05000296/LER-1996-001-04, :on 960229,reactor Scrammed After APRM High Flux Scram Signal Because of Partial Closure of Turbine Control Valves Due to Faulty EHC Frequency/Voltage Converter Card.Main Turbine Manually Tripped & Faulty Card Replaced

:on 960229,reactor Scrammed After APRM High Flux Scram Signal Because of Partial Closure of Turbine Control Valves Due to Faulty EHC Frequency/Voltage Converter Card.Main Turbine Manually Tripped & Faulty Card Replaced

ML18038B658
Person / Time
Site:	Browns Ferry
Issue date:	03/26/1996
From:	Jay Wallace TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18038B657	List: 05000296/LER-1996-001-04, :on 960229,reactor Scrammed After APRM High Flux Scram Signal Because of Partial Closure of Turbine Control Valves Due to Faulty EHC Frequency/Voltage Converter Card.Main Turbine Manually Tripped & Faulty Card Replaced IR 05000296/1996001
References
LER-96-001-04, LER-96-1-4, NUDOCS 9604010335
Download: ML18038B658 (14)

LER-1996-001, on 960229,reactor Scrammed After APRM High Flux Scram Signal Because of Partial Closure of Turbine Control Valves Due to Faulty EHC Frequency/Voltage Converter Card.Main Turbine Manually Tripped & Faulty Card Replaced

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(x)
2961996001R04 - NRC Website

text

NRC FORM 366 (4-95)

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

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

APPROVED BY OMB NO. 31504104 EXPIRES 04/30/98 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS MANDATORYINFORMATIONCOLLECTION REQUEST:

50.0 HRS.

REPORTED LESSONS LEARNED ARE INCORPORATED INTO THE UCENSING PROCESS ANDFED BACK TO INDUSTRY. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATIONAND RECORDS MANAGEMENT BRANCH (TW F33),

U.S.

NUCLEAR REGULATORYCOMMISSION.WASHINGTON,DC 205554)001, FACIUTY NAMEII)

Browns Ferry Nuclear Plant (BFN) Unit 3 OOCKET NUMBER IS) 05000296 PAGE Is) 1 OF7 TITLE te)

The reactor scrammed after an APRM high flux scram signal occurred because of a partial closure of the turbine control valves due to a faulty EHC frequency/voltage converter card.

This scram resulted in ESF actuations.

'ONTH DAY YEAR EVENT DATE (5)

LER NUMBER 6)

SEQUENTIAL REVISION NUMBER NUMBER MONTH DAY YEAR REPORT DATE (7)

FACILITYNAME NA DOCKET NUMBER 05000 OTHER FACILITIES INVOLVED(8) 29 96 96

001

00 03 26 96 FACIU'TY NAME NA DOCKET NUMBER 05000 OPERATING MODE (9)

POWER LEVEL (10)

NAME N'9.9 or more)

(11) 20.2201(b) 20.2203(a)(1) 20.2203(a)(2)(i) 20.2203(a)(2)(ii) 20.2203(a)(2)(iii) 20.2203(a)(2)(iv) 20.2203(a)(2)(v) 20.2203(a)(3)(i) 20.2203(a)(3)(ii) 20.2203(a)(4) 50.36(c)(1) 50.36(c)(2)

LICENSEE CONTACT FOR THIS LER (12) 50.73(a)(2) (i) 50.73(a)(2)(ii) 50.73(a)(2)(iii)

)(

50.73(a)(2)(iv) 50.73(a)(2)(v) 50.73(a)(2)(vii) 50.73(a)(2)(viii) 50.73(a)(2)(x) 73.71 OTHER Iow Specrfy ln Abstract be or in NRC Form 366A TELEPHoNE NUMBER IrrKrude Ares code)

UANTTO THE REQUIREMENTS OF 10 CFR: (Check one THIS REPORT IS SUBMITTED FURS James E. Wallace, Compliance Engineer (205) 729-7874 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO NPRDS

CAUSE

SYSTEM COMPONENT MANUFACTURER TO NPRDS CNV G080 SUPPLEMENTAL REPORT EXPECTED (14)

YES (Ifyes, complete EXPECTED SUBMISSION DATE).

X NO EXPECTED SUBMISSION DATE (15)

MONTH DAY YEAR ABSTRACT (Limitto 1400 spaces, I.e., approximately 15 single-spaced typewritten lines) (16)

On February 29, 1996, at 0158 hours0.00183 days <br />0.0439 hours <br />2.612434e-4 weeks <br />6.0119e-5 months <br />, Browns Ferry Unit 3 was operating at 99.9 percent power and Unit 2 at approximately 94 percent power when the Unit 3 reactor scrammed after receiving a high APRM neutron flux signal.

The reactor scram followed a pressure transient when the output of the Electric Hydraulic Control (EHC) frequency/voltage converter (FVC) card associated with the speed control drifted to a setting that created a demand to ramp down the turbine control valves.

These conditions resulted in engineered safety feature (ESF) actuations.

Therefore, this event is reportable pursuant to 10 CFR 50.73(a)(2)(iv), as any event or condition that resulted in manual or automatic actuation of any ESF including the reactor protection system.

The cause of this event resulted from a faulty turbine speed control EHC FVC card.

The immediate corrective action was to bring the reactor to a stable condition. The faulty card was replaced.

TVA plans to send the faulty card to the vendor for further investigation.

Any additional corrective actions that are developed as a result of the vendor's investigation will be implemented in accordance with TVA's corrective action process.

There was a previous LER (260/94005) that resulted from an EHC system malfunction; however, corrective actions taken'in LER 260/94005 would not have precluded this event.

'T)604010335 960326 PDR ADOCK 05000296 8

PDR 6

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

TEXT CONTINUATION FACXLZTY NAhK 1)

Browns Ferry Unit 3 DOCKET 05000296 NUMBER NUMBER PAGE 3 of 7 96 001 00 TEXT more space is requir

~ use ad inona copies o orm (17)

At 0159 hours0.00184 days <br />0.0442 hours <br />2.628968e-4 weeks <br />6.04995e-5 months <br />, the main turbine [TA) was manually tripped by the Unit Operator (utility, licensed).

At 0208 hours0.00241 days <br />0.0578 hours <br />3.439153e-4 weeks <br />7.9144e-5 months <br />, Unit 3 was stabilized in accordance with 3-AOI-100-1, "Reactor Scram,"

and the affected systems were returned to standby readiness.

All systems responded as expected during the scram.

B.

The event is reportable pursuant to 10 CFR 50.73(a)(2)(iv) as a

condition that resulted in the manual or automatic actuations of any Engineered Safety Feature (ESF) including the reactor protection system (RPS).

Ino erab1e Structures, Co

onents, or S stems that Contributed to the Event:

c.

The faulty turbine speed control EHC FVC cazd (model number 115D3332 Gl) was manufactured by General Electric Company.

Dates and A roximate Times of Ma'or Occurrences:

February 29, 1996 at 0158 CST The Unit 3 reactor control rods inserted based on an RPS actuation (high APRM neutron flux)

February 29, 1996 at 0159 CST February 29, 1996 at 0208 CST The main turbine was tripped manually.

The PCIS actuations were reset.

SGT and CREV systems are returned to standby readiness.

February 29, 1996 at 0425 CST TVA made a 4-hour nonemergency notification to NRC in accordance with 10 CFR 50.72 (b) (2) (ii).

D.

E.

Other S stems or Seconda Functions Affected:

None.

.Method of Discove The Unit 3 Control Room Operator [utility, licensed]

received a

high APRM neutron flux alarm.

This alarm was followed by additional alarms associated with a full-power reactor scram.

~I(4-95)

U.S. NUCLEAR REGULATORY COMMISSION

'LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION PACZLZTY NAME Z

Browns Ferry Unit 3 DOCKET 05000296 LER NUMBER NUMBER NUMBER PAGE

(

)

4 of 7 96 --

001 00 TEXT (

more space is requir

~ use a iuona copies o orm I17) erator Actions:

Operator actions

taken during this event were as expected.

PCIS

groups, SGT system, and CREV system were verified to have performed as expected.

The Unit 3 scram was reset.

The Unit 3 Operator initiated abnormal operations instruction (3-AOI-100-1) to ensure that the affected systems were brought to standby readiness.

G.

Safet S stem Res onses:

None.

ZZZ.

CAUSE OF THE EVENT

A.

Zmmediate

Cause

The immediate cause of this event was the partial closure of the Unit 3 turbine control valves that caused an increase of reactor pressure and resulted in an automatic scram after a high reactor flux alarm was received.

B.

Root Cause:

This, event resulted from an unexpected and random equipment failure, specifically, a faulty turbine speed control EHC FVC card.

The faulty card simulated a turbine overspeed condition and created a demand signal to ramp down the turbine control valves (from 54 percent open to 25 percent open) and to open the bypass valves (reducing the impact of the control valves closing).

Some bypass valves cycled as the turbine control valves ramped down.

However, the reactor pressure continued to

increase, and a high APRM neutron flux condition was sensed.

ZV.

ANALYSZS OF THE EVENT The throttling (closure to the 25 percent position) of the turbine control valves is similar but less severe than a previously analyzed

event, Generator Load Rejection Without Bypass (GLRWB).

In the BFN Unit 3 Cycle 7 Supplemental Reload Licensing Report, fast closure of the main turbine control valves is analyzed assuming that the Bypass valves fail to open, resulting in a pressure transient.

During this LER event, the reactor experienced an increase of less than 30 psig in about.4 seconds.

In the GLRWB event, the reactor vessel pressure increases by more than 150 psig in about 2 seconds.

Therefore, this LER event is clearly bounded by the previous analysis, and the Safety Limit MCPR was not challenged.(4-95)

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

TEXT CONTINUATION PACZLZTY NAME 3)

Browns Ferry Unit 3 DOCKET 05000296 LER NUMBER NUMBER NUMBER PAGE 5of7 96 001 00 TEXT (I more space is requir, use a diuona copies o orm (11)

CORRECTZVE ACTIONS A.

Zmmediate Corrective Actions:

Immediate corrective action

was to manually trip the main turbine and to bring the reactor to a stable condition in accordance with site procedure 3-AOI-100-1.

B.

Corrective Actions to Prevent Recurrence:

During the troubleshooting of the EHC circuitry, it was revealed that a faulty FVC card associated with the turbine speed control circuitry was malfunctioning.

The faulty card was replaced and the replacement card was successfully tested.

TVA plans to send the faulty card to the vendor to perform a failure analysis of the EHC FVC card.

Any additional corrective act'ions that are taken as a result of the vendor's investigation will be incorporated in BFN's corrective action program (BFPER960169).'Z.

ADDZTZONAL ZNFORMATZON A.

Failed Co onents:

The faulty turbine speed control EHC FVC card (model number 115D3332 Gl) was manufactured by General Electric Company.

Previous LERs on Similar Events:

One previous LER (260/94005) resulted from an EHC system malfunction.

This previous LER's root cause was a failed EHC pressure regulator setpoint potentiometer.

However, in this LER (296/96001) the failed component was not a regulating potentiometer in the pressure control circuitry.

Therefore, no

corrective actions

taken in the previous LER would have precluded this. event.

'hese additional corrective actions are considered as enhancements and are not commitments.(4-95)

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

TEXT CONTINUATION PACZLZTX NAME Z

Browns Ferry Unit 3 DOCKET" 05000296 LER NUMBER NUMBER NUMBER PAGE 6 of 7 96 --

001 00 TEXT more space is requir, use a iuoira copies o orm (17)

VZZ.

COMMZTMENTS None.

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

fXX]).

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