05000341/LER-2012-005
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 09-14-2012 |
|---|---|
| Report date: | 11-05-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 48309 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(2)(iv)(A), System Actuation - ECCS Discharge |
| 3412012005R00 - NRC Website | |
Initial Plant Conditions:
Mode� 1 Reactor Power�68 percent
Description of the Event
At approximately 1603 EDT, a fault occurred on the Z-phase of the 13.2 kV side of Transformer 1 in the 120 kV switchyard [FK]. The fault caused a transformer differential relay trip that isolated Bus 101 and resulted in a loss of power to Transformer 64, Division I emergency safety system busses 64B and 64C [EB] and balance of plant (BOP) bus 64A [EA]. The loss of BOP Bus 64A caused the loss of the center condenser pump, center heater feed pump and both north and center heater drains pumps. The loss of these pumps resulted in a trip of the operating north reactor feed pump [SJ]. Reactor water level lowered as a result of the loss of feedwater, and the unit automatically scrammed on low reactor water level 3 as designed. All control rods [JD] fully inserted, and the lowest reactor water level reached was approximately 96 inches above top of active fuel. Division I Emergency Diesel Generators (EDGs) [EK], EDG-11 and EDG-12, automatically started and loaded Division I buses. The High Pressure Coolant Injection (HPCI) [BJ] and Reactor Core Isolation Cooling (RCIC) [BN] systems automatically started as designed on low reactor water level 2 and restored reactor water level. Reactor water level increased until it reached Level 8 and the HPCI & RCIC systems automatically tripped as designed.
Reactor operators subsequently maintained reactor water level in the normal level band using the Condensate/Feed and Control Rod Drive (CRD) systems. Reactor pressure was controlled using the main turbine bypass system to the main condenser [SJ]. The maximum pressure measured was approximately 986 psig and no Safety Relief Valves actuated. All isolations and actuations for reactor water levels 3 and 2 occurred as expected, Reactor cool down was controlled within Technical Specification and administrative limits.
At the time of the scram, all Emergency Core Cooling (ECCS) and Emergency Diesel Generators were operable with the exception of EDG-11 which was available but not Operable due to ventilation equipment maintenance work. No other safety related equipment was out of service. EDG-11 and EDG-12 performed all of their functions and provided power to the Division I AC buses. Temperatures were monitored in the room containing EDG-11 and the room did not approach any temperature limits.
Significant Safety Consequences and Implications This event posed no significant safety implications because the reactor protection and safety related systems functioned as designed following the automatic reactor trip Important safety-related and non-safety related equipment performed as discussed in the description of the event, and plant response was as expected. There was no increase in reactor pressure, and the reactor core was adequately covered and cooled throughout the event.
Therefore, the health and safety of the public were not affected by this event.
This event is being reported under 10 CFR 50.73(a)(2)(iv)(A), as an event or condition that resulted in the automatic actuation of an emergency core cooling system at power as a result of a valid signal, and for the actuation of the Reactor Protection System and a reactor scram. A 4-hour non-emergency notification was made to the NRC Operations Center at 1927 EDT on September 14, 2012 (EN 48309) in accordance with 10 CFR 50.72(b)(2)(iv)(A) for any event that results in ECCS discharge into the reactor coolant system as a result of a valid signal and 10CFR50.72(b)(2)(iv)(B), any event that results in actuation of the reactor protection system (RPS) when the reactor is critical.
Cause of the Event
The cause of the trip was determined to be animal intrusion that caused a phase to ground fault at the Z-phase surge arrestor on Transformer 1 on the 120kV switchyard. A bird that appeared to be recently electrocuted was found beneath the arrestor. The fault location was evidenced by burn marks and partial melting of the wildlife protector cover for the surge arrestor. It appears that the bird pecked at a plug in the protective cover until the fault occurred. The fault caused a transformer differential relay trip that isolated Bus 101 on the 120kV switchyard. The result of the bus isolation was a loss of power to Transformer 64 which resulted in loss of power to emergency safety feature (ESF) Buses 64B and 64C and BOP Bus 64A.
Corrective Actions
The relay that tripped to isolate the 120kV switchyard was tested and found to be operating properly. The surge arrestor and associated jumpers were replaced, and the Transformer 1 cables were inspected and megger tested satisfactory. Transformer 1 was re-energized prior to plant restart.
This event has been entered into the Fermi 2 Corrective Actions Program. The associated apparent cause evaluation is still in progress and could result in additional corrective actions.
Additional Information
A. Failed Component:
Component: Surge Arrestor Function: Overvoltage Protection Manufacturer: Cooper Industries Model Number: 235-35 Failure Cause: Failure of wildlife protector B. Previous Licensee Event Reports (LERs) on Similar Problems:
There are no other LERs on similar problems noted within the past five years