ML20085N400

AO BFAO-7334W:on 731110,during Manual Trip Because of Sudden Increase in Vibration,Rcic & HPCI Sys Inoperable Due to Complete Loss of Plant Ac Electrical Power.Caused by Problem W/Control Logic.Evaluation Continuing

ML20085N400
Person / Time
Site:	Browns Ferry
Issue date:	11/19/1973
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085M910	List: ML20085M907 ML20085M913 ML20085M916 ML20085N400
References
AO-BFAO-7334W, NUDOCS 8311110005
Download: ML20085N400 (3)

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TENNESSEE VALLEY37401 AUTHOAITY L,.,L .q C]k '

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. .- 3 .a November 19, 1973 * $E"ESTd&T, P '\

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= JA Mr. John F. O'Icary, Director (4 . mKW4 Directorate of Licensing Office of Regulat, ion \ a$ 9 8

U.S. Atomic Energy Cnmf ssion O 6 Vachington, DC 20545

Dear Mr. O' Leary:

TE EESSEE VALLEY AUTHORITY - BROUii3 FERTI NUCLEAR PIRIT UNIT 1 -

DOCKET N0 50-259 - FACILITY CPERATING LICE'I3E DPR AbNOR4AL CCCURR3NCB REPORT EFAO-7334U The enclosed report ic to provide detaile concerning RCIC and EPCI ryntems' ino,crubility during complete lecc of plan, a-c electric =11 power trhich occurred on Erowns Ferry nuclear Plant unit 1 on Hovember 10;,1973, and ic submitted in accordence with Appendix A to Regulatory Guide 1.16, Revision 1, October 1973 Very truly yours, TEII: ESSE VALLEY AUTEORITY

, n Y, u ( lt-r> W U. F. Thomas Director of Power Production Enclosure CC(Enclocure):

Mr. Nomen C. Moccley, Director Region Il Regulatory Operations Office, USAEC 230 Fccchtree Street, NW.

Atlanta, Geor61a 30303

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ABNORMAL OCCURRE"CE REPORT Report No.--EFAO-733W Report Date--November 19, 1973 Occurrence Date- "ovember 10, 1973 Facility--Erowns Ferry Nuclear Plant unit 1 Identification of Occurrence RCIC and HPCI systems' inoperability during complete loss of plant a-c electrical power.

Conditions Prior to Occurrence The reactor was at 25-percent power and the turbogenerator at 179 MWe.

Prerequisites were being established in preparation for startup test EF STI-31

% (Turbogenerator Trip and Loss of Offsite Power). The transfer schemes of the 4-kV unit boards had been placed in =anual to prevent automatic transfer of the unit and shutdown aux.liary boards during the loss of power test.

Description of Occurrence The turbine was manually tripped because of a sudden increase in vibration. The turbine trip cc=bined with the inability of offsite power supplies to feed the unit and shutdown au.siliary boards caused a reactor scran due to the loss of the i reactor protection system power supplies.

The operator was unable to start the RCIC and HPCI systems until the standby diesel generators energized the shutdown auxiliary boards and the trippin6 logic

) v' to the RCIC and EPCI. systems was manually reset. q ii Q

Designation of Apparent Cause of Occurrence t

When loss of power occurred on the shutdown auxiliary boards, the instrumentation and control buses, A and B, were deener6 1 :ed. The sLnultaneous loss of power to both instrumentation c.nd control buses allowed two of the three releys, that operate on high reactor water level, to deenergize, satisfying the two out of three logic that causes tripping of EFCI, RCIC, and reactor feedwater turbines.

These tripping relays, rather than autenatically resetting on voltage restoration to the instrumentation and control buses, had to be manually reset by an operator .

A as the design of the logic calls for.

Analysis of Occurrence

' During the short period of inoperability of the HPCI and RCIC systems, reactor pressure increased only slightly and reactor water level did not decrease to the point that the RCIC or HPCI systems verg required. Had the RCIC and HPCI systems

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remained inoperable, safe shutdown of the reactor would have proceeded 'by manual or automatic blevdown of reactor pressure with the safety relief valves which serve as a backup to the HPCI system. After depressurization, both the lev- 1 pressure core in,lection and core spray systems would have maintained core coolant inventory in the reactor pressure vessel.

p, Corrective Act'oni Immediately after the occurrence, the control schemes of the HPCI and RCIC trippin6 logic were evaluated and a desi6 n change initiated. The manual recet 1 components of the ~ tripping logic have been removed, thereby eliminating operator f action 'followins a " loss of-return to" sequence of power to the tripping relays.

To reduce the possibility of a simultaneous loss of power to the relays; the power source to one of the relays has been chan6ed to the 250-volt station battery.throu6h an inverter.

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