05000483/LER-2004-002, Regarding Reactor Trip Due to Faulty Electrical Relay
| ML040850559 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 03/18/2004 |
| From: | Witt W AmerenUE |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ULNRC04964 LER 04-002-00 | |
| Download: ML040850559 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4832004002R00 - NRC Website | |
text
AmerenUE Callaway Plant PO Box 620 Fulton, MO 65251 March 18, 2004 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop P1-137 Washington, DC 20555-0001 ULNRC04964 WAmeren UE Ladies and Gentlemen:
DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT I UNION ELECTRIC CO.
FACILITY OPERATING LICENSE NPF-30 LICENSEE EVENT REPORT 2004-002-00 Reactor trip due to faulty, electrical relay.
The enclosed licensee event report is submitted in accordance with 1 OCFR50.73(a)(2)(iv)(A) to report a reactor trip that occurred as a result of a faulty electrical relay located in the main electrical generator protection circuitry.
Sincerely, Warren A. Witt Manager, Callaway Plant WAW/EWH/slk Enclosure a subsidiay of Amereir Corporation
ULNRC04964 March 18, 2004 Page 2 Mr. Bruce S. Mallett Regional Administrator U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 760114005 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Jack N. Donohew (2 copies)
Licensing Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 7E1 Washington, DC 20555-2738 Missouri Public Service Commission Governor Office Building 200 Madison Street PO Box 360 Jefferson City, MO 65102-0360 Records Center Institute of Nuclear Power Operations 700 Galleria Parkway Atlanta, GA 30339
Abstract
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 50 percent. The cause of the generator trip was a failed electrical relay.
This relay was designed to sense remote faults in order to prevent exceeding thermal limits for the stator windings. Plant systems responded as designed, including automatic actuation of the auxiliary feedwater system.
The faulted relay was repaired, calibrated, and reinstalled. This relay contained a second set of unused contacts which were used instead of the initial faulted contacts. 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.
NRC FORM 366 (7-2001)
(If more space is required, use additional copies of 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 321 G relay contact. The 321 G relay (Manufacturer:
Westinghouse Elec. Corp.-Nuclear Energy Services, Model KD-1 1) 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 321 G relay contact. The 321 G is a distance relay which is connected to main generator current and voltage circuits.
(If more space is required, use additional copies of NRC Form 366A) (17)
II.
EVENT DRIVEN INFORMATION A. SAFETY SYSTEMS THAT RESPONDED All safety systems responded as expected. When the reactor trip occurred, "B" Containment Spray pump, PEN01 B, was out of service due to planned maintenance. The unavailability of PEN01 B 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 1 E-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