05000260/LER-1994-010, :on 941005,loss of ECCS Division II Instrumentation Resulting from Blown Fuse in Atu Inverter. Caused by a Failed Capacitor.Blown DC Input Fuse Was Replaced

:on 941005,loss of ECCS Division II Instrumentation Resulting from Blown Fuse in Atu Inverter. Caused by a Failed Capacitor.Blown DC Input Fuse Was Replaced

ML18038B765
Person / Time
Site:	Browns Ferry
Issue date:	09/30/1996
From:	Davenport J TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18038B764	List: 05000260/LER-1994-010, :on 941005,loss of ECCS Division II Instrumentation Resulting from Blown Fuse in Atu Inverter. Caused by a Failed Capacitor.Blown DC Input Fuse Was Replaced 05000260/LER-1994-010-01, Forwards LER 94-010-01,clarifying Analysis of Event Section Which Division I & Division II ECCS Equipment Remained Operable for Automatic Initiation
References
LER-94-010, LER-94-10, NUDOCS 9610090110
Download: ML18038B765 (14)

LER-1994-010, on 941005,loss of ECCS Division II Instrumentation Resulting from Blown Fuse in Atu Inverter. Caused by a Failed Capacitor.Blown DC Input Fuse Was Replaced

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(e)(2)(v) 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
2601994010R00 - NRC Website

text

NRC FORM 366 (4.9S)

U.S. NUCLEAR REGULATORYCOMMISSION LICENSEE EVENT REPORT (LER)

(See reverse for required number of digits/characters for each block)

APPROVED BY OMB NO. 316~104 EXPIRES 04/30/98 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS MANDATORY INFORMATION COLLECTION REQUEST:

60.0 HRS.

REPORTED LESSONS LEARNED ARE INCORPORATED INTO THE LICENSING PROCESS AND FED BACK To INDUSTRY.

FORWARD COMMENTS REGARDING BURDEN EsTIMATE To THE INFDRMATIGN AND REcoRDs MANAGEMENT BRANCH rl-6 F33).

U.S.

NUCLEAR REGULATORYCOMMISSION WASHINGTON DC 20566 FACIUTYNAME(ll Browns. Ferry Nuclear Plant (BFN) Unit 2 ooc KEYN(s3sER Esl 05000260 PACE (3) 1 OF 7 TITLE(il Loss of the Emergency Core Cooling Systems (ECCS) Division II instrumentation resulting from a blown fuse in the Analog Trip Unit (ATU) Invsrter caused by a failed capacitor.

MONTH DAY YEAR 10 05 94 EVENT DATE l5l LER NUMBER l6)

SEQUENTIAL REVISION NUMBER NUMBER 94 010

01 REPORT DATE (7I MONTH 09 FACIUTYNAME DAY YEAR N/A FACIUTYNAME 30 95 N/A OOCKETNVMEEN DOCKETNUMEER OTHER FACILITIESINVOLVEDIB)

OPERATING MoDE (9)

POWER LEVEL (10)

N 000 20.2201 (b) 20.2203(a)(1) 20.2203(a)l2)(i) 20.2203 (a) (2)(v) 20.2203(a) (3)0) 20.2203(a)(3) (ii)

X 50.73(a)(2)li)(B) 50.73(a) (2)(ii) 50.73 (a) (2) (iii) 50.73(a) (2) (viii) 50.73(a)(2)(x) 73.71 UANTTO THE REQUIREMENTS OF.10 CFR %: (Check one o THIS REPORT IS SUBMITTED PURS r more)

(11) 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)

UCENSEE CONTACT FOR THIS LER (12) 50.73(a)(2) liv) 50.73 (e) (2)(v)

X 50.73(a)(2)lvii)

OTHER Speci(Y In Abstrect below or In NRC Form 366A NAME TELEPHONE NuMeEII anauee Aree Ceo I James W. Davenport, Regulatory Licensing Engineer (205) 729-2690 COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT l13)

CAUSE

SYSTEM COMPONENT MANUFACTURER TO NPRDS

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO NPRDS AD FU N431 X

AD INVT N431 Y

X AD C183 N

SUPPLEMENTAL REPORT EXPECTED l14)

YES' No (lf yes, complete E

SUBMISSION DATE).

EXPECTED SUBMISSION DATE l16)

MONTH DAY YEAR ABSTRACT (Limitto 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.

However, ECCS Division I instrumentation remained operable during this event.

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 6, 1994 and the Divis3.on 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).

'I)610090110 960'I)30 PDR

,ADOCK 05000260 S

PDR NRC FORM 36 l4 9

)

0 Y~<4-BSI U.S. NUCLEAR REGULATORYCOMMISSION IsZCENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1

Browns Ferry Unit 2 05000260 LER NUMBER 6

U N IA NUMBER I

I NUMBER PAGE 3

2 of 7 94 010 01 more space 4 requrre, use hs copies 0

PLANT CONDITIONS

ZZ ~

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

Ao Event 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:

~'ore Spray (CS), Divisi.on ZI [BG]

~

Residual Heat Removal (RHR), Division ZZ [BO]

~

High Press Coolant Injection (HPCI) [BJ]

~

Anticipated Transient Without Scram (ATWS), Di.vision IZ [JC]

~

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

It should be noted that Di.vision ZI of RHR and CS were inoperable due to outage activities.

Alsor HPCZ ADSr and ATWS were not required to be operable due to current plant conditions.

of both divisions of the affected systems.

However, due to current plant conditions, only one Divi.sion 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 Divi.sion IZ 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 i.nspected using vendor manual recommendations to determine the cause of the fuse failure.

There were no discrepancies identified.

The 0

II A(

QRC FORM 366A l4-95l U.S. NUCLEAR REGULATORYCOMMISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1

'Browns Ferry Unit 2 DOCKET 05000260 LER NUMBER 6

A 9

UNIA I

I N NUMBER NUMBER 94 010 01 PAGE 3

3 of 7 more specs s requ, use mons copes o DC input fuse was replaced, appropriate post maintenance testing completed, and ECCS Division ZZ 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.

B ~

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

C.

Dates and A

roximate Times of Ma'or Occurrencest ber 5, 1994 at 2220 CDT Division IZ ECCS Znstrumentation lost due to blown ATU Inverter fuse

~

October 6, 1994 at 0110 CDT DC input Fuse replaced in Division II, 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 II Instrumentation problems.

Primary among the alarms received was the ECCS ATU Trouble Alarm.

C NRC FOIIM 366A (4-95l

il 1I

NRC FORM 866A (4-95)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACZLXTX MAME Browns Ferry Unit 2 DOCKET 05000260 LER NUMBER NUMBER NUMBER 94 010

01 4,of 7 mora apaoa ra raquir

~ usa rator Actions:

There weze no TS safety system initiations required of Control Room operators.

The steps taken to identify the problem, and initiate maintenance actions were appropriate.

G. Safet S stem Res onses:

None..

ZZZ.

CAUSE OF THE EVENT

A. Zmmediate

Cause

The immediate

cause of the event

was a blown DC input fuse for the ECCS Division II, ATU Invezter.

B. Root Cause:

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.

ZV.

ANALYSZS 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,

RHR, ATWS, and ADS from their respective instrumentation logic systems.

This event did 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 of Division II of the ECCS.

However, Division I instrumentation remained available for automatic initiation of ECCS Division I and Division II equipment during this event.

If this event occurred during power. operations, Division I and Division II ECCS equipment would have remained available with the following exceptions:

(1)

HPCI would not inject water into the reactor vessel as a result of a loss of flow controller power.

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, li JI4-BSI U.S. NUCLEAR REGULATORYCOMMISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1

Browns Ferry Unit 2 DOCKET 05000260 LER NUMBER 6

NTIA NUMBER VIS I NUMBER PAGE 3

6 of 7 94 010 01 more specs ie require. use roon copies o Irli As a result of the BFN Maintenance checks and the vendor performed inspections, TVA determined that the Division I and ZZ ATU Znverters were performing properly.

The electrolytic capacitors in both Divisions I and II 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 replaced during the current refueling outage.

Vendor information states that 10 years is a reasonable expected'ervice 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 Inverter Manufacturer) service bulletin $009 dated January ll, 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 II ATU Inverters returned to 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.

VZo

ADDITIONAL INFORMATION

A. Failed Com nents:

DC input Fuse (FU1), Part No. A025F060, manufactured by Carbone-Ferraz DC Capacitor (Cl),(3300MFD, 350 Volt DC),

HDR Power Systemsr Inc. Part No. 133235, manufactured by MEPCO C

ATU Inverter (INVT), 'Part No. 6841310, Manufactured, by HDR Power

Systems, Inc.

I, tI4-96)

U.S. NUCLEAR REGULATORYCOMMISSION LZCENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1

DOCKET LER NUMBER 6

PAGE 3

Browns Ferry Unit 2 05000260 NUMBER NUMBER 7 of 7 94 010 01 more specs s require

. use rtrons copies o B. Previous LERs on Similar Eventst TVA has reviewed previous BFN LERs to determine if similar events have occurred.

LER (260/94001) was written as a result of an ATU DC input fuse failure.

However, the root cause of the event was determined to be a failure of the ECCS Division II, ATU Inverter control card.

Therefore, the corrective action taken in LER 260/94001 would not have precluded this event.

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

The root cause for this LER was determined to be a random failure of the Division I 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.

VII.

COMMITMENTS

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)).

NRC FORM 368A I4-9S)