ML20199C862
| ML20199C862 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 01/11/1999 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-1079, NUDOCS 9901190165 | |
| Download: ML20199C862 (4) | |
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USEC A Global Energy Company January 11,1999 GDP 98-1079 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001 l
Paducah Gaseous Diffusion Plant (PGDP)
Docket No. 70-7001 Event Report ER-98-30 Pursuant to 10CFR76.120(o)(2), enclosed is the required 30-day written event report covering the C-720 power outage which disabled the C-720 Criticality Accident Alarm System (CAAS) strobe lights. The Nuclear Regulatory Commisr. ion Headquarters (NRC-IlQ) operations office was notified of the event on December 12,1998 (NRC No. 35146). Commitments contained in this submittal are identified in Enclosure 2.
Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
Sincerely, 1
ulley General Manag Paducah Gaseous Diffusion Plant
Enclosure:
As Stated f
cc: NRC Region 111 Office NRC Resident inspector - PG')P t
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[I'9901190165990111 PDR ADCCK 07007001 4
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.i P.O. Box 1410, Paducah, KY 42001 Telephone 502-441-5803 Fax 502-4415801 http://www.usec. ann Offices in 1.ivermore, CA Paducah, KY Portsmouth, OH Washington, DC
Docket No. 70-7001 GDP 98-1079 Page1of3 EVENT REPORT ER-98-30 DESCRIPTION OF EVENT On December 12,1998, at 0413 hrs., an electrical fault occurred on the primary side of substation transformer M7. Substation M7 is 13,800/480 volt and is single-ended. The fault was cleared within 100 milliseconds by the automatic tripping of the 13,800 volt feeder breaker 23D5D. This feeder breaker also supplies the single-ended substation M6 and the Mi and M3 ends of the double-ended substations M1/M2 and M3/M4. Since building C-720 criticality accident alarm system (CAAS)
AC power is fed from the M3 end of the M3/M4 substation, the tripping of the breaker resulted in loss of power to the eight (8) C-720 facility CAAS building warning lights. These strobe warning lights are located on the outside of the building and provide visual indication of a CAAS alarm. The CAAS lights are required to be operable by Technical Safety Requirement 2.6.4.1. Power was restored to the CAAS lights at 0440 hrs. by manually closing tiebreaker M34T, which connects the
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M3 and M4 ends of the substation. This action providej power to the substation from the M4 transfomier. The loss of AC power to the CAAS strobe warning lights for less than 30 minutes constituted a normal response time for operation of the manual breaker during unplanned switching.
The C-720 CAAS was declared operable at 0442 hrs. Pursuant to 10 CFR 76.120(c)(2), the Nuclear Regulatory Commission Headquarters (NRC-HQ) operations office was notified of this event on December 12,1998, at 0824 hrs. Event Notification Worksheet No. 35146 was assigned to this event.
The loss of power to the C-720 facility did not afTect audibility of the CAAS horns nor detectability l
of the CAAS cluster, since both the horns and the detector modules have back-up power supplied by internal batteries. The strobe waming lights do not have a back-up power supply.
The failed M7 transformer was shipped to an outside vendor for repairs. Communication with the vendor indicates that the fault occurred on the A phase coil upper and lower insulators, which agrees l
with the field observation. The phase-to-ground faults and subsequent arcing caused damage to both the A-phase and B-phase coils. The upper insulators, where the fault is believed to have originated, were dirty and the lower insulators on all three transformer coils were dirtier than the upper insulators. The lower insulators are more difficult to access for cleaning and possibly did not receive adequate preventive maintenance. The dirt on the insulators combined with damp outside air contributed to the fault occurring.
Feeder breaker 23D5D was returned to service on December 16 at 1448 hrs.
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Enclosure I l
Docket No. 70-7001 GDP 98-1079 Page 2 of 3 CAUSES OF EVENT A.
Direct Cause The tripping of the breaker 23D5D resulting from the M7 transformer fault removed power from the C-720 building CAAS strobe warning lights.
B.
Root Cause The root cause of this event is inadequate cleanliness of the transformer, even with the recommended preventive maintenance (PM) performed. The PM frequency for auxiliary transformers, such as M7, is three years. The PM on M7 is current, with the last PM performed on February 15,1997. This PM frequency of three years is the same for all auxiliary transformers and does not consider the environment that the transformer is in, j
Transformer M7 is located in an unsealed metal building and puts it more "at-risk" to j
adverse enviromantal factors than those transformers located in permanent structures.
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CORRECTIVE ACTIONS l
A.
Corrective Actions Taken l
1.
On December 12,1998, at 0442 hrs., power was restored to the C-720 CAAS warning l
lights and the C-720 CAAS was declared operable.
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B.
Corrective Actions Planned 1.
By January 29,1999, Systems Engineering will inspect with an ultrasonic listening device dry-type transformers considered "at-risk" to adverse environmental factors. Work requests will be issued by the same date to address any identified deficiencies.
2.
By March 31,1999, Systems Engineering will define improved practices for dry-type transformer cleaning and inspection and get Maintenance concurrence. Any changes needed in PM schedules for dry-type transformers will be provided to Reliability Engineering by the same date.
3.
By April 30,1999, Reliability Engineering will update the databas: to revise PM schedules for affected dry-type transformers, as Jefined by Action No. 2.
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Docket No. 70-7001 GDP 98-1079 Page 3 of 3 4.
By June 17,1999, Maintenance will revise CP4-GP-EM6130, " Dry Type Power and Distribution Transformers, Cleaning, and Repair," to implement improved cleaning and inspection practices for dry-type transformers, as defined by Action No. 2, and will brief electrical maintenance crews on improved practices.
EXTENT OF EXFDSURE OF INDIVIDUALS TO RADIATION OR TO RADIOACTIVE MATERIALS l
None LESSONS LEARNED i
Some of the electrical switchgear at the plant deserves special consideration regarding preventive maintenance due to environmental conditions.
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Docket No. 70-7001 GDP 98-1079 Page1of1 List of Commitments Event Report ER-98-30 i
i 1.
By January 29,1999, Systems Engineering will inspect with an ultrasoni: listening device dry-type transformers considered "at-risk" to adverse environmental factors. Work requests will be issued by the same date to address any identified deficiencies.
2.
By March 31, 1999, Systems Engineering will define improved practices for dry-type i
transformer cleaning and inspection and get Maintenance concurrence. Any changes needed in PM schedules for dry-type transformers will be provided to iteliability Engineering by the sarne date.
3.
By April 30,1999, Reliability Engineering will update the database to revise PM schedules for aiTected dry-type transfonners, as defined by Action No. 2.
4.
By June 17, 1999, Maintenance will revise CP4-GP-EM6130, " Dry-Type Power and Distribution Transformers, Cleaning, and Repair," to implement improved cleaning and inspection practices for dry-type transformers, as defined by Action No. 2, and will brief electrical maintenance crews on improved practices.
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