ML18036A451

LER 91-018-00:on 911018,reactor Manually Scrammed from Approx 8% Thermal Power Due to Expected Equipment Response. Caused by Inappropriate Personnel Action.Reverse Power Relay Tested & Plant Design Will Be changed.W/911115 Ltr

ML18036A451
Person / Time
Site:	Browns Ferry
Issue date:	11/15/1991
From:	Austin S, Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-018-01, LER-91-18-1, NUDOCS 9111250170
Download: ML18036A451 (18)

Text

ACCELERATED DISTRIBUTION DEMONSTtMTION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9111250170 DOC.DATE: 91/11/15 NOTARIZED: NO DOCKET FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH. NAME AUTHOR AFFILIATION AUSTIN,S.W. Tennessee Valley Authority ZERINGUE,O.J. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 91-018-00:on 911018,reactor manually scrammed from approx 8> thermal power due to expected equipment response. D Caused by inappropriate personnel action. Reverse power relay tested & plant design will be changed.W/911115 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ( ENCL 1 SIZE:

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

NOTES'.

RECIPIENT COPIES RECIPIENT COPIES D .

ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL SANDERS,M. 1 1 HEBDON,F 1 1 D ROSS,T. 1 1 INTERNAL: ACNW 2 -.2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DS P/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB 7E 1 1 NRR/DLPQ/LHFB10 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB 8D 1 1 NRR/DST/SICB8H3 1 1 NR~RJ3ST/ LB8D1 1 1 NRR/DST/SRXB 8E 1 1 REG EI~" 02 1 1 RES/DSIR/EIB 1 1 RGN2 FILE OI 1 1 EXTERNAL: EGGG BRYCE,J.H 3 3 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC POORE,W. 1 1 NUDOCS FULL TXT 1 1 R D

D NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE O'ASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUiilENTS YOU DON'T NEED!

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Tennessee Valtey Authority. Post Otfice Box 2000. Decatur,'Alabama 35609-0; J. 'Ike'eringue Vice President. Browns Ferry Operations NOV 16 1991.

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

Dear Sir:

TVA BROWNS FERRY NUCLEAR PLANT (BFN) UNIT 2 DOCKET NO. 50-260 FACILITY OPERATING LICENSE DPR-52 LICENSEE EVENT REPORT LER-50-260/91018 The enclosed report provides details concerning a manual reactor scram due to unexpected equipment responses following a failure to open the generator exciter field breaker after a manual turbine trip. This report is submitted in accordance with 10 CFR 50.73(a)(2)(i) and 10 CFR 50.73(a)(2)(iv).

Sincerely, Enclosure cc: see page 2 9l112:o170 F'PR 91ilib AOOCK 05t)00" bv PDr;

I 4~ ii

2 U.S. Nuclear Regulatory Commission Nv 15 18gl cc (Enclosure):.

INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, Georgia 30339 NRC Resident Inspector, BFN Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323 Thierry M. Ross U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852

4~ li NRC Form 366 .. NUCLEAR REGULATORY COtRISSION Approved OHB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

FACILITY NAHE (1) (DOCKET NUMBER (2)

TITLE (4) Failure to Open the Generator Exciter Field Breaker I SEQUENTIAL (REVISION( ( (, ( FACILITY NAHES (DOCKET NUHBER(S)

I I I I I I I ( I 11 159 1 OPERATING I ITHIS REPORT IS SUBMITTED PURSUANT To THE REQUIREHENTS OF 10 CFR 5:

NODE I I (ZO.4OZ(b) (ZO.4OS(c) Iz (50.73(a)(2)(iv) (73.71(b)

POWER I (20.405(a)(1)(i) (50.36(c)( 1) (50.73(a)(2)(v) (73.71(c),

LEVEL I (20.405(a)(l)(ii) (50.36(c)(2) (50.73(a)(2)(vii) (OTHER (Specify in (20.405(a)( 1)(iii) (~(50.73(a)(2)(i) (50.73(a)(2)(viii)(A) Abstract below and in

( (20.405(a)(1)(iv) ( (50.73(a)(2)(ii) (50.73(a)(2)(viii)(B) Text, NRC Form 366A)

NAHE

( AREA CODE I I IREPORTABLEI I I I IREPORTABLEI I SUBHISSION I ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

On October 18, 1991 at 0458 hours0.0053 days <br />0.127 hours <br />7.572751e-4 weeks <br />1.74269e-4 months <br />, during a controlled shutdown, Browns Ferry Unit 2 reactor was manually scrammed from approximately eight percent thermal power due to unexpected equipment responses.

The root- cause of this event was inappropriate personnel action. A plant operator failed to follow the procedure for turbine generator shutdown when he did not open the exciter field breaker after the manual turbine generator trip. This action caused unexpected equipment responses including actuation of the generator reverse power relay and subsequent tripping of the reactor recirculation pumps.

The reverse power relay was tested. The evaluation and testing of the recirculation pump boards was completed. 'Operations personnel will receive live-'time training on the event. TVA will change the plant design to include automatic tripping of the generator field breaker when the turbine generator is tripped. The Browns Ferry simulator willbe upgraded to match plant conditions.

NRC Form 366(6-89)

4>

~'

NRC Form 366A (6-89)

U UCLEAR REGULATORY COHHISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION t Approved OHB No. 3150-0104 Expires 4/30/92 FACILITY NAHE (1) (OOCKET NUHBER (2)

I I I I SEQUENTIAL I I REVISION I I I I I Browns Ferry Unit 2 I I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

I PLANT CONDITIONS Unit 2 was undergoing a controlled shutdown and was at approximately eight percent power (Power Operations). Units 1 and 3 were shutdown and defueled.

II. DESCRIPTION OF EVENT A. gvVt:

On October 18, 1991 at 0458 hours0.0053 days <br />0.127 hours <br />7.572751e-4 weeks <br />1.74269e-4 months <br />, during a controlled shutdown, Browns Ferry Unit 2 was manually scrammed from approximately eight percent thermal power due to unexpected equipment responses.

On October 17, 1991 at approximately 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br />, TVA initiated a controlled shutdown on Unit 2. On October 18, 1991 at 0447 hours0.00517 days <br />0.124 hours <br />7.390873e-4 weeks <br />1.700835e-4 months <br />, due to high vibration, the 'main turbine [TA] was tripped and the generator power circuit breaker opened. However, the generator exciter field breaker was not opened as required by plant procedures.

On October 18, 1991 at 0456 hours0.00528 days <br />0.127 hours <br />7.539683e-4 weeks <br />1.73508e-4 months <br />, a generator reverse power abnormal alarm was received and 12 seconds later a second reverse power abnormal alarm was received. Subsequently, 19 seconds later the reverse power relay actuated causing breakers feeding unit service transformers 2A and 2B [FK] to open. Upon loss of power from the unit service transformers, all required electrical boards with exception of the 2A and'B recirculation system pump boards automatically transferred to their alternate supply resulting in a trip of the reactor recirculation [AD]

system pumps.

At 0458 hours0.0053 days <br />0.127 hours <br />7.572751e-4 weeks <br />1.74269e-4 months <br />, with the mode switch in the run position, the unit operator (utility, licensed) [UO] initiated a manual scram of the reactor.

As a result of the manual scram, TVA reports this event in accordance with 10 CFR 50.73(a)(2)(iv) as an event or condition that resulted in manual or automatic actuation of any engineered safety feature (ESF), including the reactor protection system. The loss of the reactor recirculation pumps with the mode switch in the "RUN" position is reportable in accordance with 10 CFR 50.73(a)(2)(i)(A) as the completion of any nuclear plant shutdown required by the plant's technical specifications.

B. n r bl t ct ts r t t t t i t t th None.

NRC Form 366(6-89)

li NRC Form 366A (6-89)- t NUCLEAR REGULATORY COHHISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION Approved OHB No. 3150-0104 Expires 4/30/92 FACILITY NAHE '(1) IDOCKET NUHBER (2)

'I I I I I SEQUENTIAL I I REVI S ION I I I I Browns Ferry Unit 2 I I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

C.

October 18, 1991 at 0447 CST'hetripped main turbine and was manually generator power circuit breaker verified open.

October 18, 1991 at 0456 CST Main control room received reverse power abnormal alarms and subsequent opening of the breakers feeding service transformers. The 4kV reactor recirculation pump boards fail to transfer and reactor recirculation pumps trip.

October 18, 1991 at 0458 CST UO initiated a manual scram of the

'reactor.

October 18, 1991 at 0530 CST The SOS initiated a notification of Unusual Event as required by 10 CFR 50.72(a)(3) and cited the emergency classification as "HU14" (conditions exist warranting increased awareness of plant-operating staff, state or local government, or involve other than a controlled shutdown).

I) t t A t Reactor recirculation pump boards 2A .and 2B'id not auto transfer during the event. This resulted in recirculation pumps 2A and 2B tripping.

E. t The event was immediately known to the control room operator upon receiving alarms indicating generator reverse power abnormal and tripping of the reactor recirculation pumps.

F.

Operators initiated actions to restart the reactor recirculation pumps; however,. due to an influx of water into the bottom of the vessel after the scram, a temperature differential exceeding plant administrative limits for recirculation pump operation had for'med between the vessel dome and bottom head. In order to eliminate this problem, natural circulation was

,established. After the temperature differential between the vessel dome and bottom dra'in was brought within an acceptable range, the reactor recirculation pumps were started.

NRC Form 366(6-89)

4i NR'C Form 366A (6-89) 1 NUCLEAR REGULATORY COHHISSION.

LICENSEE EVENT REPORT (LER)

Approved lj OHB No ~

Expires 4/30/92 3150-0104 TEXT CONTINUATION FACILITY NAHE (1)

I I I I SE(lUENTIAL I I REVI SION I I I I I Browns Ferry Uni t 2 I I I I I 4

TEXT (If more space is required, use additional NRC Form 366A's) (17)

G None.

III CAUSE OF THE EVENT The immediate cause of this event was failure of the operator to open the generator exciter field breaker after the manual turbine trip.

R~tm~=

The root cause of this event was inappropriate personnel action in that the operator (utility, licensed)'ailed to follow the procedure for turbine generator shutdown when he did not open the exciter field breaker after the manual turbine generator trip. This action caused unexpected equipment responses including the actuation of the reverse power relay and subsequent tripping of the -reactor recirculation pumps.

C. t t

l. Inadequate design which requires operator actions to manually trip the field breaker after a turbine trip.

2. Inadequate training. During simulator training the consequences of not tripping the field breaker after a turbine trip are not identified during manual turbine trip simulation."

IV. ANALYSIS 'OF THE EVENT A.

The reverse power relay protects the main turbine and generator should steam to the turbine be lost and the generator output breaker remain closed. The relay initiates a trip breaker to separate the turbo-generator from the switchyard- During the event, the generator output breaker and main turbine were tripped without tripping the

,generator field breaker. Therefore, as the turbo-generator coasted down, the generator continued to produce a voltage at a declining frequency.

This resulted in the inadvertent actuation of the reverse power relay.

NRC Form 366(6-89)

i)

NPC Form 366A (6-89) t . NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION Approved'HB No. 3150-0104 Expires 4/30/92 FACILITY NAME (1) ]OOCKET NUMBER (2)

I I iSEgUENTIAL i iREVISIONi J )

Browns Ferry Unit 2 I Y I-I I I TEXT (If more space is required, use additional NRC Form 366A's) (17),

The reactor recirculation pumps are not required for safe shutdown of the plant and loss of the pumps at low power level is an analyzed condition.

The manual scram of the reactor following the loss of the reactor recirculation pumps was a requirement of plant technical specifications.

All safety-related plant components operated as expected during the trip.

The safety of the plant, its personnel, and the public was not compromised.

V. CORRECTIVE ACTIONS A.

1. The reverse power relay was tested with no'eficiencies identified.

2. Testing of the reactor recirculation pump boards was performed. The results of. the testing could not identify a cause for boards to failure to transfer during the event. Maintenance history on these boards has not indicated any adverse trends in performance. TVA will continue to monitor equipment performed'hrough the Preventative Maintenance Program.

3. Operations personnel responsible for the plant restart were trained on the event.

B. r tv At t v t

l. Operations personnel will receive live-time training on the event.

2. TVA will change the plant design to include automatic tripping of the exciter field breaker when the turbine-generator is tripped.

3. Simulation of the exciter field breaker operation on the Browns Ferry simulator. will be reviewed. The simulator will be revised to match plant conditions.

VI. ADDITIONAI INFORMATION A. 1 t None.

NRC Form 366(6-89)

<5 II:

NRC Form 366A (6-89) t NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION Approved OMB No. 3150-0104

'Expires 4/30/92 FACILITY-NAME (1) iDOCKET NUMBER (2)

I (SE()UENTIAL f /REVISION/

Browns Ferry Unit 2 I Y I I I l TEXT (If more space is required, use additional NRC Form 366A's) (17)

B.

'None.

VII.

1. Operations personnel will receive live-time training on the event. This will be completed by January 17, 1992.

2. TVA will change the plant to include automatic tripping of the exciter field breaker when the turbine-generator is tripped. This will be completed prior to restart following the Unit 2 Cycle 6 refueling outage.

3. Simulation of the exciter field breaker operation on the Browns Ferry simulator will be reviewed. The simulator will be revised to match plant conditions. This will be completed by January 17, 1992.

Energy Industry Identification System (EIIS) codes are identified in the text as [ZZ].

NRC Form 366(6-89)

I IQ 10 4.

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