05000277/LER-2021-001, High Pressure Coolant Injection System Declared Inoperable Due to Instrument Power Inverter Failure

High Pressure Coolant Injection System Declared Inoperable Due to Instrument Power Inverter Failure

ML21175A057
Person / Time
Site:	Peach Bottom  (DPR-044)
Issue date:	06/24/2021
From:	Herr M Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
5522 LER 2021-001-00
Download: ML21175A057 (5)

LER-2021-001, High Pressure Coolant Injection System Declared Inoperable Due to Instrument Power Inverter Failure

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v), Loss of Safety Function 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)
2772021001R00 - NRC Website

text

W as, i

10CFR50.73 CCN:21-64 June24,2021 U.S.Nuclear Regulatory Commission ATTN:Document ControlDesk Washington, DC20555-0001 PeachBottom Atomic Power Station (PBAPS)

Unit2 Subsequent Renewed Facility Operating License No.DPR-44 NRCDocket No.50-277 Subject:Licensee Event Report (LER) 2021-001-00 HighPressure Coolant Injection System Inoperable DuetoInverter Failure

References:

ENS#55224 Thisreport isbeing submitted inaccordance with10CFR50.73(a)(2)(v)(D) foranevent or condition that atthetimeofdiscovery could havepreventedthe fulfillment ofthesafety function ofstructures orsystems that areneeded tomitigate the consequences ofan accident.

Therearenocommitments contained inthis letter.

Ifyouhaveanyquestions, pleasecontact thePeachBottom Regulatory Assurance

Manager, Matthew K.Rector at(717) 456-4351 Respectfully, 7

Matthew J.Herr Site VicePresident PeachBottom Atomic PowerStation Enclosure cc: USNRC,Administrator, Region I

USNRC,Senior Resident Inspector, PeachBottom W.DeHaas,Commonwealth ofPennsylvania S.Seaman, State ofMaryland B.Watkins, PSE&G,Financial Controls andCo-Owner Affairs

NRC FORM386 U.S.

NUCLEAR REGULATORY COMMISSION APPROVED BYOMB:NO.31600104 EXPIRES:

08/31/2023 (C>8-2020)

Estimated burden perresponse tocomply with this mandatory collection request.

80hoursReported A

A LICENSEE EVENTREPORT(LER) e"lngtrfen"mT""td e&en;nRocusm"n'""o" Send0"""%"S I

j (See Page3forrequired numberofdigits/characters foreachblock) Nuclear Regulatory Commission, Washington, DC 205550001 or by e-ma to Infocollects.Resource@nrc.gov, andthe0MB reviewer atOMBOfMce ofInformation andRegu atory g

(See NUREG-1022,R.3forinstruction andguidance forcompleting this form pe"r2n!

not%ul@ idao"nculle requesting orrequrng thecolection dsplays acurrently vaid OMBconto' umber 1.Facility Name 2.Docket Number 3.Page PeachBottom Atomic Power Station, Unit 2

0500000277 1 OF 4 4.Title HighPressure CoolantInjection SystemDeclared Inoperable DuetoInstrument PowerInverter Failure 6.Event Date

6. LER Number 7.Report Date 8.Other Facilities involved Month Day Year Year Sequential ReWon Month Day Year Number No.

g5000 04 29 2021 2021 001 00 06 24 2021"*'"*"'""

9.Operating Mode 10.PowerLevel 1

- Run 100 11.This Report laSubmitted Pursuant to the Requirements of10CFR9:

(CheckaHdietapply) 10CFRPart 20 Q20.2203(a)(2)(vi)

O 50.36(c)(2)

C 50.73(a)(2)(iv)(A) Q50.73(a)(2)(x)

O20.2201(b) Q20.2203(a)(3)(l)

O 50.46(a)(3)(II)

G 50.73(a)(2)(v)(A) 10CFRPart 73 0 20.2201(d) O20.2203(a)(3)(ll)

O50.69(g)

G50.73(a)(2)(v)(B)

G73.71(a)(4)

C 20.2203(a)(1)

Q20.2203(a)(4)

O 50.73(a)(2)(i)(A) Q 50.73(a)(2)(v)(C)

G73.71(a)(5)

G20.2203(a)(2)(i) 10CFRPart21 C 50.73(a)(2)(I)(B) 50.73(a)(2)(v)(D)

G73.77(a)(1)(I)

G20.2203(a)(2)(II)

Q21.2(c)

O50.73(a)(2)(I)(C)

G50.73(a)(2)(vil)

G73.77(a)(2)(I)

Q20.2203(a)(2)(lil) 10CFRPart60 O50.73(a)(2)(II)(A)

G 50.73(a)(2)(vill)(A)

G73.77(a)(2)(II)

O20.2203(a)(2)(ly)

O50.36(c)(1)(I)(A)

G50.73(a)(2)(II)(B)

G 50.73(a)(2)(vill)(B)

O20.2203(a)(2)(v)

Q50.36(c)(1)(II)(A)

O50.73(a)(2)(lil)

G50.73(a)(2)(lx)(A)

OOTHER(Specify here.

Inabstract.

orNRC366A).

12.Licensee Contact forthis LER Licensee Contact Phone Number (includeareacode)

Matthew K.Rector, Regulatory Assurance Manager 7174564351 13.Complete OneLineforeachComponent Fallure Described Inthis Report

Cause

System ComponentManufacturer Reportable toIRIS

Cause

System ComponentManufacturer Reportable toIRIS X

BJ JX NLi Y

14.Supplemental Report Expected Month Day Year 2 No C Yes(lf

yes, complete 15.Expected Submission Date)

Abstract

(Limit to1560spaces, ie, approximately 15single-spaced typewritten lines)

OnApril 29,2021at2354ETwith Unit 2plant operating conditions at100%rated thermal

power, the"High Pressure Coolant Injection (HPCI) systeminverter circuit failure" alarm wasreceived onaMainControl Roompanel.

Thisalarm indicates aloss ofACpowerfromtheHPCIinverter, andiscaused byeither aloss ofDCpower to,orafailure of,the inverter.

Operations personnel immediately noticed theerratic performance ofHPCIsystem instruments, digital recorders, andaloss ofexpected status display ontheHPCIflow controller.

Subsequent investigation into theHPCI inverter circuit failure alarm revealed theinverter wascycling onandoff.

Intheeventofavalid HPCIinitiation

signal, theerratic loss ofpowertotheHPCIflow controller would haveresulted inaloss ofHPCIfunction.

OnApril 30,2021 at0023ETOperations personnel declared HPCIinoperable.

At0023ET,atthedirection ofShift supervision, the inverter powersupply fuses wereremoved toarrest theinverter cycling onandoff.

TheHPCIinverter was subsequently removed fromservice, replaced

inkind, andthentested satisfactorily.

Theloss oftheHPCIfunction wasduetotheinverter failure.

There werenoactual safety consequences asaresult of this event.

Thisreport ismadepursuant to10CFR50.73(a)(2)(v)(D) foraneventorcondition that atthetimeof discovery could haveprevented thefulfillment ofthesafety function ofstructures orsystems that areneeded to mitigate theconsequences ofanaccident.

Plant Conditions:

PeachBottom Atomic PowerStation Unit2(PB2) wasoperatingatapproximately 100percent powerinMODE1.

There werenostructures,

systems, orcomponents thatwereinoperable atthestart oftheevent andcontributed tothe identified condition.

Failed component information:

Assembly/Part Number:

NLI-072034-CSI-K-5-A ModelNumber:

CSl-K-B-Q9573 Serial Number:

31A71002.

Description

RackMount1000VAInverter Assembly Manufacturer:

PARAGON ENERGY SOLUTIONS, formerly NuclearLogistics Incorporated Type:

PowerSupply

Description

OnApril 29,2021at2354ET,the"High Pressure Coolant Injection (HPCI)

System Inverter CircuitFailure" alarm was received onaMainControl Roompanel.

Operations personnel immediately noticederratic performance ofHPCI system pressure instruments andaloss ofexpected status display ontheHPCIflow controller.

Examination ofthe HPCIrack-mounted inverter revealed thepowerindicator light wascycling onandoff.

Inspection oftheHPCIpanel backplane revealed that thelogic buspower monitoring relay waschattering/cycling onandoff. There werenoother indications ofequipment degradation.

Intheeventofavalid HPCIinitiation

signal, theerratic power supply totheHPCI flow controller wouldhaveresulted inaloss ofHPCIfunction (a

single train system).

OnApril 30,2021at0023ET,Operations Shift supervision directed that theinverter power supply fuses be removed to arrest theinverter cycling onandoff andHPCIwasdeclared inoperable.

Station Instrument andControls Maintenance staff weremobilized toperform investigation andrepairs.

Simple troubleshooting confirmed inverter supply powerandprotective fuses wereperforming satisfactorily.

Inverter output voltage readings wereoutofthespecified performance range andanapparent

cause

could bedetermined.

OnApril 30,2021at0738ET,inaccordance with10CFR50.72(b)(3)(v)(D),

anon-emergency eight-hour notification to theNRCwascompleted duetothePB2HPCIinverter failure andHPCIbeing declared inoperable (a

single train system) resulting inacondition that could haveprevented fulfillment ofasafety function ofstructures orsystems that areneeded tomitigate theconsequences ofanaccident.

(Reference ENS#55224)

Anewlike-for-like inverter unit wasobtained fromstation stores andbench calibrated.

Thedegraded inverter was removed andreplaced, andthedownstream instrument functional checks werecompleted satisfactorily.

OnApril 30,2021at1434ET,all repairs werecompleted, full function wasrestored, thesystem satisfactorily tested andHPCIwasdeclared operable.

Theduration thetrain wasrendered inoperable wasapproximately 15hours.

Event CauseAnalysis:

Thefailed inverter wasexamined inthestation Instrument andControl Maintenance shopbyrestoring theinput power supply.

Theoutput voltage wasbelow required specifications andvisual examination oftheaccessible inverter

internals revealed noobvious signs of a failed sub-component ordefective piece-parts.

Theunit wasquarantined and shipped tothemanufacturer (Paragon Energy Solutions) fordetailed failure analysis.

Event CauseAnalysis (continued):

Theinverter undergoes routine preventive maintenance calibration andfunctional checks every twoyears andis replaced with anewinverter every tenyears based on vendor life cycle recommendations.Thefailed inverter was installed during themostrecent PB2refueling outagein October of2020.

Theinverter hadbeenin-service approximately five months.

Theearly life-cycle failure ismost likelyattributedtoarandom sub-component failure.

The inverter output iscontinuously monitored andannunciatedin the MainControl Room.Station alarm response procedures direct actions toidentify andmitigate potential

causes

ofidentified alarms.

Theimpact wasimmediately recognized byOperations staff through theperformance ofalarm response actions that validated observations ofthe pressure indicators andthedigital flow controller display.

There were no otherinstruments orEmergency CoreCooling System(ECCS) impacted bythis inverter failure.

Station staff areconducting acausal evaluation andhavesolicited adetailed failure analysisfromthemanufacturer.

Thetimeframe forthis report exceeds the60-day event reporting requirement. However, thefailure analysis report will notsignificantly change thecourse, significance, implications, orconsequencesof the eventasassessed below.

(Reference IRIS#498696)

Assessment ofSafety Consequence:

Thiseventisreportable per10CFR50.73(a)(2)(v)(D) duetoaneventorcondition that couldhave prevented the fulfillment ofthesafety function ofastructure orsystem that isneeded tomitigate theconsequences ofanaccident.

TheHPCIsystem isasingle-train system that isdesigned toensure that thereactor isadequatelycooled tolimit fuel-cladding temperature intheeventofasmall break inthenuclear system andaloss ofcoolant doesnot result inarapid reactor pressure vessel depressurization.

TheHPCIsystem will continue tooperate until theReactor Pressure Vessel (RPV) isbelowthepressure atwhich either operation oftheLowPressure Coolant Injection (LPCI) modeof the Residual HeatRemoval (RHR) system ortheCoreSpray(CS) system will maintain corecooling.

Uponasmall break inthenuclear system whichresults inaLossofCoolant Accident (LOCA),

HPCIprovides sufficient inventory toprevent thecorefrombecoming uncovered.

Intheeventthat HPCIisunavailable orinoperable, the Automatic Depressurization System (ADS) iscredited todepressurize theRPVtoenable operation ofthelowpressure ECCSsystems, i.e.,

CSorLPCI.

Reactor CoreIsolation Cooling (RCIC) isalsoavailable torestore andmaintain water level.

Although HPCIwasdeclared inoperable, ADS,CS,LPCI,andRCICwereoperable andavailable toprovide core cooling intheeventofasmall break LOCAoraDesign Basis Accident (DBA)

LOCATherefore, basedontheability of thestation tomitigate theconsequences ofaloss oftheHPCIsystem combined with asmall break LOCA,this eventis considered tohaveverylowsafety significance.

Corrective Actions:

Thedegraded HPCIinverter wasremoved fromservice andreplaced, andthenewinverter functionally tested satisfactorily.

Theproximate causeofinverter failure hasnotyetbeennotdetermined.

Thestation will perform an equipment causal analysis incoordination withtheoriginal equipment manufacturer todetermine thedirect causeof therandom early life-cycle failure.

Previous Similar Events:

Review ofstation historic reportable events revealed similarinstances oftheloss ofHPCIsystemfunction attributed to different electronic component failures inthe turbine control logic scheme:

LER2015-001-00 LossofHighPressure Coolant Injection System Function asaResult ofFailed FlowController Signal Converter LER2005-001-00 LossofHighPressure Coolant Injection System Function asaResult ofInoperable FlowControllerP@ 4 Of 4