ML18004B770

LER 87-013-00:on 870313,plant Manually Tripped at 49% Power Due to Loss of Main Feedwater.Caused by High Discharge Pressure Spike of Condensate Booster Pumps.Feedwater Regulating Valves stroked.W/870410 Ltr

ML18004B770
Person / Time
Site:	Harris
Issue date:	04/10/1987
From:	SCHWABENBAUER, WATSON R A CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
HO-870407-(O), LER-87-013, LER-87-13, NUDOCS 8704170051
Download: ML18004B770 (6)

Text

'I~~5 w~i~~REGULAT INFORMATION DISTR IBUTI QN STEM (R IDS)C ACCESSION NBR: 8704170051 DOC.DATE: 87/0 7/10 NOTARIZED:

NO FACIL: 50-400 Shearon Harris Nuclear Power Planti Unit 1>Carolina AUTH.NAME AUTHOR AFFILIATION SCHWABENBAUER Carolina Potller 8c Ligh+Co.WATSON'.A.Carolina Power 5 Light Co.RECIP.NAME RECIPIENT AFFILIATION DOCKET 05000400

SUBJECT:

LER 87-013-00:

on 870313>plan+manually tripped at 49/paver due to loss of main feeduater.

Caused bg high discharge pressure spike of condensate booster pumps.Feedeater regulating valves stroked.W/870410 ltr.DISTRIBUTION CODE;IE22D COP IEB RECEIVED: LTR ENCL BI ZE: TITLE: 50.73 Licensee Event Report,(LER) i Incident Rpti etc.I NOTES: App l ication f or permit reneu!al f i led.05000400 RECIPIENT ID CODE/NAME PD2-1 LA BUCKLEY'S B INTERNAL: ACRS MICHELSON ACRS WYLIE AEOD/DBP/RQAB AEOD/DSP/TPAB NRR/DEST/ADE NRR/DEBT/CEB NRR/DEBT/ICSB NRR/DEST/MTB NRR/DEST/RBB NRR/DLPG/HFB NRR/DOEA/EAB NRR/DREP/RAB RRA M LRB REG FIL 02 R FILE 01 EXTERNAL: EGSQ GROH>M LPDR NSIC HARRIS J COP IEB LTTR ENCL 1 1 1 1 1 1 2 2 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 5 5 1 1 RECIP IENT ID CODE/NAI'IE PD2-1 PD ACRS'MOELLER AEQD/DOA AEOD/DBP/TAPB NRR/ADT NRR/DEST/ADS NRR/DEST/ELB NRR/DEST/MEB

.NRR/DEST/PSB NRR/DEBT/SGB NRR/DLPG/GAB NRR/DREP/EPB NRR/DREP/RPB NRR/PMAS/PTBB REB SPEISi T H ST LOBB Y WARD NRC PDR NSIC MAYBi G CQP IES LTTR Er,'CL 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 2 2 1 1 1 1 1 1 TOTAI NUMBER OF COPIEB REQUIRED: LTTR 44 ENCL 42 NRC Forln 3ES (943)LICENSEE EVENT REPORT ILER)UA.NUCLEAR REGULATORY COMMISSION APPROVED OMB NO.31500(04 EXPIRES: 5/31/SS FACILITY NAME (I)SHEARON HARRIS PLANT UNIT 1 TITLE (4)REACTOR TRIP-LOSS OF FEEDWATER DOCKET NUMB 5 R I2)PA 050004010F04 MONTH DAY YEAR EVENT DATE l5(YEAR LER NUMBER (Sl sEQUENTIAL pzp N VMS EA farl irlvlscN NVMS Err MONTH DAY YEAR REPORT DATE (7l DOCKET NUMBER(3)0 5 0 0 0 FACILITY NAMES OTHER FACILITIES INVOLVED (Sl 0 3 138 787 0 1 3 0 0 041 0 8 7 0 5 0 0 0 OPE RATINO MODE (9)POWER LKYEL 0 4 9 C%:'r'vy N.cr., n THIS REPORT IS SUBMITTED PURSUANT T 0 THE REQUIREMENTS OF 10 CF R ()r ICireclr onr or more of tfrr follorffnpl (11)20A02(lr)20.405(e l(1)(l)20.405 le l(1 I (51 20.405(el(1)(Ell 20.405(e)(I)(lv)20.405(e)II)(rl 20.405 le)5024(c)(ll 50.73(e)(2)(lv) 50.73(el(2)(v)50.73(el(2)(rill 50.73(e)(2)(rill)(A)50.73(el l2)(vlQ)(5)50.73(el l2)(xl SOW(e)(2)50.734)(2((l)50 734)(2)(5 I 50.73le)(2)(IS)

LICENSEE CONTACT FOR THIS LER l12)73.71')73.71(c)OTHER (Specify ln Aortrect trelorrrnd In Text, HRC Fomr 3PEAI NAME R.SCHWABENBAUER

-REGULATORY TECHNICIAN TELEPHONE NUMBER AREA CODE 919 36-26 69 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBEO IN THIS REPORT l13)CAUSE SYSTEM COMPONENT MANUFAC.TURER EPOATABLE TO NPRDS P yy r y CAUSE p c SYSTEM COMPONENT MANUFAC TUAER EPOATABL TO NPADS'y r%y r c...?.iM&o SUPPLEMENTAL REPORT EXPECTFD (14)YES Ilf yer, complrrr EXPECTED SIIEMISSIOH DATE)NO ABSTRAGT ILlmlt to l 400 rpecer, I e., rppnrxlmrtrly fifteen dnpleepecr typerrrltten lined (15)EXPECTED SUBMISSION DATE (15)MONTH OAY YEAR ABSTRACT At 1616 on March 13, 1987, a manual trip of the plant was initiated from 49X reactor power due to a loss of main feedwater.

The plant had recently completed forward flushing of Auxiliary feedwater check valves and was in the process of opening the preheater bypass valves.The preheater bypass valves on B and C steam generators had been vpenedp and a small feedwater flow oscillation resulted.Opening the valve for A steam generator started a feedwater system pressure transient which caused the main feedwater regulating valves on all three steam generators to oscillate.

This transient caused trips of the running Main Feedwater Pump, both Condensate Booster Pumps, the running Heater Drain Pump, and both Condensate Pumps.Attempts to restart the pumps were unsuccessful, and the reactor was manually tripped.The Motor Driven Auxiliary Feedwater Pumps started as required on a loss of main feedwater.

The Main Steamline isolation valves were manually closed subsequent to the reactor trip to limit the cooldown of the RCS.The reactor was stabilized in Mode 3 at 557'F (zero-load Tavg).8704170051 87041 0 PDR ADOCK 05000400 S PDR NAC Form 355 (903)

NRC Form 366A ($83)UCENSEE EVENT REPORT{LER)TEXT CONTINUATION UA.NUCLEAR RECULATORY COMMI$$ION APPROVEO OMB NO.3150-0106 EXPIRES: 8/31/85 FACIUTY NAME ill SHEARON HARRIS PLANT UNIT 1 DOCKET NUMBER (3)YEAR@SEOVENTIAL NVMSER LER NUMBER (6)AEVISION NVM EA PACE (31 TEXT/SIAoro N>>co ll iotvENE I>>o IIE/Oo>>/HRC Anrr 38EAS/(IT)0 5 0 0 0 4 0 0 8 7 1 3-00 02 OF 0 4 On March 13, 1987, the plant had been operating at 49X reactor power.The feed and condensate system lineup consisted of both condensate pumps 1A and 1B in operation, both condensate booster pumps lA and 1B in operation with the speed controllers in AUTO, one heater drain pump in operation, and one main feedwater pump in operation.

Steam generator feedwater at this power level is normally provided to each steam generator through the main feedwater regulating valve supplying both the normal steam generator 16 inch preheater line and'the preheater.bypass 6 inch line.The preheater bypass line was isolated while conducting flushing of the line with auxiliary.feedwater to attempt to seat the auxiliary feedwater check valves.After securing the auxiliary feedwater flow, the bypass line was being restored to service by opening the preheater bypass isolation valve.This sequence had been performed on B and C steam generators earlier.Upon opening Steam Generator A Preheater Bypass Valve, the feedwater regulating valves of all three steam generators started swinging open and closed in rapid succession.

Before being able to take manual control, all main feedwater and condensate pumps had tripped'.Attempts to restart the feedwater system pumps failed, and a manual reactor trip was initiated at 1616 as steam generator levels were approaching 40X.Due to the low decay'heat of the core, and steam load from the moisture separator reheaters, Reactor Coolant System T was reduced to about 540'F and pressurizer level decreased to about 10X subse/uent to the trip.The Main Steamline Isolation Valves were manually closed to minimize cooldown.The plant was stabilized in Mode 3 at RCS T of 557'F which is the zero-load value.avg~Anal sis An incident investigation team was convened to determine the cause of the pump trips, and to recommend corrective actions.The following conclusions'ere reached by this investigation team'.A.The reactor trip due to loss of feedwater on February 27, 1987 (LER-87-008-00), and another feedwater transient on March 11, 1987, illustrated a tendency for main feedwater regulating valves toward divergent oscillations.

These oscillations occur on very short cycles of about a second when feedwater perturbations are experienced.

NRC'SORM 366A (IM)3)*U.S.OPO:I 088.0834.538/455.

'

n NRC Form SCCA ($63)LICENSEE EVENT REPORT (LER)TEXT CONTINUATION U.S.NUCLEAR REOULATORY COMMISSION APPROVEO OMB NO.3)60-0(04 EXPIRES: 8/31/88 PACIUTY NAME (1)SHEARON HARRIS PLANT UNIT 1 POCKET NUMBER (3)VCAR LER NUMBER (8)/a.s8 SCOVCNTIAL NVMCCR RCV<<10 M cs NVMCCSI PAPE (3l TEXT%mac<<sccc*scCM)css sssc ak////dsn/HRC Pssnn 38SA's/(IT)o s o o o 40 08 7 013-0 0 03 OFO 4~Anal sis (continued)

B~The computer data points for system parameters were generally scanned at one second intervals.

Thus, resolution of peak values was not sufficient to give a clear basis for determining the sequence of events.The available data indicated that all pumps tripped within a few seconds of each other, and that feedwater, condensate, and steam flows did not develop the wide variations observed on the main control board meters.C.The Steam Generator Main feedwater regulating valves are controlled by a level demand signal and a steam/feedwater flow mismatch signal.It was concluded that the steam/feedwater flow mismatch signal caused by feedwater perturbations had caused one feedwater regulating valve to begin oscillating, which then in turn hydraulically induced oscillations in the other steam generator feedwater regulating valves.The specific reason for the undamped nature of the oscillation could not be determined from the trip data.D~Although firm supporting data is not available, it is concluded that the condensate booster'pumps tripped due to a high discharge pressure spike which caused an immediate trip of the main feedwater pump (due to a control interlock).

The condensate pumps subsequently tripped on low flow due to slow response of the condensate pump recirculation valves.Subsequently, the trip setpoints Eor the feedwater and condensate system pumps were verified to be in calibration.

Based on this finding, a concern was raised.that the time delay period for some trips, such as low flow, may be set too low to allow recirculation valves to open and thus lead to unnecessary trips during transients.

E.A key factor contributing to this instability may be related to the high differential pressure experienced by the steam generator Eeedwater regulating valves at this power level.The response time oE the regulating valve may not match that of the overall feed and condensate train.Cause The cause of the loss of feedwater is attributed to a high discharge pressure spike on condensate booster pumps, which tripped the booster pumps and subsequently tripped the main feedwater pumps.The trip of the condensate pumps occurred because the recirculation valves could not open quick enough to prevent tripping these pumps on low flow.SIRC'SORM SCCA (083)RU.s.opo: Ieeee e8c.s38/dss p

NRC Form 388A (983)I~LICENSEE EVENT REPORT (LER)TEXT CONTINUATION US.NUCLEAR REGULATORY COMMISSION APPROVEO OMB NO.3)50-0)04 EXPIRES: 8/31/88 FACILITY NAME (11 SHEARON HARRIS PLANT UNIT 1 TEXT/9'maf gwce/8/89vka5 IN8/d/dana/HRC Fem/35589/(ITl OOCKET NUMBER (3)YEAR 4 0087 LER NUMBER (Bl N SEOUENTIAL NP.Pr'UMBER-0 1 3 REVISION NUMBER-0 0 PAGE (3)0 40F 0 4 Cause (continued)

The cause of the feedwater system instability was attributed to hydraulic pressure induced oscillations of the main feedwater regulating valves.Upon opening the preheater bypass line isolation valve, the main feedwater regulator valves on all three steam generators were observed to start oscillating with short cycles.The feedwater flow signal on the recorders and indicators were observed to have large oscillations.

Corrective.Action As discussed above, there is insufficient data to provide a speci'fic cause of action to prevent-recurrence of this transient.

Additional.

power operation and testing is required to identify an optimal solution.To minimize the possibility of recurrence and to obtain maximum benefit should a similar event occur, the following course of action has been taken: 1.Guidelines have been provided to operators concerning equipment lineup and control system modes of operation to minimize the potential for unstable operation.

'2.-A'dditional data monitoring points with improved resolution times have been established for the condensate and feedwater system.3 Time delays on condensate and feedwater system pump trip signals have been reevaluated and adjusted such as to prevent very short duration transients from causing pump trips.In addition, snubbers have been installed on the condensate booster pump discharge pressure switches to dampen out short term pressure spikes.4.Specific feedwater system testing was repeated at the 46 percent power level to measure feedwater system dynamic response.This testing was successfully completed on March 27, 1987.5.The feedwater regulating valves have been stroked to ensure proper operation.

'NRC fOAM 388A)94)3)+U.S.GPO:19804.534.538/455 Caro!ina Power~':ght Company HARRIS NUCLEAR PROJECT P.O.Box 165 New Hill, NC 27562 APR 3 0 1987 File Number: SHF/10-13510C Letter Number'HO-870407 (0)U.S.Nuclear Regulatory Commission ATTN: NRC Document Control Desk Washington, DC 20555 SHEARON HARRIS NUCLEAR POWER PLANT UNIT 1 DOCKET NO 50-400 LICENSE NO.NPF-63 LICENSEE EVENT REPORT 87-013-00 Gentlemen:

In accordance with Title 10 to the Code of Federal Regulations, the enclosed Licensee Event Report is submitted.

This report fulfills the requirement for a written report within thirty (30)days of a reportable occurrence and is in accordance wats the format set forth in NUREG-1022, September, 1983.Very truly yours, R.A.Watson Vice President Harris Nuclear Project RAW:skm Enclosure cc: Dr.J.Nelson Grace (NRC-RII)Mr.B.Buckley (NRC)Mr.G.Maxwell (NRC-SHNPP)