on this date.

Facility Licensee Emergency Classification Exelon Generation Company, LLC X Notification of Unusual Event Oyster Creek Alert Forked River, NJ Site Area Emergency Docket: 50-219 General Emergency Not Applicable

SUBJECT:

OYSTER CREEK REACTOR SHUTDOWN AND UNUSUAL EVENT DUE TO A LOSS OF OFFSITE POWER AND SHUTDOWN GREATER THAN 72 HOURS On July 23, at 3:29 a.m., Oyster Creek automatically shutdown following a loss of offsite power (LOOP) due to an electrical fault on an offsite transmission line. All control rods inserted during the scram. The licensee declared an Unusual Event (UE) at 3:41 a.m. because the LOOP exceeded 15 minutes in duration. Both isolation condensers (ICs) actuated to cool the reactor.

As a result of the loss of offsite power, both emergency diesel generators (EDGs) automatically started and provided electrical power to safety equipment. As expected, due to the LOOP and before the EDGs started, power was interrupted to the reactor protection system which caused a primary containment isolation. Plant operators used the isolation condenser, the electromatic relief valves (EMRVs) and the control rod drive pumps to control reactor pressure and level.

Offsite power was restored at 4:57 a.m., and the UE terminated at 5:38 a.m. on July 23. The licensee achieved cold shutdown on July 24.

The electrical system transmission operator determined that the loss of offsite power was the result of an electrical ground caused by a tree contacting one transmission line, as well as an unrelated electrical circuit breaker coordinator problem that affected the other transmission line running between Oyster Creek and its connection to the electrical grid. The transmission system operator repaired these problems.

In addition, Exelon initially reported to the NRC that the reactor building (secondary containment) differential pressure indicated positive 0.25 inches at 3:57 a.m., but returned to its normal negative pressure at 4:34 a.m. The cause was determined to be instrument error due to loss of instrument air, and secondary containment pressure actually remained at its normal, negative value throughout this event. Exelon will update this event report in the near future.

The resident inspectors responded to the site and closely monitored licensee actions to stabilize the plant, restore offsite power, and troubleshoot plant systems. Regional specialists assisted the resident staff in reviewing Exelons actions to address equipment issues before plant restart.

Following the repairs to the offsite electrical system by the transmission system operator, and verification of the operability of onsite plant systems, Exelon restarted the plant on June 26.

The plant reached 100% power on July 28.

The State of New Jersey was informed at the time of the event. The NRC Region I Public Affairs Office responded to media inquiries.

The information presented herein was discussed with Exelon and is current as of July 30, 2012 at 9:15 am. This PN is being issued to describe the conditions that were found to have caused this plant shutdown as well as to discuss the subsequent restart of the unit. Accordingly, no update to this PN will be issued.

ADAMS Accession Number: ML12214A163 CONTACT: Scott Barber (610) 337-5232

ML12214A163 Non-Sensitive Publicly Available x SUNSI Review Sensitive Non-Publicly Available OFFICE RI/DRP RI/SLO RI/PAO RI/DRP RI/DRP RI/ORA NAME SBarber/AMD for DTifft/ DBT DScrenci/DS GHunegs/GKH WDean/WMD DRoberts/JWC for DATE 07/30 /12 07/30 /12 07/ 30 /12 07/30 /12 07/31/12 07/ 31 /12