ML20211M694

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Forwards 30-day Written Event Rept 99-09,rev 1,for Event Involving Actuation of Brake Sys on Liquid U Hexafluoride Handling Crane at Plant.Revised Rept Includes Root Cause & Corrective Actions.List of Commitments,Included
ML20211M694
Person / Time
Site: Portsmouth Gaseous Diffusion Plant
Issue date: 09/02/1999
From: Borwn J
UNITED STATES ENRICHMENT CORP. (USEC)
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GDP-99-2046, NUDOCS 9909090179
Download: ML20211M694 (6)


Text

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USEC d A Global Energy Company September 2,1999 GDP 99-2046 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 99-09, 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 the root cause and 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,

. Morris Brown.

General Manager Portsmouth Gaseous Diffusion Plant W

Enclosures:

As Stated f

' cc:

NRC Region III Office NRC Resident Inspectors - PORTS 9909090179 990902 PDR ADOCK 07007002 C

PDR United States Enrichment Corporation Portsmouth Gaseous Diffusion Plant P.O. Ilox 628, Piketon, OH 45661 l

r-GDP 99-2046 Page 1 of 4 Event Report 99-09 Revision 1 Description of Event 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 hexafluoride (UF.) tails cylinder f om X-343, autoclave (AC) #5, when the north crane brake actuated in response to a loss of power. The loss of power caused the cylinder to be suspended approximately one foot above AC #5 for approximately 45 minutes. Personnel investigating the loss of power determined that the hoist motor breaker had tripped. In accordance with plant procedures, 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.

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" 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 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 cunent being drawn by the hoist motor due to improper static stepless control system alignment.

The three cranes in X-343 are different than other liquid UF handling cranes because they utilize the P&ll 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 is provided by a mechanical brake. A Magnetorque load brake provides speed control.

l The root cause for the event was that the procedure for performing static stepless control system 1

alignments provided conflicting guidance and was written in a confusing format. Procedure l

XP4-TE-EM6450, "X-343 Crane Static Stepless Alignment" refers to the Ilarnischfeger P&ll l

2 Mainter.ance Manual, Static Stepless Control Bulletin 562/563, for the actual performance of the I

static stepless alignment. The manual provides step by step instructions on how to adjust settings l

to obtain the correct alignment. The last step of the instructions states that the alignment is complete l

at that point, but instructs personnel to observe crane operation with a load applied and make l

n GDP 99-2046 Page 2 of 4 Event Report 99-09 Revision 1 additional adjustments ifneeded. The additional adjustments, however, can invalidate the alignment.

l A note appears after the last step of the instructions that states certain adjustments will require the l

alignment to be re-performed. The normal procedure famiat used at PORTS would require the note l

to precede the action step. Since the note was located after the last step, maintenance personnel did l

not recognize that the note applied to the final adjustments they were making. The lack of l recognition of the information contained in the note was consistent among the various maintenance l

personnel who perfonn X-343 crane alignments. The troubleshooting section of the P & H manual l

is also confusing because it da., not provide step by step instructions on how to perform I

troubleshooting. All other crane maintenance procedures have been reviewed and do not require the l

use of a vendor manual in order to perform maintenance.

l A contributing cause for the event was a lack of acceptance criteria in procedure XP4-TE-EM6450.

l The procedure requires that as-found and as-left data on crane settings be recorded but does not l

specify the acceptance criteria for each parameter. The procedure indicates that acceptance criteria j

are found in Section 11 of the P & 11 maintenance manual, but this section of the manual does not l

include acceptance criteria for all parameters. In addition, the acceptance criteria that are included l

are not readily identifiable.

l Another contributing cause for the event was that the installed crane configuration did not match the l

vendor manual. The installed configuration consists of a 25 hp,1800 rpm motor with a Magnetorque l

105. The vendor drawing specifies that a Magnetorque 83 should be used with a 25 hp,1800 rpm l

motor. The static stepless alignment settings specified in the P & H Maintenance Manual are based l

on the configurations listed in the vendor manual and are not correct for the installed configuration.

l This resulted in the alignment being perfomied with incorrect settings and caused the Magnetorque l

to apply greater torque to the hoist motor resulting in increased motor current. The incorrect settings I

also resulted in the hoist motor surging while lifting a load. As a result, adjustments to the crane following performance of the static stepless alignment were required to correct the surging condition.

l As described above, maintenance personnel did not understand that the adjustments they were l

making to correct motor surging invalidated the static stepless alignment.

l The difference between the vendor manual and the installed configuration also caused the cathode l

transformer connections on the X-343 cranes to be wired on 120V taps instead of the required 240V l

taps. A 120V tap would be correct for a Magnetorque 83, but a Magnetorque 105 requires a 240V l

power supply. When this problem was discovered and corrected on the north crane, a review of the l

middle and south cranes was also conducted. The middle crane was also wired incorrectly, but has l

been out of service since approximately October 1987. The south crane was fbund to be wired l

l correctly. Further investigation revealed that incorrect wiring of the south crane had been previously l

discovered in 1996, and corrected at that time. A search of the problem report database indicated l

Fp.

i Enclosure i GDP 99-2046 Page 3 of 4 Event Report 99-09 Revision I that this problem was not reported and was not investigated to determine the cause. As a result, an l

opportunity to detect the crane configuration problem was missed. The investigation was not able l

to determine why this problem was not reported. Ilowever, the problem reporting system was l

relatively new at that time and problems were not as rigorously documented and investigated as they j

are now.

l j

i The crane purchase specificatioris originally required a 30 hp motor. The vendor drawings would l

have required that a Magnetorque 105 be matched to the 30 hp motor. These specifications would l

have matched vendor drawings and the correct settings would have been used. The motors were l

changed to 25 hp,1800 rpm motors before they were installed by an outside contractor around 1979, l

but the Magnetorque size was not changed. The reason for why the motors were changed could not I

be determined. Ilowever, the motor substitution occurred at a time when configuration controls were l

less rigorous than the controls that are in place today. Current configuration controls would require l

substitutions to be formally evaluated and documented.

l A possible contributing cause was the use of a type of grease that was not recommended by the l

vendor. The P & 11 Maintenance Manual specifies the type of grease that should be used in a l

Magnetorque 105, but this information was not incorporated into the applicable preventive I

maintenance procedure. The P & 11 Maintenance Manual indicates that use of the wrong grease in l

the Magnetorque has the potential to increase motor current.

l The investigation also determined that XP4-TE-EM6450 and the P & 11 Maintenance Manual does j

not require hoist motor amperage readings to be taken following alignment activities. Iloist motor i

amperage readings are useful because they can provide a method of verifying if static stepless l

alignments have been perfbrmed correctly. A post maintenance test has been developed to ensure l

the hoist motor amperage is checked prior to returning an X-343 crane to service following an l

alignment.

l Corrective Actions A.

Completed Corrective Actions l

1.

On May 15,1999, re-wiring of the north crane voltage taps was completed. The middle l

crane will remain out of service.

l 2

On June 3,1999, a new post maintenance test was developed to ensure the motor hoist l

amperage was checked prior to returning an X-343 crane to service following an alignment.

S

. 4 k

GDP 99-2046

~

Page 4 of 4 Event Report 99-09 Revision 1 3.

On August 3,1999, procedure XP4-TE-EM6450 was placed on hold to prohibit static l

stepless alignments from being performed until the procedure can be revised.

l 4.

On A.ugust 3,1999, the Magnetorque brake lubricant on the south crane was changed and l

replaced with the vendor recommended lubricant.

]

5.

On August 6,1999, the Magnetorque brake on the north crane was replaced with a new brake l

containing the vendor recommended iubricant.

l B.

Planned Corrective Actions l

6.

By October 15,1999, selected maintenance procedures will be reviewed to determine if l acceptance criteria are correctly listed in procedures. If the selected reviews determine that l

this event was not an isolated case, additional corrective actions will be initiated.

j 7.

By October 15, 1999, procedure XP4-TE-EM6451 " Preventive Maintenance of P & 11 l

Overhead Crane in X-343" will be revised to require that the vendor recommended lubricants l

be used in the Magnetorque brake assembly.

l 8.

By November 19,1999, procedure XP4-TE-EM6450 will be revised so that the procedure l

will be independent of the P & H Maintenance Manual and in the correct procedure format.

l The procedure revision will include: acceptance criteria for Magnetorque, reactor and hoist l

motor amperage values, crossover current will be changed so that it is 2 amps or less, and a l

step-by-step section for troubleshooting will be added.

l Extent of Exposure of Individuals to Radiation or Radioactive Materials There were no exposures to individuals from this incident to radiation or radioactive materials.

l l

Lessons Learned i

The lack of clear acceptance criteria allowed the crane configuration problems to go undetected. If l the appropriate acceptance criteria had been specified in the procedure, maintenance personnel would l

have discovered that the procedure could not be completed successfully with the specified settings.

l The crane configuration problems would likely have been detected and corrected earlier.

l

s.

GDP 99-2046 Page1of1 Event Report 99-09 Revision 1 List of Commitments 1.

By October 15,1999, selected maintenance procedures will be reviewed to determine if l acceptance criteria are correctly listed in procedures. If the selected reviews determine that i

this event was not an isolated case, additional corrective actions will be initiated.

l 2.

Ily October 15, 1999, procedure XP4-TE-EM6451 " Preventive Maintenance of P & 11 l

Overhead Crane in X-343" will be revised to require that the vendor recommended lubricants l

be used in the Magnetorque brake assembly.

l 3.

By November 19,1999, procedure XP4-TE-EM6450 will be revised so that the procedure l

will be independent of the P & 11 maintenance manual and in the correct procedure format.

l The procedure revision will include: acceptance criteria for Magnetorque, reactor and hoist l

motor amperage values, crossover current will be changed so that it is 2 amps or less, and a j

step-by-step section for troubleshooting will be added.

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.

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