05000483/LER-2003-009, Regarding Failure of Electrical Inverter Resulted in Technical Specification Required Plant Shutdown
| ML033630592 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 12/19/2003 |
| From: | Witt W AmerenUE |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ULNRC-04930 LER 03-009-00 | |
| Download: ML033630592 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| 4832003009R00 - NRC Website | |
text
AmerenUE PO Box 620 Callaway Plant Fulton, MO 65251 December 19, 2003 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop P1-137 Washington, DC 20555-0001 wagerer
~~~~~~~~~~~ULNRC-04930 UF Ladies & Gentlemen:
DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC CO.
FACILITY OPERATING LICENSE NPF-30 LICENSEE EVENT REPORT 2003-009-00 Failure of electrical inverter results in Technical Specification required plant shutdown.
The enclosed licensee event report is submitted in accordance with 10CFR50.73(a)(2)(i)(A), to report a plant shutdown required by Technical Specifications. Repairs to electrical inverter NN1 1 were not completed within the time allowed by Technical Specifications and a plant shutdown was performed while repairs to NN 11 were completed. After repairs were completed, a plant startup was conducted and normal plant operation resumed.
Warren A. Witt Manager, Callaway Plant WAW/ewh Enclosure a subsidiary ofAmarenn Coporation
ULNRC04930 December 19, 2003 Page 2 cc:
Mr. Bruce S. Mallet Regional Administrator U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-4005 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 Manager, Electric Department Missouri Public Service Commission PO Box 360 Jefferson City, MO 65102 Records Center Institute of Nuclear Power Operations 700 Galleria Parkway Atlanta, GA 30339
I
Abstract
At 0721, 10/20/03, with Callaway Plant at 100 percent power, inverter NN1 1 failed causing a momentary loss of electrical power to safety related AC bus NN01.The Control Room staff used approved plant procedures to recover from the event and stabilize plant conditions. Subsequent repair investigations extended past the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Technical Specification (T/S)
Action time limit and a TIS required plant shutdown was performed. It was determined that the NN1 I failure was due to a faulted static transfer switch circuit board. Repairs were completed and NNI 1 was declared Operable at 2202, 10/21/03. A plant startup was performed on 10/24/03 and normal plant operations resumed.
NRC FORM 366j (I-Z01)
(if more space is required, use additional copies of SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES At 0721, 10/20/03, while Callaway was operating at 100 percent power, electrical inverter NNII1 [Model SV12075 manufactured by Solidstate Controls, Inc.) failed causing a momentary loss of voltage on safety-related 120 VAC bus NNO1. Normally, the transfer between power supplies is "bumpless" where there is no interruption of power to the downstream loads and is accomplished using a static transfer switch. In this event, a zener diode failed in the static transfer switch circuit and prevented a bumpless transfer from occurring.
When the static transfer switch circuit failed, a momentary loss of power lasting approximately four seconds occurred. As a result of the momentary power loss, the following plant perturbations were experienced:
BNLCV01 12D,the Refueling Water Storage Tank (RWST) suction supply valve to 'A" Centrifugal Charging Pump (CCP), opened, "A" and "B" Reactor Coolant Pump (RCP) Thermal Barrier Heat Exchanger component cooling water isolation valves BBHV0013 and BBHV0014 isolated, EFHV0043, "A" Essential Service Water to Service Air Compressor "A", closed, and when NNO1 re-energized:
ABPIC0001A, "A" Steam Generator Atmospheric Steam Dump (S/G ASD) controller, returned to service in the MANUAL control mode with a 50 percent OPEN signal, Pressurizer master Pressure Controller BBPK0455A, did not respond to increasing Reactor Coolant System (RCS) pressure.
When the CCP suction swapped to the RWST, the Control Room staff isolated normal letdown and maintained charging through the RCP seals. In response to BBPK0455A not operating as expected, a Reactor Operator took manual control of BBPK0455A, restored Pressurizer pressure to its normal band, returned BBPK0455A to automatic, and then verified that it operated correctly. After the initial response, the Control Room staff used plant off-normal procedure OTO-NN-0001 to respond to the event and complete required immediate actions. The plant was stabilized and power remained at 100 percent.
T/S 3.8.7 Action A, for Inverters - Operating, was entered at 0721, 10/20/03. This allowed 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to restore the faulted inverter to Operable or enter Action B which required entering Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 5 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Troubleshooting efforts had not identified the failure mechanism by the end of (If more space is required, use additional copes of NRC Fonn 366A) (17) the 24-hour Action A time limit. In anticipation of non-compliance with T/S Action A, a controlled plant shutdown was commenced at 0100, 10/21/03 and ENS Event Notification 40263 was made at 0420 (Central Time), 10/21/03.
Investigation of the NN11 failure mechanism ultimately identified the failure to be the result of a failed zener diode in the static transfer switch circuitry. Replacement of the static transfer switch electronic circuit board corrected the fault and NN11 was declared Operable at 2202, 10/21/03. A reactor startup was performed on 10/24/03 and normal power operation resumed.
During the troubleshooting process to determine the failure mechanism of NN1 1, additional investigations were conducted to determine if the observed plant perturbations were to be expected for a momentary loss of power. It was determined that all alarms and automatic actions were expected results for a loss of power to NN01, except for the automatic closure of BBHV0013 and BBHV0014. A definitive cause for closure could not be established, however, research concluded the most probable cause for their operation was due to a momentary spike in the power supply for the valve flow control circuitry when power was restored to NNO1.
E. METHOD OF DISCOVERY OF EACH COMPONENT, SYSTEM FAILURE, OR PROCEDURAL ERROR The discovery of the failure of NN1 1 was identified through simultaneous alarm annunciators and plant responses. The failure mechanism was identified through subsequent troubleshooting efforts.
II.
EVENT DRIVEN INFORMATION A. SAFETY SYSTEMS THAT RESPONDED No safety systems were actuated as a result of this event.
B. DURATION OF SAFETY SYSTEM INOPERABILITY
Inverter NN11 was inoperable for 38 hours4.398148e-4 days <br />0.0106 hours <br />6.283069e-5 weeks <br />1.4459e-5 months <br />, 41 minutes.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT.
This event did not result in a significant challenge to nuclear safety or a significant risk to the health and safety of the public. With the exception of the events immediately surrounding the momentary loss of power and the restoration of power, the components powered by NN01 remained functional. Additionally, the redundant train remained operable throughout this event.
No unanticipated alarms or automatic actions were caused by this event. An approved procedure providing specific guidance for a loss of power to NNO1 was available and was implemented. Plant operations were conducted in compliance with Technical Specification requirements.
Therefore, this event did not result in a significant challenge to nuclear safety.
Ill. CAUSE OF THE EVENT The cause of the event was the failure of the static transfer switch in NN1 1. An extensive review of internal and external Operating Experience (OE) concluded that this particular failure was an uncommon, random failure and not documented as occurring previously.
(If more space is required, use additional copies of NRC Form 366A) (17)
IV.
CORRECTIVE ACTIONS
Corrective actions were to replace the faulted static transfer switch circuit board.
Callaway Action Request (CAR) 200307636 was written to document this event. Procedure OTO-NN-0001 will be reviewed for potential revision to include actions identified by this event.
V.
PREVIOUS SIMILAR EVENTS
CAR 200307636 documents a historical review of past CARs in an effort to identify similar past occurrences. No past CARs were identified that were applicable to the static transfer switch failure.
A review of past LERs from 2000 to present was performed and no similar LERs were identified.
VI.
ADDITIONAL INFORMATION
The system and component codes listed below are from the IEEE Standard 805-1984 and IEEE Standard 803A-1984 respectively.
System:
EF Component:
INVT