ML17348A239

LER 90-003-02:on 900409,reactor Protection Sys Actuation Occurred Due to Failure of Reactor Coolant Pump Underfrequency Relay Power Supply Capacitor.Caused by Open Supply Breakers.Relay replaced.W/900508 Ltr

ML17348A239
Person / Time
Site:	Turkey Point
Issue date:	05/08/1990
From:	Harris K, Dawn Powell FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-90-143, LER-90-003-02, LER-90-3-2, NUDOCS 9005160071
Download: ML17348A239 (10)

Text

ACCELERATED DHUBUTION DEMONSTIZION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9005160071 DOC.DATE: 90/05/08 NOTARIZED: NO DOCKET FACIL:50-251 Turkey Point Plant, Unit 4, Florida Power and Light C 05000251 AUTH. NAME AUTHOR AFFILIATION POWELL, D. R. Florida Power & Light Co.

HARRIS,K.N. Florida Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 90-003-02:on 900409,unit trip due to under frequency relay failure.

W/9 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ! ENCL 1 SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 1 PD2-2 PD 1 1 EDISON,G 1 1 INTERNAL: ACNW 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DS P 2 2 DEDRO 1 1 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB9H3 1 1 NRR/DLPQ/LHFB11 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB11 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB SD 1 1 NRR/DST/SICB 7E 1 1 NRR DST SPLBSD1 1 1 NRR/DST/SRXB SE 1 1 a 1 1 RES/DSIR/EIB 1 1 RGN2 FILE 01 1 1 EXTERNAL EG&G STUART I V A 4 4 L ST LOBBY WARD 1 1 LPDR 1 1 NRC PDR 1 1 NSIC MAYS,G 1 1 NSIC MURPHY,G.A 1 1 NUDOCS FULL TXT 1 1 NOTE TO ALL "RIDS" RECIPIEhHS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 34 ENCL 34

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~AY Os tSBO L-90-143 10 CFR 50.73 U.,S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: Turkey Point Unit 4 Docket No 50-251~

Reportable Event: 90-003 Date of Event: April 9, 1990 Unit Tri Due to Underfre uenc Rela Failure The attached Licensee Event Report is being provided pursuant to the requirements, of 10 CFR 50.73 for notification of the subject event.

Very r ly yqurs, N.

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Harris Vic resident Tur y Point Plant Nuclear KNH/DRP/JEK/rat cc: Stewart D. Ebneter, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, Turkey Point Plant

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EX<<ECTED SUISSISSION DATE lll>

Ytl Ilt yrr. rt<<i<<toto tX<<tCTto SIISAIISSIOht OATtl AIITAAcTIL<<rK to Iooo At<<ca. t A. sooiorrrtsaty he>orts o<<Nsoosco tyooovt tao hors) IIII On April 9, 1990 at 1814 EDT, with Unit 4 in Mode 1 (Power Operation) at 100 percent power, a Reactor Protection System actuation occurred due to a failure of a Reactor Coolant Pump (RCP) underfrequency relay power supply capacitor.

The reactor trip occurred because one of three reactor coolant pump power supply breakers opened with the reactor at greater than 45 percent power. The faulty underfrequency 'he re'lay was replaced and Unit 4 was returned to serv'ce. RCP power supply underfrequency relays on 'both Unit 3 and Unit 4 have been replaced with new models. A review of the failure modes of the replacement relays will be performed and planned maintenance will be developed as appropriate.

On April 9, 1990, at 1914 EDT, a four hour report of the event was made to the NRC in accordance with 10 CFR 50.72.

NAC Tore 1942>

NRC Form 3ddA U.S. NUCLEAR REGULATORY COMMISSION

<983 I LICENSEE NT REPORT (LER) TEXT CONTINUA N APPROVEO OMB NO. 3150&)04 EXPIAES. Bl31 85 FACILITY NAME 11) OOCKET NUMBEA 12I LER NUMBER ld) PAGE 13)

YEAR SEOVSNTIAL h~Mi; REVISION NVMSSR NVMSSR TURKEY POINT UNIT 4 o s o o o 0 0 3 0002 OF 0 4 TEXT N more speciis reh)virid, use edChsiorhei HAC Form 38M's) l)T)

I. EVENT DESCRIPTION On April 9, 1990 at 1814 Eastern Daylight Time (EDT), with Unit 4 in Mode 1 (Power Operations) at 100 percent power, a Reactor Protection System (EIIS:JC) actuation occurred causing a reactor trip. The trip was due to a failure of Reactor Coolant Pump underfrequency relay 4B2 (EIIS:AB Component:81). The underfrequency relay monitors the 4B 4160 volt bus (EIIS:EB Component:BU) for frequency and trips the 4B and 4C Reactor Coolant Pumps (EIIS:AB Component:P) when an underfrequency condition of 56.1 Hertz or less is sensed by one of two relays. Review of recorded frequency information indicated that no underfrequency condition existed at the time of the trip. The reactor trip occurred when of one of three reactor coolant pump breakers (EIIS:AB Component:BRK) opened with the reactor at greater than 45 percent power.

After the trip, pressurizer level declined to a level resulting in letdown isolation. Volume Control Tank (VCT) (EIIS:CB Component:TK) level declined to an indicated 5 percent level. As a result, the following occurred:

Charging pump (EIIS:CB Component:P) "B" was started but tripped soon after starting. Charging pump suction did not switch automatically from the VCT to the Refueling Water Storage Tank (RWST) (EIIS:BP Component:TK) . The transfer of charging pump suction from the VCT to the RWST was made manually. After a successful second attempt at starting the "B" charging pump, all three charging pumps were used to restore pressurizer level. Letdown was then restored. At 1845 EDT, with the unit stabilized in Mode 3 (Hot Shutdown),

Control room personnel transferred from use of the Emergency Operating Procedures to General Operating Procedure 4-GOP-103, "Power Operation to Hot Standby."

At 1914 EDT, a four hour report of the event was made to the NRC in accordance with 10 CFR 50.72.

II. EVENT CAUSE The cause of the trip was the internal failure of an underfrequency relay. A capacitor (EIIS:AB Component:CAP) ih the relay's power supply failed causing the relay to change to the tripped position. This relay trip caused the trip of the supply breakers to the Protection 4B and 4C Reactor Coolant Pumps which resulted in a Reactor System trip of the reactor.

NRC FORM SddA 19 83)

NAC form 366A U.S. NUCLEAR REGULATORY COMMISSION I9431 LICENSEE ENT REPORT (LER) TEXT CONTINUA I ON APPAOVEO OMB NO 3150mTICS EXPIRES; Bl31 85 FACILITY NAME 11) COCKET NUMBER 13) LER NUMBER l61 PAGE 131 SEGVENTIAL REVISION NUMBER NVMBEA TURKEY POINT UNIT 4 o s o o o 2 0 0 3 0 0 0 3 QF 0 4 TEXT IIImoro spsseis rerrrrired, use eddin'encl HRC Form 3NA'sl lltl III. EVENT SAFETY ANALYSIS Reactor Trip The failed underfrequency relay was part of a one out of two logic. If any of four underfrequency relays fail in a manner similar to that which occurred on April 9, the result is a reactor trip. A reactor trip from 100 percent power is a previously analyzed event.

Since the reactor trip response occurred as designed, there was no impact on the'ealth or safety of plant personnel or the general public.

2. Reduced Charging Flow.

Loss of charging flow is a previously analyzed event that is covered by Emergency Operating Procedures. In accordance with these procedures, the suction of the charging pumps was transferred from the VCT to the RWST. Charging was established and pressurizer program level was restored. Therefore there was no impact on the health or safety of plant personnel or the general public.

This Licensee Event Report is submitted in accordance with 10 CFR 50.73 (a) (2) (iv) .

IV. CORRECTIVE ACTIONS Reactor Trip:

The failed General Electric model 12SFF18C1A undervoltage relay has been replaced with a newer model 12SFF31D1A. The installed model is no longer available. The new model is a direct replacement which can be installed into the original case. The 12SFF18C1A and 12SFF23C1A reactor coolant pump underfrequency relays have been replaced on both Unit 3 and 4 with new 12SFF31D1A models. Due to apparent end-of-life internal component failure an appropriate maintenance program will be developed by September 1, 1990 to reduce the probability of relay or capacitor failure.

NAC FORM 366A (9 831

NRC Form SddA U.S. NUCI.EAR REGULATORY COMMISSION (S 4131 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPAOVEO OMB NO. 3(50M(04 EXPIRES. 6/31'85 FACILITY NAME (11 DOCKET NUMBER (21 LER NUMBER (6) I'AGE (31 YEAR ggv SEGVSNTIAL NVMBSA ' S+>?

REVISION NVMSSA TURKEY POINT UNZT 4 osooo251 9 0 0 0 3 0 0 4 OF 0 4 TEXT N'more spaceis required. use eddieorIe/NRC Farm SSSA'si (171

2. Reduced Charging Flow The effected VCT level transmitter (LT) was repaired and LT 112 and 115 were recalibrated to provide for the automatic transfer of charging pump suction from the VCT to the RWST based upon low VCT level. Calibration of the Unit 3 VCT level transmitters was accomplished during the 1990 spring refueling outage. The root cause of this failure is under investigation. The evaluation will be complete and corrective action will be determined by July 15, 1990.

V. ADDZTZONAL ZNFORMATZON Previous Events Similar trips due to the malfunction of underfrequency relays have occurred at Turkey Point in the past.

Three trips occurred in late 1978; two on Unit 3 and one on Unit 4. In all three cases no relay failure mode was found. At that time the three relays were replaced with newer models. Until the failure of the capacitor on April 9 the new models have exhibited no malfunction tendencies.

2. Component Failures Underfrequency relay Manufactured by General Electric Model Number 12SFF18C1A NRC FORM Sdd*

(9 831