ML18038B206

LER 95-002-00:on 950209,reactor Scram Resulting from Turbine Trip Due to Sensed Generator Load Unbalance Condition Caused Actuation of ESF Sys.Caused by Leaking Cooling Water Line. Leaking Cooling Water Line replaced.W/950310 Ltr

ML18038B206
Person / Time
Site:	Browns Ferry
Issue date:	03/10/1995
From:	Machon R, Jay Wallace TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-95-002, LER-95-2, NUDOCS 9503200375
Download: ML18038B206 (20)

Text

F'R.I C) A.IMY'ACCELERATED'RIDS PROCESSIYv)

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESS'ION NBR:9503200375 DOC.DATE: 95/03/10 NOTARIZED: NO DOCKET FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH. NAME AUTHOR AFFILIATION WALLACE,J.E. Tennessee Valley Authority MACHON,R.D. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 95-002-00:on 950209,reactor scram resulting from turbine trip due to sensed generator load unbalance condition caused actuation of ESF sys.Caused by leaking cooling water line.

Leaking cooling water line replaced.W/950310 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

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

NOTES:

RECIPIENT COPIES RECIPIENT COPIES I D CODE/NAME PD2-4-PD LTTR ENCL 1 1 ID CODE/NAME WILLIAMS,J.

LTTR ENCL 1 1 INTERNAL: ACRS 1 1 AEOD/S PD/RAB~ 2 2 AEOD/SPD/RRAB 1 1 CENTE~02 1 1 NRR/DE/ECGB 1 1 N DE/EELB 1 1 NRR/DE/EMEB 1 1 NRR/D IS P/PI PB 1 1 NRR/DOPS/OECB 1 1 NRR/DRCH/HHFB 1 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 1 NRR/DRSS/PRPB 2 2 NRR/DSSA/SPLB 1 1 NRR/DSSA/SRXB 1 1' RES/DSIR/EIB 1 1 RGN2 FILE 01 1 EXTERNAL: L ST LOBBY WARD 1 1 LITCO BRYCE,J H 2 2 NOAC MURPHY,G.A 1 1 NOAC POORE,W. 1 1

,NRC PDR 1 1 NUDOCS FULL TXT 1 1 NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE PIELP US TO REDUCE iVASTE! CONTACTTHE DOCUifENTCONTROL DESK, ROOilI PI-37 I EXT 504'2083 ) TO ELIXIINATE YOUR NAiIE PRO~I DISTRIBUTION LISTS I:OR DOCl CLIENTS YOU DON "I'EED FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 28 ENCL 28

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R. D. tRickj Machon Vce P.esca-.. B. cvics =eg v cea >a",l March 10, 1995 U.S. Nuclear Regulatory Commission 10 CFR 50.73 ATTN: Document Control Desk Washington, D.C. 20555

Dear Sir:

BROWNS FERRY NUCLEAR PLANT (BFN) UNZTS 1~ 2~ AND 3 - DOCKET NOS. 50-259~ 50-260~ AND 296 FACZLZTY OPERATZNG LZCENSE DPR-33~ 52~ AND 68 LZCENSEE EVENT REPORT 50-260/95002 The enclosed report provides details concerning a reactor scram on February 9, 1995, that resulted from a turbine trip.

The turbine trip occurred as part of a sensed generator load unbalance condition. The reactor scram subsequently resulted in actuating the engineered safety feature system.

This report is submitted in accordance with 10 CFR 50.73 (a)(2)('v) as a condition that resulted in the automatic actuation of any engineered safety feature.

Sincerel

~ p, Q)QaL ~

R. D. Machon Site Vice President Enclosure cc: See page 2 9503200375 950310 PDR ADOCK 05000260 S

PDR

41

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U;S. Nuclear Regulatory Commission Page 2 March 10, 1995 Enclosure cc (Enclosure):

INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, G'eorgia 30339 Paul Krippner American Nuclear Insurers Town Center, Suite 300S 29 South Main Street West Hartford, Connecticut 06107 NRC Resident Inspector Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabama 35611 Regional Administrator U.S. Nuclear Regulatory Commission Region 101 II Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. J. F. Williams, Project Manager U'.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 E. V. Imbro, NRR/RSIB U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockvi.'lie, Maryland 20852 E. J. Leeds, NRR/DRPW U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike

.Rockville, Maryland 20852

NRC FORK.366 '.S. IRJCLEAR REGULATQIY CQNIISSIQI APPROVED BY QRI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPOHSE TO COHPLY lllTH THIS INFORHATIOH COLLECTIOH REOJEST: 50.0 HRS ~

LXCENSEE EVENT REPORT (LER) FORNARD COHHEHTS REGARDIKG BURDEN ESTlllATE TO THE IHFORHATIOH AND RECORDS HANAGEHENT BRANCH (HHBB 7714), U.ST KUCLEAR REGULATORY COHHISSIOH, (See reverse for required nunber of digits/characters for each block) MASNINGTOH, DC 20555-0001 AND TO THE PAPERNORK REDUCTION PROJECT (3110-0104), OFFICE OF HAKAGEHENT AND BNJGET llASHINGTOK DC 20503.

FACILITY NNK (1) DOCKET IRMGI (2) PAGE (3)

Browns Ferr Nuclear Plant BFN Unit 2 05000260 1OF7 TITLE (4) Reactor scram resulting from a turbine trip due to a sensed generator,'load unbalance condition caused the actuation of the ESF system.

'EVENT DATE 5 LER IRMKR 6 REPQIT DATE 7 OTHER FACILITIES INVOLVED 8 FACILITY NAHE NA DOCKET NlÃSER SEGUENTIAL HONTH DAY TEAR YEAR NUHBER'EVISION NUHBER HOHTH DAY TEAR FACILITY KAHE NA DOCKET KUHBER 02 09 95 95 002 00 03 10 OPERATING THIS REPQIT IS SH3HITTED PIKISUANT TO THE REEÃJIRGKHTS OF 10 CFR: Check one or more 11 IKIE (9) N 20.402(b) 20.405(c) 50.73(a)(2)(iv) 73.71(b) 20.405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c)

RXKR 100 50.36(c)(2) 50.73(a)(2)(vii)

LEVEL (10) 20.405(a)(1)(ii) OTHER 20.405(a)(1)(iii) 50.73(a)(2)(i)(B) 50.73(a)(2)(viii)(A) (Specify in 20.405(a)(1)(iv) 50.73(a)(2)(ii) 50.73(a)(2)(viii)(B) Abstract below and in Text, 20.C05(a)(1)(v) 50.73(a)(2)(iii) 50.73(a)(2)(x) NRC Form 366A I.ICENSEE CQITACT FOR THIS LER 12 NAHE TELEPHONE KIKIBER (Include Area Code)

James E. Wallace, Compliance Licensing Engineer (205)729-7874 CQC>LETE OHE LINE FOR EACH'COPOIENT FAILURE DESCRIBED IN THIS REPQIT 13 REPORTABLE REPORTABLE CAUSE SYSTEH COHPOKENT HANUFACTURER CAUSE STSTEH COHPOHENT HANUFACTURER TO HPRDS TO NPRDS RPPLHKNTAL REPORT EXPECTED 1C HOKTH OAY YEAR EXPECTED TES SIKNIISS I ON (If yes, complete EXPECTED SUBHISSIOH DATE). DATE .(15)

ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten Lines) (16)

On February 9, 1995, at '0028 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br />, the Unit 2 reactor scrammed due to a turbine trip.

This trip was a result of a sensed generator load unbalance condition. The scram then

resulted in the automatic actuation of the engineered safety feature (ESF) system. This event is, therefore, reportable in accordance with 10 CFR 50.73 (a)(2)(iv) as a condition.

responsible for an automatic actuation of the ESF system. The root cause of the event was a degraded subcomponent. Specifically, a leaking cooling water line manifold dripped water on the rectifier circuitry potentially creating a path to ground. Additionally, two generator field rectifier banks had a low-resistance to ground condition. Corrective actions to preclude recurrence are: (1) the leaking cooling water line was replaced,,and (2) a determination will be performed, for additional corrective actions based on a failure analysis of the leaking cooling water manifold and analytical tests of the rectifier cooling water tubes.

KRC FORH 366 (5-92)

4l HRC FORN 366A U.S. IN)CLEAR REGULATQIY CQHIISSIQI APPROVED BY QHI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTINATED BURDEN PER RESPONSE TO CONPLY HITH THIS INFORNATION COLLEC'IIOH REQUEST: 50.0 HRS. FORHARD CQBIENTS REGARDIHG BURDEN EST INATE TO THE INFORNAT ION AND RECORDS NANAGENENT BRANCH (NHBB 7714), U.S. NUCLEAR REGULATORY CQBIISSIOHg LICENSEE EVENT REPORT IIASHIHGTOH, DC 20555-0001, ANO TO THE PAPERIJORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104), OFFICE OF NANAGENEHT AND M)GET ~

WASHINGTON OC 20503 FACILITY IWK <<1) DOCKET IRRRER (2) LER INHALER (6) PAGE (3)

YEAR SEQUEHTIAL REVISION NQIBER NWER Browns Ferry Unit 2 05000260 95 002 00 2 of 7 TEXT lf sere s ce Is r fred use edditfonaI c Ies of MRC Form 366A (1/)

PLILNT CONDITIONS At the time this event was discovered, Unit 2 had been operating at 100 percent power for 66 days. Units 1 and 3 were shutdown and defueled.

II'ESCRIPTION OF EVENT A. Event At 0028 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br /> Central Standard Time (CST) on February 9, 1995, Unit 2 experienced a reactor scram while the unit was at full power. The Unit 2 main generator field ground relay '[TL, RLY) actuated and provided a Unit 2 main generator exciter ground alarm in the control room due to a grounding condition. The generator output breaker [TL, BKR] (PCB224) opened after a generator load unbalance was sensed. Subsequently, a generator load reject signal caused the turbine control valves (TCV) [FCV) to fast close because the turbine first stage pressure was greater than 154 psig. The TCV fast closure resulted in a reactor scram signal.

This reactor scram actuated the primary containment isolation system, specifically, group 2- shutdown cooling mode of the residual heat removal system [BO); group 3- reactor water cleanup system [CE); group 6- primary containment purge and vent

[JM), Unit 2. reactor zone ventilation [VB), refueling zone ventilation [VA), standby gas treatment system [BH) initiation, and control room emergency ventilation [VI] initiationI and group, 8- transverse in-core probes [IG] withdrawal.

On February 10, at 0657 hours0.0076 days <br />0.183 hours <br />0.00109 weeks <br />2.499885e-4 months <br /> CST the reactor was restarted and synchronized to the TVA system grid.

This event is reportable in accordance with 10 CFR 50.73 (a)(2)(iv) as a condition responsible for an automatic actuation of the ESF system.

B. Ino erable Structures Cpm nents or S stems that Contributed to the Events None.

II

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NRC FERN 36QL U.S. IRICLEAR REGUIATERY CQSIISSI ON APPROVED SY QRI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPOHSE TO COHPLY llITH THIS INFORHATIOH COLLECT I OH REOUEST I 50 ~ 0 HRS. FORNARD CQBEENTS REGARDING BURDEN EST IHATE TO THE INFORHATION AND RECORDS HANAGEHENT BRANCH (HHBB 7714), U.S. NUCLEAR REGULATORY CQHIISSIOH, LICENSEE, EVENT REPORT MASH INGTON, DC 20555-0001, AND TO THE PAPERHORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104), OFFICE OF HAHAGEHEHT AND BUDGET, l!ASH INGTOH DC 20503 FACILITY NA% (1) DOCKET IRMKR (2) LER IRMKR (6) PAGE (3)

'YEAR SEQUENTIAL REVISION NUHBER HIHEBER

'Browns Ferry Unit 2 05000260 95 002 00 3 of 7 TEXT lf more s ce is r ired use edditionei co ies of NRC Form 3 66A (17)

Co Dates and A roximate Times of Ma or OccurrencesI February 9, 1995 at 0028 CST The Unit 2 reactor scrammed due to a turbine trip. The Unit 2 emergency operating instruction (2-EOI-1) was entered because of a low reactor water level.

February 9,- 1995 at 0030 Reactor water level was normalized, Unit 2 was stable, and 2-EOI-1 was exited.

February 9, 1995 at 0225 TVA provided a 10 CFR 50.72(A)(2)(ii) notification to NRC operations center that the reactor scrammed and the ESFs automatically actuated.

February 9, 1995 at 2000 Control rods were being pulled to restart the Unit 2 reactor.

February 10, 1995 at 0657 The reactor was restarted and synchronized to the TVA system grid+

D~ Other S stems or Seconda Func'.ons Affected:

None.

Eo Method of Discove This condition was discovered when the control room received the Unit 2 main generator exciter ground alarm and subsequent turbine and reactor trips.

Fo 0 erator Actions!

Once the reactor scrammed, Operations personnel [licensed, utility]water entered 2-EOI-1 to control the reactor for a low level condition. Operations personnel then reactor responded to the scram in accordance with the approved reactor scram procedure (2-AOI-100-1), and the reactor was stabilized within two minutes. The EOI was then exited'.

0 I'

NRC F(WN 366A U.S. IN)CLEAR REGULATORY C(NBIISSI(NI APPROVED BY (NNI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESl'IHATED BURDEN PER RESPONSE TO CONPLY UITH THIS INFORNATION COLLECTION REQUEST: 50 ~ 0 HRS ~ FORMARD COINIENTS REGARDING BURDEN EST INATE TO THE INFORNAT ION AND RECORDS NANAGENENT BRANCH (HNBB 7714), U.S. NUCLEAR REGULATORY COINIISSION, LZCENSEE EVENT REPORT NASH INGTON, DC 20555-0001, AND TO THE PAPERNORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104), OFF ICE OF HAMAGEHENT AND BUDGET, llASHINGTON DC 20503 FACILITY NAlK (1) DOCKET IRRRER (2) LER IWIER (6) PAGE (3)

YEAR SEQUENTIAL REVISION NIIIBER HINGE R Browns Ferry Unit 2 05000260 95 002 00 4 of 7 TEXT If more s ce is r ired use additions( co les of NRC Form 366A ('17)

G. Safet S stem Res nsesl All safety systems responded as designed for th'is type of event.

II'AUSE OF THE EVENT A. Zsuaediate Cause:

The immediate cause of the 'event was the Unit 2 main generator exciter ground relay activated eventually resulting in a reactor scram.

B. Root Causes TVA's investigation of'his event determined that .the cause of the event was a degraded subcomponent. Specifically, a stator cooling water leak from the top of the generator field rectifying cooling water manifold in PRC 1 (See Figure 1) dripped on rectifier components potentially creating a path to ground. Additionally, two generator field PRCs (2 and 5) had a low-resistance to ground state due to internal deposition of corrosion products (copper oxides) in their teflon insulating tubes.

IV. ANALYSIS'F THE EVENT The BFN FSAR contains an analysis of a generator load re)ect/scram transient. In that transient, the FSAR assumes a starting point of greater than 100 percent power and associated steam flow. The analysis also assumes that the turbine bypass valves fail to open.

Plant systems are designed to respond to such a transient. This LER event was much less severe than the analyzed FSAR transient. Thus, this event was bounded by the plant safety analysis.

The main generator PRCs take the AC output voltage of the alternator exciter and rectifies it to produce a DC voltage which is applied to the main generator. Each rectifier circuit contains diodes that are mounted on a rectangular copper heat sink through which deionized water from the generator cooling system is circulated. The deionizing water is carried between heat sinks through metal piping and teflon insulating tubes which, also serve as electrical insulation from ground. The "as found" condition revealed two anomaliesl (1) a water leak from the upper metal manifold in PRC 1, and (2) low-resistance path to ground in two cubicles (PRCs 2 and 5).

NRC FQUI 366A U.S. IN)CLEAR REGULATORY CQBIISSIQI APPROVED BY QNI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPOHSE TO COMPLY IJITH THIS INFORMATION'OLLEC'I IOM REQUEST: 50.0 HRS. FORMARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (HHBB 7714), U.S. NUCLEAR REGULATORY CQBIISSIOH ~

LICENSEE EVENT REPORT HASHIMGTON, DC 20555-0001, ANO TO THE PAPERlORX REDUCTION TEXT CONTINUATION PROJECT (3150.0104), OFFICE OF MANAGEMENT AND BLSGETg

'WASHINGTON DC '20503 FACILITY IWK (1) NXXET IRMKR (2) LER RMBER (6) PAGE (3)

YEAR SEQUENTIAL REVISION NLNBER MIN(BER Browns Ferry Unit 2 05000260 95 002 00 5 of tf more 7'EXT s ce is r ired use edditioneL c ies of NRC Form 366A (17)

During this event, the turbine and reactor protective systems actuated as designed to mitigate a scram from 100 percent power, and Operations personnel actions brought the reactor to a stable condition within two minutes to minimize the effect of the plant scram. Consequently, the plant parameters remained well within the bounds of the BFN safety analysis. Therefore, the health and safety of plant personnel and the public as a result of this event were not compromised.

V CORRECTIVE ACTIONS A Immediate Corrective Actions:

personnel responded to the reactor scram. Operations and Technical Support personnel isolated and meggered the main generator circuitry, and identified that PRCs lg 3g 4g and 6 had B'perations a resistance of 10M ohms to ground while PRCs 2 and 5 had a resistance of 300K ohms and 100K ohms to ground, respectively.

Associated circuitry included the Alterrex stator and PRC circuitry measured in the "as found'ondition had 100K ohms of resistance to ground. When this electrical troubleshooting was being performed, a water leak was identified from the top of the PRC 1 cooling water line manifold onto rectifier components below. The PRCs 2 and 5 low-resistance conditions were eliminated by 'the cleaning/replacing of the teflon insulating tubes of the cooling water lines until a 1.5M ohms resistance was achieved in the associated circuitry.

Corrective Actions to Prevent Recurrence:

Corrective actions to preclude recurrence are: (1) PRC 1 leaking cooling water line manifold was replaced, and (2) a determination will be performed for additional corrective actions based on a failure analysis of the leaking cooling water manifold and analytical tests of the rectifier cooling water tubes.

If the results of this analysis significantly alter either the root cause or corrective actions for this event, a supplemental report will be submitted.

VI. ADDITIONAL INFORMATION Failed Com nents:

The main generator power rectifierB had multiple grounds as described i.n section III.

Ci 41 I

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NRC FORK 366A U S. WCLEAR REGULATIXIY IXXSIISSIIXI APPROVED BY (BNI NO. 3150-0104 (5-92) EXPIRES 5/3'I/95 ESTIKATED BURDEN PER RESPONSE TO CO(PLY UITH THIS INFORKATIOH COLLECTIOH REQUEST: 50.0 HRS. FORllARD CQIBIENTS REGARDIHG BURDEN ESTIKATE TO THE IHFORKATION AND 'RECORDS KANAGEKENT BRANCH (KNBB 7714), U.ST NUCLEAR REGULATORY COIBIISSIOH, LICENSEE EVENT REPORT llASHINGTON~ DC 20555-0001, AND TO THE PAPERIJORX REDUCTION TEXT CONTINUATION PROJECT (3150 0104), OFFICE OF KANAGEKENT AND BUDGET, UASHINGTON DC 20503 FACILITY IWK (1) DOCXET IRBSER (2) LER IRBIBER (6) PAGE (3)

TEAR SEQUENTIAL REVISIOH NIR(BER NIR(BER Browns, Ferry Unit 2 05000260 95, 002 00 6 of 7 TEXT tf more s ce is r ired use additional co ies of NRC Form 366A (17)

Previous LERs on Similar Eventst LER 259/84024 provided details concerning a reactor scram resulting from a turbine-generator trip. The corrective action to preclude a recurrence was to reduce the size of the in-line filter to minimize the deposition of iron and copper onto the teflon insulating tube. Since that time, TVA'as initiated a preventive maintenance task to chemically clean the teflon tubes every 36 months to further reduce the recurrence of this type of event. The change to reduce the size of the in-line filter would not have precluded this event (LER 260/95002).

VII. Co itments Not all actions described in section V of this report are Regulatory Commitments. That is, they are not actions required to restore compliance with obligations. Obligations mean an action that is a legal binding requirement imposed through applicable rules, regulations, orders, and licenses. The only commitment is identified below:

A determination will be performed'or additional corrective actions nd based on a failure analysis of the leaking cooling water manifold analytical tests of the rectifier cooling water tubes. This determination will be completed by June 16, 1995.

Energy Industry Identification System (EIIS) system and component codes are identified in the text with brackets (e.g., [XX].

~I NRC FORN 366A U.S NUCLEAR REGULATORY CONIISSION 'APPROVED BY (BIB NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTINATED BURDEN PER RESPONSE TO CONPLY MITH THIS INFORNATIOH COLLECTION REQUEST: 50.0 HRS. FORl!ARD CONHENTS REGARDING BURDEN ESTIMATE TO THE INFORHATION AHD RECORDS NANAGENENT BRANCH (HNBB 7714), U.S. NUCLEAR REGULATORY CONNISSION, LICENSEE EVENT REPORT NASHINGTON, DC 20555-0001, AND TO THE PAPERHORK REDUCTIOH TEXT CONTINUATION PROJECT (3150-0104), OFFICE OF NANAGEHEHT AND BUDGET, NASHINGTOH DC 20503 FACILITY NANE (1) DOCKET HI%BEN (2) LER Hi%HER (6) PAGE (3)

YEAR SEQUENTIAL ,REVISION HUNBER NURSER Browns Ferry Unit 2 05000260 95 002 00 7 of 7 TEXT tf more s ece is r uired use eddittonel co ies of NRC Form 366A (17)

MAIN GENERATOR ASSEMBLY TOP ViEVV I

PRC1 PRC4

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l i I PRC 5 PRO 2 c

PRC 3 PRCB f

L FIGURE 1

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