ML18039A801

LER 99-001-00:on 990515,automatic Reactor Scram Occurred Due to Tt.Caused by Failure of Mechanical Trip Cylinder to Latch When Hydraulically Reset.Operations Crew Stabilized Reactor Following Scram.With 990614 Ltr

ML18039A801
Person / Time
Site:	Browns Ferry
Issue date:	06/14/1999
From:	Rogers A, Singer K TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-99-001-05, LER-99-1-5, NUDOCS 9906210061
Download: ML18039A801 (16)

Text

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~ CATEGORY REGULATORY INFORMATION DISTRIBUTION SYSTEM ly (RIDS)'CCESSION NBR:9906210061. DOC.DATE: 99/06/14 NOTARIZED: NO DOCKET .5 FACIL:50-2'60,Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH. NAME. AUTHOR'FFILIATION ROGERS,A.T.. Tennessee,'Valley Authority SINGER,K.W. . Tennessee Valley Authority RECXP.NAME RECZP1ENT AFF1LIATION

SUBJECT:

.LER 99-001-00':on '990515,automatic reactor scram due to turbine trip was noted. Caused by failure of mechanical trip cylinder to latch when .hydraul'ically reset. Operations crew stabilized reactor following scram. With 990614 ltr.

DISTRIBUTION:CODE: IE22T COPIES RECEIVED:LTR ENCL ,SIZE:

TITLE: 50,.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

NOTES:

RECZPZENT COPIES RECIPIENT'D COPIES

.ID CODE/NAME LTTR ENCL CODE/NAME LTTR ENCL LPD2-2 PD 1 1 DEAGAZIO,A 1 1 INTERNAL: ACRS 1 1 AEOD/S PD/RRAB 1 1 FILE CENTER 1 1 NRR/DIPM/IOLB 1 .1 NRR DIPM IQMB 1 1 NRR/DRIP/REXB 1 1 NRR/DSSA/SPLB 1 1 RES/DET/EIB 1 1 RGN2'ILE 01 1 1 EXTERNAL': L ST LOBBY WARD 1 1 LMITCO MARSHALL 1 1 NOAC POORE,W. 1 1 NOAC QUEENER,DS 1 1

,NRC PDR .1 1 NUDOCS FULL TXT 1 1 NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE. TO HAVE YOUR NAME OR ORGANIZATION REMOVED FROM. DISTRIBUTION LIS OR REDUCE'THE NUMBER OF COPIES RECEIVED BY YOU OR YOUR ORGANIZATION, CONTACT THE DOCUMENT CONTR DESK (DCD) ON EXTENSION 415-2083 FUL'L TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 17 ENCL 17

i+i 0 Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 Karl W. Singer Vice President, Browns Ferry Nucfear Plant June 14, 1999 U. S. Nuclear Regulatory Commission 10 CFR 50. 73 ATTN: Document Control Desk Washington, D. C. 20555 Gentlemen:

In the Matter of ) Docket No. 50-260 Tennessee Valley Authority )

BROWNS FERRY NUCLEAR PLANT (BFN) UNIT 2 DOCKET NO. 50-260 FACILITY OPERATING LICENSE DPR-52 LICENSEE EVENT REPORT (LER) 50-260/1999001 The enclosed report provid'es details concerning an automatic reactor scram on Unit 2 from 100 percent power that resulted from a turbine trip during routine testing. All plant safety systems operated as designed in response to this event. This report is submitted in accordance with 10 CFR 50.73 (a)(2)(iv) as an event that resulted in an automatic actuation of'n engineered safety feature, including the reactor protection

.system.

Sincerely, Karl W. Sin cc: See page 2 99062i 0061 9'tl0614 PDR .ADQCK 05000260 S PDR

ii 15 U.S. Nuclear Regulatory Commission Page 2 June 14, 1999 Enclosure cc (Enclosure):

Mr. William 0. Long, Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. Paul E. Frederickson, Branch Chief U. S. Nuclear Regulatory Commission Region ZI 61 Forsyth Street, S.. W.

Suite 23T85 Atlanta, Georgia 30303 NRC Resident Xnspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, Alabama 35611

101 0 iJ

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104

{4-96) EXPIRES 04/30/98 ESTIMATED BURDEN PER RESPONSE To COMPLY WITH THIS MANDATORY INFORMATION COLLECTION REQUEST( 80.0 HRS. REPORTED LESSONS LICENSEE EVENT REPORT (LER) LEARNED ARE INCORPORATED INTO THE UCENSING PROCESS AND FED BACK To INDUSTRY. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (T.e F33), U.S.

(See reverse for required number of NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20688<00(, AND TO THE PAPERWORK REDUCTION PROJECT (3(60%(04), OFFICE OF digits/characters for each block) MANAGEMENTAND BUDGET, WASHINGTON, DC 20803.

FACIUTY NAME (1I DOCKET NUMBER (2l PAGENE (3)

Browns Ferry Unit 2 05000260 1OF5 Automatic reactor scram due to a:turbine trip EVENT DATE {5) LER NUMBER {6) REPORT'ATE (7) OTHER FACILITIES INVOLVED IS)

'ONTH DAY YEAR SEQUENTIAL REVISION MONTH DAY YEAR FACIUTY NAME DOCKETNVMBER NUMBER NUMBER NA FACIUTY NAME DOCKET NUMBER 05 15 1999 1999 001 00 06 14 1999 NA OPERATING THIS REPORT IS SUBMITTED PURSUA NT To THE REQUIREMENTS OF 10 CFR II: (Check one or moro)

MODE {9) 20. 2201 (b) 20.2203(a) (2)(v) 50.73(a)(2)(i) 50.73(a) (2) (viii)

PQWER 20. 2203(a) (1 ) 20.2203(a) (3)(i) 50.73(a)(2)(ii) 50.73(a) (2) {x)

LEVEL {10) 100 20.2203(a) (2) (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) (iv) OTHER 20.2203(a) (2) (iii) 50.36(c) (1) 50.73(a) (2) (v) Specify in Abstract below 20.2203(a) {2)(iv) 50.36(c)(2) 50.73(a) (2) (vii) or in NRC Form 366A LICENSEE CONTACT'FOR THIS LER (12)

NAME TELEPHONE NUMBER (include Area Code(

A. T. Rogers, Senior Licensing Project Manager (256) 729-2977 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT {13)

CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE To CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE NPRDS TO NPRDS SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED . MONTH OAY YEAR YES No SUBMISSION (If yes, complete EXPECTED SUBMISSION DATE). X DATE {15)

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

On May 15, 1999, at 1456 CDT, Unit 2 received an automatic scram from 100 percent reactor power due to a turbine trip that occurred during routine turbine overspeed testing. The reactor scram caused reactor water level to go below the low level setpoint (level 3) which generated a redundant scram signal and initiated the Primary Containment Isolation System, as expected.. The low reactor water level signal also initiated the Standby Gas Treatment and Control Room Emergency Ventilation Systems. All systems responded as expected and.all control rods fully inserted.

The cause was of the turbine trip was failure of the mechanical trip cylinder to latch when hydraulically reset.

TVA is reporting this event in accordance with 10 CFR 50.73 (a)(2)(iv) as an event that resulted in an automatic actuation of an engineered safety feature, including the reactor protection system.

NRC FORM 366 (4-95)

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION I4-95)

LICENSEE, EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 YEAR 'EQUENTIAL REVISION NUMBER'999 2OF5 Browns Ferry Unit 2 05000260 001 00 TEXT (If more space is required, use addi donal copies of NRC Form 366Ai' 17)

I. PLANT CONDITIONS At the time of the event, Unit 2 and Unit-3 were at 100 percent power. Unit 1 was shutdown and defueled.

II. DESCRIPTION OF EVENT A. Event:

On May 15, 1999, at 1456 CDT, Unit 2 received an automatic scram from 100 percent reactor power due to a turbine trip that occurred during routine overspeed testing: The reactor scram caused reactor water level to go below the low level setpoint (level 3) which generated a redundant scram signal and initiated the Primary Containment Isolation System (PCIS), as expected. The low reactor water level signal also initiated the Standby Gas Treatment (SGT) [BH] and Control Room Emergency Ventilation (CREV) [VI]

Systems. Ail systems responded as expected and all control rods fully inserted. At 1528 CDT, Operations reset the scram and PCIS isolations.and secured SGT and CREV.

The scram resulted in the expected automatic actuation or isolation of the following PCIS [JE] systems and components:

~ PCIS group 2, Shutdown cooling mode of Residual Heat Removal (RHR) [BO] system; drywell floor drain isolation valves; drywell equipment drain isolation valves [WP].

~ PCIS group 3, Reactor Water Cleanup (RWCU) system [CE].

~ PCIS group 6, primary containment purge and ventilation [JM], Unit 2 reactor zone ventilation [VB];

refuel zone ventilation [VA]; Standby Gas Treatment system; Control Room Emergency Ventilation system.

~ PCIS group 8, Traversing Incore Probe (TIP) [IG].

This event is. reportable in accordance with 10 CFR 50.73 (a)(2)(iv), as an event that resulted in an automatic actuation of an engineered safety feature, including the reactor protection system.

B. Ino erable Structures Com onents or S stems that Contributed to the Event:

None.

C. Dates and A roximate Times of Ma or Occurrences:

May 15, 1999, at 1456 hours0.0169 days <br />0.404 hours <br />0.00241 weeks <br />5.54008e-4 months <br /> CDT Operations received a turbine trip and reactor scram while performing routine turbine overspeed testing.

May 15, 1999, at 1528 hours0.0177 days <br />0.424 hours <br />0.00253 weeks <br />5.81404e-4 months <br /> CDT Operations reset the scram and PCIS isolations and secured SGT and CREV.

May 15, 1999, at 1825 hours0.0211 days <br />0.507 hours <br />0.00302 weeks <br />6.944125e-4 months <br /> CDT A four-hour non-emergency report is made to the NRC pursuant to 10 CFR 50.72 (b) (2) (ii).

NRc FQRM 366 (4-96I

ii i~I

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION i4-95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1) DOCKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISION NUMBER 3OF5 Browns Ferry Unit 2 05000260 1999 001 00 TEXT fffmore space is required, use additiortal copies of PVRC Form 386A/ I17)

D. Other S stems or Seconda Functions Affected:

None.

E. Method of Discove Operators received alarms and indications of the turbine trip and subsequent reactor scram.

F. 0 erator Actions:

Operations personnel responded to the event in accordance with applicable plant procedures.

G. Safet 'S stem Res onse:

All required safety systems operated as designed.

III. CAUSE OF THE EVENT A. Immediate Cause:

The immediate cause of this event.was a turbine trip while performing routine overspeed,testing.

B. Root Cause:

The cause of the of the turbine trip was systematically evaluated to determine the cause of the failure. All possible causes were evaluated using a failure modes and effects analysis and all but one failure cause was eliminated. As a result of this evaluation, the most probable cause was determined to be failure of

'he mechanical trip mechanism to relatch. The latching mechanism was inspected to the extent possible prior to restart and tested repeatedly without failure.

C. Contributin Factors:

None IV. ANALYSIS OF THE EVENT The scram was the result of a turbine trip and was initiated by the closure of the Main Steam Turbine Stop/Control Valves which occurred during routine overspeed testing. The overspeed test is a routine functional test of the overspeed trip device and the mechanical trip valve. The test does not actually overspeed'the turbine and is performed while the turbine is at rated speed and should not cause an actual turbine trip. However, the turbine tripped and resulted in closure of the turbine valves and a pressure transient within the Main Steam piping. The transient was mitigated by the automatic opening of nine Main Steam Turbine Bypass Valves and five Main Steam Safety Relief Valves. Equipment performance data was collected from the Plant Engineering Display System and from the Transient Recorder Analysis feature of the Integrated. Computer System. This data was analyzed and reviewed for appropriate equipment response.

NRC FORM 366 I4-95)

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

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISION NUMBER 4OF5 Browns Ferry Unit 2 05000260 1999 001 00 TEXT (If more space is required, use additional copies of NRC Form 366A/ I 17)

IV. ANALYSIS OF THE EVENT (continued)

Each possible failure mode which could have caused the turbine trip has been evaluated. Through personnel interviews, extensive troubleshooting, and physical inspections, the cause of the turbine trip has been determined to be failure of the trip cylinder to latch when hydraulically reset. All other potential causes, including improper procedure performance, low Electro-Hydraulic Control Nitrogen accumulator pressure,, a stuck relay contact, solenoid valve failure, throw-out disk sticking, improper linkage tolerances, and incorrect mechanical trip valve settings were systematically evaluated during the investigation. An evaluation of the trip cylinder. revealed that if it was hydraulically returned to the reset position, but not mechanically latched, the turbine would trip when the reset was released and the lockout dropped out which appears to be what happened to initiate this event. The trip cylinder is mechanically latched by resting on a 125 mil landing on the trip arm. A failure of this type would not necessarily be repeatable, which accounts for the fact that troubleshooting activities tripped and reset the turbine numerous times with no failures noted. Therefore, based. upon the'intermittent nature of this. failure m'echanism and the elimination of the other possible causes as delineated above, this failure mode is considered the most likely cause of the event. Preliminary discussions with. the vendor indicate the possible need for a PM to inspect the overspeed trip mechanism on a routine basis.

V. ASSESSMENT OF SAFETY CONSEQUENCES The evaluation of plant system and component responses to the event concluded that responses were as designed and within the time-frames expected. Personnel performance was also evaluated and found to be timely, appropriate, and met expectations for performance during an event of this type.

The overspeed test is a functional test of the overspeed trip device and mechanical trip valve. The test does not actually cause the turbine to overspeed but exercises the trip linkage and mechanical trip valve by simulating an overspeed condition. Therefore, there was no actual malfunction of the turbine control system.

There were no equipment failures during or following the scram that complicated recovery. In addition, there were,no radioactive material released and no actual or potential safety consequences as a result of this event.

Therefore, this event did not adversely affect the safety of plant personnel or the public.

VI. CORRECTIVE ACTIONS A. Immediate Corrective Actions:

The Operations crew stabilized the reactor following the scram using the appropriate operating instructions.

NRc FDRM 366 I4-95)

Oi 0 II Qr

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (4-9SI LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION NAME 1 DOCKET LER NUIVIBER 6 PAGE 3 2'ACILITY YEAR SEQUENTIAL REVISION NUMBER 5OF5 Browns Ferry Unit 05000260 1999 001 00 TEXT (If more space is required, use additional copies of IVRC Form 366AJ (17)

B. Corrective Action to Prevent Recurrence:

Work orders were issued to perform an inspection of the mechanical trip mechanism during the next available refueling outage on Unit 2 and Unit 3.

and Engineering will determine if a periodic inspection of the trip latch mechanism

'aintenance is appropriate.

testing methods will be reviewed to determine if alternate techniques are available to reduce or

'xisting eliminate the risk of turbine trip.

'II.

ADDITIONALINFORMATION A. Failed Com onents:

None.

B. Previous Similar Events:

None.

C, Additional Information:

None.

D. Safet S stem Functional Failure:

This event did not result in a safety system functional failure in accordance with NEI 99-02.

Vill. COMMITMENTS None.

TVA does not consider this corrective action a regulatory commitment. The completion of this item will be tracked'in TVA's Corrective Action Program.

NRC FORM 366 (4-95)

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