ML17223B320

Special Rept:On 911021 & 22,1B EDG Failed During 24 Hr Surveillance Runs.First Failure Caused by Broken Shaft Due to Fatigue at High Stress Location.New Shaft,Of Modified Design,Installed.Run Performed Satisfactorily on 911027

ML17223B320
Person / Time
Site:	Saint Lucie
Issue date:	11/13/1991
From:	Sager D FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-91-310, NUDOCS 9111200215
Download: ML17223B320 (5)

Text

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9111200215 DOC.DATE: 91/11/13 NOTARIZED: NO DOCKET FACIL:50-335 St. Lucie Plant, Unit 1, Florida Power 6 Light Co. 05000335 AUTH. NAME AUTHOR AFFILIATION SAGER,D.A. Florida Power & Light Co.

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

SUBJECT:

Special rept:on 911021 6 22,1B EDG failed during 24 hr surveillance runs. First failure caused broken shaft due to fatigue at high stress location. New by shaft, of modified I

design,installed.24 hr run performed satisfactorily 911027.

D*s>>@~~*a~ <<D~: p2>> C>>*~a ~<<~>>~D:>>~ ~~~L TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

NOTES:

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RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 1 PD2-2 PD 1 1 NORRIS,J 1 1 INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB 7E 1 1 NRR/DLPQ/LHFB10 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB SD 1 1 NRR/DST/SICBSH3 1 1 PLBSD1 1 1 NRR/DST/SRXB SE 1 1 02 1 1 RES/DSIR/EIB 1 1 RGN2 FILE 01 1 1 EXTERNAL: EGGG BRYCE,J.H 3 3 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC POORE,W. 1 1 NUDOCS FULL TXT 1 1 D

D D

NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

TOTAL NUMBER OF COPIES REQUIRED: LTTR 33 ENCL 33

P.O. Box 128, Ft. Pierce, FL 34S54-0128 oVfgpg L-91-310 10 CFR 50.36 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 Gentlemen:

Re: St. Lucie Unit 1 Docket No. 50-335 Special Report Date of Events: October 21 and 22, 1991 Emer enc Diesel Generator Failures The attached Special Report is being transmitted pursuant to the requirement of St. Lucie Unit 1 Technical Specifications 4.8.1.2.2 and 6.9.2. This report provides notification of two failures associated with the 1B Emergency Diesel Generator during the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> surveillance runs.

Should there be any questions on this information, please contact us ~

Very truly yours, D. A. Sager Plant Vice President DAS/JWH/kw Attachment cc: Stewart D. Ebneter, Regional Administrator, Region Senior Resident Inspector, USNRC, St. Lucie Plant II, USNRC DAS/PSL 4550-91 gpZ Plii2002l5 5'il.ij.=.

r" DR (ADOCki 05000='35 PDR c (- ~! p r an FPL Group company

Special Report 18 Emergency Diesel Generator Failures

~Fir ~Fjiilir",

St. Lucie Unit 1 was in Mode 5 and beginning a refueling outage. At 0357 on October 21, 1991, the 1B Emergency Diesel Generator (EDG) was started for its 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> surveillance run. The EDG automatically tripped at 0928 on high discharge water temperature. The radiator fan idler pulley shaft was found to be sheared.

Analysis showed that the broken shaft was caused by fatigue at a high stress location. A new shaft, of a modified design, was installed. The new shaft is made of a different material and has reduced stress risers at the shaft diameter steps to increase shaft fatigue resistance.

This surveillance run was a failure of a valid test. RG 1.108 $ 2.a.3 requires a test to be performed at least once per eighteen months to demonstrate full-load-carrying capacity for an interval of not less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The EDG ran five and one-half hours before tripping.

n F,il r The 1B EDG was restarted at 2035 on October 22, 1991. The radiator fan belts were found to be flapping excessively. Plant management decided to shutdown the EDG to determine the cause of the excessive flapping. The EDG was stopped at 0931 on October 23.

Cracks were found on the fan drive belt bearing support frame. Evaluation of the structure revealed a natural frequency at the third harmonic of the EDG rotational speed. The presence of excitation forces near the natural frequency of the structure explains the reduced life of the idler shaft and supporting frame. The excitation is produced by the torsional oscillation from the 12 cylinder EDG.

To increase the service life of the fan components and associated support structure, the cracks were repaired and stiffener plates were installed. These actions were performed on both the 1A and 1B EDGs. Future plans are to install vibration isolators on the 1A and 1B EDG power takeoff shafts.

These isolators greatly reduce the amplitude of torsional vibrations being transmitted to the fan assembly frame and have proven to be beneficial on St. Lucie Unit 2 EDGs. This long-term corrective action willbe evaluated for implementation during the next refueling outage.

The surveillance run started on October 22 was also a failure of a valid test. RG 1.108 g 2.e.7 states that tests performed to verify correction of the problem should be considered valid tests and successes or failures, as appropriate.

F ilure, imm These failures were the first and second failures of the 1B EDG since implementation of the RG 1.108-based Technical Specifications. To date, twenty valid tests have been performed. The current surveillance interval is once per seven days per Technical Specification 4.8.1.1.

The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run was performed satisfactorily from 2001 on October 27 to 2011 October 28, 1991.