ML20012A058

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Advises That Util Intends to Revise Emergency Diesel Generator Bushing Gap Measurement Insp Frequency to Each Refueling Outage in Order to Detect Extruded Bushings & Prevent Generator Failure
ML20012A058
Person / Time
Site: North Anna  Dominion icon.png
Issue date: 03/02/1990
From: Stewart W
VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
90-105, NUDOCS 9003080214
Download: ML20012A058 (4)


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. VIRGINIA ELECTRIC AND POWER COMPANY

- RICHMOND, VIRGINIA 23261 p

March 2, 1990 U. S. Nuclear Regulatory Commission Serial No.90-105 Attention: Document Control Desk NAPS /JHL

-1 Washington, D. C. 20555 Docket Nos.-50-338 50-339' License Nos. NPF-4 I

NPF-7 l

9 Gentlemen:

-VIRCINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 EMERGENCY DIESEL GENERATOR BUSHING GAP MEASUREMENT INSPECTIONS In late 1984, and throughout 1985, the North Anna Emergency Diesel Generators (EDG's) experienced several significant failures of the pistons and cylinder; liners..

One of the corrective actions implemented as a result of these EDG.

failures was'to perform EDG bushing gap measurement inspections at a specified' interval 'in order to detect extruded bushings and prevent an EDG failure.-

Virginia Electric'and Power Company letter dated March 26, 1986, committed to

-performing EDG bushing gap measurement inspections approximately every 40 ~

hours of EDG operation or every 6 months, whichever occurred first.

In our, c

letter-dated May 7,

1987, the commitment to perform the EDG bushing gap measurement inspections was revised to perform the inspections every 6 months in conjunction with normal surveillances. This letter is to notify you that the Virginia Electric and Power Company intends to revise,the EDG bushing-gap measurement' inspection frequency to each refueling outage. A discussion of past EDG failures and-the basis for this revised commitment-is provided in the attachment.

If you have further-questions, please contact us.

Very truly yours, t

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W -L.' Stewart-Senior Vice President - Nuclear Attachment l'

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.9003080214 900302 PDR ADOCK 05000338

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A'ITACHMENT -

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In1 late 1984, and_throughout'1985, the North _ Anna Emergency Diesel Generators

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.(EDG's)' experienced several significant failures of the pistons and cylinder

?

. liners.. The causal factor in the failures was extrusion of the upper piston pin ~ bushing inside the upper piston assembly. The extrusion of the bushing caused the piston to-deform and contact the cylinder liner, failing the liner Ljacket seals.. Jacket' coolant water'from the failed seals leaked into the engine. crankcase' and' flashed to steam.- Also, the scratches in the cylinder

' liner permitted conbustion gas blow-by.

Both caused engine trips on increasing crankcase pressure.

The_ cause. for the upper piston pin bushing extrusion was insufficient lubricating oil film thickness at high load operation due to oil foaming. The

' boundary lubrication on this sensitive but critical component caused the

_ localized overloading and induced axial and radial deformation.

The plastic

~ deformation of the bushing aggravated the lack of lubrication and increased the bushing loading, friction, and local temperatures.

The lubricating oil,' Gulf XHD-40, was found to have inadequate anti-foaming i

characteristics due to additive package changes prior to the 1984 EDG failures.

In November and. December 1985, the North Anna Unit 1 EDGs were overhauled. At thats time the lubricating-oil problem'was not confirmed. xThe Gulf XHD-40 oil t

was installed following the overhaul and subjected to a break in run for approximately 30. hours and a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> performance' test.

In April 1986-the oil was determined to'be the cause for bushing clearance failure., The oil in the North Anna Unit 1 EDGs was then changed to Chevron Delo-6000 (It is important to note the pistons pin 6 and' bushings had already experienced: break in runs on the Gulf XHD-40 oil-prior:ltoi' changing to the Chevron Delo-6000 oil.) No piston pins bushings were replaced at the time of-the oil change.

Also, in April 1986, the North Anna Unit 2-EDGs were' overhauled, but the

-engines were subjected to their break in runs on.the Chevron Delo-6000 oil.

Additionally, a special axial clearance measurement process to determine if piston-pin bushing extrusion was occurring was developed. The EDG bushing gap measurement inspections were to be performed approximately every 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> of EDG operation or every 6 months, whichever occurred first.

To prove that the oil change solved the problem, the 2H EDG was overhauled.

The initial gap measurements were recorded for all new piston components and the EDG was subjected to a 127 hour0.00147 days <br />0.0353 hours <br />2.099868e-4 weeks <br />4.83235e-5 months <br /> t iecial test run at greater than 2550 kw.

Cap. measurements were taken following :he test run and no adverse change in gap clearance was observed.

The

!J EDG was ' overhauled and subjected to a similar but shorter test run at s ' nilar load conditions with che same satisfactory results.as the 2H EDG.

In March 1987, a routine gap measurement inspection of the IH EDG was performed. An abnormal change was observed in the number 9 cylinder gap. The bushing was removed and a new bushing was installed. The bushing extrusion did not lead to an EDG engine failure.

The reason for the bushing extrusion f

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- and gap; reduction -1'si believed!Lto belits run. tim $ accumulated on the Gulf

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-XHD-40,1ubric'ating oil between November!1985 and' April 1986, b

bl 4 In-1987, the North Anna Unit L EDGs were. overhauled'and the' Chevron Delo-6000 a

lubricating l oil'was'Anstalledt i

tbegapmeasurementprogramwasinitiated..the1HEDGnumber9 cylinder; l

-Since.

bushing has been the_ only bushing degradation observed.

The 1H EDG has had 10 -

gap ' inspections, the IJ EDG has had 10 gap inspections,.the 2H EDG has had 8 gap' inspections and,the 2J EDG has had 9 gap inspections.

Only one bushing

-wasz ;-damaged by inspection.dueLto the inspection technique.. No other bushing failures have occurred.:

s.-

- During the past two'refualing outages the bushings have'been' inspected that'

~P' were exposed - to -the': Chevron Delo-6000 lubricating oil.: All bushings were observedLto be in excellent visual condition and within dimensional acceptance j

standards.-

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i Additional _ factors that. reduce the probability of EDG failure ine'lude improved

-maintenance -and operator awareness, added' detail: and precautions in maintenance-and -test procedures, obtaining a Technical Specifications change reducing' EDG surveillance test loading, reducing the~ testing frequency for planned: maintenance, implementing a dedicated EDG operator during testing,.

performance monitoringLand testing, and implementation of predictive and preventive maintenance programs.

In conclusion, the current:EDG bushing gap measurement-inspection frequency is.

being revised from being performed every. six. months in conjunction with'-

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- preplanned maintenance to'being performed.each' refueling outage.

Corrective?

actions'to support the: revised inspection frequency have been adequately q

1mplemented (as described.above)?and will preclude similar EDG failures.

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