ML18033A271

LER 88-001-00:on 880605,breakers Connecting Diesel Generators 3A,3C & 3D to 4 Kv Shutdown Boards Opened Just After Closing & Would Not Reclose.Caused by Open Signal Sealed in Logic.Also Reportable Per Part 21.W/880705 Ltr

ML18033A271
Person / Time
Site:	Browns Ferry
Issue date:	07/01/1988
From:	Steve Jones, Jacqwan Walker TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
REF-PT21-88-089-000 LER-88-001-04, LER-88-1-4, PT21-88-089-000, PT21-88-89, NUDOCS 8807140215
Download: ML18033A271 (12)

Text

DIJR1BUTI ON SYSTEM q 'AC CELE RATED DE M ON STJQTI ON 3

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:8807140215 DOC.DATE: 88/07/01 NOTARIZED: NO DOCKET FACIL:50-296 Browns Ferry Nuclear Power Station, Unit 3, Tennessee 05000296 AUTH. NAME AUTHOR AFFIL'IATION-JONES,S.B. Tennessee Valley Authority WALKER;J.G. Tennessee Valley Authority RECIP.NAME 'ECIPIENT AFFILIATION

SUBJECT:

LER 88-001-00:on 880605,design deficiency in diesel I generator breaker logic prevents connection to shutdown.

W/8 ltr. D DISTRIBUTION CODE: IE22D COPIES RECEIVED:LTR X ENCL 3 TITLE: 50.73 Licensee Event Report (LER), Inci ent Rpt, etc.

SIZE:

NOTES:S.Black 3 cy.l cy. ea to: Ebneter,Axelrad,S.Richardson, 05000296 B.D.Liaw,K.Barr, OI. h RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL SIMMS,M 1 1 PD 1 1 MORAN,D 1 1 GEARS,G 1 1 INTERNAL: ACRS MICHELSON 1 1 ACRS MOELLER 2 2 AEOB/DOA- .1 1 AEOD/DSP/NAS 1 1 AEOD/DS P/ROAB 2 2 AEOD/DS P/TPAB 1 1 ARM/DCTS/DAB 1 1 DEDRO 1 1 NRR/DEST/ADS 7E 1 0 NRR/DEST/CEB 8H 1 1 NRR/DEST/ESB 8D 1 1 NRR/DEST/ICSB 7 1 1 NRR/DEST/MEB 9H 1 1 NRR/DEST/MTB 9H 1 1 NRR/DEST/PSB 8D 1 1 NRR/DEST/RSB 8E 1 1 NRR/DEST/SGB 8D 1 1 NRR/DLPQ/HFB 10 1 1 NRR/DLPQ/QAB 10 1 1 NRR/DOEA/EAB 11 1 1 NRR/DREP/RAB 10 1 1 NRR/DREP/RPB 10 2 2 NRR/ SIB 9A 1 1 NUDOCS-ABSTRACT 1 1 PTZ E 02 1 1 RES TELFORD,J 1 1 E E/EIB 1 1 RES/DRPS DEPY 1 1 RGN2 FI LE 01 1 1 EXTERNAL: .EG&G WILLIAMS,S 4 4 FORD BLDG. HOY,A 1 1 H ST LOBBY WARD 1. 1 LPDR 1 1 NRC PDR 1 1 NSIC HARRIS,J 1 1 NSIC MAYS,G 1 1 NOTES 9 9 h

TOTAL NUMBER OF COPIES REQUIRED: LTTR 55 ENCL 54

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I(BC Form 355 U.S. NUCLEAR REOULATORY COMMISSION (94)3) APPROVED OMB NO 3150M)04 LICENSEE EVENT REPORT ILER) f XPIAES BISIIBS DOCKET NUMBER 12) PA 513 FACILITY NAME (II Browns Ferr Unit 3 0 5 0 0 0 2 9 1 OF 0 TitLE (4)

Desi)Pn Deficiency in Diesel Generator (DG) Breaker Logic Prevents Three DGs from Connectin to Shutdown Boards Durin Loss of Coolant Loss of Power Test OTHER FACILITIES INVOLVED (SI EVENT DATE (Sl LER NVMBEA (5) REPORT DATE (7) 5 4 QUC NT I AL ' tICVICiCN DAY YfAR FACILITYNAMES DOCKET NUMBER(SI MONTH OAY YEAR YEAR NUMSER NUMoctv MONTH Browns Ferr Unit 1 0 5 0 0 0 2 5 9 0 6 5 8 8 0 0 1 007 01 8 8 Browns Ferr Unit 2 0 5 0 0 0 2 9 OPERATINO THIS AEPORl'S SUBMITTED PURSUANT T 0 THE AEOUIR MENTS OF 10 f C FR (): (Check one or more ol the Iolloirinpl (11 MODE (5) 20.405(c) 50. 73( ~ ) Ll I (iv) 73.7((a)

N 20. 402(5) 20.405( ~ I I I I (II 50M(c) Ill 50.7 3( ~ I(2)HI 73.71(cl POWER LEYEL S0.73( ~ l(21(re I OTHER Isoeciry in Aottiect 0 0 20.405(el(1) (II) 50.35(cl(2)

Oeioir encl in Tert, iYIIC Form 20.405 le I( I ) (III) 50.73( ~ I(2)(II 50.73( ~ l(2)(rllll(A) 366AI 20.405 (4) (I ) (Ir) 50.73(e)(2)(el 50.73(e H2)(viEi) I BI 10 CFR Part 21 20.405( ~ I(1)(v) 50.73( ~ ) (2)(in) 50.73(e)(2)(el LICENSEE CON1'ACT FOR THIS LER (12)

NAME TELEPHONE )4UMBEA Ste hen B. Jones En ineer Plant 0 erations Review Staff COMPLfTE ONE LINE FOR EACH COMPONENT FAILURE OESCRIBEO IN THIS AEPOAT I(3) 2072-788 ARFA CODE MANUFAC. AEPORTABLE MANVFAC EPOATABLE CAUSE SYSTEM COMPONENT CAUSE SYSTEM COMPONENT TVREA NPADS

'O TVRER TO NPROS SUPPLEMENTAL REPORT EXPECTED (14) MONTH OAY YEAR EXPECTED SUBMISSION DATE (151 YES III yM, Ccmutete EXPECTED SU8MISSIOrY OATEI NO ABSTRAC'7 ILimit to (400 toecee i eepurommetery it(teen unpre.toece tyoevrrrtten linml IISI On June 5, 1988, during the performance of a loss of power/loss of coolant accident test, breakers connecting diesel generators 3A, 3C, and 3D to their respective 4KV shutdown boards opened just after closing, and would not automatically reclose because an open signal sealed in the logic. An operator momentarily deenergized the power to the breaker logic which reset the logic. Mhen the logic was repowered the breakers closed as required.

The sequence of events, the time response characteristics of each DG and cectain logic components, the closure circuit logic,and the trip circuit logic all contributed to the condition. The bceaker circuit is being evaluated and will be modified as required to eliminate the possibility of the breakec not closing on a valid close signal.

This event occurred with all three units shut down and defueled.

8807 140215 ~

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NRC Form 355 (9 831

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NRC,Form SSSA U.S. NUCLEAR REOULATORY COMMISSION LICENSEE EVENT REPORT {LER) TEXT CONTINUATION APPROV EO OMS NO. 8150WI04 EXPIRES: SISI/85 PACILITY NAM8 III OOCKET NVMSER LTI LER NUMSER (SI PACE ISI 88'1 y))i sdQvdNTIAI'ts YEAR RdvrsroN NVM SR N 9 NVMSSR Browns Ferry Unit 3 0 5 0 0 0 2 9 6 0 002 OF 04

'TEXT IIImore epode r'p t pdrrkerL vpe ardooreel HRC Form 808ALU I ITI DESCRIPTION This event occurred with all three units defueled. The event affected the unit 3 diesel generators (DGs) (EIIS identifier EK), but the condition has been .determined applicable to all three units.

On June 5, 1988, a loss of power'/loss of coolant accident (LOP/LOCA) test was performed. One of the eight DGs was disabled prior to the test. to simulate a DG failure. At 1320 hours0.0153 days <br />0.367 hours <br />0.00218 weeks <br />5.0226e-4 months <br />, the offsite power supply to the plant was disconnected. Approximately 6 seconds later a simulated accident signal was injected into the pl'ant logic. The seven operable DGs started, came to speed, and tied onto their respective 4kV shutdown board (EIIS identifier EB) between 6.5 seconds and 8 seconds. The breakers (BRK) connecting DGs 3A, 3C, and 3D to their associated shutdown boards opened just after the breakers had closed and remained open. An operator was dispatched to the 4kV shutdown board rooms. The operator transferred one of the shutdown board's control power from its normal supply to the alternate supply. This momentarily deenergized the breaker logic. When power was restored, the breaker closed.

This evolution was then repeated on the other shutdown boards where the DG breakers had tripped. All three DG breakers closed and remained tied to the 4kV shutdown boards.

CAUSE OF EVENT An investigation into the cause of the failure has determined the DG circuit breaker logic will allow the breaker to trip and lock out under a certain of events. The sequence of events that led to the discovery of the 'equence problem is given below along with a further explanation of the mechanics of the event.

At time zero a loss of offsite power to the plant was initiated which deenergized the 4kV shutdown boards. This initiated undervoltage detection relays (27) which started the DGs 1.5 seconds, after the LOP. At 5 seconds undervoltage relay (General Electric [GE] model number 12IAV54F1A) timed out as designed and closed a contact in the DG breaker logic close circuitr'y. At approximately 6.5 seconds into the LOP/LOCA test, three of the DGs reached rated speed which closed a contact in the breaker closure circuitry, thus completing the close logic. The DG breakers (GE model Number AMH-4.76-250-1D) then closed as expected when the close coil (52X) was energi;zed. Note the other DGs did not come to speed as quickly as the three that experienced the problem. Upon breaker closure, auxiliary contacts will energize the spring charging motor (52M) and the antipump coil (5?Y). The charging time takes approximately 2 seconds. Energizing the antipump coil (52Y) opens contacts in the breaker closing coil (52X) circuitry, preventing the breaker from reclosing during the charging time period and also closes a contact that connects the antipump coil (52Y) to the breaker closure NRC FORM SSSA I98SI

4i 41 HRC Form 3SSA V.S. NUCLEAR REOULATORY COMMISSION ISPQI LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVED OMS NO. 3150WIOO ExplRfs.'ISI/Ss FACILITY NAME III DOCKET NVMSER ISI LER NUMSER ISI PACE (SI SSQUSNTrAL;@ OVrorDN NvM erl rrUM err Browns TEXT Ferry Unit lllmoro ooooe le oerrrirerS eoe 3

aAfhbnel lYRC Anger 3SSASI I I7>

0 5 0 0 0 2 9 6 8'800100 03 oFO 4 circuitry. This circuit configuration is a standard arrangement utilized to protect large breakers from rapid cycling. At about the same time that the three DG breakers closed, an accident signal was simulated (approximately 6 seconds after the LOP as part of the test sequence). This signal generates a common accident signal (CAS relays) which closes a contact that generates a DG breaker trip. Since the DG breaker had already closed, the DG breakers tripped as designed. This deenergized the shutdown board which would retrigger the 5 second undervoltage relays. This is an undervoltage relay with a inductive motor which takes approximately the same time to go to full reset as to pick up (5 seconds). Therefore, when the undervoltage was sensed on the shutdown board, the undervoltage relay was only partially reset. The relay reversed direction and reclosed contacts a short time later, thus completing the undervoltage trip logic, and which simultaneously completed the diesel breaker close logic. Since the breaker spring had not completely recharged within this time, this breaker. close signal sealed in the antipump 52Y relays through its contact in the close circuitry. With the antipump coil sealed in, the breaker closure coil is blocked, thus preventing the breaker from actually closing. The basic problem centers around the time sequencing of the trip and relay logic which applied a breaker close signal in the same time frame of the spring charging motor rewind.

This circuit is the same in all eight DGs. The sequence of events, the t'ime response characteristics of each DG and the logic components discussed above, the closure circuit logic, and the trip circuit logic all contribute to the condition. The breaker logic circuit original design was in this configuration. Changes to the circuit did not contribute to the problem.

The original DG breaker circuit design was supplied by GE.

CORRECTIVE ACTION The circuit is being evaluated 'to determine what can be done to prevent the breaker from locking out. Necessar'y modifications to the circuit will be performed.

ANALYSIS CONDITION The condition can prevent a DG from connecting to a 4kV shutdown board if a LOP/LOCA occurs in the proper sequence. This sequence must occur within a one second window. If this sequence does not occur, the DG breaker will work as designed. If the improbable sequence of events had occurred, it could have had severe consequences if more than one DG on unit l/2 or more than one The plant design DG on unit 3 had failed to tie to their shutdown boards.

allows for the single failure of only one DG on an accident unit. Reactor operators would have responded as they did during the test and manually closed the breaker. This would permit the DGs to supply power to their respective shutdown boards.

NIIC POIIM 3SSA (903)

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NRC Form ESSA 0 V.S. NUCLEAR REOVLATORY COMMISSION I9eSI

'Irr LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVEO OMS NO. SISOW104 EXPIRES: 9/SII85 FACILITY NAME III 0OCK ET NV MS E R IE) LER NUMSER (SI PACE ISI YEAR,intro 5EQVENTIAL NVMaaa 'I"W'ayISION I NMMaaa Browns Ferry Unit TEXT IIF mora aaooo ia aorriirNE uao ~ 3 HAC Porrrr SRIATU IITI r

o 5'0 0 o 2 96 8 0 1 0 0 0 4OF 04 A fuel handling accident is the only design basis event that can occur in the present plant configuration that could require DGs. Three DGs, A, B, and 3D, would be required to power standby gas treatment which is required to maintain secondary containment. The loss of secondary containment has been analyzed for the current fuel handling activities and would not result in exceeding of regulatory release limits.

This condition was determined to be part 21 reportable on June 15, 19&8, after the investigation discovered the condition was a deficiency in the original circuit design.

PREVIOUS SIMILAR EVENTS None COMMITMENTS Evaluate circuit and modify to prevent breaker trip seal in during LOP/LOCA sequence of events.

NRC FORM 555A ISSS I

J '

lNS FERRY NUCLEAR PLANT UNIT 3 DOCKET NO. 50-296 FACILITY OPFRATING LICENSE DPR-68 REPORTABLE OCCURRENCE REPORT BFRO-50-296/88001 The enclosed report provides details concerning the design deficiency in diesel generator (DG) breaker logic which prevented three DGs from connecting to shutdown boards during loss of coolant/loss of power test. This report is submitted in accordance with 10 CFR 50.73 (a)(2)(v), 10 CFR 50.73 (a)(2)(vii),

and 10 CFR Part 21.

Very truly yours, G. (<alker P nt Manager owns Ferry Nuclear Plant Fnclosures cc (Enclosures):

Regional Administration XNPO Records Center U.S. Nuclear Regulatory Commission Suite 1500 Office of Inspection and Enforcement 1100 Circle 75 Parkway Region II Atlanta, Georgia 30339 101 Marietta Street, Suite 2900 Atlanta, Georgia 30303 NRC Resident Inspector, Browns Ferry Nuclear Plant