05000348/LER-2008-004
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 11-19-2008 |
|---|---|
| Report date: | 01-07-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3482008004R00 - NRC Website | |
Westinghouse -- Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX]
Description of Event
On November 19, 2008 at approximately 04:25, Farley Unit 1 was operating at 100 % power. Due to a gradual drop in 4160 v safety related bus voltage over the last several hours from grid conditions, Farley contacted Alabama Power - Alabama Control Center (ACC) to discuss removing the shunt reactor from service in the Farley High Voltage Switch Yard (HVSY) to raise the 230 kv grid voltage. After receiving the request, the ACC operator used an air-break disconnect switch to isolate the shunt reactor, instead of using the breakers normally used for this purpose. Opening the disconnect switch which is not designed to break load, caused a significant electrical arc and phase to phase fault. The transmission protection system tripped the appropriate devices and cleared the fault in approximately 3 cycles. However, the instantaneous HVSY voltage drop resulted in loss of breaker position indication for the 1B Reactor Coolant Pump (RCP) [AB] which initiated an automatic Solid State Protection System (SSPS) [JC] reactor trip. Flow to the reactor core was never lost. The reactor tripped without complications and all safety systems performed normally.
Unit 1 returned to power operation on November 20, 2008 at 10:33.
Cause of Event
The event was caused when the air-break disconnect switch was opened while still under load.
The ACC operator utilized a control display that was inadequate to perform the requested operation. The man-machine interface, together with the ACC operator's experience and training were insufficient to prevent the inappropriate action by the operator.
The RCP Breaker Position Reactor Trip relays are powered from one of two field supplied sources.
One power source is the safety related inverters which are powered by the Class lE Auxiliary Building Batteries, Battery Chargers or AC constant voltage source transformer. The second power source is from a separate AC constant voltage source transformer. Each AC constant voltage source transformer is powered from a Class lE AC bus. Alignment to either power source is acceptable per plant design and procedures. At the time of the trip, the RCP Breaker Position Reactor Trip relays were aligned to the AC constant voltage source transformers rather than the safety related inverters.
Review of the event indicates that the reactor trip would not have occurred from the close-in transmission fault, had the RCP Breaker Position relay power supply been aligned to the inverters instead of the AC constant voltage source transformers.
Safety Assessment This event had no adverse effect on the safety and health of the public. Reactor Coolant flow though the reactor core was never lost. All safety systems functioned per design and the unit was placed in hot standby.
Corrective Action The switching control screens for ACC have been updated to alert the ACC operator of the requirement to isolate the shunt reactor prior to operating the air-break disconnect and the requirement to use switching orders for operations at the Farley HVSY. Farley Operations shift personnel and ACC personnel have been briefed of the event.
The RCP Breaker Position Reactor Trip relay power supplies have been aligned to the inverters for all RCPs on both Unit 1 and Unit 2.
Operation Experience (OE) on the event has been issued both internally to all Southern Nuclear sites and externally to the nuclear industry.
Additional Information
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