ML20212G055

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Provides Revised 30-day Event Rept 99-06 for Emergency Condition That Was Declared Alert at Portsmouth Gaseous Diffusion Plant
ML20212G055
Person / Time
Site: Portsmouth Gaseous Diffusion Plant
Issue date: 09/23/1999
From: Jonathan Brown
UNITED STATES ENRICHMENT CORP. (USEC)
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GDP-99-2053, NUDOCS 9909290070
Download: ML20212G055 (6)


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W USEC A GW Energy Company.

l l September 23,1999 GDP 99-2053 -

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 99-06, Revision 1

. Pursuant to 10 CFR 76.120(d)(2), Enclosure 1 provides a revised 30-day Event Report for an i

emergency condition that was declared an " Alert" at the Portsmouth Gaseous Diffusion Plant. An-

" Alert" was declared when a transformer tank ruptured and released oil to the switchyard cobble bed I

in the X-533 Switchyard. The event report is being revised to include additional information l

regarding the cause and corrective actions for the transformer failure. Changes from the previous

' report are marked with a dashed vertical line in the right margin. 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, M

-f iorris Brown General Manager

. Portsmouth Gaseous Diffusion Plant

Enclosures:

As Stated.

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NRC Region Ill Office e

NRC Resident Inspector-PORTS f.

9909290070 990923 i

i PDR ADOCK 07007002 I

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O8O*']6 United States Enrichment Corporation Portsmouth Gaseous Di%sion Plant P.O. Ilox 628. Piketon, OH 45661

GDP 99-2053 Page1 of5 Event Report 99-06, Revision 1 Description of Event On April 8,1999, at approximately 0521 hours0.00603 days <br />0.145 hours <br />8.614418e-4 weeks <br />1.982405e-4 months <br />, Gas Circait Beakers 355 and 358 and Air Circuit Breakers 308T and 309T tripped offline, causing a loss of power to Transfonners T308 and T309.

Operators investigating the loss of power discovered that the transformer tank on Transformer T309 had ruptured causing a release of transformer oil. The transformer is a 125-MVA 60 Hz Power Transformer, Serial Number 7002358, manufactured by Westinghouse in 1975. The transfbrmer oil spilled from the transformer and onto a bed oflimestone cobbles in the X-533A Switchyard.

On April 8,1999, at 0700 hours0.0081 days <br />0.194 hours <br />0.00116 weeks <br />2.6635e-4 months <br />, the Emergency Operations Center was declared operational in l

response to the ruptured transformer tank. At 0710 hours0.00822 days <br />0.197 hours <br />0.00117 weeks <br />2.70155e-4 months <br />, the Crisis Manager declared an " Alert" due to concerns widi tne oil runoff escaping to the environment. At the time of the incident the transformer status was normal and no switching or maintenance was underway. The load on the transformer was less than one halfits rated capacity.

The transformer tank rupture resulted in the release of approximately 8,500 gallons of electrical insulating oil. Environmental Compliance confirmed that the oil was fully contained in the X-230J-l 6 Environmental Holding Pond by an oil boom and floating weir. The oil was later recovered. No off-site environmental impact occurred as a result of the oil release.

The oil released was a highly refined light mineral oil containing Diteriarybutyl-p-cresol or Ditertiarybutylphenol stabilizer. The oil was installed in the transformer when it was positioned in the switchyard in March 1976.

The bed of the X-533A Switchyard where the oil was released contains 1 to 3 feet of 2 to 3 inch l

(typical) diameter limestone cobbles underlain by clay soils. Above the soils and below the l

limestone there is a series of French drains designed to remove precipitation runoff from the l

switchyard. An 8-inch open joint tile beneath the transformer in the eastern half of the switchyard I

drains into a storm sewer, which flows into the X-230J-6 Environmental Holding Pond prior to l

discharging off-site to a creek via a drainage ditch. The pond itselfis designed with contingency l

equipment (i.e., an oil boom and floating weir) to d; vert oil from the main pond to an adjacent oil l

diversion / containment impoundment.

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The oil diversion structure has a baffled effluent system to contain the oil within the impoundment.

l These systems were successful in removing oil from the main pond to the oil diversion impoundment l

for subsequent removal with on-site vacuum trucks. Additional contingency measures were l

implemented by constructing a temporary carthen dam with an angled 12-inch corrugated metal pipe i

below the oil containment structure. Plywood and sandbags were used at a culvert at the Northeast l

Bypass Road to provide additional temporary retention.

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GDP 99-2053 Fage 2 of 5 Event Report 99-06, Revision 1 At 0958 hours0.0111 days <br />0.266 hours <br />0.00158 weeks <br />3.64519e-4 months <br />, after the "All Clear" was given on the emergency response to the X-230J-6 l

Environmental IIolding Pond, a Recovery Manager was assigned to monitor cleanup activities I

associated with the oil release. A layer of oil approximately 3/8 inches thick was present on the main l

pond and a layer of oil approximately 11/4 inches thick was present in the oil diversion l

impoundment. A representative from the Ohio Environmental Protection Agency (OEPA) Division l

of Emergency and Remedial Response (Southeast District Office), arrived at PORTS at l

approximately 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> on April 8,1999. Cleanup activities continued throughout the afternoon l

and during the evening hours. By the moming of April 9,1999, most of the oil had been removed,

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except for a visible oil sheen on the surface of the holding pond.

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Runoff from precipitation commencing that morning [ daily total of 0.50 inches of rainfall] caused j

the holding pond to discharge, allowing an oil sheen to migrate into the drainage ditch below the I

culvert.110 wever, oil did not migrate off-site and no sheen or discolored water reached the state l

waters. Analytical results for water samples collected approximately every four hours during the l

24-hour period following the spill were below the National Pollutant Discharge Elimination System l

daily discharge limitation for oil and grease and Polychlorinated Biphenyls at this OEPA Permit l

Outfall.

l The incident caused the loss of power to seven X-333 process cells and to auxiliary substations.

During the incident there were no safety system failures or actuations. The incident was declared I

Vert" due to a concern with the runoff of oil. At the time the " Alert" declaration was made, it a

v,a act known if the oil would be contained and successfully recovered.

An emergency condition declared as an " Alert" is reportable in accordance with 10CFR76.120(a)(4).

The incident was reported to the NRC Operations Center at 0721 hours0.00834 days <br />0.2 hours <br />0.00119 weeks <br />2.743405e-4 months <br />. The event was also reported to NRC in accordance with Safety Analysis Report 6.9, Table 6.9-1 P, because notification of the incident was made to the OEPA and a news release was issued.

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l Cause of Event y

The direct cause for the release of oil was that the transformer experienced an electrical fau!t that I

caused the tank to rupture and spill transformer oil.

1 On subsequent days following the event, Transformer T309 was inspected and extensive damage was found. Due to over-pressurization, the transfonner tank ballooned on two sides and on the top. The j

l tank rupture occurred at the lower tank flange on the two sides that ballooned. Considerable intemal l

l damage was found in the C phase end of the unit where the fiber board structure supporting the l

j tapped leads comes from the C phase transformer near the center of the C phase winding. The l

j secondary bus bar on B and C phases was found distorted and twisted by the force of the fault.

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..f' GDP 99-2053 Page 3 of 5 Event Report 99-06, Revision I l

. Evidence of arcing was found in the low voltage end of the high voltage winding, and was probably l

generated from the high voltage winding tap because ofinsulation failure. Evidence of arcing was l

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also found around the preventive auto transformer, the secondary buswork and the leads going to the -

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primary neutral bushing.

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The nature and extent of damage indicates that the fault probably occurred near the center of C phase l.

. winding deep inside the transformer tank. This area could not be inspected to determine the exact l

' fault location or cause of the fault because it would require untanking and disassembling the l

transformer core and windings.

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(The inspections described above indicate that the most likely root cause for the transformer failure l.

is insulation damage due to winding tap shift, attributable to excessive through faulta. As a result l

of past operational history, th. need to minimize through fault conditions was previously l

recognized. To addre.es this concern, operational procedures were revised to place controls on l

repeatedly energizing equipment 'when through fault conditions are suspected to be present.

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The transformer will be sent to a vendor for further disassembly and inspection. The transformer l

4 oil pumps for transformer 309 have been inspected. The pumps showed wear caused by meta! to l

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- metal contact which caused small metal particles in the transformer oil. The wear on the pumps is.l

. not believed to have contributed to the transformer failure, l

l A review of the transformer preventative maintenance program concluded that the program follows l

1 typical industry guidelines and standards. The first line of defense against transformer failure is a l

L weekly nitrogen blanket gas analysis that is conducted to determine if combustible gases are being l

produced which could be indicative of developing problems. The last gas analysis on transformer l T309 was conducted approximately 4 days prior to this event. This analysis indicated there was no l

combustible gas generation.

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l A Dissolved Gas Analysis (DGA) and an ASTM oil analysis of the transformer oil is also conducted l

every 6 months. The last transformer T309 oil analysis was taken on December 18,1998. The l

results showed no dissolved combustible gases or other indicators of problems.

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l Based on 'the above analysis and a review of past operational performance, transformer T309 was l

running normally without any known problems or abnormalities when the last nitrogen blanket gas l

l analysis was conducted on April 4,1999. It appears that the fault occurred over a short time interval.

l The benefit ofincreasing the transformer gas analysis frequency to detect rapidly developing fachs I

was evaluated. It was determined that some faults can occur over such a short thne interval that even l

continuous online gas monitoring would not provide sufficient warning to allow protective action l

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,9-e GDP 99-2053

- Page 4 of 5 -

Event Report 99-06, Revision 1 to be taken in all cases. However, plans are currently in progress to install continuous online gas.l

monitoring which wmld improve the capability to detect rapidly developing problems.

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- Additional DGA was conducted on 6 transformers that are of the same design as transformer T309. -l Signs ofpotential gassing were discovered on two of the transformers (T308 and T313). Followup l

DGA were performed on these two transformers to determine their condition. The gas levels were l

not found to be increasing, which indicated that the transformers did not have a degrading condition.

l It was determined that the level ~of gassing was not high enough to cause immcdiate concern. The 1

investigation also noted that an online gas monitor 'w,s installed on T308 but wn not operational l

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, due to a failed sensor.-

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' Additional inspections will be performed during transformer disassembly to confirm the suspected l

root cause. This event report will be revised if the additional transformer inspections change our i

understanding ~of the transformer failure mechanism or significant new corrective actions are l

developed. The corrective actions described in this report will provide enhancements to our existing l

transformer monitoring prognun that will reduce the likelihood of a recurrence of this event. There l

l were no nuclear safety concerns associated with the ruptured transformer and there was no release l

l Of oil to state waters.

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. Corrective Actions

. This investigation did not identify corrective actions that could be taken to prevent random l

' transformer failures which develop rapidly. However, the following enhancements will improve the l

ability to detect more slowly developing degraded conditions and allow preventative measures to be - l taken.

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By September 30,1999, a continuous transformer oil combustible gas monitoring system will l

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be installed on transformer T313 and the online gas monitoring system for T308 will be l

restored.

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By December 15,1999, a continuous transformer oil combustible gas monitoring system will l

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be installed on the remaining vintage transformers similar to T309; i.e. Transformers T305, l

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T306,T315,T316.

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By October 21,1999, transformer PM testing frequencies will be evaluated.

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By June 30,2000, a continuous transfomier oil combustible gas monitoring system will be l

installed on the remaining power transformers in the X-530 and X-533 Switchyards. Due l

to the transformer configuration, Transformer 203 is not included in this action item.

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GDP 99-2053 Page 5 of 5 Event Report 99-06, Revision 1 l

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B/ Tune 30,2000, new operational procedures which require increased DGA on transformers l

e.cperiencing problems will be implemented.

l Extent of Exposure ofIndividuals to Radiation or Radioactive Materials

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There were no exposures to individuals from this inciden'. to radiation or radioactive materials.

Lessons Learned from the Event

'I The declaration of an " Alert" was effective in ensuring the event was properly assessed. Emergency response personnel were activated and stationed at their emergency duty stations to help mitigate the consequences of the oil release.

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