ML20202G437
| ML20202G437 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 02/12/1998 |
| From: | Morgan J UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-98-2007, NUDOCS 9802200128 | |
| Download: ML20202G437 (4) | |
Text
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.USEC A Global Eriargy Company I
February 12, i998 United States Nuclear Regulatory Commission GDP 98 2007 Attention: Document Control Desk Washington, D.C. 20555 0001 Portsmouth Gaseous Diffusion Plant (PORTS)- Docket No. 70-7002 - Event Report 97-21, Revision 1.
Pursuant to 10 CFR 76.120 (d)(2), Enclosure 1 provides the revised 30 day written Event Report 97 21. Revision 1, for an event involving a failure of the UF. Cylinder liigh Pressure Autoclave Steam Shutoff safety system at the Portsmouth Gaseous Diffusion Plant. The revised event report is being submitted to provide the root cause and lessons learned. Changes from the previous report are marked with a vertically dashed line in the right margin.
Should you require additional information regarding this event, please contact Scott Scholl at (614) 897-2373.
Sincerely, L
UJim h1 organ Acting Gener, hianager Portsmouth Gaseous Diffusion Plant JBht:SScholl:cw
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NRC Region til D. Ihtrtland, NRC Resident Inspector, PORTS ll ll l.l:l.ll!IIllJllll 9002200128 900212 PDR ADOCK 07007002 C
PDR I!O. Ibx 800, Portsnmuth, OH 45661 Telephone 614-897-2255 Fax 614 897-2644 http://www.usec.com Oflices in 1.ivermore, CA Paducah, KY Portsmouth. Oil Washington DC
4 United States Nuclear Regulatory Commission February 12,1997 Page Two i
Distribution bec:
J. Adkins,ilQ J. Anzelmo, PORTS R. Iloelens, PORTS J. Bolling, PORTS M. Boren, PGDP S. lirawner, PGDP F. Cordier, PORTS L. Cutlip, PORTS J. Dietrich, LMUS L. Fink, PORTS R. Gaston, PORTS M. Ilasty, PORTS P. Ilopkins, PORTS J. Ilutsebaut, PORTS L, Jackson, PGDP J. Labarraque, PGDP B. Lantz, PORTS R. Lipfert, PORTS R. McDermott, PORTS J. Miller, ilQ J. Mite, PGDP J. Oppy, PORTS S. Polston, PGDP
- 11. Pulley, PGDP A. Rebuck-Main, llQ R. Robinson, PORTS S. Routh, liq S. Scholl, PORTS D. Thompson, PORTS R. Wells, ilQ Plant Shill Superintendents PORTS Record Management 0:\\ users \\nra\\ letters.nrc\\ ports \\gdp98 2.007
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Docket No. 70 7002
' Enclosure 1 Page 1 of 2 Event Report 97 21 Revision 1 Description of Event On October 22,1997, at 0635 hours0.00735 days <br />0.176 hours <br />0.00105 weeks <br />2.416175e-4 months <br />, X 343 Autoclave (AC) #7 was in Mode 11, heating a 14 ton Uran lum liexafluoride (UF ) Tails cylinder when the audible alarm for steam shutdown was 6
received. The cylinder had been heating for approximately one hour when the actuation occurred.
The Operator responding to the alarm noticed the Low Cylinder Pressure Shutoff (LCPS) safety system had actuated, causing the steam supply valves to AC #7 to close. The operator also noted that PI 705A indicated an internal UF. cylinder pressure of 50 psia. The LCPS is designed to
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actuate if the internal cylinder pressure has not reached 20 psia aller one hour of heating. Since a reading of 50 psia indicated the instrument loop had malfunctioned, the operator opened the local i
instrument cabinet to investigate the failure. When the door to the cabinet was opened, the door movement caused the instrument reading to change to 61.7 psia, which was the expected cylinder pressure. The steam supply valves to the autoclave then opened and cylinder heating resumed automatically as designed. The operator immediately initiated steam shutdown utilizing the local steam isolation controls m place the autoclave in a shutdown condition until the cause of the actuation could be determined.
The initial engineering review of the actuation concluded that the LCPS actuation was caused by an invalid low pressure signal and was not reportable. Further investigation into the cause of the failure of PI 705A revealed that the pressure transducer providing the signal to PI 705A had failed.
Engineering determined that the failed pressure transducer also rendered the UF. Cylinder liigh Pressure Autoclave Steam Shutoff (CilPASS). safety system inoperable, since the pressure transducer also provides the signal for this safety system. Following the discovery of this i
infonnation, it was determined that the failure of the AC #7 CilPASS safety system was reportable in accordance with 10 CFR 76.120 (c)(2). The event notification was made on October 24,1997, at 1735 hours0.0201 days <br />0.482 hours <br />0.00287 weeks <br />6.601675e-4 months <br />. 'Ihe pressure transducer is a 24 VDC instrument, manufactured by Moore Industries, model number PIT /3 15PSIO/4-20MA/12-42DC.
The CilpASS system is a single channel system. The heating of a UF. cylinder containing an excessive amount of" light" gases at normal heating temperatures could result in the internal cylinder pressure exceeding the hydrostatic test pressure and possibly create a UF. release in the autoclave, The safety system function of the CIIPASS ensures the pressure in the cylinder does not exceed the i
maximum allowable working pressure of the lowest rated cylinder that could be heated in the autoclave. The UF. cylinder pressure inatmment loop is required to alarm if the cylinder pressure at any time reaches 115 psia with a tolerance of + 5 psia.
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4 Dochet No. 70 7002 l
' Enclosure 1 i
Page 2 0f 2 Event Report 97 21 Revision 1 Cause of Event The direct cause of the event was a failed pressure transducer. The pressure transducer converts a pneumatic signal of 3 15 psia to a current signal of 4 20 mA. Since the loop is wired in series, when the 4 20 mA current from the pressure transducer is lost, it renders the loop inoperable.
The root cause of event was a random failure of the pressure transducer module. The module i
consists of a printed circuit board encased in a plastic housing. The unit has two electrical screw terminals anchored to the housing and soldered to the printed circuit board. Engineering analysis i
determined that the solder on the positive side of the transducer circuit board had separated. There a
was no evidence that the unit had been mishandled or that the failure was caused by too much stress i
on the connection.
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The manufacturer of the device was contacted to determine if the failed solderjoint could have been i
caused by a fabrication problem that resulted in an improper solder connection. The manufacturer i
indicated that this device has experienced a low failure rate of 0.13 percent, As a result, engineering i
believes this failure to be an isolated occurrence. This module and approximately 45 others have i
been in service for 15 years with no known failures of this type. Based on this information, i
engineering has determined that these modules are acceptable for continued use.
i Corrective Actions 1.
On October 28,1997, the pressttre transducer was replaced and the loop calibrated.
Extent of Exposure ofIndividuals to Radiation or Radioactive Materials There were no exposures to individuals from this incident to radiation or radioactive materials.
Lessons Learned When this event occurred, it was not immediately recognized that a.50 psia pressure indicator i
reading could be an indication that the pressure transducer or pressure transmitter had failed. An i
engineering evaluation detemiined that the.50 psia reading is the default condition when a pressure i
indicator loses its input signal. The loss of the input signal could be caused by any failure of the i
cylinder pressure loop, including a malfunctioning pressure transmitter or transducer. As a result i
of the presrure loop design, any failure of the pressure loop will not generate an alarm until the i
LCPS actuates aller on hour of neating. Operators were not aware of this design feature and did not i
immediately recognize that the CilPASS safety system was inoperable.
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