ML20012A058

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
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 ~ >

c hours of EDG operation or every 6 months, whichever occurred first. In our, 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'

.9003080214 900302

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

[' -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 l -Since. tbegapmeasurementprogramwasinitiated..the1HEDGnumber9 cylinder; 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.- ]

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'- i

- 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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