ML18039A779

LER 99-003-00:on 990408,declared Plant HPCI Sys Inoperable Due to Loose Wire.Caused by Failure to Properly Tighten Screw at Some Time in Past.Loose Wire Was Tightened

ML18039A779
Person / Time
Site:	Browns Ferry
Issue date:	05/06/1999
From:	Moody G TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18039A778	List: ML18039A777 ML18039A779
References
LER-99-003-01, LER-99-3-1, NUDOCS 9905140178
Download: ML18039A779 (12)

Text

NRC FORM 366 (6.1998)U.s.NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)(See reverse for required number of digits/characters for each block)APPROVED BY OMB NO.31SO-0104 EKPIREs ONsoaoot Esgmated burden per response to comply.with this mandatory Information cosecbon request: 50 hrs.Reported lessons learned are incorporated Into the licensing process and fed back to Industry.Foward comments regard:ng burden estimate to the Records Management Branch (TA F33), U.S.Nudear Regulatory CommisskxL Washington, OC 205554001, and to the Paperwork ReducUon Project, (31504104), Olce of Management and Budget, Wahhngton.

'OC 20503.If an'information cogecgon does not display a currently vshd OMB.control number, the NRC msy not conduct or sponsor, and a person is rot required to respond to.the informatbn coilectioa FACIUTY NAME (Il'rowns Ferry Nuclear Plant-Unit 3 DOCKET NUMBER lsl 05000296 PACE LSI 1of 6 TITLE I41 Unit 3 High Pressure Coolant Injection IHPCI)System Inoperab(e Due To A Loose Wire EVENT DATE (5)LER NUMBER (6)'REPORT DATE (7)OTHER FACILITIES INVOLVED (8)MONTH 04 OAY 08 1999 YEAR'EOVENTIAL REVISION NVMBER,'VM BER 1999-003-00 MONTH OAY 05 06 YEAR FACIUTY NAME NA'1999 NA OOCKET NUMBER NA OOCKET NVM BER NA OPERATING.MODE (9)POWER LEVEL (10)100 20.2201 (b)20;2203(a)(1) 20.2203(a)(2)(I)20.2203(a)(2)(v)20.2203(a)(3)(l) 20.2203(a)(3)(ii)50.73(a)(2)(l) 50.73(a)(2)(ll)

S0.73(a)(2)(lli) 50.73(a)(2)(vill)50.73(a)(2)(x)73.71 T TO THE REQUIREMENTS OF 10 CFR II: (Check one or more)(11)THIS'REPORT IS SUBMITTED PURSUAN 20;2203(a)

(2)(ii)20.2203(a)

(2)(iii)20.2203(a)

(2)(iv)20.2203(a)(4) 50.36(c)(1) 50.36(c)(2)

LICENSEE CONTACT FOR THIS'LER (12)50.73(a)(2)(lv)

X 50.73(a)(2)(v)

'0.73(a)(2)(vii)

OTHER Specify in Abstract below or In NRC Form 366A NAME Gerald F.Moody, Licensing Project Manger TELEPHONE NUMBER (Indude Aras Code)256-729-7534 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)CAUSE SYSTEM'OMPONENT MANUFACTURER

.REPORTABLE TO NPROS CAUSE SYSTEM COMPONENT MANUFACTURER

'EPORTASLE TO NPROS SUPPLEMENTAL REPORT EXPECTED (14)YES (If yes, complete EXPECTED SUBMISSION DATE).X NO EXPECTED SUBMISSION DATE (15)MONTH OAY YEAR ABSTRACT (Limit to 1400 spaces, I.e., approximately 15 single-spaced typewritten lines)(16)On April 8, 1999, at approximately.2045 hours0.0237 days <br />0.568 hours <br />0.00338 weeks <br />7.781225e-4 months <br /> Central Daylight Time (CDT)during the performance of a regularly scheduled Instrumentation surveillance on the Unit 3 HPCI Steam, Line Space High Temperature switches, a loose wire was found in the power supply pathway for the HPCI logic circuit.This loose wire had the potential to prevent adequate voltage from being supplied to the initiation and isolation logic for the Unit 3 HPCI system;The loose wire was tightened.

The potential for.inadequate voltage being available for the HPCI logic circuit resulted in the decision to declare the HPCI system inoperable.

The most likely, cause of.this event was determined to be a failure to properly tighten the screw at'some time in the past.This report is submitted pursuant to 10 CFR.50.73 (a)(2)(v)as a condition that alone could have prevented the fulfillment of the safety function of a structure or system needed to mitigate the consequences of an accident.9905i40i78 990506 PDR ADGCK 05000296 S PDR NRC FORM 3669 (6-1996) 0 NRC FORM 366A (6-19981 L'ICENSEE EVENT REPORT (LER)TEXT CONTINUATION U.S.NUCLEAR REGULATORY COMMISSION FACILITY NAME 1 Browns Ferry Nuclear Plant-Unit 3 DOCKET LER NUMBER 6 YEAR SEQUENTIAL"REVISION NUMBER PAGE 3 2of6 05000296 TEXT/If more space is required.use additional copies of NRC Form 366Ai f17I 1999 003 00 PLANT CONDITION(S)

At the time of the event, Unit 1 was shutdown and defueled.Unit 2 was in Mode 1 at 81 percent reactor power, approximately 2678 megawatts thermal, coasting down for a scheduled refueling outage.Unit 3 was in mode 1 at 100 percent reactor power at approximately 3457 megawatts thermal.DESCRIPTION OF EVENT A.Event: On April 7, 1999, at approximately 0757 hours0.00876 days <br />0.21 hours <br />0.00125 weeks <br />2.880385e-4 months <br /> Central Daylight Time (CDT)a surveillance (3-SR-3.3.6.1(3D))

was started to calibrate the High Pressure Coolant Injection (HPCI),[BJ]System Steam Line Temperature switches).

On April 8, 1999, at approximately 2045.hours CDT during, the performance of this regularly scheduled Instrumentation surveillance, a loose wire was found in the'power supply pathway-for the HPCI logic circuit.This loose wire had the potential to prevent adequate voltage from being supplied to,the initiation and isolation logic for.the Unit 3 HPCI system.The potential for inadequate voltage being available'for the HPCI logic circuit resulted in.the decision to declare the HPCI system inoperable.

As required.by Technical Specifications, Browns Ferry Unit 3 entered a fourteen-day Limiting Condition for Operation (LCO)for an inoperable HPCI system.A 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />,Non-Emergency notification was made to the.NRC in accordance with 10 CFR 50.72 (b)(2)(iii).Repairs were completed and following post maintenance testing, HPCI was returned to an operable status on April 9, 1999 at 0122 hours0.00141 days <br />0.0339 hours <br />2.017196e-4 weeks <br />4.6421e-5 months <br /> CDT.This report is submitted pursuant to 10 CFR 50.73 (a)(2)(v).as a condition, that alone could have, prevented the fulfillment of the safety function of a structure or system needed to mitigate the consequences of an accident.B.Ino erable Structures Com onents or S stems that Contributed to the Event: , None., C.'Dates and A roximate Times of Ma or Occurrences:

April 7, 1999, 0757 hours0.00876 days <br />0.21 hours <br />0.00125 weeks <br />2.880385e-4 months <br /> CDT Surveillance SR 3.3.6.1(3D)

-HPCI Steam Line Temperature Switch calibration started.April 8, 1999, 2045 hours0.0237 days <br />0.568 hours <br />0.00338 weeks <br />7.781225e-4 months <br /> CDT A loose terminal was.found on a fuse feeding the HPCI logic bus.HPCI was declared inoperable and repairs were started.April 8, 1999, 2351 hours0.0272 days <br />0.653 hours <br />0.00389 weeks <br />8.945555e-4 months <br /> CDT A 4 Hour Non-Emergency notification was made to the NRC in accordance with 10 CFR 50.72 (b)(2)(iii).April 9, 1999, 0122 hours0.00141 days <br />0.0339 hours <br />2.017196e-4 weeks <br />4.6421e-5 months <br /> CDT HPCI system was returned to operable status.NRC FORM 366 I6-1998).

Ib 0 NRC FORM 366A (6-1998),LICENSEE EVENT'REPORT (LER)TEXT CONTINUATION U.S.NUCLEAR REGULATORY COMMISSION FACILITY NAME 1 Browns'Ferry, Nuclear Plant-Unit 3 DQGKET LER NUMBER 6 YEAR SEQUENTIAL REVISION NUMBER PAGE 3 3 of 6 , 05000296 TEXT (If more spece is required, use eddi tionel copies of NRC Form 366A j)17)1999 003 00.D.Other S stems or Seconda Functions Affected None.E.Method of Discove During performance of a regularly scheduled instrumentation surveillance on Unit 3 HPCI Steam Line Space High Temperature switches, a'loose wire was found in the power supply pathway for ,the HPCI logic circuit.F.0 erator Actions No operator actions contributed to this event.G.Safe S stem Res onses None.III.CAUSE OF THE EVENT A.Immediate Cause The immediate cause of this event was a loose electrical connection.

The terminal connection was loose to the touch and manipulation of the attached wire caused the associated relays to cycle.Arcing could be observed at the connection as the wire was manipulated.

Therefore, it was concluded that.the single bad connection found in the (+)side.power bus was the cause.B.Root Cause The terminal screw required approximately

/~turn to.tighten properly.The terminal strip is located in a fixed panel in the auxiliary instrument room where the absence of vibration and infrequent human handling minimizes the potential of any, failure mechanism that could loosen the terminal screw over time.Therefore, the cause of the loose screw was most likely failure to properly tighten the screw at some time in the past.There was no recent work activity in the panel, (prior to development of.the symptoms)that would have disturbed the wire.C.Contributin Factors None NRC FORM 366)6-1998)

II II\'

NRC FORM 366A (6.1998)0 U.S.NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)TEXT CONTINUATION FACILITY NAME 1 Browns Ferry Nuclear Plant-Unit 3 DOCKET LER NUMBER 6 YEAR SEQUENTIAL REVISION NUMBER PAGE 3 4 of 6 05000296 TEXT (lf more space is required, use additional copies of NRC Form'36GA/

l17)1999 003 00 IV.ANALYSIS OF THE EVENT The'following malfunctions in the HPCI system logic were observed between 0757 on April 7, 1999 and 0122 on April 9, 1999.During 3-SR-3.3.6.1(3D), two temperature switches failed to actuate their associated relays as expected.It was also noted that the Integrated Computer-System (ICS)[JA]did not indicate a.tripped condition for the associated data points.These switches were jumpered at the field location and the associated relays again.failed to actuate.It was also observed that another relay was cycling or not energized when conditions called.for it to be energized.

This relay (23-A-K16) was associated with the HPCI minimum flow valve.These relays and ICS points are all powered from.HPCI logic bus B and are the only devices that would have been called upon to energize given the existing plant conditions and ongoing activities.

Therefore, they are the only devices that would.be expected to exhibit observable symptoms during a power-supply interruption.

HPCI logic bus B is powered from 250V-DC-power.[EJ).

The (+)logic power Is supplied to the individual devices through.a wiring chain made'from lugged wires connecting a series of terminals on a terminal strip.Similarly; the (-;)logic power is supplied to the individual devices through a wiring chain made from lugged wires connecting a series of terminals on the individual devices themselves (so called daisy-chain).All of the listed devices and computer points are on the same,(+).side wiring chain but they do not have the same (-'),side chain.The (+)side connections are all located, on the.same terminal strip.During troubleshooting each wire terminal in the (+)circuit was manipulated-while observing relay 23-A-K16.Terminal 1 of fuse F1-3-058CA (located at the bottom of terminal strip CC)was the only connection that caused relay operation when manipulated.

The terminal connection was loose to the touch and manipulation of the attached.wire caused relays to cycle.Arcing could be observed at the conne'ction as the wire was moved.Therefore, it was positively concluded that the'single bad connection found in the (+)side power bus was the cause.The cause.of the loose screw was most.likely failure to properly tighten the screw some time in the past.A search of work orders and design documentation did not indicate any work that would have involved terminal 1 of fuse FU1-3-58CA.

Therefore, the cause could not be linked to a specific work activity.There was no recent work activity in the panel (prior to development of symptoms)that would have disturbed wires.The wire lugs and loose terminal were in physical contact and,would not have been able to completely

'eparate.That configuration would be expected to cause intermittent problems with the electrical characteristics of the connection degrading over time due to oxide and arc residue buildup.Several quarterly suiveillances are performed which would have identified, an existing circuit interruption.

Also,.alarm window 3-XA-55-3F-28.(HPCI GLAND SEAL CONDENSER LEVEL LOW)would'have activated in the control room alerting the operators to the problem.The recent surveillance tests were completed satisfactorily.

Therefore, the condition was not serious enough to effect operability until these events occUI'red.

NRC FORM 366 l6-1998l Ik Il t, Py NRC FORM'366A (6-1998)L'ICENSEE EVENT REPORT (LER)TEXT CONTINUATION U.S.NUCLEAR REGULATORY COMMISSION FACILITY NAME 1 Browns Ferry Nuclear Plant-Unit 3 DOCKET 05000296 LER NUMBER 6 YEAR'EQUENTIAL NUMBER 1999" 003 00 PAGE 3 5 of 6 TEXT (I/more spece is required, use eddirionel copies of NRC Form 366A/I17)V.ASSESSMENT OF'THE SAFETY CONSEQUENCES The HPCI system is provided to assure that the reactor is adequately cooled to limit fuel cladding temperature in the event of a small pipe break in the nuclear system and loss of coolant which does not result in rapid depressurization of the reactor vessel.The HPCI system permits the nuclear plant to be shut down, while maintaining sufficient reactor vessel water inventory until the reactor vessel is depressurized.

The HPCI system continues to operate until the reactor vessel pressure is below the pressure at which Low Pressure Coolant Injection (LPCI)[BO]operation or Core Spray (CS)[SM]operation maintains core cooling.In the event HPCI is not available or not sufficient to maintain reactor water level, the Automatic Depressurization.System (ADS)[SB]functions to reduce reactor pressure so that flow from the LPCI and CS systems enter the reactor vessel in time to cool the core and limit fuel cladding temperature.

BFN Technical Specifications allow continued reactor operation for up to fourteen days if HPCI is inoperable, provided ADS, CS, LPCI, and Reactor Core Isolation Cooling,(RCIC)

[BN]systems are-.operable.RCIC provides an alternate supply of high pressure makeup while ADS would'depressurize the reactor to allow CS and LPCI.to provide adequate low pressure ECCS makeup to the reactor.The availability of these redundant and diversified systems provides adequate assurance of core cooling while the HPCI system is inoperable.

For this event,'HPCI was,inoperable approximately 4 l*hours of the 14 days allowed by, the LCO..During the period that the HPCI system was inoperable, these required systems were operable and would have performed their design function if called upon.Accordingly, there was no reduction in the degree of protection provided to public health and safety.Furthermore, the safety of the plant, its personnel, and the public was not compromised.

VI.CORRECTIVE ACTIONS A.Immediate Corrective Actions Troubleshooting:was performed to identify the bad connection and confirm that it was the cause of the problem.The loose terminal was immediately tightened under appropriate plant work instructions and testing was completed on the circuit'.This corrected the physical condition.

B, Corrective Actions to Prevent Recurrence None.VII.ADDITIONAL INFORMATION A.Failed Com onents None.NRC FORM 366 (6-1998)

Il Ol NRC FORM 366A I6-1998I'ICENSEE EVENT REPORT (LER)TEXT CONTINUATION U.S.NUCLEAR REGULATORY COMMISSION FACILITY NAME 1 Browns Ferry Nuclear Plant-Unit 3 DOCKET LER NUMBER 6 YEAR SEQUENTIAL

~REVISION NUMBER PAGE 3 6of6 05000296 1999 003 TEXT llf more space is required, use additional copies of NRC Form 366AJ I17I 00 B.Previous LERS on Similar Events There have been no previous LERs involving the inoperability of equipment due to a loose wire.Villi.COMMITMENTS None.NRC FORM 366'I6-1998)

Energy Industry:Identification System (EIIS)system and component codes are identified in the text withbrackets e, XX.

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