ML20199C325

Forwards Required 30-day Written Rept for C-310 Power Losses Which Resulted in Disabling of High Voltage UF6 Release Detection Sys.Target Date for Suppl Rept to Be Issued in 980119

ML20199C325
Person / Time
Site:	Paducah Gaseous Diffusion Plant
Issue date:	11/14/1997
From:	Polston S UNITED STATES ENRICHMENT CORP. (USEC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GDP-97-1046, NUDOCS 9711190307
Download: ML20199C325 (4)

Text

e United States Inrihment Ccrpraton.

Paducah Site Ofrut PO Ikn 1410 Paducah. KY 42001 Tel. 502 4415803 ras: 502 4415801 November 14,1997 United States Nuclear Regulatory Commission SERIAL: GDP 971046 Attention: Document Control Desk Washington, D.C. 20555 0001 Paducah Gaseous Diffusion Plant (PGDP). Docket No. 70-7001 - Event Report ER-97-18 Pursuant to 10 CFR 76.120(d)(2), attached is the required 30-day written report for the C-310 power losses which resulted in the disabling of the high voltage UF. release detection system. This was initially reported on October 17 and October 18,1997 (NRC No. 33124 and 33126). Investigation activit es are continuing. The target date for a supplemental report to be issued is January 19,1998.

Should you require further information on this subject, please contact Bill Sykes at (502) 441 6796.

Sincerely, General Manager Paducah Gaseous Diffusion Plant SP:WES:JNil:mel Attachment cc:

NRC Region 111 3 ;72..I NRC Senior Resident Inspector, PGDP C

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Event Report

- ER 9718 DESCRIPTION OF EVENT

~ On October 1.7,il997, at approximately 2315, the C-310 East Normetex product withdrawal pump tripped during the startup of the pump. - A subsequent lamp test indict..ed that power _had -

been lost to the alarm annunciator panel in the Area Control Room (ACR). This panel includes thialarm for the high voltage process gas leak dete: tion (PGLD) system. The heads for the C-310A high voltage PGLD system were fired and no alarm was received in the ACR which -

confirmed that the high voltage PGLD system had been disabled. This safety system provides -

UF. detection above the UF condensers, accumulators, and heated housings inlC-310A and 6

when activated will sound alarms in the ACR. This safety system is required by technical safety -

l requirement (TSR) limiting conditions for operation (LCO) 2.3.4.4 to be operable wnen the alTected process equipment is in Mode 2 or 3 and UF. pressure is above atmospheric pressure.

immediately following the power loss, the PGLD safety system was declared inoperable, and a.

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smoke watch was established as required by LCO 2.3.4.4 action step A. The DC power was manually thrown over to the battery room by the building operators; however, this action did not restore the alarm power, as expected. At approximately 2340, the breaker supplying DC power-1 to the No.~ 1 annunciator cabinet was found to be tripped. The breaker was reset and power was restored,- This restored the alarm function of the PGLD system. Alarm panel capability was lost

. for approximately 25 minutes. The PGLD heads were tested and alarms were received, as r

- required. Following the restoration of power, DC alarm power was switched from the battery room back to " normal" power by closing a breaker to the rectifier.

On October 18,1997, at approximately 1400, the C-310 East Normetex pump tripped while running on-stream. It was determined that alarm power related to the high voltage PGLD system '

" had been lost again. The breaker in the No. I annunciator cabinet was reset again at L approximately 1402 which restored power to the alarms on the PGLD system. Alarm capability _

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was lost for approximately 2 minutes. While resetting the breaker in the annunciator cabinet,'

operations personnel observed that the cabinet was excessively hot and found that the cabinet :

ventilation fans were not running. Upon checking the fans, a fan breaker was found to be -

tripped.1 The fans were restarted at approximately 1442 by resetting the fan breaker.

Both instances of power loss to the alarms of the PGLD system were reported to the plant shift

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i superintendent (PSS) and documented on problem reports in a timely manner, but were initially -

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incorrectly determined to be non-reportable. The losses of alarm power on the PGLD system

- which occurred on October 17 and October 18,1997, were reported to NRC on October 21 at 0341 and 1238, respectively. By 10 CFR 76.120(c), verbal notification should be made to NRC

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- awithiti 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of discovery of disabled equipment which is required by TSR to be available and 1

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Ibcket No. 70-7001 Page 2 of 3 operable. (Reference NRC Event Notification Worksheet No. 33124 and No. 33126.)

' Subsequent to these notifications, it was discovered that the event notification worksheets incorrectly stated the " event times and dates." These worksheets were corrected and faxed to the NRC llQ Operations Duty Officer. Additionally, the description section of Notification Worksheet No. 33124 indicated that the loss of power affected the PGLD for the West Normetex pump under LCO 2.3.4.3. The correct description should have been that the loss of power afketed the high voltage POLD under LCO 2.3.4.4. Problem reports were issued to evaluate these concerns.

The breaker which tripped was located in the C-310 No. I alarm annunciator cabinet. This caninet provides alarm contact relaying for over one hundred alarm points in the C-310 building.

The cabinet is located in the C-310 basement adjacent to the No. 2 annunciator cabinet and includes a free standing cabinet, terminal sta., alarm annunciator racks, ventilation fans, and a 10-amp two-pole DC breaker. The original design of the cabinet had nine alarm annunciator racks mounted in the cabinet. Each one of the racks was fed 125 VDC from the breaker mounted in the cabinet. At a later date, six additional units were mounted on the wall behind the cabinet and connected to the nine original units. The original racks each contained 12 alarm points, and the six newer units each contained six points. This gives the cabinet a total alarm point count of 144 alarm points, llistorie.lly, problems wah the alarm annunciators have been failed relays, resistors, and bad connecoons Given the large munber of alarm points in each cabinet, failure of a component alarm point is not unexpected. Since an alann point component failure could, on occasion, trip the breaker, further testing will be done to detennine potential failure points in the No. I annunciator cabinet. This testing will consist ofinfrared thermography and breaker current measurement.

Following the problems on October 17 and October 18, Electrical Maintenance (EM) was called in to troubleshoot the system and determine the cause of the main breaker trip. Since there was a concern that the tripping of the East Normetex pump was associated with or caused the tripping of the No. I annunciator cabinet main power breaker, testing was completed to simulate the inercase in current caused by the three alarms that came in as a result of the Normetex pump trip.

It was first suspected that the combined effect of these Normetex alarms coming in at the same time exceeded the rating of the main breaker and caused the trip. EM attempted to recreate the alarm condition to see if the breaker would trip again. The breaker did not trip and ammeters on the load side of the breaker lugs indicated a peak load of 6.7 amps, well under the breaker rating of 10 amps. EM went on to simulate some alarm points that had recently been disconnected because they were no longer required for the East Normetex pump. Again the peak load was well below the breaker's rating.

The possibility of high cabinet temperature due to failed ventilation fans affecting the breaker trip point was also investigated. The data sheet from the breaker manufacturer indicates that this breaker utilizes a hydraulic-magnetic solenoid to trip the breaker. This type of cunent sensing

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Docket No. 70-7001'

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provides precision over-current protection without regard to thermal influences. Field tests

. performed on a replacement breaker identical to the creaker feeding the annunciator cabinet =

yielded trip values within the stated ranges. At this time, EM has not found the direct cause of -

__ the breaker trip. The No. I alarm' annunciator cabinet continues to function normally. The

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~ ; breaker which tripped will be removed for further testmg.

At this time, the cause of the breaker trip is not known. To verify operability, a surveillane is performed which test fires the high voltage UFf detection system twice per shift when the -

- equipment it serves is in mode 2 or 3 and the UF. pressure is above atmospheric pressure.- This.

- : surveillance is required by TSR SR 2.3.4.4-1. Additionally, a lamp test is performed once per'-

'l shift on the annunciator panel where the high voltage l>F alarm is displayed to ensure the alarm -

6 displays are functional. The annunciator panel is located in the ACR which is staffed by -

Loperators on a continuous basis.

Since the cause of the breaker trip is not known at this time, a supplemental report will be issued

.when troubleshooting is complete and the root cause and associated corrective actions have been determined.- The target date for the supplemental report is January 19,1998.

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CAUSES OF EVENT To be determined z

' CORRECTIVE ACTIONS To be determined EXTENT OF EXPOSURE OF INDIVIDUALS TO RADIATION OR TO RADIOACTIVE

- MATERIALS No exposure to radiation or radioactive materials occurred during the outage of the high voltage PGLD system.'

LESSONS LEARNED To be determined 4

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