Design of a new experimental loop and of a coolant purifying system for corrosion experiments of EUROFER samples in flowing PbLi environment

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Fusion

Engineering

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Design

j ourna l h o m e pa g e :w w w . e l s e v i e r . c o m / l o c a t e / f u s e n g d e s

Design

of

a

new

experimental

loop

and

of

a

coolant

purifying

system

for

corrosion

experiments

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EUROFER

samples

in

ﬂowing

PbLi

environment

D. Martelli

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_G.

_Barone

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_M.

_Tarantino

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_M.

_Utili

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a_University_of_Pisa,_Dipartimento_di_Ingegneria_Civile_e_Industriale,_Largo_Lucio_Lazzarino_2,₅₆₁₂₂_Pisa,_Italy b_ENEA_Brasimone,₄₀₀₃₂_Camugnano,_Bologna,_Italy

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•DevelopmentofanexperimentalfacilityforthestudyofEUROFERcorrosioninﬂowingPbLi. •Developmentofacoldtrapsystem.

•Calculationofthemaximumallowablecorrosionsourceasafunctionofthecoldtraptemperature.

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Articlehistory:

Received29September2016

Receivedinrevisedform26January2017 Accepted28January2017

Availableonline14February2017 Keywords:

EUROFERcorrosion LIFUSII

Coldtrap

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Theuseofferritic/martensiticRAFMsteelsinPbLiblanketapplicationsrequiresabetterunderstandingof materialcompatibilityrelatedtophysical/chemicalcorrosionphenomenainthe450–550◦_C_temperature range.Theimpactofcorrosionincludesdeteriorationofthemechanicalintegrityoftheblanketstructure duetothewallthinning.Furthermore,seriousconcernsareassociatedwiththetransportofactivated corrosionproductsbythePbLicoolant.Inthisframe,thepresentworkaimstoillustratethedesignof anewexperimentalfacilitynamedLIFUSII(LIthiumforFUSionII)intendedtoextensivelyinvestigate corrosionmechanismsrelatedoncoated(Al2O3based)anduncoatedEUROFERsamplesatconstant tem-peratureof550◦_C,_for_three_different_velocities_and_four_different_exposure_times._Moreover,_a_“cold_trap” puriﬁcationsystemisdesignedtoremoveimpuritiesandcorrosionproductsdissolvedintheliquidmetal viaupperconcentrationlimitsimposedbytemperature-dependentsolubilityconstrains.

1. Introduction

Thereducedactivationferritic/martensitic(F/M)steel EURO-FERiscurrentlyconsideredthereferencestructuralsteelforPbLi breedingblanketsinthefutureEuropeanDEMOreactor[1].Due totheextremeoperatingcondition,EUROFERcorrosionand cor-rosionproducttransportphenomenaconstitutestronglimitations fortheblanketdesignandforthePbLiloopsafety(plugging phe-nomenaandregionwithhighconcentrationofactivatedmaterials). AvailableexperimentaldataonthecorrosionrateforF/Msteels inﬂowingPbLishowalargedispersion,predictingvaluesathigh temperatures(450–500◦C)from5␮m/yrtoafewhundred␮m/yr [2].ThesameissueisobservedforthesolubilityofironinPbLi:

∗ Correspondingauthor.

E-mailaddresses:daniele.martelli@ing.unipi.it,martelli.daniele@gmail.com

(D.Martelli).

datafromdifferentcorrelationsareaffectedbyadispersionof sev-eralordersofmagnitude[3].Moreover,detailedinformationabout experimentalconditions,suchasthePbLiflow velocityandthe amountofimpuritiesdissolvedinthePbLialloy,areoftenmissing. ThislackofdataprecludesalsoarationaldesignofaPbLi purifica-tionsystemaffectingtheimpuritiessourcetermandthemaximum solubilityvalueabovewhichprecipitationoccurs.Inthisframenew experimentalactivitiesareforeseeninordertoinvestigate EURO-FERcorrosionbehaviourfortemperaturesandvelocitiessignificant fortheHeliumCooledLithiumLead,WaterCooledLithiumLeadand DualCoolantLithiumLeadBreedingBlanketdesign.The develop-mentofanewexperimentalapparatus,toberealizedattheENEA BrasimoneR.C.,ishereproposedaimingatassessingcorrosionrates onuncoatedandcoatedEUROFERsamplesataconstant tempera-tureof550◦C,forthreedifferentvelocities0.01,0.1and1m/sand fourdifferentexposuretimes1000,2000,4000and8000h.

http://dx.doi.org/10.1016/j.fusengdes.2017.01.054

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Fig.1.LIFUSIIP&ID.

2. Descriptionofthefacility

LIFUSII(seetheP&IDreportedinFig.1)isalooptype exper-imentalfacilitydesignedwithaclassical“eightshape”.Twotest sections(TS-1,2)areinstalledinseriesinthehotlegoftheloop withanoperatingPbLitemperatureof550◦C.Onthecoldleg, oper-atedat400◦C,areinstalledtheelectromagneticpump(EP-100),the inductionflowmeter(IFM-105)andtheby-passtodriftaportion ofthetotalmassflowratetowardsthecoldtraps(CT-101,CT-102) forthepurificationprocess.

Thehotandcoldlegsarecoupledthroughaneconomizer (E-300)consistinginashellandtubePbLi/PbLiheatexchanger.The hotfluid(Th,in550◦C)enterstubesidesandcoolsdownto450◦Cat theexitsectionoftheheatexchanger.Onthecontrary,thecoldfluid (400◦C)entersshellsideandisheatedupto500◦C.Consideringthe totalmassflowrateof∼4.6kg/sandatemperaturejumpacrossthe economizerTECO∼100◦Ctheheatexchangedisabout87kW.The PbLiintheshellsideisthenchannelledtowardsthehotlegwhere, throughasubsequentheatingmodules(HT-350),reachesthe oper-atingtemperatureof550◦C(requiredpower∼45kWsuppliedby aseriesofelectricalheatingbandsinstalledona2½pipe,Fig.1).

PbLienteringthecoldlegneedstobefurthercooledtoreach 400◦C.Thisoperationisaccomplishedsplittingthetotalflowinto a portion channelled towards thepurification system where it is cooled down(e.g. 270◦C),while theother portionat 450◦C bypassesthepurificationsystem.TheflowrepartitionandtheCold Trap(CT)outlettemperaturearesuchthatthetwopartitionsre-join downstreamthepurificationzoneatanominalcoldtemperatureof 400◦C.Thereby,theCTcoversthedualfunctionofloopcoolingand purificationsystem.SuchaCTarrangementoffersaflexible opera-tionintermsoftreatedflow,permittinghence,awiderassessment ofthepurificationsystemefficiency.FromaheatbalancetheCT mustbedesignedtoremove∼45kWinordertomeettherated coldlegtemperaturerequirementof400◦C.ThedesiredPbLimass flowrateisguaranteedbyanelectromagneticpump(EP-100)with permanentmagnet(PMP,alternatingtravellingmagneticfield gen-eratedbya rotatingmagneticsystemwithpermanentmagnets poleswithalternatingpolarity)installeddownwardsthecoldtrap andoperatingatatemperatureof400◦C.Aninductionmassflow meter(IFM-105)isusedtomonitorandcontroltheloopmassflow rate.Thereferencestructuralmaterialforpipingandcomponents (HXEconomizer,TestSections,etc.)issteel2¼Cr-1Mo(ASTMA335 Gr.P22),whoserelativelylowcorrosionrate(lownickelcontent

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Fig.2. CompositionofAl,Fe,CrandOwithinanAl-baseddiffusioncoatingabove theEUROFERsteel[7].

andconsequentlowdegradationbyprecipitation)contributesto minimizationofthecorrosionproductsdissolvedinthealloy.The mainpipelineofthecircuitconsistsof2Sch.80XSpipes,which guaranteesarelativelylowPbLipipingvelocity(0.25m/s) minimis-ingthepipelinecorrosion.Thecircuitiscompletedbythestorage vesselS-100withﬁllinganddraininglines,theexpansionvessel S-200andaremovablegloveboxinstalledabovethetestsections toensurethespecimensextractioninacontrolledandprotected atmosphereavoidinganycontaminationoftheloopwithoxygen duringthisphase.Inordertoreducethepluggingrisk,together withtheCTcomponentdesign,acoatingtreatmentofallthe struc-turalsteelinPbLiistakenintoconsideration.Accordingto[4–6], theAl-basedcoatingsuitableforoperationinPbLiisadiffusion doublelayerwheretheexternallayerconsistsoftheAl-Fephase andtheinternallayerconsistsof˛-Fe(Al)phase.Abovethedouble layerthereisalsoathinAl2O3layerwhichprovidesanenhancing protectionfeature.Fe-Aland,inparticular,␣-Fe(Al)andAl2O3are theprotectivephasesofthecoatingsincetheyhavelow solubil-ityinPbLi.OtherAl-enrichedphases(suchasFeAl2andFe2Al5)are unwantedandmustbeavoidedsincetheyarebrittleandsolublein theliquidmetal.Anexampleofgoodprotectivecoatingsfor oper-ationinPbLiisreportedin[6],wherethecompositionsofAlwithin eachAl-phasesarereportedinFig.2.Clearlyvisiblearetheexternal Al2O3layerwith40%ofAlandthe␣-Fe(Al)phaseswithabout15% ofAl.Thecoatingthicknessis50␮m.

3. Testsection

Twoidenticaltestsections(TS-1and2,Figs.1and3),vertically arrangedplacedinsequenceandworkingatconstanttemperature, areforeseeninthehotlegoftheloop(550◦C).TheﬁrstTSwill beadoptedforshortandmedium-termtests(1000,2000,4000h) whilethesecondonewillbeusedforlongtermtest(8000h).Each TSisdesignedwiththreespeciﬁccrosssectionscharacterizedby increasingtheinnerdiameter(1,3and10)inordertoprovide therequestedvelocitiesinsideeachTS(respectively1.0,0.1and 0.01m/s).

Foreachvelocitysection,asetof6specimensareforeseen(3 uncoated+3coatedwithouterdiameterof10mmandalengthof 37mm(M5),screwedtogethertoformarodtobeinsertedinside thetestsection).DummyelementsareforeseenintheTSregion wherecrosssectionvariationoccurs.Thesamplesrodwillbe fas-tenedintheupperpartoftheTSwhilekeptfreetoexpandinthe lowerparttoavoidstressesduetodifferentthermalexpansions.In

Fig.3.TestSection.

Table1themainparametersthatcharacterizetheTSgeometryand theﬂowconditionsarereported.

The proposed corrosion-resistant coating is an Aluminium-based layer consisting of an amorphous matrix of Al2O3 with nano-crystallineinclusionsobtainedbymeansofPLD(PulsedLaser Deposition)techniquein theCNST(Center ofNano-Science and Technology) laboratories at IIT (Italian Institute of Technology) [8,9].

4. Puriﬁcationsystem

TheCTsystemconsistsofaheatandmasstransferdevice,where asupersaturatedsolutionofimpuritiesisgeneratedastheresultof PbLicooling,causingthecrystallizationoftheimpuritiesbothon theimmovablesurfacesandinsuspension.TheprincipleoftheCT istomaintaintheimpurityequilibriumconcentrationintheloop belowthePbLisolubilityat400◦C(coldzonetemperature).Such anapparatushasthepurposeofcollectingtheimpuritiesgenerated duringtheoperation,avoidingtherefore,thecorrosionproducts precipitatingintheloop.Althoughthepurificationprincipleis rel-ativelysimple,thedesigndifficultiesofacoldtraparesignificant andarerelatedtothelackofreliableexperimentaldataorempirical correlationon:

-steelcomponentssolubilityinPbLi(e.g.CrandFe); -thekineticsgoverningtheprecipitationphenomena; -thetotalsourcetermofthecorrosionproducts.

Foragenericsystemsolute/solventsystemwithasourceterm andprovidedwithapuriﬁcationapparatus,theimpurities concen-trationC(t),inppm,canbeobtainedfromabalanceequation:

C(t)=C∞(1−e ˙mctM t) (1)

whereMisthePbLitotalmassinthesystem(kg), ˙mctisthemass flowintheCT,theCTefficiencyandC∞theasymptotic concen-tration(t→∞)definedas:

C∞=

S ˙mct +C Sat ct

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Table1

TSmainparameter.

Quantity Unit Sec-1 Sec-2 Sec-3 NOTE

v m/s 1 0.1 0.01 Sectionvelocity Ap m2 4.7910−4 4.6910−3 4.8110−2 FlowArea Di mm 26.64 (1_Sch.40) 77.92 (3_Sch.40) 247.65 (10_Sch.60)

Secinnerdiameter (Size)

dh=4A/PW m 1.6610−2 6.7910−2 2.3810−1 Hydraulicdiameter

L m 0.304 0.466 0.55 Sectionlength

Re=␳VL/ – 1.56105 ₆₅₀₅₅ ₂₂₁₉₉ _Reynolds_number

m kg/s 4.6 Massﬂowrate

Pas 1.0210−3 _PbLi_viscosity_at₅₅₀◦_C

kg/m3 _9541.5 _PbLi_density_at₅₅₀◦_C

d m 0.01 Sampleouterdiameter

Fig.4.IronsolubilityinPbLi.

whereSisthesourceterm(␮g/s),CSat

ct representstheironsolubility attheminimumCTtemperature,Tct(beingtheironthemain com-ponent).ConcerningtheCTefﬁciency,itcanbegenericallydeﬁned as:

=Cin−Cout Cin−CctSat

(3) andinaninitialassessment,itisassumedtohavethesameform oftheCTefficiencydefinedforthesodiumpurificationsystem:

= 1

1+pq (4)

where␶representstheﬂuidresidenttime(min)intheCTandp,q arecoefﬁcientssetequalto122and3.4respectivelyforsodiumCT [10].TheappropriatenessofsuchacorrelationforPbLicorrosion systemwillbeevaluatedexperimentallywithchemicalanalysisof PbLisamplingupstreamanddownstreamtheCT.

Inapreliminarydesign,theavailablecorrelationsfor determin-ingironsolubilityinPbLi[2](Fig.4)wereinvestigatedtodetermine themaximumcorrosionsourceasafunctionofTct,(Fig.5)obtained fromEq.(2) imposing C∞<CSat

400◦C in order toavoidanymetal precipitationinthecoldzoneoftheloop(T_cold=400◦C):

Smax₌_˙m ct

Csat 400◦C−Cctsat

(5) According to the Smolentsev [2] correlation, chosen as ref-erence, themaximum source termallowablein order to avoid precipitation of corrosion products in thecold leg of the loop (T∼400◦C)foraCTtemperatureintherange270–300◦Cisabout 3.6_␮g/s(0.11kg/yr).

The saturation concentration signiﬁcantly decreases in the rangefrom450to250◦C,forthisreasonaminimumCT

temper-Fig.5. Maximumallowablecorrosionsource.

atureofT_CT=270◦Cisfixedtokeepanacceptablesafetymargin fromthesolidificationtemperature(235◦C).ForTCT=270◦C the minimumflowbypassedinCTisabout1.3kg/s(beingtheCT cool-ingpowerfixedtoabout45kW).Themaximumtemperatureinthe CTis400◦CifweconsidertoprocessallthePbLimassflowrate.

AnothersignificantparametertobedefinedistheCTresidence time,␶,affectingthedepositionkineticsandthereforetheCT effi-ciency. This parameter depends on the CTvolume, VCT and is inverselyproportionalto ˙mct.ThevalueofVCThasbeensettoabout 50l,inordertoobtainaresidencetimemaximumvalue␶≈400s (for ˙mct=1.3kg/s)andaminimumvalue␶≈110s(for ˙mct=4.6kg/s). RegardingthelayoutoftheCT,ashellandtubeheatexchangerwith 2-passtubesideconfigurationisproposed.PbLienters,shellside,at 450◦Candexitsat270◦C–400◦C.Theinnerdiameteroftheshellis 303.23mm(12Sch.40)andthevelocityofthePbLiisintherange 2–6mm/srespectivelyfor1.3and4.6kg/s.Aseriesofbaffleassures bothaneffectiveliquidmetalcirculationandanincreasedCT pre-cipitationsurface.ThepreliminarysketchoftheCTisreportedin Fig.6.

The purification system will be arranged in a parallel con-figuration in order to ensure the continuous operation of the experimentalfacility(ifneeded,theflowwillbedivertedinthe secondCT-102,whilethefirstone(CT-101)canbedrainedand dis-assembledformaintenanceorreconditioning,e.g.removalofthe pluggedimpurities).UpstreamanddownstreamtheCTsasampling devicesisforeseentoextractthecirculatingPbLiandtoanalyzeits impuritiescontentaimingatassessingtheCTefficiency.

Thesecondarysideofthepurifyingsystemconsistsina pres-surizedwaterloop(seetheP&IDSchemeinFig.7).Thepressure ofthesecondaryloopissetto20bar(Tsat=212◦C),theinletand

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Fig.6. PreliminaryCTconﬁguration.

outletwatertemperaturesare160◦Cand193◦Crespectively,with awatermassflowraterangeof0.2–1kg/s.Thewaterflowsthrough abundleof12(U-tubeconfiguration),double-walltubeswitha stainlesssteelpowderfillingthegapbetweenthetwotubes(Fig.6). Thisgeometryprovidesadoublephysicalseparationbetweenthe twofluidsthatallowsthethermo-mechanicallydecouplingofthe

TheAirCooler,E-501,isdesignedtoremovethepowerfrom watersecondaryﬂuidwhile,theheatingsystemHT-501is consid-eredinordertopre-heatthewaterattheoperatingconditions.

5. Conclusions

A new facility named LIFUS-II, to be constructed at ENEA BrasimoneR.C.,hasbeendesignedtoinvestigatetheRAFM/PbLi corrosionaspectsforthecurrentbreedingblanketconcepts.The LIFUS-IIexperimentalcampaignwillbedevotedtoevaluatethe corrosionrateofthereferencesteeland thechemical compati-bilityofanewAl-basedcoating proposedasanti-corrosionand anti-permeationbarrierinﬂowingPbLi.Therefore,uncoatedand coatedEUROFERsampleswillbeexposedtodifferentPbLiﬂow velocities(1.0,0.1and0.01m/s)atatemperatureof550◦C. Exper-imentaldatawillbecollectedatdifferentexposuretimes(1000, 2000,4000and8000h).

Finally,aCTpreliminarydesignisproposedtogetherwiththe samplingsystemtomaintainimpuritiesconcentrationbelowthe coldzonesaturationpoint,avoidingprecipitationinthecoldestpart oftheloopandprovidingdetailedinformationaboutexperimental conditions.Moreover,theexperimentalcampaignwillbeusefulin ordertoassesstheparametersaffectingthepuriﬁcationefﬁciency.

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Acknowledgments

This work has been carried out within the framework of theEUROfusionConsortium and hasreceivedfundingfromthe Euratomresearchandtrainingprogramme2014–2018undergrant agreementNo633053.Theviewsandopinionsexpressedhereindo notnecessarilyreﬂectthoseoftheEuropeanCommission.

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[2]S.Smolentsev,etal.,Numericalstudyofcorrosionofferritic/martensitic steelsintheﬂowingPbLiwithandwithoutamagneticﬁeld,J.Nucl.Mater. 432(2013)294–304.

[3]M.Abdou,etal.,Blanket/ﬁrstwallchallengesandrequiredR&Donthe pathwaytoDEMO,FusionEng.Des.100(2015)2–43.

[4]H.Glasbrenner,etal.,CorrosionbehaviourofAlbasedtritiumpermeation barriersinﬂowingPb-17Li,J.Nucl.Mater.307–311(2002)1360–1363.

[5]J.Konys,etal.,Comparisonofcorrosionbehaviorofbareandhot-dipcoated EUROFERsteelinﬂowingPb-17Li,J.Nucl.Mater.367–370(2007)1144–1149.

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developmentforfutureDEMOblankets,J.Nucl.Mater.417(2011)1233–1236.

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[9]F.GarcíaFerré,etal.,AdvancedAl2O3coatingsforhightemperature operationofsteelsinheavyliquidmetals:apreliminarystudy,Corros.Sci.77 (2013)375–378.

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Design of a new experimental loop and of a coolant purifying system for corrosion experiments of EUROFER samples in flowing PbLi environment

Fusion

Engineering

and

Design

Design

of

a

new

experimental

loop

and

of

a

coolant

purifying

system

for

corrosion

experiments

of

EUROFER

samples

in

ﬂowing

PbLi

environment

D.

Martelli

,

G.

Barone

,

M.

Tarantino

,

M.

Utili

h

i

g

h

l

i

g

h

t

s

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t



_,

_G.

_Barone

_,

_M.

_Tarantino

_,

_M.

_Utili