05000254/LER-2002-002
| Quad Cities Nuclear Power Station Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2542002002R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Quad Cities Nuclear Power Station Unit 1 05000254 (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
Automatic Initiation and Loading of Emergency Diesel Generator due to Loss of Voltage to Emergency Bus as a Result of Door to Potential Fuse Drawer Falling Open A. C CONDITION PRIOR TO EVENT Unit: 1 T Event Date: November 13; 2002 ' Event Time: 0458 hours0.0053 days <br />0.127 hours <br />7.572751e-4 weeks <br />1.74269e-4 months <br /> 'Reactor Mode: 5 T Mode Name:- Refueling T Temp: 84 degrees F -Refueling (5) - Mode switch in the Shutdown or Refuel position with fuel in the reactor vessel and one or more vessel head closure bolts less than fully tensioned.
, B. C DESCRIPTION OF EVENT - On November 13, 2002, with Unit 1 in Refuel Mode (Mode 5) and no fuel moves in progress, an electrical maintenance crew was completing a support activity for the installation of a modification to the Division II Emergency Bus (Bus 14-1) [EK] [BU]. Inside the cubicle adjacent to the cubicle that the crew was working on there are two drawers mounted one over the other. The top drawer houses the Bus 14-1 potential transformer [XPT] fuses [FU]. Each drawer has a door [DR] that is hinged on the bottom. The drawers are designed such that opening the door causes the potential transformer fuses to disconnect. This causes the bus instrumentation to sense a loss of voltage at the bus and open the input breakers [BKR] to the bus, causing an actual loss of voltage.
The activity in progress involved the removal of a flange between the two cubicles.
At 0458 hours0.0053 days <br />0.127 hours <br />7.572751e-4 weeks <br />1.74269e-4 months <br />, while the second of six rivets holding the flanges in place was being removed, the door to the upper potential transformer fuse drawer fell open. As a result of the door opening, the breakers providing power to the bus tripped open and the Unit 1 Emergency Diesel Generator (EDG) [DG] started automatically and loaded to the bus. Indications of a loss of power to Bus 14-1 and an automatic start and load of the Unit 1 EDG were received in the control room.
The electricians conducting the work notified the control room. Operations personnel were sent to the bus and closed the door to the potential transformer fuse drawer. The locking mechanism appeared to operate properly when the door was shut.
The door for the potential transformer fuse drawer in Bus 14-1 is similar to drawers in the emergency buses and the buses that supply the emergency buses for both divisions on both units. There are also similar drawers for each of the EDGs. Door construction and operation in each of these drawers is identical.
DOCKET NUMBER (2) PAGE (3) FACILITY NAME (1) LER NUMBER (6 � (If more space is required, use additional copies of NRC Form 366A)(17) The doors to the potential transformer fuse drawers for the Unit 1, Division I and II, EDGs, emergency buses, and the buses that supply power to the emergency buses were verified to be closed and latched. This was accomplished by pushing on each of the doors to free the latch and allow it to engage fully. During verification that the door to the Unit 1 Bus 14 drawer was latched, the door latch clicked shut, indicating that it had previously been not fully latched but was now fully latched. Bus 14 provides power to Bus 14-1.
All such doors on Unit 2 were verified by radiography to be fully latched.
C. CAUSE OF EVENT
The root cause of the event was that Operations department personnel were not aware of the vulnerability associated with the door locking mechanism that existed in the design of the potential fuse compartment door. Operations department personnel were not aware that the door could be closed with the handle in the closed position, but the latch be in a less than fully latched condition. This resulted in the failure of the latching mechanism to adequately engage the door frame to lock the potential fuse compartment door shut. When,properly latched,, the door will not fall open.
D. SAFETY ANALYSIS
The safety significance of having the doors to two potential transformer fuse drawers not fully latched was minimal. Although the two- doors that were not fully latched (one on Bus 14-1 and one on Bus 14, which is the bus that supplies offsite power to Bus 14-1) were capable of falling open during a seismic event, it was determined that they would not have been damaged during the seismic event such that they could not have been reclosed. It was also determined that the doors remaining open during the seismic event would not have caused other relay actuations to occur.
The effect of the doors falling open would be to render the Division II emergency bus incapable of carrying emergency loads until the door was reclosed. Although the EDG would have started and loaded to the bus, the equipment that was shed as a result of the loss of voltage to the bus would not reclose to the bus until the undervoltage trip signal was cleared. This would require the door to be reclosed.
Therefore, the Division II Residual Heat Removal (RHR) [BO] and Core Spray [BM] pumps would not have had power after a seismic event.
This affected only Unit 1 Division II. The Division I equipment was not affected by this issue.
E. CORRECTIVE ACTIONS
Immediate Actions:
The door to the Bus 14-1 drawer was closed and latched.
DOCKET NUMBER (2) LER NUMBER (6 FACILITY NAME (1) PAGE (3) Quad Cities Nuclear Power Station Unit 1 05000254 � (If more space is required, use additional copies of NRC Form 366A)(17) Corrective Actions Completed:
The doors to the potential transformer fuse drawers for the Unit 1, Division I and II, EDGs, emergency buses, and the buses that supply power to the emergency buses were verified to be closed and latched. This was accomplished by pushing on each of the doors to free the latch and allow it to engage fully. During verification that the door to the Unit 1 Bus 14 drawer was latched, the door latch clicked shut, indicating that it had previously not been fully latched but was now fully latched.
All such doors on Unit 2 were verified by radiography to be fully latched.
Corrective Actions to be Completed:
The results of the investigation regarding the operation of the potential fuse compartment door locking mechanism will be reviewed with the operating crews.
Training regarding the vulnerability associated with the potential fuse compartment door locking mechanism will be incorporated into the Operations recurring training program.
A checklist that provides a method to positively check the condition of the potential fuse compartment door when it is shut will be incorporated into the appropriate Operations procedures.
A placard will be attached to the affected potential fuse compartment doors that warns of the failure of the handle to provide positive indication that the door is properly latched and that includes instructions that direct the manner in which the door should be operated.
F. PREVIOUS OCCURRENCES
No previous events at Quad Cities Nuclear Power Station were identified that were similar to the event described above.
G. COMPONENT FAILURE DATA
The potential transformer fuse drawers with this type of latching mechanism are in General Electric Magne Blast AMH switchgear.