05000483/LER-2004-002
| Callaway Plant Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4832004002R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
This event is being reported per 10CFR50.73(a)2)(iv)(A), system actuation. Both the Reactor Protection System (RPS) and PWR auxiliary feedwater systems were actuated during this event.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
Callaway Plant was in Mode 1 at 100 percent power.
C. STATUS OF STRUCTURES, SYSTEMS OR COMPONENTS THAT WERE INOPERABLE AT THE
START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT
"B" Containment Spray pump, PENO1B, was inoperable due to planned maintenance when the reactor trip occurred. The unavailability of PENO1B did not contribute to this event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES
At 1830, 1/27/04, while at 100 percent power, Callaway Plant experienced a main electrical generator trip which in turn caused a reactor trip due to power being above the P-9 setpoint of 50 percent power. Plant systems actuated per design. Plant operators responded to the reactor trip using plant procedures and stabilized the unit in Mode 3 at normal operating temperature and pressure.
The cause of the generator trip was a failed 321G relay contact. The 321G relay (Manufacturer:
Westinghouse Elec. Corp.—Nuclear Energy Services, Model KD-11) is a distance relay which is connected to main generator current and voltage circuits. This relay was designed to sense remote faults in order to prevent exceeding thermal limits for the stator windings. A defective relay contact shorted, and resulted in actuation of the main generator lockout relays and tripping of the main generator output breakers, MDV53 and MDV55. The actuation of the main generator lockout relays generated the main turbine trip, and resulted in a reactor trip. The faulted relay was repaired using a second set of unused contacts, calibrated, and reinstalled. This relay configuration was successfully retested and plant operation resumed without further problems.
A review of relevant operating experience did not identify similar failures, and a review of past plant preventative maintenance did not reveal abnormalities. Preventive maintenance procedures will be revised to provide additional detailed instructions for inspection of these relay contacts for this failure mechanism.
E. METHOD OF DISCOVERY OF EACH COMPONENT, SYSTEM FAILURE, OR PROCEDURAL
ERROR
Troubleshooting performed using planned work documents determined that the cause of the plant trip was a failed 321G relay contact. The 321G is a distance relay which is connected to main generator current and voltage circuits.
3 II. � EVENT DRIVEN INFORMATION
A. SAFETY SYSTEMS THAT RESPONDED
All safety systems responded as expected. When the reactor trip occurred, "B" Containment Spray pump, PENO1B, was out of service due to planned maintenance. The unavailability of PENO1B had no impact on this event.
B. DURATION OF SAFETY SYSTEM INOPERABILITY
Not applicable to this event.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT.
- Based on the Conditional Core Damage Probability (CCDP) for this event being less than 1E-6, this event is of very low risk significance.
III. � CAUSE OF THE EVENT Troubleshooting performed using planned work documents determined that the cause of the plant trip was a failed 321G relay contact. The 321G is a distance relay which is connected to main generator current and voltage circuits. This relay was designed to sense remote faults in order to prevent exceeding thermal limits for the stator windings. A defective relay contact shorted, and resulted in actuation of the main generator lockout relays and tripping of the main generator output breakers, MDV53 and MDV55. The actuation of the main generator lockout relays generated the main turbine trip, and resulted in a reactor trip.
IV. � CORRECTIVE ACTIONS Preventive maintenance procedures will be revised to provide additional detailed instructions for inspection of these relay contacts for this failure mechanism.
V. � PREVIOUS SIMILAR EVENTS A review was conducted of the Callaway Action Request System (CARS) and no additional failures of this relay were discovered. This event is described in Callaway Action Request (CAR) 200400629.
A review of Callaway LERs from 2000 until present did not reveal any similar events.
VI. � ADDITIONAL INFORMATION The system and component codes listed below are from the IEEE Standard 805-1984 and IEEE Standard 803A-1984 respectively.
System:
�
TB
Component: � 21