ML17219A684

LER 87-013-00:on 870614,experienced Main Turbine Runback to 60% Power Due to Loss of Steam Generator Feed Pump.Cause Not Identified.Investigation of Problem in progress.W/870710 Ltr

ML17219A684
Person / Time
Site:	Saint Lucie
Issue date:	07/14/1987
From:	Mohn S, Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
L-87-286, LER-87-013-01, LER-87-13-1, NUDOCS 8707160802
Download: ML17219A684 (7)

Text

REGULA Y INFORMATION DISTRIBUTIQ YSTEM (RIDS)

ACCESSION NBR: 8707160802 DOC. DATE: 87/07/14 NOTARIZED: NO DOCKET FACIL: 50-335 St. Lucie Planti Unit iI Florida Power 5 Light Co. 05000335 AUTH. NAME AUTHOR AFFILIATION MOHN. S. E. Florida Power 5 Light Co.

WOODYI C. O. Florida PoUjer 5 Light Co.

RECIP. NAME" RECIPIENT AFFILIATION

SUBJECT:

LER 87-013-00: on 870614I experienced main turbine runback to 60/ power due to loss of steam generator feed pump. Cause not identified. Investigation of problem in progress. W/870710 1 tr.

DISTRIBUTION CODE: IE22D COPIES RECEIVED: LTR 1 ENCL J SIZE:

TITLE: 50. 73 Licensee Event Report (LER)> Incident Rpti etc.

NOTES:

REC IP I ENT COP IES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 1 PD2-2 PD 1 .1 TOURIGNYz E 1 1 INTERNAL: ACRS MICHELSQN 1 1 ACRS MOELLER 2 2 AEQD/DOA 1 1 AEOD/DSP/ROAB AEQD/DSP/TPAB 1 1 DEDRO 1 1 NRR/DEST/ADE 1 0 NRR/DEST/ADS 1 0 NRR/DEST/CEB 1 NRR/DEST/ELB 1 1 NRR/DEBT/ICSB 1 1 NRR/DEST/MEB 1 1 NRR/DEST/MTB 1 NRR/DEST/PSB 1 1 NRR/DEBT/RSB 1 1 NRR/DEST/SGB 1 1 NRR/DLPG/HFB 1 NRR/DLPG/GAB 1 NRR/DOEA/EAB 1 1 NRR/DREP/RAB 1 1 NRR/DREP/RPB 2 2 MAS/ILRB 1 NRR/PMAS/PTSB 1 REG FIL 02 1 1 RES DEPY GI 1 1 CF DI J 1 1 RES/DE/EIB 1 RGN2 FILE 01 1 1 EXTERNAL: EGRG GRQHI M 5 5 H ST LOBBY WARD 1 1 LPDR 1 1 NRC PDR 1 1 NSIC HARRISI J 1 1 NSIC MAYSI G 1 1 TOTAL NUMBER OF COPIES REQUIRED: LTTR 44 ENCL 42

NRC form 3$ 5 (943) U.S. NUCLEAR REGULATORY COMMISSION APPROVED OM 8 NO. 3150410O LICENSEE EVENT REPORT (LER) EXPIRES: Si31iSS FACILITY NAME (II DOCKET NUMBER l2) PA E St. Lucie, Unit 1 050003351OF04 REACTOR TRIP ON HIGH PRESSURE DUE TO TURBINE RUNBACK CAUSED BY LOSS OF 1B SGFP EVENT OATS (5) LER HUIABEtl (5) REPORT DATE (7) O'THER FACILITIES INVOLVED (5)

MONTH DAY YEAR YEAR SEQUENTIAL IICVdlOrt NUMBER i.' IIUMoe R MONTH OAY YEAR FACILITYNAMES DOCKET NUMBERIS)

N/A 0 5 0 0 0 06 487 87 0 1 3 0 0 0 7 148 7 0 5 0 0 0 THIS REtORT IS SUBMITTED PURSUANT 7 0 THE REOUIREMENTS Of 10 Cf R (II (Core>> onr or mort oi tnr iopowinfi ill)

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LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER AREA CODE S. E. Mohn Technical Staff 30 546 5-3 5 50 COMtLETE ONE LINC FOR EACH COMtOHEHT FAILURE OESCRISEO IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFAC. EPORTABLE MANUFAC. EPORTABLE TURER TO NPROS CAUSF. SYSTEM COMPONENT TURER TO NPRDS Qsgrirg~i+'Pg~:

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SUttLCMEHTAL RCPORT EXPECTCO (III MONTH OAY YEAR EXPECTED SUBMISSION DATE (15)

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On 14 June 1987, while operating at 100 percent power (Mode 1), St. Lucie Unit 1 experienced a main turbine runback to 60 percent power due to the loss of the lB Steam Generator Feed Pump (SGFP). The utility licensed operators restarted the SGFP and manually inserted control rods to reduce the primary/secondary power mismatch. The unit automatically tripped on high pressure approximately 22 seconds into the event. The trip was uncomplicated and the unit was quickly stabilized in hot standby.

The cause of the 1B SGFP trip has not been conclusively identified; however, personnel are continuing to evaluate potential causes.

The intention of the main turbine runback is to reduce the turbine steam load in response to the reduced feedwater flow and subsequent decrease in S/G inven-tories. Zt is not required for reactor safety. The Reactor Protection System will assure reactor safety by automatically tripping the unit and the main turbine on low S/G level or high pressure as it did in this event. This will assure sufficient S/G inventories to provide an adequate primary heat sink. At no time during this 'event were the 1A SGFP or auxiliary feed water system affected.

8707360802 8707JPI gFgrt PDR ADOCI( 05000335 S PDR NRC Form 3$ $

I9 531

NRC Fbrm 3SSA U.S. NUCLEAR REOULATORY COMMISSION (9431 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVED OMB NO, 3150&(04 EXPIRES: B/31/BB FACILITY NAME (Il OOCKET NUMBER (3( LER NUMBER (S) PACE (3I YEAR SSg> SEQUENTIAL REVISION St. Lucie, Unit 1 :r.P/ NUMBE4 V0d NUMSER p 5 p p p 3 3 5 8 7 0 1 3 0 0 0 2 OFO 4 TEXT ///morv Avvrv lr rvr/used, vFF Fddiv'orrv/NRC Frpmr SSSA'r/ ptl DESCRIPTION OF EVENT On 14 June 1987, St. Lucie Unit One was operating at 100 percent power steady state in Mode 1. There were no evolutions nor were there any surveillances in progress. All automatic controllers were in automatic with the exception of the Control Rod Drive System (EIZS:JD) which was in ROFFR. The Steam Bypass Control System (EIIS:JI) was in automatic with one of the five bypass valves isolated due to seat leakage.

At 2350 hours0.0272 days <br />0.653 hours <br />0.00389 weeks <br />8.94175e-4 months <br />, the 1B Steam Generator Feed Pump (SGFP) (EZZS:SJ) tripped and initiated a main turbine runback (EIISEJJ) to 60 percent power. The utility licensed operators having been alerted to the event by various annunciator alarms (EIZS:IB) restarted the 1B SGFP and manually inserted control rods (EIZSEAA) to reduce reactor (EIIS:AC) power. Primary temperature and pressure were rising rapidly due to the increasing power mismatch caused by the main turbine runback.

The main turbine runback was stopped when the operators restarted the 1B SGFP approximately ll seconds after it initially tripped. The operators continued to insert the control rods to reduce the reactor power level and thereby minimize the primary temperature and pressure surge. However, the power mismatch was too severe and the unit automatically tripped (EIISTJC) on high pressurizer (EZZS:AB) pressure at 2400 psia approximately 22 seconds into the event.

The trip was an uncomplicated trip and all systems functioned normally. The Power Operated Relief Valves (PORV) (EIZS:AB) automatically lifted as designed at 2400 psia to reduce primary pressure and then reseated. The SBCS operated to reduce primary average temperature (T-avg) to the zero power setpoint of 532 degrees F. Auxiliary Feedwater Actuation System (AFAS) (EIIS:BA) actuated on low steam generator (S/G) level due to the shrink caused by the rapid post trip power reduction. The standard post trip actions were completed and the unit was quickly stabilized in hot standby (Mode 3).

CAUSE OF EVENT The cause of the main turbine runback and the subsequent automatic reactor trip was the loss of the 1B SGFP. The root cause of the event, why the 1B SGFP tripped, has not been conclusively identified. Following the unit trip the Electrical Department commenced extensive troubleshooting of the 1B SGFP motor, breaker (EIIS:EA),'and associated SGFP control and protective circuits.

No abnormalities were discovered. Investigation into potential causes of the 1B SGFP trip is continuing.

NRC FORM SSSA rn FFI

NRC form 3ESA U.S. NUCLEAR R EGULATOR Y.COMMISSION 194)3)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVED OMB NO, 3150&)04 EXPIRES: B/31/BB FACILITY NAME (Il OOCKET NUMBER (2) LER NUMBER (El PAGE (3)

YEAR P@ SEOUENTIAL SS REVISION St. Lucie, Unit 1 NUMBER '.~tC/ NUMBER o s o o o 87 0 13 0 0 0 3 OF 04 TEXT /i/m<<c <<>>toit ror)rr/rcrL rr>> cr/r/5onV NRC %%drm 356r4'4/((2)

ANALYSIS OF EVENT This event is reportable under 10 CFR 50.73 (a)(2)(iv), "any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature, including the Reactor Protection System".

The temporary loss of the 1B SGFP resulted in a main turbine runback and a reduction in normal feedwater flow. The main turbine runback is initiated when one of the two running SGFPs trip and main turbine load, as measured by the main turbine's first stage pressure, is greater than 60 percent. The main turbine, runback is not required for reactor safety. It is intended to reduce the main turbine steam demand in response to the reduced feed flow and subsequent decrease in S/G feedwater inventories. Had the main turbine runback failed to activate, the Reactor Protective System (RPS) (EIIS:JC) would have automatically tripped the reactor on low S/G level and then tripped the main turbine. This would have assured sufficient S/G feedwater inventories to provide an adequate heat sink for the primary system.

If the 1B SGFP had not been able to be restarted, the turbine runback would have continued until main turbine load was less than 60 percent. The RPS would have automatically tripped the reactor on either low S/G feedwater levels or on high pressurizer pressure as it did in this event. In both of the above trips the RPS would have also tripped the main turbine on reactor trip. Again, sufficient S/G feedwater inventories would have been available to provide an adequate primary heat sink.

At no time during this event was the normal feedwater flow from the lA SGFP affected. The auxiliary feedwater system was also available during the entire event and was successfully actuated when the S/G levels decreased due to shrink following the trip.

The St. Lucie Unit 1 updated Final Safety Analysis Report (FSAR) has analyzed both the "Loss of Load" (15.2.7) and the "Loss of Feedwater Flow" (15.2.8) accidents and has determined that no violation of the reactor safety limits would occur. At no time during the event were the health and safety of the public endangered.

NRC FORM SEEA ro ool

NRC Farm 388A US. NUCLEAR REOULATORY COMMISSION (943)

LICENSEE EVENT REPORT ILER) TEXT CONTINUATION APPROVEO OMB NO. 3150&(04 EXPIRES: 8/31/88 FACILITY NAME (I) OOCKET NUMBER (21 LER NUMBER (81 PAOE (3)

YE*h SSOUSNTIAL hSVISION NUM S Sl NUMSSII St. Lucie, Unit 1 p 5 o o o 33 587 0 1 0 0 4 OF 0 4 TExT /// mors spsss is ssr/rr/rsrL rrss ~ /'a'orrs/HRC bream 3IMA's/ (12)

CORRECTIVE ACTIONS Following the trip the unit was stabilized in hot standby. Plant personnel are continuing to evaluate potential causes of the SGFP trip.

ADDITIONAL INFORMATION

1. Com onent Identification There were no specific component failures identi'fied during .this event.

2. Previous Similar Events See LER N335-87-10 for the previous reactor trip event.

NRC FORM 386A (9831

P. O. 14000, JUNO BEACH, FL 33408.0420 JuLY L-87-286 10 CFR 50.73 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Gentlemen:

Re: St. Lucie Unit No. 1 Docket No. 50-335 Reportable Event: 87-13 Date of Event: June 14, 1987 Reactor trip on high pressure caused b Loss of Steam Generator Feed Pum The attached Licensee Event Report is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.

Very truly yours, C. O..Wo Group V President Nuclear Energy COW/GR M/cn cc: Dr. J. Nelson Grace, Regional Administrator, Region ll, USNRC Senior Resident inspector, USNRC, St. Lucie Plant an FPL Group company C'R M5/062/1