ML17221A631

LER 87-013-01:on 870614,1B Steam Generator Feed Pump Tripped & Initiated Main Turbine Runback.Cause May Have Been Due to Failure of Differential Current Relay.Unit Stabilized in Hot standby.W/880218 Ltr

ML17221A631
Person / Time
Site:	Saint Lucie
Issue date:	02/19/1988
From:	Mohn S, Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
L-88-75, LER-87-013, LER-87-13, NUDOCS 8802230053
Download: ML17221A631 (6)

Text

ACCESSION)'- NBR: 8802230053 DQC. DATE: 88/02/19 NOTARIZED: NO DOCKET 0 FACIL: 50-335 St. Lucie Plant. Unit 1> Florida Power 5 Light Co. 05000335 AUTH. NAME AUTHOR AFFILIATION MOHN> S. E. Florida Poeer u4 Light Co.

WOODY> C. O. Florida Poeer 5 Light Co.

RECIP. NAME RECIPIENT AFFILIATION

SUBJECT:

LER 87-013-01: on 870614> 19 steam generator feed pump tripped 8c initiated main turbine runback. Cause may have been due to failure of diffeTential current relay, Unit stabilized in hot standby. W/880218 ltr.

DISTRIBUTION CODE: IE22D COPIES RECEIVED: LTR ENCL SIZE:

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

NOTES:

RECIPIENT COPIES REC IP IENT COP IES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 PD2-2 PD 1 1 TOURIGNY> E 1 1 INTERNAL: ACRS MICHELSQN 1 1 ACRS MOELLER 2 AEOD/DOA 1 1 AEOD/DSP/NAS 1 AEOD/DSP/ROAB 2 2 AEOD/DSP/TPAB 1 ARM/DCTS/DAB 1 1 DEDRO 1 NRR/DEST/ADS 0 NRR/DEST/CEB 1 NRR/DEST/ELB 1 1 NRR/DEST/ I CSB 1 NRR/DEST/MEB 1 NRR/DEST/MTB 1 NRR/DEST/PSB 1 1 NRR/DEBT/RSB 1 NRR/DEST/SGB 1 NRR/DLPG/HFB 1 NRR/DLPG/GAB 1 1 NRR/DOE*/EAB 1 NRR/DREP/RAB 1 NRR/DREP/RPB l NRR/D SIB NRR/PM*S/ILRB

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HRC Sorrn 244 U S. NUCLEAR REGULATORY COMMISSION 19 41I APPROVEO OMS NO. 1150410e LICENSEE EVENT REPORT (LER) EXPIRES. SI1) i4$

SACILITY NAMt lll DOCKET NVMSKR )1( PA I St. Lucie, Unit 1 o 5 o o o 335 >orp TITLE (e)

REACTOR TRIP ON HIGH PRESSURE DUE TO TURBINE RUNBACK CAUSED BY LOSS OF 1B SGFP CVCHT DATE(4I L ~ R NUMSER (4) REPORT DATE (7) OTHER FACILITIES IHVOLVED (N MOHTH Vt*R

$ $ QUtHTIAL Rtvrelorr FACILITYrrAMES OAY YEAR ~ rUMttR rrUM$ ER MOHTH OAY YEAR DOCKET HVMSERISI N/A 0 5 0 0 0 0614 8 7 8 7 1 3 0 1 02 19 88 0 5 0 0 0 THIS REPORT IS SUSMITTEO PURSUANT 7 0 THC REOUIRtMENTS OS 10 CSR ((; IChoce onc oi n orc ot the torro~inpt (11 Opt RAT(NO MOOR (Sl 20.602 ($ 1 20,404(cl l0,71(el Q I(irl 72.7) ($ 1

~ OOICR 20.6(N(el(I IIII ~ 0.$ 4(till ) 40.7 2(el 12 I 4 I 72.7)(cl LtVEL 1 p p I'I0) 20.604 4) llI I 4 I 40.$ 4(el(1) 40.71(cl(2l(ro) OTHER ISOCCrirr n nettrctt octo>> ono in Tert, rrRC Form 20.e(N(el(1114) I 40.72( ~ l(1)(II 40.72(el(2)(ritl(AI 266AI 20.6044llll(hl ~ 0.72(el(1)(4) 40.72(e)(21(rr41(4) 20.104(el)lilt) 40.72(el(1)04) 40.71( ~ I (2)(el LICENllt CONTACT FOR THIS LCR (12)

HAME TELEPrrOHE HVMSER S. E. Mohn - Technical Staff AREA CODE 305 465 -355 COMPLCTE OHE LINC SOR EACH COMPONENT SAILURK DESCRI ~ CO IN THIS REPORT (11)

CAUSE SYSTEM COMPOHCHT MAHUFAC EPORTA4LC MAHVFAC EPORTASLE TVRCR P~.'r. CAUSE SYSTEM COMPOHFHT TVRER TO HPRDS B E A 8 7 W 1 2 0 Yes ~ q@>4+pc SUPPLEMENTAL REPORT CXPECTlO (14 MOrr7>> Dhv vEAR EXPECTED SU4MISSIOH DATE (15)

YCS IIIyce. corroHto EXPECTED SVSMISSIDH DATE) HO A44TRAcT ILirnit to Iot)0 coocoo, i,a, esororirnotory ttttocn <<npr>> chore typorrrrtton o'neet Ill)

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 1B 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 events 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, a failure of the differential current relay, type SA-l, in the 1B SGFP is believed to have been the cause. An upgrade has been installed in all Unit 42 and in one Unit I)l type SA-1 relays. The remaining upgrades for Unit fl type SA-1 relays are on order.

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. It is not required for reactor safety. The Reactor Protection System will assure reactor safety by automatically tr'ipping 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.

HRC Fort<< 244

'9 41r 8802230053 8802i9 PDR ADOCK 05000335 8 PDR

NRC FoIoI 35OA U.E. NUCLEAR REGULATORY COMM(5$ I (943 I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROYEO OMB NO, 3(5C~IQA EKPIAES: E/31/

FACILITY NAME (11 DOCKET NUMSER (21 LE R N UMEE R (EI ~ AGE (3l 5EQIIENTIAL:~>.

YEAR NUM 5<< ' '~ IIEVI5ION NUMOEA St. Lucie, Unit TEXT llfmon <<>>co>> Ioooiod, 1

ooo oooioonol HRC %%dmI 3(E(A 3 I IITI o 5 o o o 01301 0 2 OF DESCRIPTION OP 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 weze in automatic with the exception of the Control Rod Drive System (EIISEJD) which was in "OFF". The Steam Bypass Control System (EZIS: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) (EIZS:SJ) tripped and initiated a main turbine runback (EZISEJJ) to 60 percent power. The utility licensed operators having been alerted to the event by various annunciator alarms (EIISEZB) restarted the 1B SGFP and manually inserted control rods (EIISEAA) 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 SGPP approximately 11 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 (EZZSEJC) 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) (EZZSEAB) 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 P. 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 OP EVENT The cause of the main turbine runback and the subsequent automatic reactor trip was the loss of the 1B SGFP. Following the unit trip the Electrical Department commenced extensive tzoubleshooting of the 1B SGPP motor, breaker (EIZSEEA),

and associated SGPP control and protective circuits. No abnormalities were discovered. Subsequent failure of the 1B SGFP differential current relay on 18 October 1987, indicates that June 1987 trip.

it was most likely the root cause of the 14 The failure mode was such that the relay failure was spurious, intermittent, and its actuation flag did not lock in. This explains the original difficulty in the detection of the root cause for the 14 June event.

NRC FORM 5OOA

NRC form 344A U Sr NUCLEAR REOULATORY COMMIS (9.43 I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVED OM4 NO 3150&lao EXPIRES: 4/3(/(4(

FACILITY NAME (I) DOCKET NUMEER (1( PAGE I31 LER NUMEER (El YEAR .'ro( SEOVENT/AL .I ."r AEV/5/ON rrvM ER o NOME( R St. Lucie, Unit 1 87 13 0 5 0 0 0 0 01 0 3 OF0 4 TEXT ////rroro soosois ror/rsror/ rrso sdr//oorrs/HRC  %%drrrr 3(R(A'/(ITI 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) (EIISEJC) 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 1A 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.

Nrrc sorrM 3oo*

NRC Form 3EBA U.S. NUCLEAR REGULATORV COMMIS(

(943 I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVEO OMB NO, 3ISOWIOO EXPIRES: 9/3(/IEI FACILITY NAME III OOCKET NUMBER (2(

LER NUMBER (El ~ AOE (3i

/

TEAR SEOUENTIAL IIEVtSION P'? Ni/M ER 9? I Ir v M B ~ II St. Lucie, Unit 1 p 3 3 5 8 7 013 010 4 OF 5 p p p TEXT /I/ more g>>oe>> reeorred, o>> eddro'or>>/ HRC %%dnII 3BSAB/ (ITI CORRECTIVE ACTIONS

1. Following the trip the unit was stabilized in hot standby.

2. Upgrades for the Type SA-1 relay have been installed in all Unit %2 relays (6) and in one Unit Nl relay. Parts for the remaining Unit 01 relay upgrades (5) are on order.

ADDITIONAL INFORMATION

1. Com onent Identification Westinghouse Electrical Corp.

Type SA-1 Differential Current Relay

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

I/RC FOIIM 3OOA

P. O. Bo 0, JUNO BEACH, FL 33408 0420 FEBRUARY. 2 8 1988 L-88-75 10 CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: St. Lucie Unit 1 Docket No. 50-335 Reportable Event: 87-13 Revision 1 Date of Event: June 14, 1987 Reactor Trip on High Pressure Caused b Loss of Steam Generator Feed Pum The attached Licensee Event Report (LER) is being submitted pursuant to the requirements of 10 CFR 50.73 to provide an update on the subject event.

Very truly yours, Executi Vice President COW/GRM/gp Attachment cc: Dr. J. Nelson Grace, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, St. Lucie Plant GRM/021. LER an FPL Group company