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Event Notification Report for December 13, 2006

U.S. Nuclear Regulatory Commission
Operations Center

Event Reports For
12/12/2006 - 12/13/2006

** EVENT NUMBERS **


43046 43047

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Power Reactor Event Number: 43046
Facility: CALVERT CLIFFS
Region: 1 State: MD
Unit: [1] [ ] [ ]
RX Type: [1] CE,[2] CE
NRC Notified By: BRIAN HAYDEN
HQ OPS Officer: BILL HUFFMAN
Notification Date: 12/12/2006
Notification Time: 11:17 [ET]
Event Date: 12/12/2006
Event Time: 09:07 [EST]
Last Update Date: 12/12/2006
Emergency Class: NON EMERGENCY
10 CFR Section:
50.72(b)(2)(iv)(B) - RPS ACTUATION - CRITICAL
Person (Organization):
RICHARD CONTE (R1)

Unit SCRAM Code RX CRIT Initial PWR Initial RX Mode Current PWR Current RX Mode
1 M/R Y 100 Power Operation 0 Hot Standby

Event Text

MANUAL REACTOR TRIP DURING TURBINE CONTROL SYSTEM MAINTENANCE

"At 0907 Calvert Cliffs Unit 1 experienced a manual reactor trip during turbine control maintenance. Maintenance was being performed on turbine control to replace circuit cards. This system is a two out of three logic system. Only one logic branch was being de-powered at a time. When the first logic branch was de-powered, the control room supervisor noticed a transient on the reactor coolant system and ordered a manual trip.

"Decay heat is being removed via normal methods through the Turbine Bypass Valves to the condenser. At the time of the trip, 11 Auxiliary Feedwater (AFW) Pump was being tested but it was not feeding the steam generators.

"This was an uncomplicated trip. The plant responded normally to the event. All control rods fully inserted. The plant is stable and operators are maintaining the unit in Hot Standby.

"The licensee notified the NRC Resident Inspector."

The trip had no effect on Unit 2, The licensee was in no significant safety system LCO action statement at the time (other than for the AFW 11 surveillance that was in progress at the time of the event.) The steam generators remained on normal feed throughout the event. No Porv's or safeties lifted during the transient. All systems functioned as required. The licensee is investigating how de-powering only one control system logic circuits resulted in the transient.

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Power Reactor Event Number: 43047
Facility: DIABLO CANYON
Region: 4 State: CA
Unit: [ ] [2] [ ]
RX Type: [1] W-4-LP,[2] W-4-LP
NRC Notified By: TONY CHITWOOD
HQ OPS Officer: PETE SNYDER
Notification Date: 12/12/2006
Notification Time: 16:59 [ET]
Event Date: 12/12/2006
Event Time: 13:22 [PST]
Last Update Date: 12/12/2006
Emergency Class: UNUSUAL EVENT
10 CFR Section:
50.72(a) (1) (i) - EMERGENCY DECLARED
50.72(b)(2)(iv)(B) - RPS ACTUATION - CRITICAL
50.72(b)(3)(iv)(A) - VALID SPECIF SYS ACTUATION
Person (Organization):
LINDA SMITH (R4)
JOHN THORPE (NRR)
PETER WILSON (IRD)
BRUCE MALLET (R4)
JIM DYER (NRR)
INZER (DHS)
DISCOE (FEMA)

Unit SCRAM Code RX CRIT Initial PWR Initial RX Mode Current PWR Current RX Mode
2 A/R Y 23 Power Operation 0 Hot Standby

Event Text

CIRCULATING WATER PUMP FAILURE CAUSES EXPLOSION IN INTAKE STRUCTURE

"On December 12, 2006, at 1322 PST, while conducting power ascension operations with Unit 2 at approximately 25 percent power, an electrical failure occurred in the Unit 2 circulating water pump motor enclosure (CWP) 2-1. A loud bang and explosion was reported to the Unit 2 control room. At 1322 PST, an electrical transient was experienced on Unit 2 12-Kv non-vital bus 'D' which in turn caused reactor coolant pump (RCP) 2-2 and RCP 2-4 motor breakers to trip on 12kV non-vital bus 'D' undervoltage, initiating an automatic reactor trip. The reactor trip signal was initiated when 2 out of 4 RCP motor breakers opened. All control rods fully inserted in response to the reactor trip and all plant systems functioned as required. The auxiliary feedwater system for Unit 2 was manually actuated per plant procedures, before an auto-start signal for this system was generated. At 1356 PST, DCPP Fire Department first responders reported that the fire was out. "

At 1340 the licensee declared a Notice of Unusual Event (NUE), number 23, 'Confirmed Explosion Onsite'.

Decay heat is being removed via auxiliary feedwater to the steam generators steaming to the atmospheric dump valves. Emergency power is being supplied via offsite power.

"The NRC resident inspector has been informed and was onsite at the time of the Unit 2 reactor trip. Diablo Canyon Power Plant [DCPP] Unit 2 is presently in Mode 3. There were no injuries associated with this event. Investigations into the electrical transient are ongoing. DCPP Unit 2 will remain in Mode 3 pending the results of this investigation. An estimated restart of DCPP Unit 2 is not known at this time. DCPP Unit 1 is unaffected and remains in Mode 1 at 100% power."

* * * UPDATE AT 1730 EST ON 12/12/06 FROM T. CHITWOOD TO P. SNYDER * * *

The licensee terminated the Unusual Event at 1430 PST. The Notice of Unusual Event was terminated due to the fact the licensee assessed the damage to the circulating water pump and determined that the explosion was caused by a breaker in the local area. The licensee fire brigade was satisfied that the fire was extinguished and that the damage was confined to the local area of circulating water pump 2-1.

The licensee notified the NRC Resident Inspector.

Notified the R4DO (Smith), NRR EO (Highland), IRD (Wilson), DHS (Inzer), and FEMA (Discoe).

* * * UPDATE AT 1841 EST ON 12/12/06 FROM T. CHITWOOD TO J. ROTTON * * *

The licensee provided an update to make the formal 4 hour notification pursuant to 10 CFR 50.72 (b)(2)(iv)(B) due to the RPS actuation while critical, and the formal 8 hour notification pursuant to 10 CFR 50.72 (b)(3)(iv)(A) due to the actuation of the auxiliary feedwater system.

The licensee notified the NRC Resident Inspector.

Notified the R4DO (Smith), and NRR EO (Highland).

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