05000254/LER-2005-002
| Quad Cities Nuclear Power Station, Unit 1 | |
| Event date: | 03-27-2005 |
|---|---|
| Report date: | 12-08-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| Initial Reporting | |
| 2542005002R01 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Quad Cities Nuclear Power Station Unit 1 05000254 NUMBER NUMBER 2005 (If more space is required, use additional copies of NRC Form 366A)(17)
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor, 2957 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
EVENT IDENTIFICATION
Trip of Unit 1 Division I 4kV Emergency Bus Feed to 480 VAC Emergency Buses in Both Divisions Due to Ineffective Previous Corrective Actions.
A. CONDITION PRIOR TO EVENT
� � Unit: 1 Event Date: March 27, 2005 Event Time: 1930 hours0.0223 days <br />0.536 hours <br />0.00319 weeks <br />7.34365e-4 months <br /> � Reactor Mode: 5 Mode Name: Refueling Power Level: 000% Unit: 2 EventDate: March 27, 2005 Event Time: 1930 hours0.0223 days <br />0.536 hours <br />0.00319 weeks <br />7.34365e-4 months <br /> �Reactor Mode: 1 , Mode Name:-Power Operation Power Level: 085% Power Operation (1)- Mode switch in'the RUN position with average reactor coolant temperature at any temperature.
Refueling (5) - Mode switch in the Shutdown or Refuel position with average reactor coolant temperature at any temperature and fuel in the reactor vessel with one or more vessel head closure bolts less than fully tensioned or with the head removed.
B. DESCRIPTION OF EVENT
Division I 4kV Emergency Bus [BU] [EA] (Bus 13-1) and.Division I 480 VAC Emergency Bus [ES] (Bus 18) tripped.
At the time of the breaker trip, Unit 1 was in the Refueling Mode and fuel moves were in progress, although there were no fuel bundles suspended from the refuel bridge. Bus 18 was feeding Bus 19 (Division II 480 VAC Emergency Bus) due to work on Bus 14-1 (Division II 4KV Emergency Bus that normally feeds Bus 19) that was in the process of being completed. The Unit 1 Emergency Diesel Generator [EK] was inoperable for planned maintenance. Both trains of Reactor Recirculation [AD] were off and Alternate Decay Heat Removal (ADHR) was being satisfied by Fuel Pool Cooling [DA] and the Reactor Building Closed Cooling Water system (RBCCW) [CC]. No operations with the potential to drain the reactor were in progress.
As a result of the trip of the main feed breaker from Bus 13-1 to Bus 18, power was lost to both Bus 18 and Bus 19. This caused isolation of Reactor Building Vents [VA], initiation of 1/2A Standby Gas Treatment, loss of power to two of the fuel pool cooling pumps and the RBCCW pumps, loss of power to the lA Core Spray injection valve, loss of the 1A 125VDC battery charger [EJ], loss of the Instrument FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Quad Cities Nuclear Power Station Unit 1 05000254 NUMBER NUMBER 2005 0 (If more space is required, use additional copies of NRC Form 366A)(17) Bus [EF] and Essential Service Bus, loss of power to the Control Room Emergency Ventilation (CREV) system (which applies to both units) and a Reactor Protection System (RPS) [JC] trip with no control rod movement.
In response to the breaker trip, fuel moves were halted. At 2001 hours0.0232 days <br />0.556 hours <br />0.00331 weeks <br />7.613805e-4 months <br />, Bus 19 was reenergized from Bus 14-1, after the return to service was expedited following completion of the work on Bus 14-1. The 1B RBCCW pump and 1B Fuel Pool Cooling Water pump were restarted from Bus 19. Following reestablishment at 2012 hours0.0233 days <br />0.559 hours <br />0.00333 weeks <br />7.65566e-4 months <br /> of the cross-tie between Bus 18 and Bus 19, but with Bus 19 feeding Bus 18 this time, power was restored to the Instrument Bus, the Essential Service Bus, the lA Core Spray injection valve and the lA 125 VDC battery charger, and the 1A RBCCW pump was restarted. At 2015 hours0.0233 days <br />0.56 hours <br />0.00333 weeks <br />7.667075e-4 months <br />, the 1A Fuel Pool Cooling Water pump was restarted, fully restoring ADHR. At 2342 hours0.0271 days <br />0.651 hours <br />0.00387 weeks <br />8.91131e-4 months <br />, the CREV system was declared operable. At 2357 hours0.0273 days <br />0.655 hours <br />0.0039 weeks <br />8.968385e-4 months <br />, Unit 1 fuel moves recommenced.
At 0012 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> on March 28,_2005, the NRC was notified of the event through the Emergency Notification System in accordande with 10CFR50.72(b)(3)(v), "event or condition that could have prevented fulfillment of a safety function.
C. CAUSE OF EVENT
It was determined, following extensive testing on the Bus 18 feed breaker, that the breaker trip was due to long-time over-current rather than equipment malfunction or personnel error. The long-time over-current condition was due to high base loads involving operating all of the drywell coolers, coupled with cyclic loads, while the buses were cross-tied. While this lineup was not procedurally prohibited, it is not typical that this would occur during a refueling outage at Quad Cities Nuclear Power Station.
The root cause of the trip of the feed breaker from Bus 13-1 to Bus 18 was ineffective corrective action for two prior events. On February 11, 1984, (LER 265/83-003) and November 1, 1987, (LER 265/87-014), similar events occurred involving unexpected loss of the 480 VAC busses due to the addition of large loads while they were cross-tied. Although precautions concerning the potential for unexpected breaker trips were added to the cross-tie procedure in response to both of the previous events, they were ineffective in controlling loading on the busses while they were cross-tied. There were no opportunities to identify the ineffective procedure between 1987 and this event because the drywell coolers were not operated with the 480 VAC Emergency Buses cross-tied.
D. SAFETY ANALYSIS
The safety significance of this event was minimal. As a result of this event, two of the four operating fuel pool cooling pumps were de-energized. An analytical simulation of the fuel pool temperature demonstrated that the two operating pumps had the capacity to maintain and decrease fuel pool temperature below 170 degrees F. Therefore, although the ADHR was degraded, it retained the capability to cool the fuel pool.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) (If more space is required, use additional copies of NRC Form 366A)(17) Also, the safety significance of the loss of power to the 1/2A Core Spray injection valve was minimal. The system was conservatively declared unavailable, but the reactor cavity was flooded and the injection valve could have been manually opened if needed for reactor inventory.
This event is being reported as a condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat (i.e., ADHR degradation) and mitigate the consequences of an accident (i.e., loss of power to CREV, which applies to both units).
E. CORRECTIVE ACTIONS
Corrective Actions Completed:
- A temporary procedure change was implemented during the refuel outage to add additional more restrictive operational precautions concerning the cross-tying of Buses 18 and 19.
Corrective Actions to be Completed:
The procedure for cross-tying the 480 VAC Emei-gency Buses will be revised to add additional precautions to administratively- limit the loads on the cross-connected 480 VAC buses, and to provide a specific procedural reference concerning the appropriate method to provide increased monitoring.
F. PREVIOUS OCCURRENCES
On February 11, 1984, (LER 265/83-003) and November 1, 1987, (LER 265/87-014), similar previous events occurred involving unexpected loss of the 480 VAC busses due to the addition of large loads while they were cross-tied. The corrective actions for these events were insufficient to preclude this event.
G. COMPONENT FAILURE DATA- There were no component failures associated with this event.