ML20211Q717

From kanterella
Jump to navigation Jump to search
Forwards Required 30-day Written Event Rept 99-14,rev 1,re 990628 Event Involving Actuation of Brake Sys on Liquid U Hexafluoride Handling Crane at Plant.Revised Rept Includes Corrective Actions.Commitments in Rept Also Encl
ML20211Q717
Person / Time
Site: Portsmouth Gaseous Diffusion Plant
Issue date: 09/08/1999
From: Jonathan Brown
UNITED STATES ENRICHMENT CORP. (USEC)
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GDP-99-2049, NUDOCS 9909150131
Download: ML20211Q717 (6)


Text

O

.USEC A Global Energy Company September 8,1999 GDP 99-2049 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001 Portsmouth Gaseous Diffusion Plant (PORTS)

Docket No. 70-7002 Event Report 99-14, Revision 1 Pursuant to the Safety Analysis Report, 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 a liquid uranium hexafluoride handling crane at the Portsmouth Gaseous Diffusion Plant. The revised event report includes corrective actions. Enclosure 2 is a list of commitments contained in this report. Changes from the previous report are marked with a vertical dashed line in the right margin.

Should you require additional information regarding this event, please contact Scott Scholl at (740) 897-2373.

Sincerely, W

J. Morris Brown General Manager f

Portsmouth Gaseous Diffusion Plant

Enclosures:

.As Stated

/

cc:

NRC Region III Office qI NRC Resident Inspectors - PORTS i,

9909150131 990908 PDR ADOCK 07007002 C

PDR l

United States Enrichment Corporation Portsmouth Gascous DifTusion Plant P.O. Box 628, Piketon. OH 45661

1 GDP 99-2049 Page1of4 Event Report 99-14 Revision I

)

Description of Event On June 28,1999, at approximately 0105 hours0.00122 days <br />0.0292 hours <br />1.736111e-4 weeks <br />3.99525e-5 months <br />, an operator was removing a 10 ton liquid uranium

)

hexafluoride UF,, cylinder from X-343 autoclave (AC) #6 when the south crane brake actuated in response to a loss ofpower. The crane brake functioned as designed to prevent the uncontrolled f

dropping of the cylinder. Following the actuation, the cylinder was len suspended approximately two feet above the AC #6 rollers. Immediately aner identifying the south crane suspended cylinder, X-343 personnel started suspended cylinder actions according to procedure XP2-TE-TE5030,

" Emergency Handling of Suspended Cylinders Containing UF." At approximately 0142 hours0.00164 days <br />0.0394 hours <br />2.347884e-4 weeks <br />5.4031e-5 months <br /> the e

Emergency Operations Center was staffed to provide the technical support necessary to coordinate resolution of the suspended load.

As a precautionary measure, temporary cribbing was placed below the suspended cylinder, minimizing the distance the cylinder could fall if the brakes failed. All other operational !! quid handling cranes were tagged out of service pending an investigation to determine the reason ihr the failure. A ugmeering evaluation was performed to verify that the temporary cribbing used to block j

the suspended cylinder above AC #6 rollers was adequate. An engineering evaluation on the X-343 l

crane load bearing structures was also performed to dete 3 if the north crane could continue to l

be used while the cylinder was suspended from the souti. r ae. The evaluation determined that the l

structural steel and crane rail could support both the n and south crane each holding a full l

cylinder.

l The decision was made to leave the cylinder suspended until it cooled and became solid. On July 1,1999, following completion of the required 5-day cooling period, the cylinder was lowered into AC #6 using a temporary procedure that was written to control this activity.

The uncontrolled dropping of a liquid UF, cylinder could result in 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

6 quality class items. The hoist brake actuation is being considered a valid safety system actuation and is reportable in accordance with Safety Analysis Report (SAR), Section 6.9, Table 6.9-1, J(2).

Cause of Event The direct cause for the actuation of the brakes on the south crane was power to the hoist motor was interrupted when a hoist motor heater overload device tripped. This overload consists of heater elements, one for each of the three phases. If a high current condition exists in one of the hoist motor phases, the heat produced by the heater element will cause a bimetallic element to open a contact, thereby interrupting power to the hoist motor.

GDP 99-2049 Page 2 of 4 l

Event Report 99-14 Revision 1 The root cause for this event was inattention to detail by electrical maintenance personnel who tested and installed the hoist motor heater overload device on the south crane. An inspection of the overloads following this event revealed that the screw that holds the middle heater element in place was not fully tightened. Following this event, the overload was removed from the crane and tested to determine if the as found condition of the middle screw would cause the overload to trip prematurely. This testing confirmed that the loose connection created additional electrical resistance and heat, causing the overload to trip below the desired level. An overload test conducted after the screw was correctly tightened demonstrated that the overload trip point was within acceptable limits.

A discussion of the circumstances that led to this event is provided below.

Prior to this event, investigation activities relating to the actuation of the X-343 north crane brake that occurred on May 4,1999 (Event Report 99-09), led to the removal and testing of the hoist motor overloads on the north and middle X-343 cranes. The testing demonstrated that the overloads did not trip at the correct setpoint. New overloads were obtained and tested with the old heater elements to verify the trip setpoints were within limits. As part of this activity, the screws on the overload blocks were loosened to allow test equipment to be connected. When testing was completed on June 18,1999, maintenance personnel did not properly tighten the screws after the test equipment was removed.

On June 25,1999, the south crane was declared inoperable because of concems relating to the design of the crane hoist motor and Magnetorque brake assembly. As part of the activities to restore the crane to an operable status, it was determined that the hoist motor overloads should be replaced. The south crane motor hoist overloads were replaced with overloads that had been successfully tested as part of the north and middle crane work described above. The maintenance personnel who installed the overloads did not verify that all connections were properly tightened. Following replacement of the hoist motor overloads, the crane was successfully tested under 100% load conditions with the loose connection. Ilowever, the overload tripped when the first UF cylinder was lifted following 6

overload replacement. Tighiening all fasteners disturbed is considered skill of the craft and ensuring that all fasteners and connections are tightened at the end of each job is a part of their training.

The errors that led to this event are mainly preventable through rigorous adherence to the Stop Think Act Review (STAR) self checking process and attention to detail. The maintenance personnel who tested the overload should not have left the overload screws loose. The maintenance personnel who installed the overload should have conducted a thorough visual inspection of the overload which would have likely detected the loose screws. It should be noted that during efforts to return the north crane to service following this event, one of the overloads tested on June 18.1999, was installed on the north crane. During installation a different group of maintenance personnel detected the loose

l j

GDP 99-2049 Page 3 of 4 Event Report 99-14 Revision I screw and tightened it as part of the installation activity.

A contributing cause for the event was the failure to maintain adequate installation control of the hoist motor heater overload device. The overload does not perform a safety function and is controlled as a non-safety (NS) component. The configuration management program requirements for NS equipment are not as rigorous as the requirements for "Q" equipment. Similar events have occurred in the past (Event Reports 98-07 and 98-09) where equipment designated as NS caused a safety system to actuate. As a result of past events, procedure XP3-EG-EG1067 " Enhanced Commercial Controls Requirements Process" was developed to provide for enhanced controls for selected NS components. This event demonstrated the need to evaluate the hoist motor breaker and overloads in accordance with this process.

Corrective Actions 1.

On August 3,1999, a PMT was developed for use in work packages involving supply power l

components such as overloads, contacts and/or breakers for hoist motors on liquid UF,,

l handling cranes. This PMT will ensure that all disturbed connections including heater I

terminations are tightened.

l 2.

By September 15,1999, Maintenance will develop a lessons learned that covers an overview l

of this event which emphasizes the importance of attention to detail and the Stop Think Act l

Review (STAR) process. The need to insure a thorough visual inspection of new/ replaced l

components for deficiencies that could affect their operation and the need to check for l

adequate tightness of all disturbed contact fasteners prior to completion of maintenance tasks l

will also be emphasized.

l l

3.

By October 15,1999, the lessons learned will be presented ;;. maintenance personnel that l

conduct or supervise electrical maintenance activities.

l 4.

By November 5,1999, Engineering will evaluate the hoist motor breaker and heater overload l

devices used in the X-343 overhead crancs using procedure XP3-EG-EG1067 " Enhanced l

l Commercial Controls Requirements Process" for increased procurement and installation I

controls.

l Extent of Exposure ofIndividuals to Radiation or Radioactive Materials There were no exposures to radiation or radioactive materials due to this event.

1 i

l l

l

)

I GDP 99-2049 Event lleport 99-14 Ilevision 1 Lessons Learned 1

When working with new or replaced components of a system it is important to perform a thorough visual inspection of the component to detect deficiencies that could affect their operation and to i

check for adequate tightness of all disturbed fasteners prior to completion of maintenance task.

l

\\

l i

I l

I e

GDP 99-2049 l

Page1of1 t

l Event Report 99-14 j

Revision 1 List of Commitments 1.

By October 15,1999, the lessons learned will be presented to maintenance personnel that l

conduct or supervise electrical maintenance activities.

l 2.

By November 5,1999, Engineering will evaluate the hoist motor breaker and heater overload l

devices used in the u-343 overhead cranes using procedure XP3-EG-EG1067 " Enhanced l

Commercial Controls Requirements Process" for increased procurement and installation l

controls.

l l

  • Regulatory commitments contained in this document are listed here. Other actions listed in this submittal are not considered regulatory commitments in that they are either statements or actions completed, or they are considered enhancements to USEC's investigation, procedures, or operations.

L