05000327/LER-2021-001, Sequoya Nuclear Plant, Unit 1, Reactor Trip on High Neutron Flux Rate Due to Dropped Control Rods
| ML21202A441 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 07/21/2021 |
| From: | Marshall T Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2021-001-00 | |
| Download: ML21202A441 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) |
| 3272021001R00 - NRC Website | |
text
TENNESSEE VALLEY AUTHORITY Sequoyah Nuclear Plant, PostOffice Box2000,SoddyDaisy, Tennessee 37384 July 21,2021 10CFR50.73 ATTN:Document Control Desk U.S.Nuclear Regulatory Commission Washington, D.C.20555-0001 Sequoyah Nuclear
- Plant, Unit1 RenewedFacility Operating LicenseNos.
DPR-77 NRCDocket No.50-327 Subject:Licensee EventReport 50-327/2021-001-00, Reactor TriponHighNeutron FluxRateDuetoDroppedControl Rods Theenclosed licensee eventreport provides details concerning anautomatic reactor trip on highneutron flux rate asaresult ofControl BankBinserting into the core.
Thiseventisbeing reported inaccordance with10CFR50.73(a)(2)(iv) asaneventthat resulted inanautomatic actuation ofthereactor protection system andtheauxiliary feedwater system.
Therearenoregulatory
commitments
contained inthis letter.
Should youhaveany questions concerning this submittal, please contact Mr.Jeffrey Sowa,Site Licensing Manager, at (423) 843-8129.
Respectfully, Marshall,,ogitaii,yjgned byMarshall, ThomasB.
oate:2o2,.oz.2,
,4:4s:os-o4oo ThomasMarshall Site VicePresident Sequoyah Nuclear Plant
Enclosure:
Licensee Event Report 50-327/2021-001-00 cc:
NRCRegional Administrator
- - Region II NRCSenior Resident Inspector
- - Sequoyah Nuclear Plant
NRC FORM 366 U.S.NUCLEARREGULATORY COMMISSIONAPPROVED BYOMB:NO.3150-0104 EXPIRES:
08/31/2023 (08-2020)
Estimated burden perresponse tocomply with this mandatory collection request:
80hours.
- %q Reported lessons learned areincorporated into thelicensing process andfedback toindustry.
f LICENSEEEVENTREPORT(LER)
Send comments regarding burden estimate tothe
- FOIA, Library, andInformation Collections Branch g
(T-6 A10M),
U.S.
Nuclear Regulatory Commisson, Washington, DC20555-0001, orbye-mail to 7
f (See Page3forrequired number ofdigits/characters foreachblock)
Infocollects.Resource@nrc.gov, andtheOMBreviewer at:OMBOffice ofInformation and
/
(See NUREG-1022, R.3forinstruction andguidance forcompleting thisRegulatory
- Affairs, (3150-0104),
Attn:
Deskail:@.
TheNRCmaynot h* P form
) conduct orsonsorndaperson s ofreui tore ndto coection ofnformat nunless 1.Facility Name 2.DocketNumber 3.Page Sequoyah NuclearPlant Unit1 05000327 1OF5 4.Title Reactor TrionHihNeutron FluxRateDuetoDro edControl Rods 5.EventDate 6.LER Number 7.Report Date 8.Other Facilities Involved Facility Name DocketNumber Month Day Year Year SS9uuential Rev Month Day Year NA 05000 Facility Name DocketNumber 05 24 2021 2021 -001 00 07 21 2021 NA 05000 9.Operating Mode 10.PowerLevel 1
100 11.This Reportis Submitted Pursuant tothe Requirements of10CFR: (Check allthat a ly) 10CFRPart20 O20.2203(a)(2)(vi)
O50.36(c)(2)
E 50.73(a)(2)(iv)(A)
O50.73(a)(2)(x)
O20.2201(b)
O20.2203(a)(3)(i)
O 50.46(a)(3)(ii)
O 50.73(a)(2)(v)(A) 10CFRPart73 O20.2201(d)
O20.2203(a)(3)(ii)
O50.69(g)
O 50.73(a)(2)(v)(B)
O73.71(a)(4)
O20.2203(a)(1)C20.2203(a)(4)
O50.73(a)(2)(i)(A)
O 50.73(a)(2)(v)(C)
O73.71(a)(5)
O20.2203(a)(2)(i) 10CFRPart21 O50.73(a)(2)(i)(B)C 50.73(a)(2)(v)(D)
O73.77(a)(1)(i)
O20.2203(a)(2)(ii)
O21.2(c)
O50.73(a)(2)(i)(C)
C 50.73(a)(2)(vii)
O 73.77(a)(2)(i)
O20.2203(a)(2)(iii) 10CFRPart50 O50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viil)(A)
O73.77(a)(2)(ii)
O20.2203(a)(2)(iv)
C50.36(c)(1)(i)(A)
O50.73(a)(2)(ii)(B)
C 50.73(a)(2)(viil)(B)
O20.2203(a)(2)(v)
O50.36(c)(1)(ii)(A)
O50.73(a)(2)(iii)
C 50.73(a)(2)(ix)(A)
OOther (Specify
- here, inAbstract, orinNRC366A).
12.Licensee Contact forthis LER Licensee Contact Phone Number(include AreaCode)
Scott Bowman 423.843.6910 13.
Complete OneLine foreachComponent Failure Described inthis Report
Cause
System Component Manufacturer Reportable ToIRIS
Cause
System Component Manufacturer Reportable ToIRIS X
AA CON W120 Y
X AA ECBD W120 Y
14.Supplemental Report Expected Month Day Year
@No O Yes(if
- yes, complete 15.Expected Submission Date)
Abstract
(Limit to1560spaces, i.e.,
approximately 15single-spaced typewritten lines)
OnMay24,2021,at0915eastern daylight time(EDT),
SQNUnit1experienced anautomatic reactor trip.
Approximately 0.5seconds before thereactor
- trip, anunexpected RodControl Urgent Failure alarm annunciated andControl
- BankB, Group2rodsbegantolower.
Thereactor trip first outalarmindicated thetrip wasfromaPowerRangeHighNeutron Flux Ratedetected bythePowerRangeNuclear Instruments.
During troubleshooting, itwasdiscovered that there werebadpinconnections onthebackplane ofthephasecard associated withControl BankB(the cardconnection between theControl BankB,Group2stationary gripper phase control cardandthebackplane ofits cardcage).
Allplant safety systems responded asdesigned.
Allrodsfully inserted asrequired.
Thedirect causeofthefailure hasbeenattributed tothecardconnection between Control BankBGroup2stationary gripper phasecontrol cardandthebackplane ofthecardcage.Periodic instruction procedure, Pl-674 Periodic Calibration oftheFull Length RodControl Power,directs activities toremovephasecontrol cardsduring calibration whichcanresult inpindeformation.
Therefore, thecorrective action forthis eventistorevise theprocedure tomodify howcalibration activities areperformed basedonlearnings obtained fromtheequipment failure evaluation.
I. Plant Operating Conditions Before theEvent Atthetimeoftheevent, Sequoyah NuclearPlant(SQN)
Unit1wasinMode1atapproximately 100percent rated thermal power (RTP).
II. Description
ofEvent A. Event Summary:
OnMay24,2021,at0915eastern daylight time (EDT),SQNUnit1experienced anautomatic reactor trip.
Approximately 0.5seconds before thereactortrip, anunexpected RodControl Urgent Failure alarm annunciated andControl Bank B,Group2rods[EIIS:
AA)beganto lower.
Thereactor trip first outalarm indicated the trip wasfromaPowerRangeHigh Neutron FluxRatedetected bythePowerRange Nuclear Instruments.
Norodtesting wasin progress.
Noworkwasinprogress intherodcontrolpower orlogic cabinets.
During troubleshooting, itwasdiscovered that there werebad pin connections [EllS:
CON) on thebackplane ofthephasecontrol card[EllS:
ECBD) associated with ControlBankB(the cardconnection between theControl BankB,Group2stationary gripper phasecontrol card andthebackplane ofitscardcage).
Thephasecardwasreplaced and tested.
Pin reformation (the scopeofpinreformation consisted ofall five rod control power cabinetsand thelogic cabinet) andsystemfunctional testing wasperformed bythe vendor.
Allplant safety systems responded asdesigned.
Allrodsfully inserted asrequired.
Theevent isreportable inaccordance with10CFR50.73(a)(2)(iv)(A),
asaneventthat resulted inanautomatic actuation oftheReactor Protection System[EIIS:
JC)andthe Auxiliary Feedwater (AFW)
System[EllS:
BA).
B. Status ofstructures, components, orsystems that wereinoperable atthestart oftheevent andcontributed totheevent:
Noinoperable structures, components, orsystems contributed tothis event.Page2of5U.S.NUCLEARREGULATORY COMMISSIONAPPROVEDBYOMB:NO.3150-0104 EXPIRES:
08/31/2023 (o8-2020)
Estimated burden perresponse tocomply with this mandatory collection request:
80hours.
Reported fms lessons learned areincorporated into thelicensing process andfedback toindustry.
Sendcomments
/
. T LICENSEE EVENTREPORT(LER) regarding burden estimate totheFOIA,
- Ubrary, andInformation Collections Branch (T-6 A10M),
U.S.
P f
Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mailto
Q2 CONTINUATION SHEET Infocollects.Resource@nrc.gov, andtheOMBreviewer at:OMBOffice ofInformation andRegulatory
- Affairs, (3150-0104),
Attn:
DeskaitM.
TheNRCmaynotconduct or (See NUREG-1022, R.3for instruction andguidance forcompleting this formsponsor, andaperson isnotrequired torespond to,acollection ofinformation unless thedocument
)
requesting orrequiring thecollection displays acurrently valid OMBcontrol number.
1.FACILITY NAME 2.DOCKETNUMBER 3.LERNUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 1 05000-327 NUMBER NO.
2021
- - 001
- - 00 C. Datesandapproximate times ofoccurrences:
Date/Time (EDT)
Description
05/24/21 0900 Unit1 was atapproximately 100percent RTP,Control BankDat 217steps withdrawn, andallother banksat228steps withdrawn.
09:15:27.261 Unit1received aRodControlUrgent Failure annunciator.
09:15:27.790 Unit1receiveda High Neutron FluxRateChannel IValarm.
Unit 1simultaneously received aHighNeutron FluxRateChannel Ill 09:15:27.811 alarm andaHigh Neutron Range ReactorTrip signal.
Unit1 automatically tripped andentered Mode3.
D. Manufacturer andmodelnumberofeachcomponent that failed duringtheevent:
Thecomponents that failed wereaWestinghouse Phase Control Cardmodel number6050A11G01 andWestinghouse Backplane Connector Pins forAMPmanufactured connections partnumber67168-2.
E. Other systems orsecondary functions affected:
Therewerenoother systems orsecondary functions affected bythis event.
F. Method ofdiscovery ofeachcomponent orsystemfailure orprocedural error:
Maincontrol room(MCR) alarms andannunciators provided indication totheoperators during the reactor trip.
G. Failure mode,mechanism, andeffect ofeachfailed component:
Thefailure modewasattributed topoorpinconnection onthephasecontrol cardassociated with Control BankBandthebackplane ofitscardcage.
H. Operator actions:
MCRoperators responded tothereactor
- trip, asrequired, andthentransitioned topost-trip response procedures.
I. Automatically andmanually initiated safety system responses:
Thereactor protection
- system, including feedwater isolation andAFWstart, responded tothe
- trip, asdesigned.Page3of5U.S.NUCLEARREGULATORY COMMISSIONAPPROVEDBYOMB:NO.3150-0104 EXPIRES:
08/31/2023 (o8-2020)
Estimated burden perresponse tocomply with this mandatory collection request:
80hours.
Reported fws lessons learned areincorporated into thelicensing process andfedback toindustry.
Sendcomments
/
- . T LICENSEE EVENTREPORT(LER) regarding burden estimate totheFOIA,
- Ubrary, andInformation Collections Branch (T-6 A10M),
U.S.
A f
Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mailto
Q2 CONTINUATION SHEET Infocollects.Resource@nrc.gov, andtheOMBreviewer at:OMBOffice ofInformation andRegulatory
- Affairs, (3150-0104),
Attn:
DeskaitM.
TheNRCmaynotconduct or (See NUREG-1022, R.3for instruction andguidance forcompleting this formsponsor, andaperson isnotrequired torespond to,acollection ofinformation unless thedocument
)
requesting orrequiring thecollection displays acurrently valid OMBcontrol number.
1.FACILITY NAME 2.DOCKETNUMBER 3.LERNUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 1 05000-327 NUMBER NO.
2021
- - 001
- - 00 III.CauseoftheEvent A. Causeofeach component orsystemfailure orpersonnel error:
Thedirect causeofthefailure hasbeenattributed tothecardconnection between Control BankB Group2stationary gripper phase control cardandthebackplane ofits cardcage.
B. Cause(s)
andcircumstances foreach human performance related rootcause:
There wasnoidentified humanperformance related rootcause.
IV.Analysis oftheEvent:
Theplant safety system responses during andafter the reactor trip werebounded bythe responses described intheUpdated Final Safety Analysis Report (UFSAR). TheUFSAR Chapter 15eventthat mostclosely matches thereactor trip is the RodCluster Control Assembly Misalignment.
Therefore, this eventdidnotadversely affect the health andsafety ofplant personnel orthegeneral public.
V. Assessment ofSafety Consequences Therewerenoactual safety consequences asaresult ofthereactor trip.
A. Availability ofsystems orcomponents that could haveperformed thesamefunction asthe components andsystems that failed during theevent:
None.
B. Forevents that occurred whenthereactor wasshutdown,availability ofsystems or components neededtoshutdown thereactor andmaintain safeshutdown conditions, removeresidual
- heat, control therelease ofradioactive
- material, ormitigate the consequences ofanaccident:
Theeventdidnotoccur whenthereactor wasshutdown.
C. Forfailure that rendered atrain ofasafety system inoperable, anestimate oftheelapsed timefromdiscovery ofthefailure until thetrain wasreturned toservice:
Therewasnofailure that rendered atrain ofasafety system inoperable.
VI. Corrective Actions Theevent wasentered into theTennessee Valley Authority Corrective Action Program (CAP) under condition report number1696187.Page4of5U.S.NUCLEARREGULATORY COMMISSIONAPPROVEDBYOMB:NO.3150-0104 EXPIRES:
08/31/2023 (o8-2020)
Estimated burden perresponse tocomply with this mandatory collection request:
80hours.
Reported fws lessons learned areincorporated into thelicensing process andfedback toindustry.
Sendcomments
/
- . T LICENSEE EVENTREPORT(LER) regarding burden estimate totheFOIA,
- Ubrary, andInformation Collections Branch (T-6 A10M),
U.S.
A f
Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mailto
Q2 CONTINUATION SHEET Infocollects.Resource@nrc.gov, andtheOMBreviewer at:OMBOffice ofInformation andRegulatory
- Affairs, (3150-0104),
Attn:
DeskaitM.
TheNRCmaynotconduct or (See NUREG-1022, R.3for instruction andguidance forcompleting this formsponsor, andaperson isnotrequired torespond to,acollection ofinformation unless thedocument
)
requesting orrequiring thecollection displays acurrently valid OMBcontrol number.
1.FACILITY NAME 2.DOCKETNUMBER 3.LERNUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 1 05000-327 NUMBER NO.
2021
- - 001
- - 00 A. Immediate Corrective Actions:
Troubleshooting was performed.
Itwasdiscovered that there werebadpinconnections on thebackplane ofthe phase card associated withControl BankB.Thephasecardwas replaced andtested.
Pinreformation (the scopeofpinreformation consisted ofallfive rod control powercabinets andthe logic cabinet) andsystem functional testing wasperformed by thevendor.
B. Corrective Actions toPrevent Recurrence ortoreduce probability ofsimilar events occurring inthefuture:
Periodic instruction procedure, PI-674 Periodic Calibration oftheFull Length RodControl
- Power, directs activities toremovephasecontrol cards during calibration which canresult inpin deformation.
Therefore, thecorrective action forthis event istorevise theprocedure tomodify howcalibration activities areperformed basedonlearnings obtained fromtheequipment failure evaluation.
VII.Previous Similar Events attheSameSite:
A review ofprevious similar events atSQN,identified LERs1-2015-001 and 1-2019-003.
Both LERsidentified anautomatic reactor trip duetoacontrol rod,H-8, dropping intothecore.For LER1-2015-001, thecauseoftheeventwasfailure ofamaintenance procedure toprovide inspection guidance andacceptance criteria oncontrol roddrive mechanismvertical panel connections.
Theassociated corrective action wasrevising themaintenance procedure and periodic preventive maintenance ofCRDMconnections.
ForLER1-2019-003, thecause ofthe eventwasdetermined tobethat excessive weartothecontrol rodstationary gripperlatch mechanism resulted intheinability tomaintain thecontrol rodinthefully, ornearly
- fully, withdrawn position foranextended period oftime.
Thecorrective action wastosubmit a license amendment request anddevelop anengineering design change topermanently remove Control RodH-8.
VIll.
Additional Information Thereisnoadditional information.
IX. Commitments:
Therearenocommitments.Page5of5