ML20207F528
| ML20207F528 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 06/03/1999 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-2030, NUDOCS 9906080303 | |
| Download: ML20207F528 (4) | |
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?e USEC A Global Energy Company j
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June 3,1999 GDP 99-2030 i
i U. S. Nuclear Regulatory Commission j
Attention: Document Control Desk
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Washington, D.C. 20555-0001 Portsmouth Gaseous Diffusion Plant (PORTS)
Docket No. 70-7002 Event Report 99-09 Pursuant to the Safety Analysis Report (SAR), Section 6.9, Table 6.9-1, J(2), Enclosure 1 provides the required 30-day written Event Report for an event involving an actuation of the brake system on I
a liquid uranium hexafluoride (UF.) handling crane at the Portsmouth 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 July 24,1999. There are no new commitments contained in this report.
Should you require additional information regarding this event, please contact Scott Scholl at (740) 897-2373.
Sincerely, f
W
. Morris Brown General Manager Portsmouth Gaseous Diffusion Plant
Enclosures:
As Stated f
cc:
NRC Region III Office l
NRC Resident Inspectors - PORTS g6 S ;I 9906000303 990603 PDR ADOCK 07007002 C
PDR,
United States Enrichment Corporation Portsmouth Gaseous Diffusion Plant P.O. Box 628, Piketon, OH 45661 l'
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GDP 99-2030 i
Page1of3 i
Event Report 99-09 Description of Event l
On May 4,1999, at approximately 1350 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.13675e-4 months <br />, an operator was removing a 14 ton liquid uranium I
hexaflouride (UF ) tails cylinder from X-343, autoclave (AC) #5, when the north crane brake 6
actuated in response to a loss of power. The loss of power caused the cylinder to be suspended l
approximately one foot above AC #5 for approximately 45 minutes. Personnel investigating the loss l
of power determined that the hoist motor breaker had tripped. In accordance with plant procedures, l
the hoist breaker was reset and the cylinder was moved to the X-343 liquid uranium cool down area.
Prior to the event the cylinder was being heated to perform required sampling. As a result of a false cylinder high temperature safety system actuation, the cylinder heating was stopped before the sampling could be performed. The cylinder was being removed from the autoclave at the time of the event to allow maintenance personnel to investigate the cause of the actuation.
j 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" i
6 quality class items. The crane braking system is designed to prevent an uncontrolled drop upon loss of power. An actuation of the crane brake is reportable in accordance with the Safety Analysis Report (SAR), Table 6.9-1, J(2).
Cause of Event i
The direct cause for the actuation of the brakes on the north crane was power to the hoist motor was interrupted when the 40 amp hoist breaker tripped. The hoist breaker tripped as a result of high current being drawn by the hoist motor during low speed operation. Investigation activities to determine the causes for this event are continuing. This event report will be revised when the investigation is complete. The following provides information that is currently known about the event.
The three cranes in X-343 are different than other liquid UF handling cranes because they utilize 6
the P&H static stepless hoist drive control system. This system is designed to control the speed / torque characteristics of 3-phase AC, wound-rotor induction motors. In this system, braking l
is provided by a mechanical brake. A Magnetorque load brake provides speed control and would reduce the speed of descent in the event ofloss of power and failure of the mechanical brake.
The static stepless control system sets the Magnetorque brake to work in conjunction with the hoist motor. A cathode transformer supplies the voltage for the control system. The cathode transformer is designed with two taps,120V and 240V. He cranes in X-343 are designed to use the 240V tap connection for the brake circuit.
L GDP 99-2030 i
Page 2 of 3 Event Report 99-09 1
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' During the investigation, it was discovered that the cathode transformer on the north crane was incorrectly wired on the 120V instead of the 240V tap. This caused the wrong voltage to be supplied
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- to the brake portion of the control system. This condition pn: vented the electricians from performing L
. the alignment correctly which caused the Magnetorque brake to continuously oppose the hoist motor.
Although the crane will function in this configuration, the hoist motor will experience high amperage due to continuous opposition from the Magnetorque. It is believed that the north crane has been operating with incorrect wiring since the time of original installation, which occurred in the 1979 timeframe.
A review of the middle and south crane cathode transformer connections was also conducted. It was determined that the middle crane cathode transformer voltage tap connection was also incorrectly wired. The middle crane has been out of service since approximately October of 1997. The south crane, however, was found to be wired correctly. Further investigation revealed that incorrect wiring on the south crane had been previously discovered in 1996 and corrected at that time. The investigation was not able to determine why the north and middle cranes were not inspected and corrected following the 1996 discovery that the south crane was incorrectly wired.
- A review ofprocedure XP4-TE-EM6450, "X-343 Cranes Static Stepless Alignment" was conducted.
l The procedure directs the performance of the static stepless alignment in accordance with Hamischfeger P&ll Maintenance Manual, Static Stepless Control Bulletin 562/563. The procedure requires as-found and as-left amperage values to be recorded for the reactor and Magnetorque brake, l
but does not list acceptable ranges for these values. The acceptance criteria are listed in the P&H Maintenance Manual.
It has also been noted that procedure XP4-TE-EM6450 and the P & H Maintenance Manual, do not require that hoist motor amperage readings be taken following alignment activities. Hoist motor amperage readings in conjunction with appropriate acceptance criteria would have led to further investigation which may have detected the incorrect cathode transformer connection and any alignments that were not performed correctly.
A review of crane operating practices has revealed that a common practice by the crane operators is to inch the hoist, which means they repeatedly push the hoist button either in the up or down direction to move cylinders. The high hoist motor currents in the low speeds and the probab'e j
inching by the operators worked together to cause the breaker to trip and suspend the cylinder. Crane operators who would move UF cylinders and are assigned to the X-343 Feed and Transfer Facility 6
are required to complete training module OUF01.10.01 "UF Cylinder Handling Using Cranes and 6
Lifting Fixtures" as part of the qualification standard. In addition, XP2-TE-TE2030, " Operation of UF Handling Cranes and Lifting Fixtures", covers operation of the liquid UF handling cranes. The qualification training and procedure does not address the improper practice of excessive inching of l
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GDP 99-2030 Page 3 of 3 Event Report 99-09 the hoist controls. Testing performed on the north crane prior to correction of the wiring and alignment indicated that if the controls were inched consecutively ten times, the hoist motor breaker would trip. Testing completed aller repairs were made indicated that the crane could handle more inching.
Corrective Actions Taken l
1.
On May 27,1999, a daily operating instruction was issued for X-343 operators, to make them aware that excessive inching can cause the hoist motor breaker to trip and to instruct them to limit inching as much as possible when lifting UF cylinders.
6 2.
On June 3,1999, a new post maintenance test was developed to ensure the motor hoist amperage is checked prior to returning an X-343 crane to service following an alignment.
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 Lessons learned will be provided with the revised event report.
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