ML20199K950
| ML20199K950 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 11/24/1997 |
| From: | Morgan J UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-97-2036, NUDOCS 9712010240 | |
| Download: ML20199K950 (5) | |
Text
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United States Entschment Corpor tion
.I 2 Democracy Center
- 1 6903 Rockledge Drive Betnesda, MD 70817 jh lei. i311)564 3200 Fac(301)564 3201 November 24,1997 United States Nuclear Regulatory Commission GDP-97 2C36 Attention: Document Control Desk Washington, D.C. 20555 0001 Portsmouth Gascous Di#usion Plant (PORTS)- Docket No. 70 7002 - Event Report 97-22 Pursuant to 10 CFR 76.120 (d)(2). Enclosure i provides the required 30 day written Event Report (ER) for an event involving a failure of the UF. Cyliadcr liigh Pressure Autoclave Steam Shutoff safety system at the Portsmouth Gaseous DifTusion Plant. Enclosure 2 is a list of commitments made in the report.
Should you require additional information regarding this event, please contact Scott Scholl at (614) 897 2373.
Sincerely, n
.h a
Acting General Manager Portsmouth Gaseous Diffusion Plant DIA:SScholl:cw i
1 673 cc:
y NRC Region 111 D. liartland, NRC Resident inspector, PORTS
@6[kIIkkfk 9712010240 971124 PDR ADOCK 07007002 C
PM OFices in uvemore.Caldornia Paducah, Kentucky Portsmouth. Ohio Washingto, DC
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I Ibcket No. 70 7002
. Enclosure 1 Page1of3 Event Report 97 22 Description of Event October 25,1997, at 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br />, X 344 Autoclave (AC) #3 was in Mode !!, heating a Uranium '
ilexafluoride (UF.) cylinder. The cylinder had been heating for approximately 25 minutes when the operator noted that pressure indicator PI 165 indicated an internal UF. cylinder pressure of 50 psia.
Since a reading of 50 psia indicated the instrument had malfunctioned, the operator immediately initiated steam shutdown manually, utilizing the local steam isolation controls to place the autoclave In a shutdown condition until the cause of the 50 psia instrument !ndication could be detennined.
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- After the faulty PI 165 reading was first observed on October 25,1997, Maintenance personnel initially observed that PI 165 was reading the expected pressure when they arrived to investigate.
Maintenance personnel checked the instrument loop and determined that the "as found" instrument I
readings for the loop were within tolerance. While Maintenance personnel were perfoiming closeout activities they noticed that the PI 165 cylinder pressure, PI 169 sample loop pressure and PI-186 manifold pressure were all reading -50 psia. Further investigation indicated that the power cord to the transducer cabinet, which supplies power to all three systems, v as loose. The plug was tightened and all PI readings retumed to normal. Maintenance personnel trlieved that the loose power cord was the cause for the faulty PI readings. Operations then perfbrmed the Cylinder liigh Pressure Test and Cylinder Low Pressure Test successfully and returned the autoclave to service.
On October 27,1997, Operations Management recognized that the condition that caused the erroneous reading on Pl.165 may have also caused the UF. Cylinder liigh Pressure Autoclave Steam Shutofr(CilPASS) safety system to be inoperable. A similar pressure indicator failure at X 343 AC
- 7 had occurred on October 22,1997, and caused the CllPASS to be inoperable (reference Event Report 97 21). Since investigation activities were unable to determine if the CllPASS would still function with the identified deficiencies,it was detennined that the system may not have been able to perfomi its design function as a result of this event. The failure ephe C'IPASS safety system is reportable in accordance with 10CFR 76.120 (c)(2).
The CllPASS system is a single channel system. The heating of a UF. cylinder containing an excessive amoent of' light' gases at normal heating tempe atures could result in the internal cylinder pressure ecceding the hydrostatic test pressure and possibly create a UF. release in the autoclave.
The safety system function of the CllPASS ensures the pressure in the cylinder does not exceed the maximum allowable working pressure of the lowest rated cylinder that could be heated in the autoclave. The UF. cyiinder pressure instrument loop is required to slarm if the cylinder pressure at any time reaches 115 psia.
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4 Docket No. 70 7002 Page 2 of 3 Event Report 97 22 Cause of Event
'lhe direct cause of the event was inadequate electrical connections between the pressure transducer and the CllPASS safety system circuitry. During investigation activities conducted by Maintenance and Engineering, it was observed that movement of the wiring and terminal strip that connects the pressure transducer to Pl 165 caused the PI to read 50 psia. This terminal strip also provides the connections between the pressure transducer and the CllPASS circuitry. Although it is not known for certain that the loose electrical connections alTected the CilPASS circuitry, the investigation was not able to prove that the CllPASS was operable when this condition was discovered. As a result, it was conservatively determined that the loose wiring could have prevented the CllPASS from performing its design function.
PI 165 is the pressure indicator for cylinder pressure on X-344 AC #3. The cylinder pressure loop contains a pressure transmhter, a pressure transducer, a pressure indicator, and high and low pressure switches.1he pressure transmitter is located on the UF. drain line just outside tne head of the autoclave. The pressure transmitter converts UF pressure to a mV signal. The pressure transducer convens the mV signal to a mA signal and consist of two cards. One card converts the mV signal to 04 Volts DC. The other card converts 0 5 Volts DC to 4 20 mA and contains the high and low pressure switches. The pressure indicator converts the mA signal to a pressure reading in psia.
Engineering detennined that a 50 psia reading on PI 165 was a result of a signal loss to the Pl. The Pl design is such that it interprets a O mA reading as -50 psia. The signal loss can res.nlt from inadequate electrical connections from the transducer to the Pl, signal loss within the 1:ansducer, a loss of signal within the pressure transmitter or a power loss to the pressure transduccr.
The loss of power to the transducer was eliminated as a possible cause because the ClIPASS did not alarm when the fauhy PI 165 reading was first observed. The design of the system will cause an alarm if power is lost. The pressure transmitter was also eliminated as a cause because the inmsmitter perfonned as designed through all pressure ranges during testing, The transmitter is a mechanical device and any failure of the transmitter would be repeatable.
During the investigation Engineering and Maintenance observed thatjiggling the wiring and tenninal strips that connect the transducer to PI 165 would cause the readings to change from 50 psia to the expected reading. W.e.nociated wiring was re terminated and the two transducer boards were replaced as a prvemttion ry measure. Afler calibration was performed on the equipment, Pl.165 was again observed to rea -50 psia. Since replacement of the transducer cards did not correct the problem, it was suspec,ed that the problem was caused by faulty electrical connections.
The root cause for the event was determined to be inadequate design of the transducer housing
Docket No. 70 7002
. Enclosure i Page 3 of 3 Event Report 97-22 mounting which resulted in faulty electrical connections. During the investigation it was noted that the transducer housing was placed on a small pedestal without any method of attaciunent. To access the terminal strips on the transducer, the housing is turned or rotated on the pedestal. It was observed that when the transducer was rotated, erroneous readings wcre obtained on PI 165.
The lack of permanent mounting also allowed stress to be p! aced on the terminal strips. The wires exit from the bottom of the housing such that the weight of the housing is allowed to exert force on the wires. 'Ihis creates stress on the wires that can degrade the t.lectrical connection. 'Ihe transducer cards also plug into the tenninal strip and could be affected by movement of the wires. With this type of arrangement, rny movement of the transducer housing can afTect the integrity of the electrical connections. Since the transducer connections are part of the CllPASS safety system, it was concluded that the CIIPASS may have been affected by this deficiency.
An engineering walkdown was conducted to determine if this mounting deficiency exists at other autoclave installationa. No additional mounting problems were noted.
Corrective Actions 1.
The autoclave cylinder pressure transducer cards and terminal strip connecting the transducer to pl 165 were replaced. Pressure indicator PI-165 and its associated wiring were replaced.
These actions were completed by October 30,1997.
2.
On October 30,1997, the pressure transducer housing was temporarily mounted to the pedestal table to prevent inadvertent movement and to prevent the housing from exerting force on the wires and terminal connections.
3.
Ily February 4,1998, a design modification will be completed to provide permanent mounting of the UF. cylinder pressure transducer housing.
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 Safety systems must be properly mounted and secured to ensure they will remain capable of performing their design function.
i Docket No. 70 7002 EncJosure 2 Page1ofI Event Report 97-22 List of Commitments 1.
Ily February 4,1998, a design modification will be completed to provide permanent mounting of the UF. cylinder pressure transducer housing.
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