ML17223A162

Special Rept:On 890406,emergency Diesel Generator 2A Failed. Caused by Thrust Bearing Failure Due to Excessive Clearance Between Bearing Collar & Fan Shaft.Cooling Fan Blades & Shroud Repaired

ML17223A162
Person / Time
Site:	Saint Lucie
Issue date:	06/05/1989
From:	Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-89-185, NUDOCS 8906090135
Download: ML17223A162 (3)

Text

AC CELE P~TED Dl BI'TIO~ DEMON STPQTIOY SYSTEM (2) f REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:8906090135 DOC.DATE: 89/06/05 NOTARIZED: NO DOCKET FACIL:50-389 St. Lucie Plant, Unit 2, Florida Power & Light Co. 05000389 AUTH. NAME AUTHOR AFFILIATION WOODY,C.O. Florida Power & Light Co.

RECIP..NAME RECIPIENT AFFILIATION Document Control Branch (Document. Control Desk)

SUBJECT:

Special rept: on 890406,2A emergency diesel generator failure.

DISTRIBUTION CODE: IE22D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), ncident Rpt, etc.

NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 1 PD2-2 PD 1 1 h NORRIS,J 1 1 INTERNAL: ACRS MICHELSON 1 1 ACRS MOELLER 2 2 ACRS WYLIE 1 1 AEOD/DOA 1 1 AEOD/DS P/TPAB 1 1 AEOD/ROAB/DS P 2 2 DEDRO 1 '1 IRM/DCTS/DAB 1 1 NRR/DEST/ADE 8H 1 1 NRR/DEST/ADS 7E 1 0 NRR/DEST/CEB 8H NRR/DEST/ICSB 7 NRR/DEST/MTB 9H 1,1 1

1 1

1 NRR/DEST/ESB NRR/DEST/MEB NRR/DEST/PSB 8D 9H 8D 1

1 1

1 1

1 NRR/DEST/RSB 8E 1 1 NRR/DEST/SGB 8D 1 1 NRR/DLPQ/HFB 10 1 1 NRR/DLPQ/PEB 10 1 1 NRR/DOEA/EAB 11 1 1 F RPB 10 2 2 NUDOCS-ABSTRACT 1 1 EG FIL 02 1 1 RES/DSIR/EIB 1 1 R SR/PRAB 1 1 RGN2 FILE 01 1 1 EXTERNAL EG&G WILLIAMSg S 4 4 FORD BLDG HOY ~ A 1 1 L ST LOBBY WARD 1 1 LPDR 1 1 NRC PDR 1 1 NSIC MAYS,G 1 1 NSIC MURPHY' ~ A 1 1 I D

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NCTE K) ALL "RIDS" RECIPIENTS S

PLEASE HELP US 'IO iKDUCE WASTE! CXWZACZ 'IHE DOCUMEhl7 CGVZROL DESK, RXN Pl-37 (EXP. 20079) %0 EZJ2GXATE VCR NAME PBCH DIBTEGBUTIGN-LISTS FOR DOCUMENZS YOU DGN~T NEEDt TOTAL NUMBER OF COPIES REQUIRED: LTTR 43 ENCL 42

P.O. Box 14000, Juno Beach, FL 33408 0420 JUNE 5 1989 L-89-185 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: St. Lucie Unit 2 Docket No. 50-389 Date of Event: April 6, 1989 S ecial Re ort on Diesel Generator Failure The attached Special Report is being transmitted pursuant to the requirements of Technical Specification 4.8.1.1.3 to provide notification of a 2A Emergency Diesel Generator failure.

Very truly yours, C~

>.C. O.~~oody Acting Senior -Vice President Nuclear COW/GRJ1/gp Attachment cc: Stewart D. Ebneter, Regional Administrator, Region Senior Resident Inspector, USNRC, St. Lucie Plant II, USNRC 8~0<0901,=-:5 89060(

PDj @DOCK 0":000=%'DC

SPECIAL REPORT DIESEL GENERATOR FAILURES 2A DIESEL GENERATOR FAILURE:

In accordance with NRC Regulatory Guide 1.108, Section C.2.e, this event is considered to be a valid diesel generator failure.

At 1640 on April 6, 1989, the 2A diesel (D/G) was started and loaded for a one hour surveillance run before declaring the D/G back in service after maintenance. Approximately 55 minutes into the run, a utility operator stationed at the D/G noticed sparks coming from the south cooling fan due to contact with its shroud housing on the 16 cylinder engine. The D/G was immediately stopped.

The cause of the cooling fan axial displacement and contact against its shroud was due to a thrust bearing failure on the fan shaft.

The root cause of the thrust bearing failure was due to excessive clearance between the bearing collar and the fan shaft. The small clearance measured was sufficient to permit movement between the bearing collar and the fan shaft which lead to fatigue failure of .

the collar. The bearing collar is held onto the shaft with set screws. The design tolerance was never specified in any plant drawing, and therefore was not considered critical or required to be measured.

The failure of the 2A D/G was the third failure in the past 100 valid tests. The current 2A D/G test frequency is once per 31 days'he following corrective actions were implemented:

1) The cooling fan blades and shroud were repaired.

2) The thrust bearing was replaced and the new clearance between the shaft and bearing collar was determined to be satisfactory by the bearing manufacturer.

3) Other D/G fan shaft bearings susceptible to this failure mechanism were inspected on both the 2A and 2B D/G's. A total of 40 bearings were inspected which included fan shaft, idler shaft, and drive shaft bearings. Five thrust bearings and two floating bearings were replaced. Maintenance procedures will be revised to require periodic inspection of the D/G fan shaft bearings".

4) The south fan on the 2A 12 cylinder engine was found to have a damaged shaft due to excessive shaft to collar clearance.

A new fan shaft was manufactured for the 2A D/G and installed with satisfactory shaft to bearing collar clearance. A similar condition was found on a fan drive shaft for the 2B D/G. A new shaft was manufactured and installed on the 2B D/G.

5) A surveillance run was performed and the 2A D/G was declared back in service on April 11, 1989.