ML20085M751

AO BFAO-7338W:on 731115,at 25% Power W/Msiv Closed,Rcic & HPCI Sys Failed.Caused by Movable Contact of Dc Contactor Being Hung in Arcing Horn.Contactor Repaired

ML20085M751
Person / Time
Site:	Browns Ferry, 05000000
Issue date:	11/23/1973
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085M697	List: ML20085M723 ML20085M729 ML20085M744 ML20085M751
References
AO-BFAO-7338W, NUDOCS 8311090219
Download: ML20085M751 (3)

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' TENNESSEE VALLEY AUTHO AITY [*7tT . 6 CHATTANOOGA, TENNESSEE i 3740*I L ' _'_ / /~ 1

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ANNIVE A SARY OF PECPLE IN PAATN E ASHIP November 23, 1973 k[f Nk i kW Mr. John F. O' Leary, Director Directorate of Licensing Office of Regulation U.S. Atomic Energy Commission Washington, DC 205+5 1

Dear I/x. O' Leary:

TENNESSEE VALLEY AUTHCRI2Y - BRCEINS FERRY NUCLEAR PIANT UNIT 1 -

DOCKET No. 50-259 - FACILITY OPERATING LICENSE DPR ABHOR!/AL ,

OCCURRENCE REPORT BFAO-7338W The enclosed report is to provide details concernine RCIC and HPCI failures which occurred on Browns Ferry Nuclear Plant unit 1 on November 15, 1973, and is submitted in accordance with Appendix A to Regulatory Guide 1.16, Revision 1, October 1973.

Very truly yours,

, TENNESSEE VALIEY AUTHORITY

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/<.. 'LDirector CME.F. of Thomas Power Production Enclosure CC(Enclosure):

Mr. Norman C. Moseley, Director Region II Regulatory Operations Office, USAEC 230 Peachtree Street, NW.

Atlanta,' Georgia .30303 Q5 - ,.

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ABNORMAL OCCURRENCE REPORT ,

Report No.--BFAO-733W Report Date--November 23, 1973 Occurrence Date--November 15, 1973 i . Facility--Browns Ferry Nuclear Plant unit 1 Identification of Occurrence RCIC and HPCI failures. .

e Conditions Prior to' Occurrence 2 The reactor was at rated pressure with the MSIV's closed following the

. initiation of STI-31, " Loss of TG and Offsite Power," at 25% reactor power.

Description of Occurrence At approximately 3 a.m., following the initiation of STI-31 at 25% reactor

!- power, the RCIC system failed to operate when manually initiated. The-steam -

supply valve would not open. The HPCI system was then manually initiated to restore vessel water level to normal. Upon initial actuation, HPCI i isolated and tripped. The HPCI steam leak temperature high alarm was .

! present at this time. The isolation circuit was immediately reset and ,

, HPCI functioned satisfactorily to restore reactor vessel water level.

Reactor veter level did not decrease.to the automatic. initiation level of the HPCI and RCIC. ~

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I Designation of Apnarent Cause of Occurrence The;RCIC steam supply valve failed to open because a moveable contact of. the DC contactor was hung in the arcing hcrn. At this time, no apparent cause of

! the HPCI system isolation has been determined.

Analysis of Occurrence Safe shutdown of the reactor would have.bcen possible because all remaining j safety systems were available. HPCI operated satisfactorily after the isolation circuit was reset.

' Corrective Action The contactor on the RCIC steam. supply valve was. repaired to give sufficient clearance between the arcing horn'and the-moveable contact. The valve was

, successfully operated several times.

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Extensive effort has been exerted to determine the exact cause of the HICI isolation. Each area that will cause an isolation has been investigated.

Calibration of all HPCI steam line space temperature switches was verified and found acceptable. The steam line differential pressure switches were satisfactorily tested. Investigation during HPCI operation showed that the turbine exhaust diaphragm was not ruptured. Heating due to loss of reactor building ventilation was investigated,and no significant rise in temperature was observed with the ventilation off for a period of 45 minutes. It is possible that shock wavec cr vibration initiated the isolation since the isolation occurred concurrent with a rain steam relief valve open. Special testing in an effort to recreate as many as possible of the conditiens present at the thae of the occurrence failed to reveal the cause of the isolation. During this test, HPCI was manually initiated twice and was operdted during a relief valve operation. At no time during this test was an isolation experienced. At this time investi 6ation is continuing in an effort to determine a cause of the HPCI isolatien.

Failure Data The nameplate data for the DC contactor that filed on the RCIC steam supply valve is as follcws: e Contactor - General Electric 250V DC GE Catalog Number IC28001607F2H This is the first occurrence of this type breaker failure. "

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