ML18038B008

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LER 94-010-00:on 941005,loss of ECCS Division II Instrumentation Resulting from Blown Fuse in Atu Inverter Caused by Failed Capacitor.Blown Dc Input Fuse Was Replaced & Instrumentation Logic restored.W/941104 Ltr
ML18038B008
Person / Time
Site: Browns Ferry Tennessee Valley Authority icon.png
Issue date: 11/04/1994
From: Davenport D, Machon R
TENNESSEE VALLEY AUTHORITY
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-010-01, LER-94-10-1, NUDOCS 9411170046
Download: ML18038B008 (20)
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Text

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(ACCELER CI ED RIDS X. J REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)'CCESSION NBR:9411170046 DOC.DATE: 94/11/04 NOTARIZED: NO DOCKET N FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH. NAME AUTHOR AFFILIATION DAVENPORT,D.W. Tennessee Valley Authority MACHON,R.D. Tennessee Valley .Authority RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 94-010-00:on 941005,loss of ECCS division II instrumentation resulting from blown fuse in ATU inverter caused by failed capacitor. Blown dc input fuse was replaced

& instrumentation logic restored.W/941104 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR TITLE: 50;73/50.9 Licensee Event Report (LER)',

ENCL j SIZE:

Incident Rpt, etc.

NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-4-PD 1 1 WILLIAMS,J. 1 1 INTERNAL: ACRS AE~O/MO~AB DSP 2 2 AEOD/SPD/RRAB ILE CENTER 02 1 1 NRR/DE/EELB RR= DE/EMEB 1 1 NRR/DORS/OEAB NRR/DRCH/HHFB 1 1 NRR/ DRCH/HIC B NRR/DRCH/HOLB 1 1 NRR/DRSS/PRPB NRR/DSSA/SPLB 1 1 NRR/DSSA/SRXB NRR/PMAS/IRCB-E 1 1 RES/DSIR/EIB RGN2 FILE 01 1 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 EMOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP L'S TO RFDL'CE iVKSTE! COiTAC I"I HE DOCL'iIEiTCOiTROL DES~K. ROOXI PI 37 (EAT. SN'-2083 ) TO ELI XI IRATE 5'OL'R iAiIL F I<Oil DISTRIBL'TIOiLISTS FOR DOCI:iIEi'I'S YOL'Oi "I'LI'.I)!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 27 ENCL 27

A, Tee essee vasey A.":"cary, pas: 0".ce Bcx 2~. Deca'~ . A ant a 3"R,9 200C R. D. (Rick) Machon Vce P'es cent. Bevn Fe~y Much'act November 4, 1994 U.S. Nuclear Regulatory Commission 10 CFR 50.73 ATTN: Document Control Desk Washington, D.C. 20555

Dear .Sir:

BROWNS FERRY NUCLEAR PLANT (BFN) UNITS 1I 2~ AND 3 - DOCKET NOS 50-259~ 50-260~ AND 296 FACILITY OPERATING LICENSE DPR-33~ 52~ AND 68 LICENSEE EVENT REPORT 50-260/9402.0 The enclosed report provides details concerning a loss of instrumentation input logic for the plant's Division II Emergency Core Cooling Systems (ECCS). The event was caused by a blown fuse to the ECCS Division II, Analog Trip Unit (ATU) Inverter. The blown fuse resulted from a failed capacitor in the ATU Inverter capacitor bank.

Section VII of the report provides a description of TVA's commitment regarding this event. This report is submitted pursuant to 10 CFR 50.73(a)(2)(vii), and 50.73(a) (2)(i)(B)

Sincerely, R. D. M on Site Vi e President PAB 1E-BFN Enclosure cc: See page 2 9411170046 941104 PDR ADQCK 05000260 S PDR gp',

0 U.S. Nuclear Regulatory Commission Page 2 November 4, 1994 Enclosure cc (Enclosure):

INPO .Records Center Suite 1500 1100 Circle 75 Parkway.

Atlanta, Georgia 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

NRC FORH 366 U.S. NUCLEAR REGULATORY CQHIISS ION APPROVED BY INIB MO. 3150-0104 (5-92) EXP I RES '5/31/95 ESTIMATED BURDEN PER RESPONSE TO COHPLY WITH THIS. INFORHATION COLLECTION REQUEST: 50.0 HRS.

LZCENSEE EVENT REPORT (LER) FORWARD COMMENTS REGARDIHG BURDEN ESTIHATE TO THE INFORMATION AND 'RECORDS HANAGEHENT BRANCH (HNBB 7714), U.S. HUCLEAR REGULATORY COMHISSION, (See reverse for required neer of digits/characters for each block) 'WASHINGTON, DC 20555-0001 REDUCTION PROJECT AND TO THE PAPERWORK (3150-0104), OFFICE OF MANAGEMENT AND BUDGET WASHINGTON OC 20503.

FACILITT lOWE (1) DOCKET NNIBER (2) PAGE (3)

Browns Ferr, Nuclear Plant BFN Unit 2 05000260 1 OF 7 TITLE (4) Loss of the Emergency Core Cooling Systems (ECCS) Division'll instrwentation resulting from a blown fuse in the Analog Trip. Unit (ATU) Inverter caused by a failed capacitor.

EVENT DATE 5 LER HINSER 6 REPORT DATE 7 OTHER FACILITIES INVOLVED 8 SEQUEHT IAL REVISION . YEAR FACILITY NAHE N/A DOCKET NUMBER MONTH DAY YEAR YEAR HONTH DAY NUMBER NUHBER FACILITY NAHE N/A DOCKET NUMBER 10 05 94 94. 010 00 11 04 94 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS 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)

POWER 20.405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c) 000 LEVEL (10) 20.405(a)(1)(ii) 50.36(c)(2) X 50.73(a)(2)(vii) 'THER 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 belou and in Text, 20.405(a)(1)(v) 50.73(a)(2)(iii) 50.73(a)(2)(x) NRC Form 366A LICENSEE CONTACT FOR THIS LER 12 NAHE TELEPHOHE NUHBER (Include Area Code)

James W. Davenport, Regulatory Licensing Engineer (205)729-2690 DNPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPIRT 13 SYS REPORTABLE REPORTABLE CAUSE COHPONEHT HANUFACTURER CAUSE SYSTEH COMPONENT HANUFACTURER TEH TO NPRDS TO NPRDS X AD FU N43 1 N AD INVT N431 X AD C183 N SUPPLEMENTAL REPORT EXPECTED 14 EXPECTED MONTH DAY YEAR YES SUBMISSION X HO (I f yes, cccpiete'EXPECTED SUBHISSION DATE). DATE (15)

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

On October 5, 1994 at 2220 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.4471e-4 months <br /> CDT, with Unit 2 in a refueling outage,, Control Room operators received alarms that indicated a loss of Unit 2, Division II, Emergency Core Cooling Systems (ECCS) instrumentation. Operators declared Division II of ECCS instrumentation inoperable, in accordance with TS 3.2.B, resulting in all of the ECCS being declared inoperable. Since the unit was already shutdown, no further operator

'action was required. Operators initiated troubleshooting that found a fuse had cleared on the ECCS Division II Analog Trip Unit (ATU) Inverter. The fuse cleared during a transfer of the 2A 250 Volt DC Reactor Motor Operated Valve board to its normal power source following a battery discharge test. The fuse was replaced at 0110 hours0.00127 days <br />0.0306 hours <br />1.818783e-4 weeks <br />4.1855e-5 months <br /> on October 6r 1994 and the Division II ECCS was declared operable. Further investigation identified the root cause of the event to be a. failed capacitor in the ATU inverter capacitor bank. This event is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) as any operation or condition prohibited by the plant's TS. Additionally, this event is reportable in accordance with 10 CFR 50.73(a)(2)(vii).

NRC FORM 366 (5-92)

0 NRC FORH 366A U.S. IN)CLEAR REGULAT(H(Y CQHISSION APPROVED SY (HEI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE TO CCHPLY MITS THIS IHFORHATION COLLECT ION REQUEST: 50.0 HRS. FORIIARD COHHEH'TS REGARDING BURDEN EST IHATE TO THE IHFORHAT I ON AND RECORDS HANAGEHENT BRANCH (HNBB 7714), U.S. NUCLEAR REGULATORY COHHISSIONf LICENSEE EVENT REPORT MASHIHGTON, DC 20555-0001, AND TO THE PAPERUORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104), OFFICE OF HANAGEHENT AND BUDGET, NASHIHGTOH OC 20503 FACILITY NAHE (1) DOCKET HWSER (2) LER NINSER (6) PAGE (3)

TEAR SEQUENTIAL REVISION Browns Ferry Unit 2'5000260 94 HUHBER 010 NUHBER 00 2 of 7 TEXT tf more s ce is r ired use edditionsl co ies of NRC Form 366A (17)

PLANT CONDITIONS Unit 2 was shutdown in a refueling outage with the reactor cavity flooded, fuel pool gates removed, and fuel off-loading in progress.

Units 1 and 3 were shutdown and defueled.

DESCRIPTION OF EVENT A'o Eventt On October 5, 1994 at 2220 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.4471e-4 months <br /> CDT, Control Room operators received alarms indicating a loss of Division ZI Instrumentation for the plant's Emergency Core Cooling Systems (ECCS) . Level and/or pressure input signals were lost to the instrumentation logic for the following ECCS subsystems:

Core Spray (CS), Division IZ [BG)

Residual Heat Removal (RHR), Division II [BO)

~

~

~ High Press Coolant In)ection (HPCI) [BJ)

~ , Anticipated Transient Without Scram (ATWS), Division ZZ [JC]

~ Automatic Depressurization System (ADS), Division ZI [JC)

Zt should be noted that Division II of RHR and CS were inoperable due to outage activities. Also, HPCI, ADS, and ATWS were not required to be operable due to current plant conditions.

ECCS Division I instrumentation remained operable and was available for manual initiation of both divisions of,the affected systems. However, due to current plant conditions, only one Division of CS and RHR was required to be operable.

The event did not require plant operators to take any actions other than initiation of troubleshooting activities.

Plant maintenance personnel conducted troubleshooting of the ECCS Division. ZI instrumentation logic. TVA determined that the event was initiated when a direct current (DC) input fuse [FU) on the ECCS Division II, Analog Trip Unit (ATU) Inverter [INVT) cleared causing a loss of input signals from the affected systems to the control room instrumentation. The fuse had cleared during a transfer of the 2A 250 Volt DC Reactor Motor Operated Valve (RMOV) board to its normal power source following a battery discharge test. This transfer had been performed previously on several occasions with no adverse consequences.

The ATU Inverter internal components were visually inspected using vendor manual recommendations to determine the cause of the fuse failure. There were no discrepancies identified. The

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NRC FORM 366A U.S. NUCLEAR REGULATORY CQIIISSI ON 'APPROVED BY (NQI HO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS IHFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD COMHENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT, BRANCH'MNBB 7714) ~ U.S. NUCLEAR REGULATORY COMMISSION, LICENSEE EVENT REPORT WASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION TEXT CONTINUATZON PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON DC 20503 FACILITY NAIL (1) DOCKET HIHIBER (2) LER HINIBER (6) PAGE (3)

YEAR SEQUEHTIAL REVISION NUMBER 'UMBER Browns Ferry Unit 2 05000260 94 010 00 3 of 7 TEXT If more s ce is r uired use additional co ies of NRC Form 366A (17)

DC input fuse was replaced, appropriate post maintenance testing completed, and ECCS Division IZ instrumentation declared operable at 0110 hours0.00127 days <br />0.0306 hours <br />1.818783e-4 weeks <br />4.1855e-5 months <br /> CDT on October 6, 1994.

TVA determined this event to be reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by plant TS.

This resulted when the limiting conditions for, operation (TS 3.2.B) for instrumentation that initiates or controls the core and containment cooling. systems (i.e., CS and RHR for current plant conditions) were not satisfied. As a result CS and RHR were declared inoperable. This resulted in noncompliance with TS 3.5.A.4 and TS 3.5.B.9 for CS and RHR, respectively, when the reactor vessel pressure is atmospheric. The event was also determined to be reportable in accordance with 10 CFR 50.73(a)(2)(vii) as .any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems.

Bo Ino erable Structures Com nents or S stems that Contributed to the Eventl None.

C~ Dates and A roximate Times of Ma 'or Occurrences:

October 5, 1994 at 2220 CDT Division II ECCS Instrumentation lost due to blown ATU Inverter fuse.

October 6, 1994 at 0110 CDT DC input Fuse replaced in Division ZI, ECCS ATU Inverter and Instrumentation logic restored.

D. Other S stems or Seconda Functions Affected:

None.

E. Method of Discove This event was promptly discovered at 2220 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.4471e-4 months <br /> CDT on October 5, 1994 when Control Room alarms indicated,ECCS Division IZ Instrumentation problems. Primary among the alarms received was the ECCS ATU 'Trouble Alarm.

II fl

NRC FOR)l 366A U.S. IRICLEAR REGULATORY CQBIISSION APPROVED BY QBI NO. 3150-0104 (5-92) EXP I RES . 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY MITH THIS INFORMATION COLLECT IOM REOUEST: 50.0 HRS FORNARD COMMENTS REGARD INC BURDEN ESTIMATE TO THE INFORMATION AMD RECORDS MANAGEMENT BRANCH (NHBB 7714), U.S. NUCLEAR REGULATORY COMMISSION ~

LICENSEE EVENT REPORT 'NASHIHGTOH; DC 20555-0001, AND TO THE PAPERNORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104), OFFICE OF HANAGEHENT AND,BUDGET, WASHINGTON DC 20503 FACILITY MANE (1) DOCKET HNSER (2) NQIBER (6) PAGE (3)

TEAR SEQUENTIAL REVISION Browns Ferry Unit 2 05000260'ER 94 NUMBER 010 NUMBER 00 4 of 7 TEXT If more s ce is r ired use additional co ies of HRC Form 366A (17) 0 orator Actionst There were no TS safety system initiations required of Control

=.~Room operators. The steps taken to identify the problem, and initiate maintenance actions were appropriate.

0. Safet S stem Res onses:

None.

III ~ CAUSE OF THE EVENT Immediate Causes, The immediate cause of the event was a blown DC input fuse for the ECCS Division II, ATU Inverter.

B~ Root Causes Based on the results of BFN's troubleshooting and,scheduled Preventive Maintenance activities, and the field service inspection by the vendor, TVA has determined the root cause of the event to a failed Cl Capacitor in the Division II, ATU Inverter capacitor bank.

C. Contributin Factors:

None.

IV. ANALYSIS OF THE EVENT A blown DC input fuse on the ECCS Division II, ATU Inverter caused a loss of level and/or pressure input signals to the HPCI, CS, RHRg, ATWS, and ADS from their respective instrumentation logic systems.

This event di.d not result in a condition outside the plant's design basis for the following reasons:

~ This event resulted from a power supply failure to the instrumentation logic for Division II of the ECCS. However/

Division I instruments remained operable during the event and were available to Control Room operators for manual initiation of both divisions of ECCS.

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0

NRC FORM 366A U.S. IRICLEAR REGULATORY C(HBIISSIQI APPROVED'BY MB NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATION COLLECT IOH REQUEST: 50.0 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSIONS LICENSEE EVENT REPORT WASHINGTON, DC 20555-0001, AHD TO THE PAPERWORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON DC 20503 FACILITY NAME (1) DOCKET HWER (2) LER HWBER (6) PAGE (3)

YEAR SEQUENTIAL REVISION NUMBER NUMBER Browns Ferry Unit 2 05000260 94 010 00 5 of 7 TEXT If more s ce is r ired use additional co ies of HRC Form 366A (17)

~ The BFN Final Safety Analysis Report (FSAR), Section 6.5. 1, states in part that "... the reliability and redundancy of the controls and instrumentation for the Emergency Core Cooling Systems shows that no failure of a single initiating sensor either prevents or falsely starts the initiation of these cooling systems. No single control failure prevents the combined cool'ing systems from providing the core with adequate cooling."

~ The event did not result in any plant transient described in the BFN FSAR, Chapter 14 accident analyses.

Therefore, based on the above, this event did not result in a condition outside the design basis of the plant nor did affect the health and safety of plant personnel or the public.

it adversely V. CORRECTIVE ACTIONS Immediate Corrective Actions:

The blown DC Inverter and input fuse was replaced in the ECCS Division the instrumentation logic restored.

II ATU Bo Corrective Actions to Prevent Recurrence:

Since the unit was in a refueling outage and one Division's ATU Znverter could be removed from service, more extensive troubleshooting was performed in conjunction with previously scheduled 18 and 72 month Preventive Maintenance activities.

The following actions were taken:

~ Performed vendor recommended checks for the ATU Inverters.

~ Performed testing of ATU Inverter capacitors.

~ The ATU Inverter vendor's representative performed an evaluation/inspection of both Divisions' and ZZ ATU Inverters.

As a result of the BFN Maintenance checks and the vendor performed inspectionsr TVA determined that the Division I and ZI ATU Inverters were performing properly. The electrolytic capacitors in both Divisions I and IZ capacitor banks were removed and tested. Testing of the capacitors revealed one "failed" Cl Capacitor in each Division's capacitor bank. Each of these capacitors was in the 6th year of a 6-year service life. The capacitors were scheduled in the PM program to be

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HRC FORII 366A U.S. IN)CLEAR REGULATORY C(NBIISSION APPROVED BY (NRI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY NITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORNARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT LICENSEE EVENT REPORT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATORY COMlllSSIOH, llASHIHGTOH, DC 20555-0001, AND TO THE PAPERNORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET,

'MASHIHGTOH DC 20503 FACILITY IQIK (1) DOCKET NLNBER (2) LER NINQER (6) PAGE (3)

YEAR SEQUENTIAL REVISI OH NUMBER NUMBER Browns Ferry Unit 2 05000260 94 010 00 6 of 7 TEXT If more s ce is 'r ired use edditionsl co ies of HRC Form 366A (17) replaced during the current refueling outage. Vendor information states that 10 years is a reasonable expected service life for these types of capacitors. The capacitors in both Divisions I and II capacitor banks, described above, were replaced with the exception of 1 C2A (1 Micro Farad (MFD), 1000 Volt DC) capacitor. Since this capacitor was supplied by a different manufacturer than the failed Cl capacitors, TVA elected to test (passed test) and leave in service.

Additionally, the vendor provided a copy of HDR Power Systems (ATU Znverter Manufacturer) service bulletin f009 dated January 11, 1991. This service bulletin indicates that DC capacitors manufactured by Mepco/Centralab (3300MFD, 350 Volt DC, Part Number 133235) between the 30th week of 1986, and the 50th week of 1987, have shown a defect that results in low or no capacitance when failed. The failed BFN Cl capacitors described above were from this manufacturer and vintage. The capacitors were replaced, as prescribed by the BFN Periodic Maintenance Program, and the Division I and IZ ATU Inverters returned to service. TVA was not aware of the above referenced vendor service bulletin. This issue will be further evaluated to determine whether additional corrective actions are warranted.

Based on the above, no further actions are necessary to prevent recurrence.

VI ~ ADDITIONAL INFORMATION Ao Failed Com onentsl DC input Fuse (FU1), Part No. A025F060, manufactured by Carbone-Ferraz DC Capacitor (Cl) (3300MFD, 350 Volt DC), HDR Power Systems, Inc. Part No. 133235, manufactured by MEPCO ATU Inverter (INVT), Part No. 6841310, Manufactured by HDR Power Systems, Inc.

B. Previous LERs on Similar Events:

TVA has reviewed previous BFN LERs to determine events have occurred. LER (260/94001) was written as a result if similar of an ATU DC input fuse failure. However, the root cause of the event was determined to be a failure of the ECCS Division IZ, ATU Znverter control card. Therefore, the corrective action taken in LER 260/94001 would not have precluded this event.

NRC FORM 366A U.S. IN)CLEAR REGULATORY CQNII SSIDH APPROVED BY QS NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATION COLLECT ION REQUEST: 50.0 HRS. FORIIARD CCMHENTS REGARDING.

BURDEH ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, LICENSEE EVENT REPORT'EXT NASHINGTON~ DC 20555-0001, AND TO THE PAPERNORK REDUCTION CONTINUATION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, NASHINGTOH DC 20503 FACILITY NAME (1) DOCKET NWBER (2) LER NW8ER'6) PAGE (3)

YEAR 'EQUENTIAL REVISION NUMBER NUHBER Browns Ferry Unit 2 05000260 94 010 00 7 of 7 TEXT tf more s ce is r ired use edditionsl co ies of NRC Form 366A <<17)

There has also been one recent event (LER 260/94006) related to an ECCS Division I, ATU Inverter, 250 Volt DC RHOV breaker trip.

The root cause for this LER was determined to be a random I

failure of the Division ATU Inverter caused by a shorted Silicon Controlled Rectifier -(SCR). However, based on the root

.cause determination for this event (260/94010), the failed Cl capacitor in the Division I ATU Inverter capacitor bank may have contributed to the shorted SCR.

A commitment made in 260/94006 states that TVA will evaluate the ECCS ATU power distribution design to determine if system reliability enhancements are feasible. 'This evaluation is ongoing and is scheduled to be completed by November 30, 1994.

Corrective actions resulting from this evaluation may preclude future events of this type.

VZ.Z . Commitment TVA will evaluate the process utilized by the ATU vendor and its suppliers for notification of equipment service issues and/or maintenance updates. This evaluation will be completed by February 3, 1995.

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

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