ML16217A398

LER 16-004-00 for Watts Bar, Unit 2, Regarding Reactor Trip and Safety Injection Actuation Caused by Turbine Governor Valve Failure

ML16217A398
Person / Time
Site:	Watts Bar
Issue date:	08/04/2016
From:	Simmons P Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 16-004-00
Download: ML16217A398 (7)

Text

Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 August 4, 2016 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C 20555-0001

Subject:

10 cFR 50 73 Watts Bar Nuclear Plant, Unit 2 Facility Operating License No. NPF-96 NRC Docket No.50-391 Licensee Event Report 391/2016-004-00, Reactor Trip and Safety lnjection Actuation Caused by Turbine Governor Valve Failure This submittal provides Licensee Event Report (LER) 39112016-004-00.

This LER provides details concerning a recent reactor trip with safety injection as a result of a turbine governor valve failure. This report is being submitted in accordance with 1 0 cFR 50.73(a)(2)(ivXA).

Please direct any questions concerning this matter to Gordon Arent, WBN Licensing Director, at (423) 365-2004.Paul Simmons Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Pag e 2 Respectfully, U.S. Nuclear Regulatory Commission Page 2 August 4, 2016 cc (Enclosure):

NRC Regional Administrator - Region ll NRC Senior Resident lnspector - Watts Bar Nuclear Plant NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION

{11-2015)$tto*"t'o" iw;e-:Y.c LTcENSEE EVENT REPoRT (LER)-r a*rl APPROVED BY OMB: NO. 3150-0104 EXPIRES: t0/31/2018 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />, Reported lessons learned are incorporated into the licensing process and fed back to industry, Send comments regarding burden estimate to the FOIA, Privacy and lnformation Collections Branch (T-5 F53), U,S, Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to lnfocollects.Resource@nrc,gov, and to the Desk Officer, Office of lnformation and Regulatory Affairs, NE0B-10202, (3150-0104), ffice of Management and Budget, Washington, DC 20503 lf a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection, 1. FACILITY NAME Watts Bar Nuclear Plant, Unit 2 2, DOCKET NUMBER 0500039 1 3. PAGE 10F5 4. TITLE Reactor Trip and Safety lnjection Actuation Caused by Turbine Governor Valve Failure 5. EVENT DATE 6. LER NUMBER 7. REPORT DATE 8. OTHER FACILITIES INVOLVED MONTHI DAY I YEAR YEAR I 'i,Hrut$REV NO, MONTH I DAY YEAR FACTLTTY NAME I DOCKET NUMBER N/A lN/A 06 05 I 2016 2016 -004 -00 08 a4 2016 FACILITY NAME I DOCKET NUMBER N/A IN/A 9. OPERATING MODE IT.THISREPORTISSUBMITTEDPURSUANTTOTHEREQUlREMENTSOFl0CFR$: (Checkallthatapply) 1 n zo.z2o1(b) tr zo.2zo3(aX3Xi) tl 50 73(aX2Xii)(A) tr 50 73(a)(2Xv.iiXA) n 20 2zo1(d)n 2o.2zo3(aX3Xii) n so 73(aX2XiiXB) n 50 73(aX2XviiiXB) n 2o.z2o3(a)(1) n 20.2203(aX4) n 50.73(a)(2)(iii) tr 50 73(ax2X.x)(A) n 2o.22os(aX2)(i) tl 50,36(cxl xixA)X 50.73(ax2xivxA) n 50.73(ax2)(x) 10, POWER LEVEL 12.5 t] 20.z2o3(aX2Xii) n 50,36(c)(1Xii)(A) tl 50.73(a)(2xv)(A) tl nl1 (aX4)n 20.2203(aX2Xii.)

n 50 36(cX2)n 50.73(aX2XvXB) tl rc r1(aX5)n zo.22o3(aX2Xiv) n 50 46(ax3xii) n 50.73(aX2XvXc) n rc.tr(a'lr) n 2o.2zo3(aX2Xv) n 50.73(aX2)(i)(A) n 50.73(a)(2XvXD) tl ft Tl(ax2)(i) n zo.2zas(aX2Xvi) n 50.73(aX2XiXB) n 50.73(aX2xvii) n ft.77(a)(2)(ii) n 50 73(ax2)(i)(c) t] OTHER Specify in Abstract betow or in NRC Form 366A 12, LIEENSEE CONTACT FOR THIS LER TICENSEE CONTACT Dean Baker, Licensing Engineer TELEPHONE NUMBER (lnclude Area Code)423-452-4589 t3. COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT cAUSE I svsrerta lconrnoNENrlro.ruRER REPORTABLE TO EPIX CAUSE SYSTEM I COMPONENT MANU- I REPORTABLE FAcTuRER I ro EPrx B I SB I LVDT ISIEMENS N NO 14. SUPPLEMENTAL REPORT fJ ves (f yes, comptete 15.EXPECTED EXPECTED SUBMISS/Oru DATE)x 15. EXPECTED SUBMISSION DATE MONTHI DAY I YEAR ABSTMCT (Limit to 1 4 00 spaces, i.e., approximately 1 5 single-spaced Upewfitten lines)On June 5,2016 at 1227 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant Unit 2 was in MODE 1 at approximately 12.5 percent power when a safety injection (Sl) actuation occurred, followed by an automatic reactor protection system (RPS) trip. No primary safety barriers (Reactor Coolant System, containment and fuel clad) were challenged and no primary or secondary safety or relief valves actuated during the event. The Unit 2 plant trip was considered a complicated trip due to Sl actuation.

Safety equipment operated as expected and Sl was promptly terminated.

The reactor trip and Sl were caused by a turbine governor valve failing open, causing a steam header pressure rate of decrease Sl actuation signal.NRC FORM 366 (1 1-201s)

Page 2 of 5 NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (11-2015)LICENSEE EVENT REPORT (LER)CONTINUATION SHEET APPROVED BY OMB: NO.3150-0104 EXPIRES: 1013112018 Estimated burden per response to comply with this mandatory collection request: B0 hours, Reported lessons learned are incorporated into the licensing process and fed back to industry, Send comments regarding burden estimate to the FOIA, Privacy and lnformation Collections Branch (T-5 F53), U.S Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to lnfocollects,Resource@nrc.gov, and to the Desk 0fficer, Office of lnformation and Regulatory Affairs, NEOB-10202, (3150-0104), Ofiice of Management and Budget, Washington, DC 20503 lf a means used to impose an information collection does not display a currently valid OMB control number, the NRC may nol conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME Watts Bar Nuclear Plant, Unit 2 2. DOCKET NUMBER 0500039 1 3. LER NUMBER YEAR 2016 SEQUENTIAL NUMBER- 004 REV NO.-00 NARRATIVE I PLANT OPERATING CONDITIONS BEFORE THE EVENT Watts Bar Nuclear Plant (WBN) Unit 2 was in Mode 1 at 12.5 percent rated thermal power (RTP)II. DESCRIPTION OF EVENT A. Event On June 5, 2016 at1227 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant (WBN) Unit 2 was in MODE 1 at approximately 12.5 percent powerwhen a safety injection (Sl) actuation occurred, followed by an automatic reactor protection system (RPS) trip. The cause of the trip with Sl was a failure of the No.1 high pressure turbine governor valve {EIIS:XCV}

in the open position causing a steam header pressure rate of decrease Sl actuation signal. At1245, Operations personnel secured safety injection and Unit 2 was stabilized in MODE 3 at normal operating pressure and temperature.

No primary safety barriers (reactor coolant system, containment and fuel clad) were challenged and no primary or secondary safety or relief valves actuated during the event. The Unit 2 plant trip was considered a complicated trip due to Sl actuation.

Safety equipment operated as expected and Sl was promptly terminated.

This event was reported to the Nuclear Regulatory Commission (NRC) on June 5, 2016 via Event Notification 51982 pursuant to 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(bX3XivXA).

B. lnoperable Structures, Components, or Systems that Contributed to the Event A bracket for the No.'! turbine governor valve linear variable differential transmifter (LVDT) failed due to vibration induced fatigue.C. Dates and Approximate Times of Occurrences Date Time (EDT) Event 613116 2038 Power level increases from 0 percent power. Governor valve vibration levels estimated between2.4 and 4 inches per second (ips). Vibration information obtained during Unit 2 start-up subsequent to this event.614116 1658 Power level reached 127 Megawatt Electric (MWe). Valve position approximately 9.3 percent open, vibration estimated between 2.5 and 4 ips.615116 1122 Unit 2 generator synchronized with governor valve 1 between 4 and 5 percent open. Expected vibration 4 ips.615116 1204 Governor valve 1 7.5 to 8 percent open 615116 1227 Unit 2 trips with Sl actuation.

Operations enters procedure 2-E-0, Reactor Trip or Safety lnjection 615116 1236 Transition to procedure 2-ES-1.1, Sl Termination 615116 1245 Slsecured.

615116 1320 Plant transitions to 2-GO-5, Unit Shutdown from 30 percent Reactor Power to Hot Standby NRC FORM 366A (1 1-2015) a e5()NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (11-2015).":::* *'n":?,^* \l:=.. :4.iffi} LTcENSEE EVENr REPoRT (LER)"";-::S*.*NO CONTINUATION SHEET't*r*r APPROVED BY OMB: NO.3150-0104 EXPIRES: 101312A18 Estimated burden per response to comply with this mandatory collection requestr 80 houm. Reported lessons learned are incorporated into the licensing process and fed back to industry, Send commenB regarding burden estimate to the FOIA, Privacy and lnformation Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to lnfocollects,Resource@nrc,gov, and to the Desk Officer, 0ffice of lnformation and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. lf a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME Watts Bar Nuclear Plant, Unit 2 2. DOCKET NUMBER 0500039 1 3. LER NUMBER YEAR 2016 SEQUENTIAL NUMBER- 004 REV NO.00 NARRATIVE D. Manufacturer and Model Number of Components that Failed A bracket that mounted the LVDT to the No. 1 governor valve failed due to vibration related fatigue.E. Other Systems or Secondary Functions Affected During the event, anomalies were noted with the 2B Motor Driven Auxiliary Feedwater Pump (MDAFWP) and the Turbine Driven Auxiliary Feedwater Pump (TDAFWP).

The 28 MDAFWP was shutdown due to smoke coming from the pump packing. After discussion with the vendor, this was determined to be an expected condition for this type of new packing with minimal break-in time and the pump was restarted.

During operation of the TDAFWP, no oil was noted in one of the bearing sight glasses and the pump was manually secured. This was determined to be an issue with the sight glass providing inaccurate indication and not a lack of oil. The pump was subsequently returned to service.F. Method of discovery of each Component or System Failure or Procedural Error The failure became apparent after the plant trip.G. Failure Mode and Effect of Each Failed Component The No. 1 governor valve mounting bracket failed from vibration related fatigue.H. Operator Actions This reactor trip was complicated by a concurrent Sl. Operations personnel were able to promptly terminate Sl in accordance with plant procedures and restore the plant to a normal shutdown alignment.

L Automatically and Manually lnitiated Safety System Responses All automatic and manualsafety systems responded as expected.III. CAUSE OF THE EVENT A. The cause of each component or system failure or personnel error, if known.The Unit 2 No. 1 governor valve LVDT bracket experienced failure due to short term cyclic fatigue during extended start-up conditions.

B. The cause(s) and circumstances for each human performance related root cause.There were no apparent human performance related root cause.NRC FORM 3664 (11-2015)Paqe 3 of 5 Page 4 of 5 NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (1 1-201s).":':* "ou:h i ffii LTcENSEE EVENr REPoRT (LER)-f+^.<ffi>.C;T-CONTINUATION SHEET , t11*t APPROVED BY OMB: NO.3150-0104 EXPIRES: 10/31/2018 Estimated burden per response to comply with this mandatory collection request: B0 hours, Reported lessons learned are incorporated into the licensing process and fed back to industry, Send commenb regarding burden estimate to the FOIA, Privrcy and lnformation Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to lnfocollects,Resource@nrc,gov, and to the Desk Officer, Office of lnformation and Regulatory Affaim, NE0B-10242, (3150-0104), Office of Management and Budget, Washington, DC 20503 lf a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection, 1. FACILITY NAME Watts Bar Nuclear Plant, Unit 2 2. DOCKET NUMBER 0500039 1 3. LER NUMBER YEAR 2416 SEQUENTIAL NUMBER- 004 REV NO.-00 NARRATIVE IV. ANALYSIS OF THE EVENT The turbine governor valves experience high vibration when operated at low steam flow. This flow induced vibration is inherent to the turbine governor valve design when its position is less than 20 percent open.Vibration is highest with the valve less than 12 percent open. While operating WBN Unit 2 at low power for an extended period, a bracket supporting a position transducer failed, causing an associated failure on the LVDT position rod. During operation, the broken LVDT core rod "walked off'the actuator arm, giving a false low position of the governor valve. The control system, based on the false indication, provided an open demand signal to the No.1 governor valve, which lead to a steam header pressure rate of decrease safety injection actuation signal and an automatic reactor trip.V. ASSESSMENT OF SAFETY CONSEQUENCES WBN Unit 2 experienced a safety injection with an automatic reactor trip. All safety equipment responded as expected and operations personnel promptly terminated safe$ injection.

The plant was stabilized in Mode 3 without any additional complications.

The risk associated this event was determined to be less than 1E-6.A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event The failure that occurred was on a non-safety related turbine component.

No safety systems were impacted as a result of this failure .B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat control the release of radioactive material, or mitigate the consequences of an accident Not applicable.

C. For failure that rendered a train of a safety system inoperable, an estimate of the elapsed time from the discovery of the failure until the train was returned to service Not applicable.

VI. CORRECTIVE ACTIONS This event was entered into the Tennessee Valley Authority (TVA) Corrective Action Program and is being tracked under condition report 1178855.A. lmmediate Corrective Actions The plant was placed in a safe condition.

The failed turbine governor components were replaced.NRC FORM 366A (11-2015)

Page 5 of 5 NRC FORM 366A U.S. NUCLEAR REGULATORY COM]I'IISSION (1 1-201s)LICENSEE EVENT REPORT (LER)CONTINUATION SHEET APPROVED BY OMB: NO.3150-0104 EXPIRES: 1013112018 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />, Reported lessons learned are incorporated into the licensing process and fed back to industry, Send comments regarding burden estimate to the FOIA, Privacy and lnformation Collections Branch (T-5 F53), U S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to lnfocollects,Resource@nrc.gov, and to the Desk Officer, 0ffice of lnformation and Regulatory Afiains, NE0B-10202, (3150-0104),Office of Management and Budget, Washington, DC 20503 lf a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME Watts Bar Nuclear Plant, Unit 2 2. DOCKET NUMBER 0500039 1 3. LER NUMBER YEAR 2016 SEQUENTIAL NUMBER- 004 REV NO.00 NARRATIVE B. Corrective Actions to Prevent Recurrence Plant operating procedures will be revised to minimize governor valve operation when the valve position is less than 12 percent open. TVA will work with the turbine vendor to determine if work can be performed within the existing valve design requirements to reduce flow induced vibration.

VII. ADDITIONAL INFORMATION A. Previous similar events at the same plant No similar events have been identified at the Watts Bar plant .B. Additional lnformation None.C. Safety System Functional Failure Consideration This condition did not result in a safety system functionalfailure.

D. Scrams with Complications Consideration There was an Sl associated with this plant trip. Operations personnel were able to promptly terminate Sl in accordance with plant procedures and restore the plant to a normal shutdown alignment.

VIII. COMMITMENTS None.NRC FORM 366A (1 1-2015)