ML20028H034

Special Rept:On 900905,discovered Cracked Turbocharger Axial Strut Support on South End of Diesel During Insp.Caused by Fatigue Failure.Diesel Declared Inoperative & Cracked Plate Cut Out & Saved for Further Analysis

ML20028H034
Person / Time
Site:	River Bend
Issue date:	09/27/1990
From:	Odell W GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9010050253
Download: ML20028H034 (3)

Text

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AHL A CODf 4td 6J6 tOb4 346 %$1 September 27, 1990 RBG- 33664 File Nos. G9.5, G9.25.1.4 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555 Gentlemen:

River Bend Station - Unit 1 Docket No. 50-458 Enclosed is Gulf States Utilities Company's Special Report concerning a valid failure of the Division I diesel generator at River Bend Station. This report is submitted pursuant to River Bend Station Technical Specifications 4.8.1.1.3 and 6.9.2.

Sincerely, fu W.Manager-Oversight H. Odell River Bend Nuclear Group LA /PDG/RGW/DNL/DCH/G H/pg Enclosure cc: U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011  :

NRC Senior Resident inspector Post Office Box 1051 St. Francisville, LA 70775 h

O w' h 'Z .Y y ems ,ee 2, noocx, 030004se a

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. REP'0[tTED CONDITION At 0800 on 09/05/90 with the reactor operating at 65% power (Operational  ;

Condition 1), while performing a routine visual inspection on Division I r diesel, the system engineer discovered a cracked turbocharger axial strut -

support plate on the south end of the diesel. Note that the Division I j diesel generator was manufactured by Transamerica Delaval. Inc., model DSR  !

48. The crack was 4" long and began at the outermost edge of the vertical  ;

fillet weld joining the plate to the exhaust manifold support and proceeded I diagonally towards a notch in the plate. This cracked member never resulted in the Division I diesel being unable to fulfill its design  ;

purposes. However, this is classified as a valid failure in accordance  ;

with Regulatory Guide (R.G.) 1.108, position C.2.e.8. This Special Report t is submitted pursuant to Technical Specifications 4.8.1.1.3 and 6.9.2. [

INVESTIGATION l

The support plate is 3/4" thick, carbon steel and is welded to an adjoining n haust manifold support on one side and welded to the turbocharger support  !

pedestal on the adjacent side. The strut is connected to the plate by two 1 bolts, mating a welded strut end piece with the support plate. '

The diesel was declared inoperative at 0800 on 09/05/90 and the cracked I plate was. cut out and saved for- further analysis. Several observed conditions seem to point to a fatigue failure due to vibration and stress. i They are: (1) poor fitup of the strut end piece to the plate causing a  :

stress loading of the plate in the upward direction and (2) review of t vibration data shows Division I diesel turbocharger vibration levels are consistently higher than the Division II diesel turbocharger levels. The  ;

Division I diesel generator turbocharger vibration levels also showed an '

' increasing trend in the axial direction in the month prior to the discovery of the. crack.

GSU continues to evaluate this failure. When the failure evaluation'is ,

concluded, a revision will be made to this Special Report and submitted to t the NRC by March 1, 1991.

CORRECTIVE ACTION i The; cracked support plate was removed and a redesigned support plate was fabricated and installed. This new su) port plate is 3/4" A516-GR70 carbon '

steel .with the notch removed, whici resulted in a four-fold increase in section~ modulus. The fitup between the strut end piece and the plate was corrected and the strut end piece was bolted to the plate. The horizontal fillet weld size was increased to 1/2" to provide greater strength.

Vibration tests performed following the repair indicated that the vibration levels in the axial direction have decreased to' normal levels.

The support plate on the Division II diesel was visually inspected for any  ;

signs of failure. None were found. It was noted, additionally, that the strut end piece and the support plate did not have the poor fitup exhibited by the Division I diesel. The Division I diesel was declared operable at 1700 on 09/05/90.

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L.: L'ength of Time Diesel Generator was Out-of-Service: 15' hours 1

', Current Surveillance Interval: ,

. Division 1. Monthly i Division 11 ' Monthly i Division III Monthly. I t

Test Intervals Conforms to Technical Specification:' l Yes l

. I Failures for Division I: ,

i 1 Valid. failure (s)inthelast 20 Valid Tests ~

1 Valid failure (s) in the.last 100 Valid Tests 1

. i Failures for Division II: i 1

0 Valid failure (s) in the last 20 Valid Tests 4 Valid failure (s) in the last 100 Valid Tests  !

Failures for Division III:

EValidfailure(s)inthelast-20ValidTests 2 Valid failure (s) in the last 100 Valid Tests. i Number of' Valid Failures in previous'100 Valid Tests of all Diesel [

Generators at River Bend Station: .;

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