ML20206C104
| ML20206C104 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 04/22/1999 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-1012, NUDOCS 9904300180 | |
| Download: ML20206C104 (5) | |
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USEC A Global Energy Company
' April 22,1999 GDP 99-1012 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001 Paducah Gaseous Diffusion Plant (PGDP)
Docket No. 70-7001 Event Report ER-99-04 Pursuant to 10CFR76.120(d)(2) enclosed is the required 30-day written event report for the interruption of power to the Criticality Accident Alarm System (CAAS), in Buildings C-333;
-333-A; -337; -360; -710; -720; and -746-Q. The Nuclear Regulatory Commission Headquarters (NRC-HQ) operations office was notified of the event on April 4,1999 (NRC No. 35543).
~ 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, l
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'ulley General Manager Paducah Gaseous Diffusion Plant
Enclosures:
As Stated cc: NRC Region III Office NRC Resident Inspector - PGDP W
x.G 9904300100 990422
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PDR ADOCK 07007001 6
C PDR l
P.O. Box 1410, Paducah, KY 42001 i
Telephone 502-441-5803 Fax 502-441-5801 http://www.usec.com l
Offices in Livermore, CA Paducah, KY Portsmouth, OH Washington, DC
m Docket No. 70-7001 GDP 99-1012 Page1of3 EVENT REPORT ER-99-04 DESCRIPTION OF EyENT On April 3,1999, at approximately 1340 hrs., electrical power was temporarily interrupted to the Criticality Accident Alarm System (CAAS) building horns and lights located in Buildings C-333;
-333-A; -337; -360; -710; -720; and -746-Q. The CAAS power interruption occurred as a result of a breaker trip (cluster relay power and annunciation power) located in the radiation alarm annunciator relay cabinet "B" in the basement of Building C-300. During the interruption CAAS audibility was lost (building horns) and the building warning beacons were partially disabled in all of the above-mentioned facilities, with the exception of C-746-Q which has no building horn, and
- C-720 which has an alternate method to actuate building horns independent of the 48-volt direct current (VDC) circuit. The loss of the 48-VDC did not adversely affect the CAAS cluster's ability I
to detect a criticality. The power interruption was annunciated on the CAAS alarm panel located in Building C-300 central control room as a loss of CAAS 48-VDC power trouble alarm. Because of the short duration of the power interruption (approximately two minutes), there were no Limiting Conditions for Operation (LCO) entered. On April 4,1999, at 11:58 hrs., the Nuclear Regulatory
. Commission Headquarters (NRC-HQ) operations office was notified of the event in accordance with 10CFR76.120(c)(2) (NRC Event 35543).
On April 3,1999, prior to this event, Instrument Maintenance (IM) was conducting troubleshooting of the CAAS "AQ" cluster located in Building C-710.- As an integral part of troubleshooting, the surge suppression diodes located in the basement of Building C-300 radiation alarm annunciator cabinet "B" were examined. Two surge suppression diodes, manufactured by General Instruments, model no. IN4007, located on electrical relays TR-AQ and TR-AR were blackened and cracked.
'_While inspecting one of the two questionable diodes to ascertain the model number and extent of damage, an employee attempted to move the diode with his finger causing the diode to disintegrate allowing the wire leads on opposite ends of the diode to come in contact creating an electrical short
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circuit. The short circuit caused two electrical breakers (cluster relay power and annunciator power) to trip resulting in the CAAS inoperability (horns and lights) in the affected buildings. The affected breakers were re-closed and power restored to the CAAS.
The troubleshooting conducted prior to this event-was in accordance with procedure CP2-GP-GP1038, " Troubleshooting Guidelines," and in-hand procedure CP4-GP-IM6239, "C-710 Criticality Accident Alarm System Annual Cluster Replacement And Functional Tests."
Additionally, a maintenance work package (R 9903280-01) for troubleshooting Building C-710 CAAS clusters was approved and permission to start work signed off by the Plant Shift
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Docket No. 70-7001 L
GDP 00-1012 Page 2 0f 3 Superintendent (PSS). Examination of the bumed diode "in-place" is considered " skill of the crafl";
however, the extent of disintegration of the diode was not anticipated. Prior to initiating an l
. examination of the bumed diode, the 48-VDC was not de-energized to preclude a breaker trip. To l
de-engergize the 48-VDC would have necessitated the CAAS system being declared inoperable within the same buildings which were affected in this event and would have necessitated required LCOs to be entered.
l Immediately prior to this event, there was a lightning storm in the area. The diodes involved in this event were probably destroyed as a result of an electrical surge caused by the lightning, which exceeded the maximum voltage rating and/or maximum current rating for the diode. The diodes failed in a manner consistent with maximum electrical rating values being exceeded; however, the diodes are appropriately sized for the circuit conditions at the time of the event, excluding lightening strikes.
The safety significance of this event was the temporary interruption of power to the CAAS building horns and lights for approximately two minutes; however, this was partially mitigated by the continued operability of the CAAS detectability function and operability oflocal CAAS cluster horns in the affected buildings.
I CAUSE OF THE EVENT l
A. Direct Cause The direct cause of the interruption of power to the CAAS in Buildings C-333; -333-A; -337;
-360; -710; -720; and -746-Q, was an electrical short circuit that resulted when an employee moved a diode to determine the extent of damage to it.
B. Root Cause l
Failure to maintain a questioning attitude. When the employee manipulated the diode it caused the diode to disintegrate resulting in an electrical short circuit. A visual determination that the surge suppression diode was burned and cracked should have been sufficient evidence to l
generate a question whether manipulation of the diode could lead to further adverse consequences impacting the operability of the CAAS.
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- Docket No. 70-7001 GDP 99-1012 l
Page 3 of 3 CORRECTIVE ACTIONS A.1 Completed Corrective Actions
- 1. On' April 4,1999, the damaged diodes and trouble alarm relays were replaced.
B. Planned Corrective Actions
- 1. By May 21,1999, Maintenance will complete a crew briefing of appropriate Maintenance personnel to include a discussion of this event and re-emphasizing the necessity for maintaining a questioning attitude.
- 2. By May 21, 1999, Maintenance will complete a review of CP2-GP-GP1038,
" Troubleshooting Guidelines," to enhance the procedure. The analysis will focus on possible additional action steps involving. investigation of causes for equipment damage; manipulation and testing of damaged equipment; and to determine the potential impact of manipulation and testing on in-service / energized plant safety systems.
- 3. By September' 15, 1999, Maintenance will publish a revised CP2-GP-GP1038,
" Troubleshooting Guidelines," to incorporate the results of the review in corrective action number 2, above.
-4.
By October 29,1999, Maintenance will complete a crew briefing of appropriate Maintenance personnel relative to changes to CP2-GP-GP1038, " Troubleshooting Guidelines."
1 EXTENT OF EXPOSURE OF INDIVIDUALS TO RADIATION OR RADIOACTIVE MATERIAL None LESSONS LEARNED Prior to manipulating electrical equipment supplying power to safety systems, it is important to consider the efTects of such actions on the continued operability of the safety system.
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Docket No. 70-7001 GDP 99-1012,
Page1of1 List of Commitments Event Report ER-99-04 l
- 1. By May 21,1999, Maintenance will complete a crew briefing of appropriate Maintenance
. personnel to include a discussion of this event and re-emphasizing the necessity for maintaining a questioning attitude.
. 2. By May 21,1999, Maintenance will complete a review of CP2-GP-GP1038, " Troubleshooting
' Guidelines," to enhance the procedure. The analysis will focus on possible additional action l
steps involving investigation of causes for equipment damage; manipulation and testing of l
damaged equipment; and to determine the potential impact of manipulation and testing on in-service / energized plant safety systems.
- 3. By September 15,1999, Maintenance will publish a revised CP2-GP-GP1038, " Troubleshooting l
Guidelines," to incorporate the results of the review in corrective action number 2, above.
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- 4.. By October 29,1999, Maintenance will complete a crew briefimg of appropriate Maintenance personnel relative to changes to CP2-GP-GP1038 " Troubleshooting Guidelines."
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