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LER 94-010-01: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: ML18038B763; ML18038B765;
References
	LER-94-010, LER-94-10, NUDOCS 9610090110
	Download: ML18038B765 (14)
	v • d • e

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 316~104 (4.9S) EXPIRES 04/30/98 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS MANDATORY INFORMATION COLLECTION REQUEST:

LICENSEE EVENT REPORT (LER) 60.0 HRS. REPORTED LESSONS LEARNED ARE INCORPORATED INTO THE LICENSING PROCESS AND FED BACK To INDUSTRY. FORWARD COMMENTS REGARDING (See reverse for required number of BURDEN EsTIMATE To THE INFDRMATIGN AND REcoRDs digits/characters for each block) MANAGEMENT BRANCH rl-6 F33). U.S. NUCLEAR REGULATORY COMMISSION WASHINGTON DC 20566 FACIUTY NAME (ll ooc KEY N(s3sER Esl PACE (3)

Browns. Ferry Nuclear Plant (BFN) Unit 2 05000260 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.

EVENT DATE l5l LER NUMBER l6) REPORT DATE (7I OTHER FACILITIES INVOLVED IB)

FACIUTY NAME OOCKETNVMEEN SEQUENTIAL REVISION MONTH DAY YEAR MONTH DAY YEAR NUMBER NUMBER N/A FACIUTY NAME DOCKETNUMEER 10 05 94 94 010 01 09 30 95 N/A OPERATING THIS REPORT IS SUBMITTED PURS UANT TO THE REQUIREMENTS OF.10 CFR %: (Check one o r more) (11)

MoDE (9) N 20.2201 (b) 20.2203 (a) (2) (v) X 50.73(a)(2)li)(B) 50.73(a) (2) (viii) 20.2203(a)(1) 20.2203(a) (3) 0) 50.73(a) (2)(ii) 50.73(a)(2)(x)

POWER LEVEL (10) 000 20.2203(a)l2)(i) 20.2203(a)(3) (ii) 50.73 (a) (2) (iii) 73.71 20.2203(a) (2) (ii) 20. 2203(a) (4) 50.73(a)(2) liv) OTHER 20.2203(a) (2)(iii) 50.36(c)(1) 50.73 (e) (2) (v) Speci(Y In Abstrect below or In NRC Form 366A 20.2203(a) (2) (iv) 50.36(c) (2) X 50.73(a)(2)lvii)

UCENSEE CONTACT FOR THIS LER (12)

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 REPORTABLE CAUSE SYSTEM COMPONENT MANUFACTURER TO NPRDS TO NPRDS AD FU N431 X AD INVT N431 Y X AD C183 N SUPPLEMENTAL REPORT EXPECTED l14) EXPECTED MONTH DAY YEAR YES' SUBMISSION SUBMISSION DATE). No DATE l16)

(lf yes, complete E ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single. spaced typewritten lines) (16)

October 5, 1994 at 2220 hours0.0257 days 0.617 hours 0.00367 weeks 8.4471e-4 months CDT, with Unit 2 in a refueling outage, Control Room operators received alarms that indicated a loss of Unit 2, Division II, Emergency Core On 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 0.0306 hours 1.818783e-4 weeks 4.1855e-5 months 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 tofailed capacitor in the ATU inverter capacitor bank. This event is reportable pursuant 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 )

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION

<4-BSI IsZCENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1 LER NUMBER 6 PAGE 3 U N IA I I NUMBER NUMBER Browns Ferry Unit 05000260 2 of 7 2

94 010 -- 01 more space 4 requrre, use hs copies 0 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.

ZZ ~ DESCRIPTION OF EVENT Ao Event On October 5, 1994 at 2220 hours0.0257 days 0.617 hours 0.00367 weeks 8.4471e-4 months 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 inoperable due to outage activities. Alsor HPCZ were 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 NRC FORM 366A <4.9SI

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

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 A 9 UNIA I I N NUMBER NUMBER

'Browns Ferry Unit 2 05000260 3 of 7 94 010 -- 01 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 0.0306 hours 1.818783e-4 weeks 4.1855e-5 months 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 0.617 hours 0.00367 weeks 8.4471e-4 months 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

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NRC FORM 866A U.S. NUCLEAR REGULATORY COMMISSION (4-95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACZLXTX MAME DOCKET LER NUMBER NUMBER NUMBER Browns Ferry Unit 2 05000260 4,of 7 94 010 01 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.

NRC FORM 366A (4 SS)

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TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 NTIA VIS I NUMBER NUMBER Browns Ferry Unit 05000260 6 of 7 2

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 removed and II capacitor banks were 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.

NRC FORM 366A <4-95)

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION I4-96)

LZCENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 NUMBER NUMBER Ferry Unit 05000260 7 of 7 Browns 2 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 LER (260/94001) was written as a result of an ATU have occurred.

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 commitment made in 260/94006 states that TVA will evaluate A

the ECCS ATU power distribution design to determine if are feasible. This evaluation is system reliability enhancements to ongoing and is scheduled 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)

ML18038B765

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