ML20248M183
| ML20248M183 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 06/09/1998 |
| From: | Polston S UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-1037, NUDOCS 9806150120 | |
| Download: ML20248M183 (5) | |
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USEC A Global Energy Company June 9,1998-GDP 98-1037 -
United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 Paducah Gaseous Diffusion Plant (PGDP)
Docket No. 70-7001 Event Report ER-98-10 Pursuant to 10CFR76.120 (c)(2), enclosed is the required 30-day written event report covering the partial failure of the plant air system when three air compressors in Building C-335 failed.
The Nuclear Regulatory Commission (NRC) was notified of the event on May 11,1998, at 1100 hrs. (NRC No. 34206). Enclosure 2 is a list of commitments made in this report.
Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
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- cerely, Iv teve Polston f
General Manager Paducah Gaseous Diffusion Plant l
Enclosures:
As Stated cc: NRC Region III Office NRC Resident Inspector - PGDP l
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9906150120 N 9
PDR ADOCK 07007001 C
PDR P.O. Box 1410, Paducah, KY 42001 Telephone 502-441-5803 Fax 502-441-5801 http://www.usec.com Offices in Livermore, CA Paducah, KY Portsmouth, OH Washington, DC u_________________
L Docket No. 70-7001 GDP 98-1037.
Page1of3 EVENT REPORT ER-98-10 l
. DESCRIPTION OF EVENT On May 10,1998, at i135 hrs., a partial failure of the plant air system occurred when three air
- compressors in Building C-335 stopped operating. The partial failure of the plant air system caused the Criticality Accident Alarm System (CAAS) to be declared inoperable, due to inadequate air i
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. capac ty to t e CAAS building horns. CAAS alarm capabilities supplied by plant air were declared inoperable due to inaudibility; however, CAAS detectability was not affected. Appropriate Limiting l
Conditions for Operations (LCO) actions, as required by Technical Safety Requirements (TSR),
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were implemented. On May. I1,1998, at 1100 hrs.,.the Nuclear Regulatory Commission Headquarters (NRC-HQ) office was notified of this event in accordance with 10CFR76.120(c)(2)
Dry compressed air is required at the PGDP to operate pneumatic instruments, controllers and valves -
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. for plant processes. Air is also used for plant support production operations, steam plant operations, j
test facilities and maintenance functions. Dry compressed air is supplied from three buildings
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. (C-600, -620, -335) and an auxiliary air supply is located in Building C-607. The air compressor facilities may be operated separately or together to maintain air supply to the distribution headers.
Dry compressed air is also used as the primary motive force to sound building horns associated with 1
CAAS. The requirements for compressed air capacity relative to the CAAS requirements have been assessed in Engineering Notice (EN) EN-C-822-98-027, Rev. O, effective April 3,1998. Plant 1
Utility. Operations issued Long Term Order (LTO) C600-98-01, Rev. 2, dated May 5,1998, to assure the initial conditions of the EN, including CAAS operability, are maintained.
. On May 10,1998, at approximately 1135 hrs., a low air pressure alarm was received by Utilities operators in Building C-600. Concurrently, a low air pressure alarm in the C-300 Central Control
. Facility (CCF) indicated a failure of three air compressors in Building C-335. Actions were initiated to mitigate the loss of air according to procedure. At approximately 1142 hrs., the CAAS system was declared inoperable. At i150 hrs., two compressors located in Building C-607 were placed in
' service and at 1208 hrs., the plant air pressure began returning to normal. At 1220 hrs., the three p*
compressors located in Building C-335 were restarted and at 1225 hrs., plant air pressure returned.
- to normal. The CAAS system was declared operable at 1320 hrs., with the exception of Building C-400 CAAS which ramained inoperable until nitrogen bottles were changed.
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Docket No. 70-7001 GDP 98-1037 Page 2 of 3 On May 10,1998, troubleshootmg was mitiated to identify the cause for partial loss of plant air. It
{ was determined two Bussman 6-ampere potential transformer (PT) fuses were open and were replaced with two Bussman 8-ampere PT fuses in an attempt to restore the air supply. PT fuses supply 120-volt alternating current (VAC) to a substation under-voltage relay system. During loss of voltage, which the under-voltage relay senses as a loss of substation voltage (4,160-VAC), relays -
trip all loads on the substation bus. At the time of this event, loads that tripped were two XLE compressors; one Centac compressor; one purge and evacuation pump; and one B booster pump located in Building C-335. The PT circuit overload was attributed to the number of XLE
. compressors operating at the time of the event. It was determined that control power for both of the j
XLE compressors was supplied from the PT circuit located in the 4,160-VAC substation. However, the 6-ampere fuse is the recommended size for the 600-VAC (5-ampere) PT that the fuse is protecting. A design problem exists in which the electrical load (7-ampere) is connected to a-l 6-ampere power source. L A single XLE compressor can be operated from the 6-ampere power
. source; however, when two XLE compressors are operating this configuration will overload the PT.
= and the fuses will open to provide overload protection. ' On May 14,1998, a modification was
- completed that relocates control power source to 120-VAC lighting panel circuits (two 20 ampere dedicated circuits, one for each compressor). This modification removes the overload from the PT
.l circuit. Further, the two Bussman 8-ampere PT fuses are being retumed to the original configuration I
of two Bussman 6-ampere fuses.
The plant is taking aggressive actions to bring on-line increased air system capacity currently not available.
' The safety significance of this event was a partial loss of plant air supply affected the CAAS alarm g
. capabilities supplied by plant air; however, the CAAS detectability was not affected. Additionally, L the feed autoclave high pressure isolation valves in C-333-A and C-337-A utilize plant air to assist in closure that could be affected by the loss of air, although the valves are designed to fail in the sat'e (closed) position.
CAUSE OF THE EVENT A. Direct Cause -
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The direct cause of this event was a loss of electrical power to the compressors in Building C-(
- 335. The inoperability of the compressors and partial loss of the plant air system resulted in a
' CAAS inaudibility.
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p-Docket No. 70-7001 GDP 98-1037 Page 3 of 3 B. Root Cause The root cause for this event was electrical design specifications wer less than adequate. One XLE compressor can operate from the current electrical configuration; however, the operation of a second XLE compressor overloads the potential transformer (PT) which causes the fuse to open providing overload protection.
1 CORRECTIVE ACTIONS A. Planned Corrective Actions
- 1. By July 27,1998, Engineering will complete a walkdown of Buildings C-600, C-620 and C-607, to determine whether an electrical configuration similar to the one in Building C-335
- exists, j
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- 2. Within 60 days after completion of planned corrective action number 1, if similar electrlcal l
configurations are found, Engineering will prepare an appropriate corrective action plan.
- 3.. By December 15,1998, Engmeermg wdl complete a construction project to reduce CAAS
- dependence on the existing air system by installing air accumulators and air distribution piping that will be dedicated to supplying compressed air to CAAS horns.
EXTENT EXPOSURE OF INDIVIDUALS TO RADIATION OR RADIOACTIVE MATERIALS L,
None LESSONS I EARNED L
The implementation of required modifications to safety systems or safety system components L-
- reduces the potential for occurrence'of similar events.
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Docket No. 70-7001 GDP 98-1037 Page1of1 Event Report ER-98-10 List of Commitments i
- 1. By July 27,1998, Engineering will complete a walkdown of Buildings C-600, C-620 and C-607,
- to determine whether an electrical configuration similar to the one in Building C-335 exists.
- 2. Within 60 days after completion of planned corrective action number 1, if similar electrical L
configurations are found, Engineering will prepare an appropriate corrective action plan.
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- 3. By December 15,1998, Engineering will complete a construction project to reduce CAAS
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. dependence on the existing air system by installing air accumulators and air distribution piping -
l that will be dedicated to supplying compressed air to CAAS homs.
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