ML19270H228

LER 79-006/01T-0 on 790607:vendor Notified Util of Possibility That Turbocharger Thrust Bearing Could Be Damaged Under Certain Repeat Start Operating Modes. Procedures Modifided & Improved Lube Oil Sys Being Designed

ML19270H228
Person / Time
Site:	Arkansas Nuclear
Issue date:	06/20/1979
From:	Shively C ARKANSAS POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19270H227	List: ML19270H225 ML19270H228
References
LER-79-006-01T, LER-79-6-1T, NUDOCS 7906250266
Download: ML19270H228 (4)

Text

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NRC FORM 366 87 77) U. S. NUCLE AR REGUL ATOR Y COMMISSION LICENSEE EVENT REPORT EXHIBIT A CONTROL 8 LOCK: l l l l l l 6\h IPLEASE PRINT OR TYPE ALL REOUIREO INFORMATION) o i j AlR l Al N 0 ]1 l{)' O j0 l -l0 l 0 l 0l 0l 0 l- l 0 l0 g4 {1 l 1l1 l 1 g l 7 11 9 LICENSE E CCaDE 18 iS LICENSE NVMB E R 25 7s LeC LNLE tv4 JJ b? CA T bal CON'T IoIiI P e 3 ,'% LL_j(s)l015 60 61 p l0 I o 13 l 1 l3 l@l DOCKET NUM8gR 68 63 O6i i 0 l7 i 7 l 9lgi ci 6l2l0l7l9lg EVENT DATE 14 TS HE OH1 OA*E 80 EVENT DESCRIPTION AND PROSAOLE CONSEQUENCES h o 2 I While in a refuelinc shutdown. the Emercency Diesel Generator vendor i loI31I notified this utility that under certain repeat start operating modes; i o . I eg., fast hot starts 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 shutdown, I e s I after draining the accessory oil system for any reason, or if a i o e ileak at the top of the oil cooler occurred, there was a t o 7 Ipossibility that the turbocharger thrust bearing could be damaged. I 7

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ITestine revealed that the reported repeat start operating modes ii ,i i would create a loss of the accessorv lubricating oil system, " prime" g; i,2 1 causing a loss of lubrication at the turbocharger thrust bearing.

3 l Procedures were modified to insure no repeat start operating modes would i i ,. exist. An improved lube oil system is beint desicned. I

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Reportable Occurrence Report No. 50-313/79-006

2. Report Date: 06/20/79 3. Occurrence Date: 6/7/79 4 Facility:

Arkansas Nuclear One - Unit One Russellville, Arkansas 72801

5. Identification of Occurrence:

Condition degrading reliability of the Emergency Diesel Generator Engine that requires remedial action and corrective measures to prevent possible operation in a manner less conservative than as-sumed in the Technical Specifications.

6. Conditions Prior to Occurrence:

Steady-State Power Reactor Power MWth ibt Standby Net Output MWe Cold Shutdown Percent of Full Power  %

Refueling Shutdown X load Changes During Routine Routine Startup -

~-

Operation Routine Shutdown Operation Other (specify)

7. Description of Occurrence:

The Emergency Diesel Generator Engine vendor notified this utility that recent lubricating oil system tests conducted at Electro Motive Division, General Motors Corporation, indicate that certain repeat start operatin,; modes could result in turbocharger thrust bearing damage which might ultimately cause a turbocharger failure.

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Reportable Occurrence -Report No. 50-313/79-006

8. Designation of Apparent Cause of Occurrence:

• Design X Procedure Fbnufacture Unusual Service Condition Including Environmental Installation /

Conc t ruct ion Component Failure (See Failure Data)

Gperator Other (speci fy)

9. Analysis of Occurrence:

When the engine is in the normal standby mode, the lubricating oil is supplied to the turbocharger bearings at about 1150F through a relief valve which serves to keep the entire accessory lubricating oil system primed to support a fast start. If the engine receives a repeat rapid start within 15 minutes to 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> af ter a hot shut-down from a previous run, the lube oil could exceed 1600F, as nor-mal operating temperature is about 2000F. Under these circumstances, due to the reduced flow resistance created by the icwcr viscosity of the hot lubricant, the relief valve would not supply the oil. During the cooling period following a full load run, some of the oil con-tained in the cooler and filter will drain back to the engine sump via the lube oil scavenging pump, and some of the oil from the strain-er box will be sucked into the cooler by the vacuum that develops.

The result is that when a fast start occurs from a minimum of 15 minutes to a maximum of 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, sufficient

" prime" oil will have drained to retard the buildup of engine oil pressure in the event a restart is required. Restarting prior to adequate cooling may cause some smearing of the bearing metal, so that cumulative damage from several similar starts could result in a turbo-charger failure.

2238 242

Reportabic Occurrence Report No. 50-313/79-006

10. Correct ive Action:

Immediate action included procedure changes to ensure that:

(1) Repeat fast hot starts 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 shut-down is avoided.

(2) Operate circulating oil pump for at 1 cast 30 minutes following changing oil filter elements for draining the accessory oil system for any reason to ensure strainer box is full before starting engine.

(3) Correct any small leaks at top of oil cooler as soon as it is noticed to make sure air is not sucked into the cooler during shutdown.

(4) kbintain one diesel in the running mode for a minimum of 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> following the shutdown of the other diesel if both diesels are run concurrently.

Final corrective action will include a design change of the lube oil system.

11. Failure Data:

There have been no similar occurrences.

2238 243

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