Event Notification Report for November 27, 2005
U.S. Nuclear Regulatory Commission
Operations Center
EVENT REPORTS FOR
11/26/2005 - 11/27/2005
EVENT NUMBERS
42171
!!!!! THIS EVENT HAS BEEN RETRACTED !!!!!
!!!!! THIS EVENT HAS BEEN RETRACTED !!!!!
Power Reactor
Event Number: 42171
Facility: OCONEE
Region: 2 State: SC
Unit: [] [2] []
RX Type: [1] B&W-L-LP,[2] B&W-L-LP,[3] B&W-L-LP
NRC Notified By: NOEL CLARKSON
HQ OPS Officer: BILL GOTT
Region: 2 State: SC
Unit: [] [2] []
RX Type: [1] B&W-L-LP,[2] B&W-L-LP,[3] B&W-L-LP
NRC Notified By: NOEL CLARKSON
HQ OPS Officer: BILL GOTT
Notification Date: 11/27/2005
Notification Time: 11:11 [ET]
Event Date: 11/27/2005
Event Time: 05:30 [EST]
Last Update Date: 01/26/2006
Notification Time: 11:11 [ET]
Event Date: 11/27/2005
Event Time: 05:30 [EST]
Last Update Date: 01/26/2006
Emergency Class: NON EMERGENCY
10 CFR Section:
50.72(b)(3)(v)(B) - POT RHR INOP
10 CFR Section:
50.72(b)(3)(v)(B) - POT RHR INOP
Person (Organization):
KERRY LANDIS (R2)
KERRY LANDIS (R2)
| Unit | SCRAM Code | RX Crit | Initial PWR | Initial RX Mode | Current PWR | Current RX Mode |
|---|---|---|---|---|---|---|
| 2 | N | N | 0 | Hot Standby | 0 | Hot Standby |
LOSS AND RESTORATION OF BACK-UP INSTRUMENT AIR TO FEEDWATER CONTROL VALVES
"Event:
"At 0530 hours on 11/27/2005, while in Mode 3 following a Unit 2 refueling outage, it was discovered that the nitrogen backup supply to 2FDW-315 and 2FDW-316 was valved out. 2FDW-315 and 2FDW-316 are the emergency feedwater (EFW) control valves which function to regulate steam generator level on a loss of main feedwater event. Motive force to these valves is normally supplied by instrument air and nitrogen provides backup to instrument air in the event that instrument air becomes unavailable. At 0530 hours on 11/27/2005, both EFW flow paths were declared inoperable and Technical Specification 3.7.5, Conditions B and E were entered. Condition E of TS 3.7.5 specifically deals with the inoperability of two EFW flow paths. The Required Action is to initiate actions to restore one EFW flow path to operable status, immediately.
"Initial Safety Significance:
"2FDW-315 and 2FDW-316 are the control valves for the Unit 2 'A' and 'B' steam generators, respectively. These valves must be able to function in order to control steam generator level during an event where main feedwater is lost. The motive force for these valves is normally instrument air. However, in the unlikely event where main feedwater is lost, and instrument air is unavailable, these valves rely on a nitrogen backup to supply their motive force. The events where this nitrogen backup is credited are a station blackout (SBO) and a loss of instrument air. While nitrogen backup to 2FDW-315 and 2FDW-316 was unavailable between 0530 hours and 0710 hours on 11/27/2005, it is reasonable to assume that the ability to remove decay heat would have been available. In the case of a loss of instrument air, 2FDW-315 and 2FDW-316 fail open, with the motor driven EFW pumps providing EFW supply to both steam generators. In this case, the Emergency Operating Procedure (EOP) provides guidance to realign EFW through the electric powered startup control valves. Should this realignment attempt fail, the EOP provides further guidance to control EFW flow by manually throttling closed on 2FDW-315 and 2FDW-316. In the event of an SBO, power to the instrument air compressors would be lost, resulting in a loss of instrument air header pressure. The motor driven EFW pumps would be unavailable, however, the turbine driven EFW pump would automatically start and provide EFW flow. As with the loss of instrument air event, 2FDW-315 and 2FDW316 would fail open. The EOP provides guidance to dispatch operators to manually throttle closed on these valves to control flow to the steam generators. Additionally, while not credited for this event, Oconee has diesel driven air compressors which auto start on low instrument air pressure and supply the instrument air header. Also, in the event of a SBO, the Standby Shutdown Facility (SSF) is manned within 10 minutes of event initiation. The SSF is a SBO coping facility with a dedicated diesel generator and the pumps and valves necessary to supply and control steam generator feed in the event of an SBO.
"Corrective Action(s):
"At 0702 hours on 11/27/2005, nitrogen was realigned to 2FDW-316 and TS 3.7.5, Condition E was exited. At 0710 hours on 11/27/2005, nitrogen was realigned to 2FDW-315 and TS 3.7.5 Condition B was exited."
The licensee is investigating the cause of the valve line up problem. The licensee notified the NRC Resident Inspector.
* * * RETRACTION OF EVENT RECEIVED BY JOE O'HARA FROM TRACY ROLAND AT 1333 0N 1/26/06 * * *
"After detailed review of this event, it was concluded that Technical Specification 3.7.5 limiting conditions for operation were met at all times during this event. Control valves 2FDW-315 and 2FDW-316 fail open on loss of air/nitrogen by the spring return design of the actuators. Therefore, the required flow path would not have been lost due to the failure of normal air supply and the isolation of nitrogen supplies to the actuators. It has been further concluded that all throttling functions of these control valves could have been performed manually by use of a local handwheel on each valve actuator. Appropriate procedure guidance exists to operate the system with these valves failed open until the operators can access the local handwheel and take local control. Therefore, the valves and the associated flow paths were operable during this event. As a result of this determination, no reportability criteria under 50.72 and 50.73 apply to this event and the associated event report is hereby retracted."
The licensee notified the NRC Resident Inspector. R2DO(Payne) was notified.
"Event:
"At 0530 hours on 11/27/2005, while in Mode 3 following a Unit 2 refueling outage, it was discovered that the nitrogen backup supply to 2FDW-315 and 2FDW-316 was valved out. 2FDW-315 and 2FDW-316 are the emergency feedwater (EFW) control valves which function to regulate steam generator level on a loss of main feedwater event. Motive force to these valves is normally supplied by instrument air and nitrogen provides backup to instrument air in the event that instrument air becomes unavailable. At 0530 hours on 11/27/2005, both EFW flow paths were declared inoperable and Technical Specification 3.7.5, Conditions B and E were entered. Condition E of TS 3.7.5 specifically deals with the inoperability of two EFW flow paths. The Required Action is to initiate actions to restore one EFW flow path to operable status, immediately.
"Initial Safety Significance:
"2FDW-315 and 2FDW-316 are the control valves for the Unit 2 'A' and 'B' steam generators, respectively. These valves must be able to function in order to control steam generator level during an event where main feedwater is lost. The motive force for these valves is normally instrument air. However, in the unlikely event where main feedwater is lost, and instrument air is unavailable, these valves rely on a nitrogen backup to supply their motive force. The events where this nitrogen backup is credited are a station blackout (SBO) and a loss of instrument air. While nitrogen backup to 2FDW-315 and 2FDW-316 was unavailable between 0530 hours and 0710 hours on 11/27/2005, it is reasonable to assume that the ability to remove decay heat would have been available. In the case of a loss of instrument air, 2FDW-315 and 2FDW-316 fail open, with the motor driven EFW pumps providing EFW supply to both steam generators. In this case, the Emergency Operating Procedure (EOP) provides guidance to realign EFW through the electric powered startup control valves. Should this realignment attempt fail, the EOP provides further guidance to control EFW flow by manually throttling closed on 2FDW-315 and 2FDW-316. In the event of an SBO, power to the instrument air compressors would be lost, resulting in a loss of instrument air header pressure. The motor driven EFW pumps would be unavailable, however, the turbine driven EFW pump would automatically start and provide EFW flow. As with the loss of instrument air event, 2FDW-315 and 2FDW316 would fail open. The EOP provides guidance to dispatch operators to manually throttle closed on these valves to control flow to the steam generators. Additionally, while not credited for this event, Oconee has diesel driven air compressors which auto start on low instrument air pressure and supply the instrument air header. Also, in the event of a SBO, the Standby Shutdown Facility (SSF) is manned within 10 minutes of event initiation. The SSF is a SBO coping facility with a dedicated diesel generator and the pumps and valves necessary to supply and control steam generator feed in the event of an SBO.
"Corrective Action(s):
"At 0702 hours on 11/27/2005, nitrogen was realigned to 2FDW-316 and TS 3.7.5, Condition E was exited. At 0710 hours on 11/27/2005, nitrogen was realigned to 2FDW-315 and TS 3.7.5 Condition B was exited."
The licensee is investigating the cause of the valve line up problem. The licensee notified the NRC Resident Inspector.
* * * RETRACTION OF EVENT RECEIVED BY JOE O'HARA FROM TRACY ROLAND AT 1333 0N 1/26/06 * * *
"After detailed review of this event, it was concluded that Technical Specification 3.7.5 limiting conditions for operation were met at all times during this event. Control valves 2FDW-315 and 2FDW-316 fail open on loss of air/nitrogen by the spring return design of the actuators. Therefore, the required flow path would not have been lost due to the failure of normal air supply and the isolation of nitrogen supplies to the actuators. It has been further concluded that all throttling functions of these control valves could have been performed manually by use of a local handwheel on each valve actuator. Appropriate procedure guidance exists to operate the system with these valves failed open until the operators can access the local handwheel and take local control. Therefore, the valves and the associated flow paths were operable during this event. As a result of this determination, no reportability criteria under 50.72 and 50.73 apply to this event and the associated event report is hereby retracted."
The licensee notified the NRC Resident Inspector. R2DO(Payne) was notified.