05000498/LER-2003-005, Regarding Auxiliary Feedwater Pump 11 Breaker Failure to Close
| ML033110602 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 11/03/2003 |
| From: | Halpin E South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NOC-AE-03001625, STI: 31665708 LER 03-005-00 | |
| Download: ML033110602 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| 4982003005R00 - NRC Website | |
text
Nuclear Operating Company Go AN South ThsIftiyctElctd E ric GenratinS Station
. 8 282 Ptidsonvh. Txas 77483 A
November 3, 2003 NOC-AE-03001625 1 OCFR50.73 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852 South Texas Project Unit 1 Docket No. STN 50-498 Licensee Event Report 1-03-005 Auxiliary Feedwater Pump 11 Breaker Failure to Close Pursuant to 1 OCFR50.73, the South Texas Project submits the attached Unit 1 Licensee Event Report 1-03-005 regarding Auxiliary Feedwater Pump 11 Breaker failure to close for Unit 1. This event did not have an adverse effect on the health and safety of the public.
There are no commitments contained in this event report. Resulting corrective actions will be handled in accordance with STP Corrective Action Program.
If there are any questions on this submittal, please contact S. M. Head at (361) 972-7136 or me at (361) 972-7849.
E. D. Halpin Plant General Manager Jal/wrb Attachment: LER 1-03-005 (South Texas, Unit 1)
LER 1-03-005.doc STI: 31665708
NOC-AE-03001 625 Page 2 of 2 cc:
(paper copy)
(electronic copy)
Bruce S. Mallett Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852 Richard A. Ratliff Bureau of Radiation Control Texas Department of Health 1100 West 49th Street Austin, TX 78756-3189 Jeffrey Cruz U. S. Nuclear Regulatory Commission P. O. Box 289, Mail Code: MN116 Wadsworth, TX 77483 A. H. Gutterman, Esquire Morgan, Lewis & Bockius LLP L. D. Blaylock City Public Service David H. Jaffe U. S. Nuclear Regulatory Commission R. L. Balcom Texas Genco, LP A. Ramirez City of Austin C. A. Johnson AEP Texas Central Company Jon C. Wood Matthews & Branscomb C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 LER 1-03-005.doc STI: 31665708
Abstract
On September 4, 2003, Unit 1 was operating at 100% power when a routine surveillance test run of Auxiliary Feedwater Pump (AFWP) 11 was attempted. When operators attempted to start the pump, the supply breaker failed to close. The pump had been successfully run twice since the breaker was overhauled in June 2003. After the breaker was replaced with a spare, the surveillance was completed satisfactorily.
The cause of the failure was determined to be increased mechanical resistance of the breaker mechanism caused by a random build up of tolerances from wear and case distortion which our existing overhaul program did not identify, coupled with a significant reduction in latch spring rotational torque capability (6 turn spring).
It was determined that AFWP 11 was out of service while Standby Diesel Generator (SDG) 13 was out of service on August 18 and 19, 2003, in violation of Technical Specification 3.8.1.1, Action D.
This event resulted in no personnel injuries, no offsite radiological releases, and no damage to safety-related equipment. There were no challenges to plant safety.
NRC FORM 366 (7-2001)
(If more space is required, use additional copies of SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES On September 4, 2003, Unit 1 was operating at 100% power when a routine surveillance test run of AFW Pump 11 was started at approximately 1355. When operators attempted to start the pump, the supply breaker failed to close. When the breaker was inspected locally, it was found that the closing springs were not charged. The breaker was replaced with a spare and the surveillance was completed successfully.
Shop inspection of the breaker found that the spring charging motor was burned up. The only visual clue was the trip latch return spring (6-turn) was different than the one removed (5 turn) as part of a recent overhaul. Preliminary investigation found that the weaker (6-turn) spring did not always reset the trip latch assembly. As a result, the operating mechanism cam continued to rotate and cycle the spring charging motor ON and OFF until the motor overheated and failed.
Investigation by the vendor (ABB) determined that the 6-tum spring was correct per the original design drawings. The stronger 5-turn spring was introduced in 1992. ABB has been unable to determine the reason the 5-turn spring came into use. A check of the parts bin at ABB found both 5 and 6 turn springs available.
LER 1-03-005.doc STI: 31665708
(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Fonn 366A) (17)
IIl. CAUSE OF THE EVENT The cause of the failure was determined to be increased mechanical resistance of the breaker mechanism caused by a random build up of tolerances from wear and case distortion which our existing overhaul program did not identify, coupled with a significant reduction in latch spring rotational torque capability (6 turn spring).
In working with ABB on the root cause investigation, several differences were found between the STP 5HK and the ABB overhaul program. The most significant difference is the level of detailed inspection of individual parts of the mechanism following disassembly. The STP program relies on refurbishment using a standard overhaul parts kit. Other parts are inspected and replaced only when obvious damage is found. The ABB program inspects all parts to a very high level of detail.
IV. CORRECTIVE ACTIONS
A. Remove 6 turn springs from STP stock and restock with 5 turn springs.
B. Changed the procurement description of the ABB refurbishment kit to specify 5 turn springs.
C. Replaced the breaker with the failed charging spring motor with a spare breaker and completed the AFW 11 surveillance satisfactorily.
D. Upgrade the STP 5HK breaker overhaul program to incorporate improvements identified during the ABB investigation.
E. Inspect other ABB breakers overhauled within the past 12 months to determine if 5 turn or 6 turn springs are installed.
V. PREVIOUS SIMILAR EVENTS
A. One possible similar failure was reported by Duke Power. Unfortunately, no root cause was performed and the mechanism was discarded. As such we could not confirm if the two events were related.
B. On 10/23/03 Limerick station contacted STP Electrical Maintenance personnel to report a mechanism failure following refurbishment where the spring charging motor continuously cycled. The failure was found prior to installation in the plant as part of the post maintenance bench testing of the breaker.
LER 1-03-005.doc STI: 31665708
(If more space is required, use additional copies of NRC Form 366A) (17)
VI. ADDITIONAL INFORMATION
STP has no operating experience with a similar failure.
LER 1-03-005.doc STI: 31665708