After electrical switchyard fault an explosion reported at Sequoyah nuclear switchyard

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Power Reactor Event Number: 47660
Facility: SEQUOYAH
Region: 2 State: TN
Unit: [1] [2] [ ]
RX Type: [1] W-4-LP,[2] W-4-LP
NRC Notified By: TIM REED
HQ OPS Officer: HOWIE CROUCH
Notification Date: 02/12/2012
Notification Time: 09:26 [ET]
Event Date: 02/12/2012
Event Time: 08:34 [EST]
Last Update Date: 02/12/2012
Emergency Class: UNUSUAL EVENT
10 CFR Section:
50.72(a) (1) (i) – EMERGENCY DECLARED
Person (Organization):
JOSELITO CALLE (R2DO)
VICTOR MCREE (R2RA)
BOB BOGER (NRR)
JASON KOZAL (IRD)
TAB BEACH (DHS)
DWIGHT FULLER (FEMA)
JEANNE BERGER (NICC)
MICHELE EVANS (NRR)

 

Unit SCRAM Code RX CRIT Initial PWR Initial RX Mode Current PWR Current RX Mode
1 N Y 100 Power Operation 100 Power Operation
2 N Y 100 Power Operation 100 Power Operation
UNUSUAL EVENT DUE TO ELECTRICAL FAULT IN 161 KV SWITCHYARD

“At 0756 [EST] on 2/12/12, an electrical event occurred in the 161 kV switchyard that resulted in bus differential relay operating, and opening all PCBs [Protective Circuit Breakers] within 161 kV bus 2-2. Shortly after, a call was received from site security regarding an explosion in the switchyard.

“At 0820, a report was received that visible damage was present on an insulator between a PCB and a Motor Operated Disconnect (MOD) in the 161 kV switchyard, which is where the fault occurred. Follow up reports indicated an oil leak from a current transformer. Two other PCBs were identified to have visible damage. After the event, while opening MODS for PCBs that tripped open, the ‘A’ phase for one MOD did not open.

“No safety related equipment required to establish or maintain safe shutdown was affected. All the Diesel Generators remain in operable standby conditions.

“Unit 1 remained steady at 100% with no transients.

“Unit 2 had a 2B Condenser Circ Water pump trip off. Crew responded to the pump trip and Unit 2 remains at 100%.

“One offsite power source is inoperable and second offsite power source has been verified operable. Grid status is Yellow.”

There were no personnel injuries reported due to the fault and resulting explosion. The loss of the offsite power source resulted in the licensee entering a 72-hr. LCO. The licensee is investigating both the cause of loss of offsite power and the circulating water pump trip.

The licensee has notified the State of Tennessee and the NRC Resident Inspector.

* * * UPDATE FROM KEVIN WILKES TO HOWIE CROUCH AT 1056 EST ON 2/12/12 * * *

At 1019 EST, the licensee terminated their Notification of Unusual Event. The basis for termination was that the fault was cleared and the conditions for EAL entry no longer exists.

The licensee has made state and local notifications and has notified the NRC Resident Inspector.

Notified R2DO (Calle), IRD (Kozal), NRR (Evans), DHS (Beach), FEMA (Fuller), and NICC (Berger)

Source: NRC Event Notifications

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