ML20236M571
| ML20236M571 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 07/10/1998 |
| From: | Pulley H UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-1049, NUDOCS 9807140132 | |
| Download: ML20236M571 (6) | |
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, A Global Energy Company.
I July 10,1998 GDP 98-1049 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-98-13, Rev.1 Pursuant to 10CFR76.120 (d)(2), enclosed is the required 30-day written Event Report covering the partial failure of the plant air system when two air compressors in Building C-335 tripped.
The Nuclear Regulatory Commission (NRC) was notified of the event on May 14,1998, at 1653 hrs. (NRC No. 34236). On June 12,1998, an interim report relating to this event was provided to NRC. Changes are annotated by vertical lines in the right margin of this report. Enclosure 2 is a list of commitments.
Any questions regarding this matter should be directed to Larry Jackson at (502) 441-6796.
Sincerely, I
l Ho d Pulk General Manager Paducah Gaseous Diffusion Plant
Enclosure:
-' As Stated cc: - NRC Region III Office NRC Resident Inspector - PGDP 9807140132 990710 I PDR ADOCK 07007001
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C PDR; P.O. Box 1410, Paducah, KY 42001 Telephone 502-441-5803 Fax 502-4415801 http://www.usec.com l-Offices in Uvermore, CA Paducah, KY Portsmouth, OH Washington, DC I
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Docket No. 70-7001 GDP 98-1049 u
Page 1 of 4 EVENT REPORT ER-98-13, Rev.1
' DESCRIPTION OF EVENT
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On May 14,1998, at 0901 hrs., a partial failure of the plant air system occurred when'two air
-- compressors in Building C-335 tripped off-line. The partial failure of the plant air system caused the Criticality Accident Alarm System (CAAS) to be declared inoperable, due to reduced air capacity determined to be potentially required for the CAAS building horns. CAAS alarm capabilities
- supplied by plant air were declared inoperable due to inaudibility. However, CAAS detectability was not affected. Because of the rapid response to the trips, restart of the compressors occurred l
while. Limiting Conditions for Operation (LCO) actions, as required by Technical Safety Requirements (TSR), were being determined. Therefore, LCO actions were not initiated. On May
.14,1998, at 1653 hrs., the Nuclear Regulatory Commission Headquarters (NRC-HQ) office was notified of this event in accordance with 10CFR76.120(c)(2) (NRC Event 34236).
Dry compressed air is required at the Paducah Gaseous Diffusion Plant (PGDP) to operate pneumatic instruments, controllers, and valves for plant processes. Air is also used for plant support production operations, steam plant operations, test facilities, and maintenance functions. Dry compressed air is supplied from three buildings (C-600, -620, -335) and an auxiliary air supply is located in Building C-607. 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 CAAS building horns. The requirements for compressed air capacity relative to the CAAS requirement.s have been assessed in Engineering Notice (EN) EN-C-822-98-027, Rev. O, effective
" April 3,1998.' Plant 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.
The LTO defines the expectation for on-line plant air availability to be maintained at, or above,
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11,250 sefm. The EN and LTO were subsequently refined to 11,000 scfm.
On May '14,1998, at approximately 0850 hrs., a Centac compressor in Building C-335 tripped,
- discontinued operating, and was manually restarted in less than one minute. At approximately 0900 hrs., the same Centac tripped a second time and was immediately restarted. At approximately 0927
- hrs., an XLE compressor tripped, discontinued operations, and was manually restarted after approximately three minutes. Both Centac compressor trips reduced plant air availability to less than l
j-11,250 scfm; however, the XLE trip did not.
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Docket No. 70-7001 GDP 98-1049 Page 2 0f 4 L
On May 14,1998, troubleshootmg was mitiated to determine the cause for the partial loss of plant j
j air. The Centac tripped, on both occasions, due to a reduction in water flow to the compressor which l
caused an increase in the compressor's oil temperature (2 to 6 degrees Fahrenheit) which led to the l
- trip, as designed. The reduction in water is attributed to spray-down testing of the deluge system for l
transformer No. 72, C 537 switchyard. Compressor trips have previously occurred during spray-l down testing of the' deluge systems in the switchyards. To minimize the risk of a compressor trip, l
1 prior to this event, testing was initiated with the transformer deluge system's S2 valve closed. This l
1 method had been used previously with no resultant compressor trips. To preclude a surge of water l
that could reduce water flow, the S2 valve was slowly opened. However, the full flow of water l
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through the transformer deluge system resulted in a reduced flow of cooling water available to the l
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Centac compressor. As an additional precaution, prior to this event, a Utilities operator was assigned l
to Building C-335 to assure operation of the compressors and to initiate appropriate actions to restart l
- the compressors in the event a compressor tripped. Pre-positioning of the operator led to a rapid l
restart of the compressors subsequent to each trip. Water flow adjustments being made to the Centac l
resulted in the XLE compressor trip.
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l On May 15,1998, delt smo down testing of the switchyard transformers was suspended. On ' l I
June 19,1998, routine mac orme or testing of fire hydrant and suppress' ion systems that place flow l
l demands on the' sanitary a..J Gre water systems were curtailed. Since the implementation of these.1 two short-term corrective actions, there have been no additional compressor trips attributed to a j
reduction in water flow'to the compressors.
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_On June 15,1998, Plant Opemtions established a committee of subject matter experts (SME) to
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- analyze causes, and make recommendations for short-term corrective actions, relative to the partial-l D
. loss of plant air resulting from compressor trips and subsequent CAAS inoperability. Additionally, l
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" the committee will examine the need for conducting reliability assessments of selected non-safety l
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_ systems impacting safety-related systems. An appropriate corrective action plan will be published l
by July 22,1998.
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The safety significance of this event was a partial loss of plant air supply affected the CAAS alarm l
capabilities supplied by plant air, however, the CAAS detectability was not affected. Additionally, l
_l four of the feed autoclave high pressure isolation valves in C-333-A and C-337-A utilize plant air l
l to assist in closure that could be affected by the loss of air, although the valves are designed to fail - l in the safe (closed) position.
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Docket No. 70-7001 l
GDP 98-1049. l Page 3 of 4 l
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L CAUSE OF THE EVENT l
1 A. Direct Cause l
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j The direct cause ofthis event was the inoperability of the Centac compressors in Building C-335.
l The failure ~of the compressors and partial loss of the plant air system resulted in a CAAS-l
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' inaudibility.
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l B. Root Cause l
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. The root cause for this event was a failure to implement effective controls of the activity to l
prevent recurrence of the compressor trips. An awareness that previous compressor trips l
. occurred as a result of spray-down testing of transformers existed and steps were initiated to l'
prevent recurrence by slowly opening the S2 valve to preclude a water surge that would reduce l-l the flow of cooling water availability to the compressors. This method had been successful in l
the past. However, these precautions were not sufiicient to prevent the trips.
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l CORRECTIVE ACTIONS l
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. A. Completed Corrective Actions l
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On February 16,1998, Engineering Service Order (ESO) Z99920 was issued which will l
L upgrade the cooling water supply to the compressors in Building C-335 to minimize trips by j L
- the Centac compressors.
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'2.' ; On May 15,1998, to maintain effective control of this activity to prevent recurrence, the l
- deluge system spray-down testing of the switchyard transformers was suspended. This l
. suspension will mmain in place until corrective actions are sufficient to prevent recurrence.
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. 3. ~ On June 19,1998, routine testing or maintenance of fire hydrant and suppression systems l
that place flow demands on the sanitary and fire water system were curtailed to further l
l enhance effective controls of this activity to prevent recurrence. This suspension sill remain l
in place until corrective actions are sufficient to prevent recurrence.
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l Docket No. 70-7001 l
GDP 98-1049 l
Page 4 of 4 l
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i B. Planned Corrective Actions l
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- l. By August 3,1998, Engineering will complete re-assessment of ESO Z99920 relative to l
cooling water flow capabilities in Building C-335 plant air compressors, as related to I
supporting CAAS demands, to determine whether additional actions are necessary to l
enhance water flow.
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- 2. By October 1,1998,, Operations will prepare an appropriate corrective action plan in l
response to the cooling water flow re-assessment in corrective action 1 above, as applicable.
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- 3. By December 15,1998, Engineering will complete a construction project that will remove l
the CAAS dependence on the existing air system by installing air accumulators and air l distribution piping that will be dedicated to supplying compressed air to the CAAS horns.
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l EXTENT EXPOSURE OF INDIVIDUALS TO RADIATION OR RADIOACTIVE MATERIALS l
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None l
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LESSONS LEARNED l
1 If the possibility exists that, based on previous experience, an event may occur upon initiation of an l
activity, the endeavor should not be undertaken. If conditions warrant proceeding, an appropriate l
LCO should be entered and steps taken to minimize the risk.
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l Docket No. 70-7001 l
GDP 98-1049 l
Page1of1 l
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Event Report ER-98-13, Rev.1 l
List of Commitments l
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- 1. By August 3,1998, Engineering will complete re-assessment of ESO Z99920 relative to cooling l
water flow capabilities in Building C-335 plant air compressors, as related to supporting CAAS l
demands, to determine whether additional actions are necessary to enhance water flow.
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By October 1,1998, Operations will prepare an appropriate corrective action plan in response l
to the cooling water flow re-assessment in corrective action 1 above, as applicable.
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- 3. By December 15,1998, Engineering will complete a construction project that will remove the l
CAAS dependence on the existing air system by installing air accumulators and air distribution l
piping that will be dedicated to supply:ng compressed air to the CAAS horns.
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