ML19332B938

Special Rept:On 891017,invalid Failure of Div 1 Diesel Generator Occurred Due to Trip.Trip Caused by High Vibration Signal from Turbocharger Vibration Switch.Switch Reset Per Maint Work Order R056445

ML19332B938
Person / Time
Site:	River Bend
Issue date:	11/14/1989
From:	Booker J GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RBG-31756, NUDOCS 8911220066
Download: ML19332B938 (3)

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. GULF STATES UTELETIES COMPANY '

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AREA C000 604 635 6034 . 346 8651 c..

November 14,1989 ,

RBG- 31756- .

File Nos. G9.5, G9'.25.1.4 4 p

L. U. S. Nuclear- Regulatory C6mmission :

l' - Document Control-Desk-Washington, D.C. 20555-Gentlemen: < <

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. ' River Bend Station' ' llnit 1

' Docket No. 50-458- ,

Enclosed is.. 'GUIf. States ' Utilities Company!s Special'-Report concerning an invalid failure offthe Division I diese1<. generator- '

at River Bend < Station. This: report is-being submitted pursuant

- to' River =: Bend Station Technical Specification 4.8.1.1.3- and-

6.9.2. ,

Sincerely, g ,

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A J.' E. Booker Manager-River Bend Station River Bend Nuclear Group JEB/TFP/ GW/JHM/TES/ch cc: U. S. uclear RegulatoryTCommission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011

,1 NRC Seriior Resident Inspector Fost Office Box 1051

" f St.'Francisville,;.LA 70775' Enclosure-9911220066 891114

1. DR ADOCK 05000458 S PDC [6 1

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• SPECIAL REPORT power while b

'At--0959 on _10/17/89, with the reactor operating at full performing surveillance: testing on the Division I diesel; generator (DG), an ,

invalid failure l of the DG occurred.due to a trip caused by a nigh vibration J signal from the turbocharger vibration switch.- In accordance with Regulatory

- Guide. I'.108,' the .following information is provided:

Diesel Generator Unit Designation and Number:

-Division I,'1EGS*EG1A Cause of Failure:-

H At=. 0959 on- 10/17/89, while performing Surveillance Test -Procedure i (STP)-309-0201," Diesel Generator Division I Operability- Test", the DG i tripped. due. to a high vibration -signal from the-turbocharger vibration  ;

. switch. The DG had been started at 0946 and the output breaker was closed at 0951 . 'The! DG was then loaded to 3100 kw (100 percent load) in less than 60 seconds to demonstrate the "184 day loading" ~ requirement of the: Technical Specification'Surieillance Requirement 4.8.1.1.2.a.5.

This trip- is categorized as an " invalid failure" in accordance with Regulatory Guide 1.108 Position C.2.e(2) since vibration trip signals are

' bypassed _ during the emergency operating mode. During a subsequent troubleshooting run of the DG at 1336 on the same day,_ vibration levels at the turbocharger and other engine locations were determined to be within the,

-_ baseline readings. This demonstrated that no excessive vibration condition .

existed which would have interfered with the DG performing its design' function.

INVESTIGATION:

This same DG experienced earlier trips on 5/17/89 and 8/23/89 due to high vibration signals from the turbocharger vibration switch (reference Special Reports dated 6/15/89 (RBG-31090) and 9/15/89 (RBG-31520)). Since the .

' occurrence of those trips, the DG was restored to OPERABLE status with the vibration switch disconnected from the DG controls. ,

On 10/16/89 maintenance. personnel reset the vibration switch in accordance with Maintenance Work Order (MW0) #131144. In order to perform this

" resetting", the DG was started at 2119 on 10/16/89 and loaded to' full load for approximately eleven minutes to determine " ambient" conditions under which to set the vibration switch. In order to properly set the vibration

-switch, it is necessary to operate the DG under load for 30 to 45 minutes to bring it to normal operating temperatures. On 10/16/89, the DG was under load for only 11 minutes which failed to bring DG up to normal operating temperature. This error resulted in an incorrect setting of the vibration switch.

The vibration switch is required to be set at 2.59 above " ambient" conditions or normal turbocharger vibration levels. On 10/17/89, during the troubleshooting start at 1336 after vibration levels had been determined not to be excessive, the vibration switch was reset in accordance with MWO Page 1 of E

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JM56445. This setting ~ was performed after the DG had been at 100 percent lo3d for over 40 minutes. The' vibration switch was then- closely monitored for any indication of tripping during an additional 30 minutes of operation

'at 100 percent load., Since the vibration switch response indicated that .it had _been properly set under " ambient" conditions at 100 percent load under fnormal engine operating temperatures, the vibration switch output was then

= connected to normal DG controls.

At- 0031 on 10/18/89, with. the vibration switch' properly connected to DG controls, the. surveillance test was again performed. The DG operated satisf actorily and was declared operable upon completion of the STP.

Length of Time' Unavailable:

The above described DG trip' occurred during a scheduled monthly " preventive maintenance and inspection" period in which the DG was already inoperable.

'The vibration switch problem was corrected within the time span allowed by

-Technical Specifications for scheduled maintenance and did not require any changes to be. made in plant operation. The DG was restored to operable status approximately 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> after the trip but would have been available to _

respond to an emergency start signal. 1 Current Surveillance Interval:

Division I Monthly Division II Monthly Division III Monthly.

Test Intervals Conform to Technical Specification: Yes Failures for Div. I:

0- Valid failures in the last 20 valid tests 0 Valid failures in the last 100 valid tests ,

Failures for Div. II:

Of Valid failures in the last 20 valid tests 4 Valid failures in the 91 valid tests Failures for Div. III:

1_ Valid failure in the last 20 valid tests 2 Valid failures in the last 100 valid tests Number of Valid Failures in Previous 100 Valid Tests of all Diesel Generators at River Bend Station: 2 Page 2 of 2

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