ML19209C441

Final Deficiency Rept Re Diesel Generator Turbocharger Lubrication Problem.Caused by Defect in Soakback Pump. Operating Instructions for Diesel Generators Revised & Lubricating Oil Sys Will Be Modified

ML19209C441
Person / Time
Site:	Sequoyah
Issue date:	10/04/1979
From:	Mills L TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML19209C431	List: ML19209C430 ML19209C441
References
NCR-MEB-79-26, NUDOCS 7910150567
Download: ML19209C441 (2)

Text

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ENCLOSURE SEQUOYAll NUCLEAR PLANT UNITS 1 AND 2 DIESEL GENERATOR TURBOCHARGER LUBRICATION NCR MEB 79-26 10 CFR 50.55(e)

FINAL REPORT Description of Deficiency P( 1 OftB M L This deficiency was reported by the diesel manuf acturer, Electro-;iotive Division (Et1D) of General Motors, to TVA's contractor for the emergency diesel generators, Power Systems a division of Morris-Knudsen. Power Systems subsequently reparted this, deficiency to TVA. This deficiency was also reported to the NRC, which issued IE circular No. 79-12. The deficiency occurs when the diesel generator has been operated lon,; enough for the lube oil to reach operating reaperature, shutdown, then restarted between 15 minutes and 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />. During this period, if a restart is attempted, damage to the diesel engine turbocharger thrust bearing r.ay occur. This could lead to failure of the turbocharger aad the emergenc/

diesel generator.

The cause of this deficiency appears to be related to tne "scakback" pump which is designed to supply lubrication to the turbocharger beariags during standby conditiens and to keep the accessory luoricating oil system primed to support a fast start. Following operation of tae a;esel generator the viscosity of the lubricating oil is such that tae acces;ory lubricating oil systen does not receive any oil, therefore repeated restarto during the period of 15 minutes to 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> following a hot shutdcwn of th-diesel generator can cause engine damage due to lack of prime c'.1 systcm pressure. Occasional instances of restart during these period, are .aconse-quential. However, repeated unneccessary restarts for ,sur. .s of testing or machinery exercise during the period of 15 minutes to 3 i4vurs after chutdown needlessly accelerates wear and detracts f.om total en tr.e s .11e.

TVA considers this deficiency reportable because it could .ead to reouccc reliability and availability of the emergency onsite power source wnich is required to ensure that the plant can reach and maintain a sate snut-down unden all conditions.

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l Safety Implications If this deficiency had remained uncorrected, it is possibic that repeated restarts during the period of 15 minutes to 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> following a shutdown of the diesel generator from hot conditions could have led to failure of the emergency diesel generator at a time when that unit was required to pro ide emergency electric power to support shutdown of the nuclear unit.

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Corrective Action Operating instructions at Sequoyah Nuclear Plant have been revised to stats that the diesel generators shall not be unnecessarily started between 15 minutes and 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> following shutdown from a previous run la which the engine has reached full operating temperature.

In addition, EMD, Power Systems, and TVA employees have inspected the Sequoyah diesel generator turbochargers and have found no thrust bearing damage.

EMD is developing a lubricating oil system modification which will preclude the restriction on test starting during the period of 15 minutes and 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> after a hot shutdown. Power Systems Division is expected to make a recom-mendation to TVA for installation of this modification in the emergency diesel generators at Sequoyah and Watts Bar Nuclear Plants at some future date.

Since no turbocharger thrust bearing damage was found on the Sequoyah diesel generator units, TVA has placed them in service with the restric-tion on test starting in the period from 15 minutes to 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> after a shutdown of the diesel generator from hot conditions. Operation with this ,

restriction will not detract from the diesel generators' ability e perform their intended safety function because there will be no restrist on on diesel generator starting in response to an emergency start signal. Turbo-charger thrust bearing damage of sufficient severity to cause diesel generator failure would only result from repeated starts of the diesel generator fol-lowing shutdown from operating temperature. For these reasons, TVA believes that the emergency diesel generators can perform their intended safety function with the testing restriction in effect.

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