05000219/LER-2009-003
| Docket Number Sequential Revmonth Day Year Year Month Day Year N/A N/Anumber No. | |
| Event date: | 04-25-2009 |
|---|---|
| Report date: | 6-10-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2192009003R00 - NRC Website | |
Plant Condition Prior to Event Event Date:�April 25, 2009� Event Time:�1715 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 April 25, 2009, at 1715, alarms (M1A CLG POWER FAIL) and (M1A TROUBLE) were received in the control room while the M1A Main Power Transformer [XFMR] temperatures began to trend up. Operators were dispatched to the field to investigate and reported that there was smoke in the M1A control panel but no active fire. All the MIA pumps [P] and fans [FAN] were off and could not be restored. The Shift Manager was notified and a reactor load reduction was commenced in accordance with the alarm response procedures to maintain M1A temperatures below the alarm set points. While reactor power was being reduced, the decision was made to limit M1A service to 30 minutes without forced cooling. Operations secured the power reduction and manually scrammed the reactor from 74% power in accordance with plant procedures. The post scram response was normal and the required notifications were made.
Analysis of Event:
This event is reportable under the provisions of 10CFR50.73(a)(2)(iv)(A) as an event that resulted in a manual actuation of the reactor protection system [JC]. There were no safety consequences impacting the plant or public safety as a result of this event. All safety systems, structures, and components operated normally during this event.
During the reactor shutdown, all required safety systems responded appropriately. There was no loss of any function that would have prevented fulfillment of actions necessary to (1) shutdown the reactor and maintain it in a safe shutdown condition, (2) remove residual heat, (3) control the release of radioactive material, and (4) mitigate the consequences of an accident.
This event did not result in any safety system functional failure.
Cause of Event:
The loss of M1A cooling was caused by a faulted contactor coil [CNTR] in the cooling bank [CLR], motor starter [MSTR], resulting in the failure of the M1A auxiliary control power transformer [XFMR], and subsequent loss of control power for the remaining cooling bank motor starters. At the time of the event, there were no surveillances or work in progress. Although troubleshooting found an incorrect rated fuse installed for protection of the control power transformer, the faulted motor starter contactor coil would have still resulted in a loss of all M1A cooling.
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Corrective Actions:
The M1A Main Power Transformer, replaced in February 2009, was supplied to Oyster Creek from the Eddystone Generating Station. There is no pertinent equipment history information for this auxiliary control power transformer or the motor starter, contactor coil. The control power transformer and the #1 cooling bank motor starter assembly were replaced, properly rated fuses were installed, and the cooling system control circuitry was modified to have a backup independent power supply to address a single point vulnerability. In order to prevent future similar failures and eliminate another single point vulnerability, modifications were performed for the cooling circuits on both Main Power Transformers (M1A and M1 B). These modifications added individual fuses for each cooling group and coordinated the rating of the control power fuses such that only one cooling group circuit is lost on an electrical fault within that same cooling group circuitry.
The plant returned to power operation on March 2, 2009.
Additional enhancements were incorporated into the Alarm Response Procedures. Guidance was provided for the maximum allowable operation time for a total loss of cooling to the main transformers and actions to take in an attempt to restore cooling power.
Previous Occurrences
There have been no similar Licensee Event Reports events at Oyster Creek in the last three years, involving a loss of a main transformer's cooling system leading to a reactor scram.
Component Failure Data
Component: Motor Starter (CR106C002AA with a 15D21G2 contactor coil) Manufacturer: GE (Supplied with the main transformer from the Eddystone Generating Station) Serial No: N/A Cause: Faulted (shorted coil) Component: Control Power Transformer (460/115 VAC, 0.500KVA — MOD# 9T55Y50) Manufacturer: GE (Supplied with the main transformer from the Eddystone Generating Station) Serial No: N/A Cause: Overload failure of its windings