ML20209B934
| ML20209B934 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 06/28/1999 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-2035, NUDOCS 9907080319 | |
| Download: ML20209B934 (4) | |
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d USEC A Global Energy Company i
June 28,1999 GDP 99-2035 U. S. Nuclear Regulatory Commission Attention: Docunent Control Desk Washington. DC 20555-0001 Portsmouth Gaseous Diffusion Plant (PORTS)
Docket No. 70-7002 Event Report 99-13 Purstian' to the safety analysis report, section 6.9, table 6.9-1, J.2 Enclosure 1 provides the required t
30 dav Event Report for an event invo'Iving a liquid UF handling crane in the X-330 Process 6
Buildag tails withdrawal area at the Pcrtsmouth Gaseous Diffusion Plant. Investigation activities are continuing to determine the root cause and corrective actions for this event. This report will be revised following completion of these activities. The revised event report is scheduled for August 11,1999. There are no new commitments contained in the report.
Should you require additional information regarding this event, please contact Scott Scholl at (740) 897-2373.
Sincerely, M
h
. Morris Brown General Manager
- Portsmouth Gaseous Diffusion Plant f
Enclosures:
As Stated NRC RegioriIII Office h[
cc:
NRC Resident Inspector - PORTS 9907000319 990629 PDR ADOCK 07007002 C
PDR,
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(I UUC United States Er:richment Corporation gjt, 2 UM Portsmouth Gaseous Diffusion Plant P.O. Box 628, Piketon, Oli 45661
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GDP 99-2035 Page1of3 Event Report 99-13
- Description of Event At 1714 hours0.0198 days <br />0.476 hours <br />0.00283 weeks <br />6.52177e-4 months <br /> on May 28,1999, the hoist brake on the south Tails withdrawal crane actuated. The actuation occurred while a full 14-ton ligtS UF Tails cylinder was being placed on a rail car to begin the required 5-day cool down period. While actuated, the crane brake functioned as designed l
to prevent uncontrolled dropping of the cylinder. Following the actuation, the cylinder was left suspended approximately 12 inches above the rail car cradle. The steps of procedure XP2-TE-TE5020, " Emergency Handling of Suspended Cylinders Containing UF," were followed, but did not ' result in the cylinder being lowered. At 1852 hours0.0214 days <br />0.514 hours <br />0.00306 weeks <br />7.04686e-4 months <br /> the decision was made to staff the Emergency Operations Center to provide the technical support necessary to coordinate resolution of the suspended load.'
As a precautionary measure, a temporary cradle was placed below the suspended cylinder, minimizing the distance the cylinder could fall if the brakes failed. All other liquid handling cranes were tagged out of service pending an investigation to determine the failure mechanism. An engineering evaluation of the Tails trane load bearing structures was also performed. The evaluation determined that the structural steel and crane rail could support both cranes each holding a full
- cylinder. The evaluation was performed to support the eventual return of the north crane to service following the initial investigation.
The decision was made to leave the cylinder suspended until it cooled and became solid. On June 2,1999, follov.ing the required 5-day. cooling period and the issuance of a temporary procedure for moving the cylinder, the cylinder was lowered onto the railcar cradle.
The uncontrolled dropping of a liquid cylinder could result in the rupture of a cylinder and potential release of up to 28,000 pounds of UF. As a result, liquid UF, handling overhead cranes are "Q" 6
quality class items. The crane braking system is designed to prevent an uncontrolled liquid UF 6
cylinder drop. The hoist brake actuation is being considered a valid safety system actuation and
- accordingly, is reportable in accordance with the safety analysis report, section 6.9, Table J.2.
The south Tails overhead crane was manufactured by Shepard Niles, serial number 64711.
Cause of Event The direct cause of the event has been determined to be broken wires in the mane control pendant cable which controls the crane hoist.- With the wires broken, the hoist moter would not operate and the brakes would not release when the control button was pushed to lower the load. The crane
. pendant cable is not part of the "Q" boundary.
4 l,
e GDP 99-203 Page 2 of 3 Event Report 99-13 When Maintenance first investigated the cause for the failure it was noted that a pin, which is part of the mechanism that keeps the hoist brakes in an open position, was not in the correct position.
The pin for the left actuating amt had backed out and the actuating arm was loose. This pin, which is threaded into a common bracket with the right side ami, should have been retained by use of ajam nut. Thisjam nut and thejam nut for the right side arm were found in the bottom of the assembly.
After the actuating mechanism was repaired it was discovered that the crane hoist would still not function to allow the load to be lowered. Further investigation revealed a broken wire in the pendant cable. A spare wire in the cable was then connected to restore the broken circuit. The restoration of this circuit allowed the crane to function and lower the load. The existing pendant cable was then replaced. An inspection of the replaced pendant cable revealed three additional broken wires.
Based on initial observations of the failed wires, it appears that the wires failed as a result of an improperly installed clamp associated with the pendant stress relief chain. The clamp was installed in a manner that allowed the weight of the pendant push button station to be supported by the cable.
The resulting stress exerted on the cable apparently caused the wires to break.
The remaining liquid UF handling cranes were inspected and functionally tes ed prior to being 6
returned to service. No similar mechanical or electrical failures were discovered. In addition, pendant cables in the remaining liquid UF handling cranes were inspected to ensure that the cables 6
were not improperly stressed.
After the crane pendant cable was replaced, additional testing was performed to simulate operation of the crane hoist with the pin removed from the left actuating arm mechanism. With the pin removed, the brake functioned correctly and allowed proper operatica of the hoist with a 14-ton test weight. This demonstrated that the incorrectly positioned pin did not prevent proper operation of the brake and was not the cause of;his event.
The investigation also noted that both brake solenoids were replaced in the crane brake assembly in October 1998. This activity would have required removal and reinstallation of the actuator arms and pins. A review of maintenance and inspection procedures revealed weaknesses which may have contributed to the actuator pin and jam nuts being incorrectly positioned. Although the incorrectly positioned actuator pin was not a cause for this event, corrective actions will be developed to address the noted weaknesses.
Investigation activities are continuing to confirm the causes for this event and develop appropriate corrective actions. When the causes and corrective actions have been fully determined, this event report will be revised.
- f.,
GDP 99-2035 Page 3 of 3 Event Report 99-13 Corrective Actions Corrective actions will be provided with 'the revised event report.
5 Extent of Expost re ofIndividuals to Radiation or Radioactive Materials
. There was no exposure to radiation or radioactive materials due to this' event.
1 Lessons Learned.
Lessons learned will be provided with the revised event ' report.
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