Design and fabrication of a permeator against vacuum prototype for small scale testing at lead lithium facility

Design and fabrication of a Permeator Against Vacuum prototype for small scale testing at Lead Lithium facility F D s B J a b h • • • • • a A R R A A K D P M P 1 c ( a t t A t h 0 0 ARTICLE IN PRESSG[.]

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j o u r n a l h o m e p a 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 and fabrication of a Permeator Against Vacuum prototype for

small scale testing at Lead-Lithium facility

Belit Garcinu ˜ noa,∗, David Rapisardaa, Iván Fernández-Bercerueloa, David Jiménez-Reya,

a CIEMAT-LNF, Av Complutense 40, 28040 Madrid, Spain

b UNED, Dept of Energy Engineering, C/Juan del Rosal 12, 28040 Madrid, Spain

•ThemanufacturingdesignofaPermeatorAgainstVacuumprototypeispresented

•ThePAVwillbeimplementedinaPbLilooptodemonstratethetechnique

•Operationalinputs(massflow,temperature)areevaluatedforafixedgeometry

•Twoapproachesarecomparedintermsofefficiency,assemblyandendurance

•APAVbasedonvanadiummembranesandsteelsupportingstructureisproposed

Article history:

Received 3 October 2016

Received in revised form 15 February 2017

Accepted 15 February 2017

Available online xxx

Keywords:

DEMO

Permeation against vacuum

Membrane

Prototype

TritiumrecoveryisoneofthemajorissuesofafutureDEMOreactor,inordertocomplywiththe require-mentsoftritiumself-sufficiency.WithintheEUROfusionProgrammethepermeationagainstvacuum (PAV)techniquehasbeenconsideredasbaselineforthoseblanketswhichusePbLiasbreeder

A conceptual design of a rectangular multi-channel PAV for its implementation in an exper-imental PbLi loop, under construction at CIEMAT, has been produced A comparison between vanadium/niobium/tantalumand␣-Femembraneshasbeenperformedintermsofcosts,machining, mechanicalresistanceandefficiencyresultinginadesignbasedonvanadiummembranesandastainless steelstructure

Structuralcalculationsarealsopresented,payingspecialattentiontotheinterfacebetweenthe mem-branesandthemainstructureinordertoavoidleakages.Otherimportantaspectssuchaskeepingan adequatevacuumlevelhavealsobeenconsidered

©2017TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-ND

license(http://creativecommons.org/licenses/by-nc-nd/4.0/)

1 Introduction

TheDualCoolantLithiumLead(DCLL)isoneoftheblanket

con-ceptswhicharebeingconsideredforEU-DEMO.Itusesliquidmetal

(eutecticPbLi)asprimarycoolant,tritiumbreeder,tritiumcarrier

andneutronmultiplier[1]

Oneofthemostimportantfunctionsoftheblanketistoachieve

tritiumself-sufficiency[2];consequentlythedevelopmentof

tri-tiumrecoverysystemsfromthebreederismandatory.Permeation

AgainstVacuum(PAV)hasbeenselectedasfirstcandidatefor

tri-tiumextractionfromPbLiintheDCLL[3].Itsworkingprincipleis

∗ Corresponding author.

E-mail address: belit.garcinuno@ciemat.es (B Garcinu ˜ no).

basedontritiumdiffusionthroughapermeablemembranein con-tactwiththeflowingliquidmetal.Then,thetritiumisextractedby

avacuumpumpwhichdrivesittothetritiumplant.However,this techniquehasnotbeenexperimentallyvalidated,andsomeefforts arebeingperformedinEuropewiththepurposeofdemonstrating itscapabilities

ThepresentworkprovidesthedesignofasmallscalePAV proto-typebasedontheconceptualdesignpresentedin[4].Adescription

of thePbLi loopdriving thePAV design ispresented inSection

2;geometricalcharacteristicsofthedeviceareshowninSection

3;structuralcalculationsandmainissuesconcerningits fabrica-tionarepresentedinSection4andthePAVauxiliarysystemsare describedinSection5.Finally,conclusionsaredrawninSection6

http://dx.doi.org/10.1016/j.fusengdes.2017.02.060

0920-3796/© 2017 The Authors Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4 0/ ).

Parameter Value

PbLi max velocity in PAV-DCLL 1 m/s

2 Facility for tritium extraction from PbLi at high velocity

WithintheEUROfusionR&Dprogrammedifferent

experimen-talactivitiesrelatedtoadvancedtritiumextractiontechniquesare

beingperformed[3].Thus,PAVhasbeenconsideredasthemost

promisingtechniqueforextractingtritiumfromflowingPbLi.Its

operationalconditionsdependontheblanket conceptwhich is

beingconsidered;inthecaseofaDCLLtheseconditionscanbe

foundin[5].TheconstructionofaPbLiloopfordemonstratingthe

PAVtechniqueathighPbLiflowsisbeingimplementedatCIEMAT

Thisloopwillmanageonlya1.5%ofthemassflowrateexpectedfor

oneoftheDCLLloops[4],butworkingatDCLLconditionsinterms

ofPbLitemperatureandvelocityinsidethePAVchannels.Themain

objectivesofthisPbLiloopwillbeto:

-Testhydrogen/deuterium permeationin flowing PbLi atDCLL

conditionsoftemperature,velocityandtritiumpartialpressure

-Testdifferentpermeatorconceptsorconfigurationsforefficiency

assessment

-TestdifferentmaterialstobeusedasmembraneofthePAV

Thetarget efficiency of theTritium Extraction System(TES)

hasnotbeenfullyassessed.Differentworkshaveproposed

tar-getvaluesashighas90%[6]or80%[7].Thereforeitiscommonly

agreedthat tritiumrecovery efficiencyshall beas highas

rea-sonablyachievable[8],andaconservativevalueof80%hasbeen

consideredtobeenoughforaproperoperationoftheplant[4].For

thisPbLiloopandPAVprototypeanefficiencytargethasnotbeen

fixedasanobjectivesinceoncethefeasibilityofthetechniqueis

demonstrated,theefficiencycanbeincreasedbyachangeinthe

PAVgeometry.Furthermore,itwillgiveanimportantbenchmark

withthemodelstoextrapolatetheresultstotheDCLLTES

Theloopwillbedividedintotwosectionswithdifferent

tem-peratures:acoldleg workingat300◦C whichis equippedwith

anelectromagneticpumpandaflowmeterwithloweroperational

requirementsintermsoftemperature;ahotleg(550◦C)wherethe

testsectionisinstalled.Table1summarizesthemainparameters

oftheloop

3 PAV design optimization

Accordingtothecalculationmethodpresentedin[4],asmall

scaleprototypeofPAV,TRITON(TRITiumpermeatiON),hasbeen

developed.ItsdesignisconditionedbythePbLiloopparameters

presentedinSection2.AlthoughtestswillbedoneatdifferentPbLi

velocities,thetargetvalue,relevantforaDCLLDEMO,is1m/s[4]

Forthisreason,thestudyoftheinfluenceofeach parameterto

optimizethedesignhasbeenperformedbyfixingthatvelocity

Takingintoaccounttheavailablespaceforthepermeator

imple-mentation,namely1.5mintheexperimentalroom,themembrane

hasto be limited to 1mlength (L) Thus, the main parameter

affectingTRITONdesignisthePbLimassflowrate(m)whichwill

determinethenumber of channels(N) and theirwidth(a) [4]

Anotherimportantparameteristhechannelheight(h).Lowh

val-uesleadtohighpressuredrops,andregardingtherangeofmass

flowrate,theheighthasbeenmaintainedat5·10−3m.Itiseasy

Fig 1.Efficiency dependence with mass flow rate (h = 5·10 −3 m;

z = 1·10 −3 m; a = 0.085 m; N = 7; T = 823 K;  Fe = 1.75·10 −10 mol/m/s/Pa 0.5 ;

 V = 1.52·10 −7 mol/m/s/Pa 0.5 ).

tofollowthatadecreaseinthemembranethickness(z)resultsin

animprovementofefficiencydue totheincrease ofthe perme-ationflux.Regardless,themechanicalresistanceofthemembrane shouldbetaken into account; thereforez isset to1·10−3m. A

slightincreaseoftheefficiencywithgrowingvaluesofahasbeen observed.Consideringtherangeofmassflowrateachievablein theloop(Table1 thechannelwidthisfixedto0.085mandthe numberofPbLiflowingchannelto7(therefore8vacuumchannel) Hence,thePbLiisabletoreach1m/sinsidethePAVandthereis alsocertainflexibilityonitsoperation

ThebestmaterialsforthePAVmembrane arevanadium(V), niobium(Nb)andtantalum(Ta)duetotheirgoodpermeability(˚) [10]andcompatibilitywithPbLiinstaticconditions[11].Forthis firstprototypeareducedpricewouldbedesirableinorderto miti-gaterisksintheoverallbudgetoftheProject.Thus,inordertosave costsand consideringtheavailabilityofmaterials,itwas estab-lishedtouse␣-Femembranesforthefirstprototype.Inspiteofits lowpermeability[12],thismaterialcanleadtoenoughextraction capabilityinordertodemonstratethepermeationtechnique

Itisimportanttonotethatthereissomedispersionin mea-suredhydrogensolubilityinPbLi.Dependingonthemethodology followedforitsachievingandtheeutecticgradeofthealloyitcan changeuptotwoordersofmagnitude[13].Forthisreason,Sievert’s constantsfromReiter[14]andAiello[15]havebeenusedforthe studyasthemostoptimisticandpessimisticcases,respectively Figs.1and2showthedifferencebetweenPAVefficienciesfor bothVandFemembranes.Fig.1showsthedependenceofthe effi-ciencywiththePbLimassflowintheloop,accordingtoEq.(2)from [4],usingthetwovaluesofhydrogensolubility[14,15].Asexpected,

anincreaseonthemassflowrate,withthesubsequentincreaseon velocity,impliesadecreaseontheefficiencyfollowingthe expo-nentialrelationshowedin[4].InthecaseofVmembranes(higher permeability)thepermeationfluxisdrivenbymasstransport(i.e tritiumtransportinthePbLi).Hence,achangeinthesolubilityis lessaccentuated.Onthecontrary,whenusingFethepermeationis limitedbymembraneprocesses,causinghigherimpactonthePAV efficiency

Aninterestingsituationarises whenthetemperatureis var-ied(Fig.2)atafixedmassflow(28.4kg/scorrespondingto1m/s

inthePAVchannels)followingEq.(2)from[4].Although

hydro-Fig 2.Efficiency dependence with temperature (m = 28.4 kg/s; h = 5·10 −3 m;

z = 1·10 −3 m; a = 0.085 m; N = 7; T = 823 K;  Fe = 1.77·10 −8 exp(-31600/R/T)

mol/m/s/Pa 0.5 ;  V = 4·10 −9 exp(24900/R/T) mol/m/s/Pa 0.5 ).

Table 2

TRITON main parameters.

Channel height 0.005 m

Membrane thickness 0.001 m

Number of channels 7 (15)

Membrane area 1.26 m 2

Table 3

PAV efficiency.

Mass flow Material Reiter Aiello

gensolubilityinPbLiincreaseswithtemperature(fasterforAiello;

disfavoringtheextractionprocess),theincreaseofthediffusivity

inthealloyisfasterandhencetheefficiencyisenhanced

How-ever,hydrogenpermeabilitythroughVdecreaseswithtemperature

(contrarytowhathappensinFe)andfortemperatureshigherthan

652◦CthehugesolubilitygivenbyAiellodiminishestheefficiency

Accordingtoallthesedatathemainparametersresultingfor

thepermeatorprototypedesignaresummarizedinTable2

4 Manufacturing

Regardingthemanufacturing process,structural calculations

andassemblypossibilitieshavebeenperformedwhen

consider-ingtwodifferentapproaches (FeorV).Therangeofefficiencies

achievedwiththesematerialsisalsopresentedasafunctionofthe

massflowrateandthehydrogensolubilityinPbLi

4.1 ˛-Femembrane

Accordingtothemassflowratelimits(Table1 theproposed

designshows anefficiencyfor␣-Femembranesrangingfrom4

to28%,consideringReiter’ssolubility.WhenAiello’ssolubilityis

applied,theefficiencyrangesfrom0.1%to2%,Table3

Fig 3.a) ␣-Fe von Mises stress (MPa); b) ␣-Fe total deformation (mm); c) Steel structure von Mises stress (MPa); d) V sheets von Mises stress (MPa) (For interpre-tation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Forthepermeatorconstructionthemostfeasibleoptionseems

tobethestackingofplatesinalateralstructure,alsomadeofFe,

todefinethechannels.Stiffeningelementslocatedinsidevacuum channelsareneededinordertoavoid membranedeformations Fig.3ashowspreliminaryelasticanalysesperformedinorderto finda suitable arrangementof thestiffeners The resultingvon Misesequivalentstressesareunderthereferenceyieldstrength foriron(150MPa).However,therearesomeissuesrelatedtothe useofthismaterial.Theferriticstructureof␣-Fewithlow con-tentoncarboncomplicatesthemechanizationduetoitssoftness andmagneticproperties.Therefore,thepossibilityofusingother membranes,inspiteofthepriceoravailability,hasbeenexplored 4.2 V,Nb,Tamembrane

Asstated,V,NbandTahavegreatpermeabilityproperties.The efficiencyachievedwiththesethree materialsispractically the same,rangingfrom38-39%to21-26%dependingonthehydrogen solubilityinPbLi,seeTable3.ThehugedifferencebetweenFeand V/Nb/Tapermeabilitiesleadstoadifferentrelationbetweenthe coefficientofsolubilityusedandtheefficiencyprovidedbyeach material,asitwasexplainedinSection3

Thepriceofthesematerialsisratherhigh.Accordingto[16]it

isabout4timeshigherthanFe.Inordertoreducethetotalamount material,achangeontheassemblydesignhasbeenintroduced: onlythemembranesaremadeofV/Nb/Tawhilethesupporting structureisfabricatedwithstainlesssteelAISI410.Duetothehuge meltingtemperatureofNbandTa(higherthan2500◦C)the weld-ingwithstainlesssteelisnotstraightforward,henceitisneeded

aninterface.ThiscomplicationisavoidedwiththeuseofV mem-braneswhichhaveameltingtemperatureof1900◦C,neartothat

ofthesteel,1530◦C.Therefore,TIGweldingcanbeusedforthe fabricationofthePAV.Itmustbeunderlinedthattheemployof twomaterialswithdifferentaveragecoefficientsofthermal expan-sion (∼16␮m/m/◦C and 8.3␮m/m/◦C at room temperature for

austeniticsteelsandV,respectively)cancauseintolerablethermal stresseswhenthePAVisheatedupto550◦C.Theselectionofthe structuralmaterialisintherangeofmartensiticsteels,whichhave averagecoefficientsofthermalexpansionofabout10␮m/m/◦Cat

roomtemperature.Resultsfortheelasticanalysisunderthemost

Fig 4. a) TRITON design based on vanadium sheets (red) embedded on a stainless

steel structure (grey); b) PAV general view with vacuum devices and circuit

connec-tion (For interpretation of the references to colour in this figure legend, the reader

is referred to the web version of this article.)

unfavorableconditionsthatthepermeatorcanwithstand(500◦C

andPbLi velocity of1m/s) showthat themaximumvon Mises

equivalentstressforthesteelstructureisbelowtheyieldstrength

ofAISI410,Fig.3c.InthecaseofVsheets,Fig.3d,themaximum

vonMisesequivalentstressisaroundthehighestvalueindicated

bythesupplier(rangebetween124and172MPa).Themaximum

deformationalongthehorizontalaxisis7mmandwillnotaffect

thePbLiflow

5 PAV final design

Fromthetwo manufacturingdesigns presented,theV-based

PAVhasbeenselectedsinceitsolvesissuesrelatedtomachining

andstructuralresistance

TRITONfinaldesignisshowninFig.4a.Asupportingstructureof

stainlesssteelwithsplinestoallocatethe1mmthickand1mlong

Vmembranewasdesigned.14sheetsof90mmwidthareneeded

toform7PbLiflowingductsand8vacuumchannels.Thestructure

hassomelateralholesforvacuumextraction

Toclosethestructureandintegratethevacuumsystemabox

containingthe flange and feedthroughs for the vacuumpump,

thermocouples,pressuresensorsandheatingelementshasbeen

designed (Fig 4b) The connection to the PbLi circuitis made

througharoundtosquarediffusertodistributetheflowoverthe

PbLiducts

WithalltheseintegrationsthefinaldimensionsofTRITONare:

1.4mlength,28.4cmwidth(includingthevacuumflange

connec-tion)and20cmheight

DifferentauxiliarysystemsmustbeimplementedinthePAV

toproceedwiththeexperimentalphaseandareexplainedinthe

following

Sincetritiumpermeationfluxisdrivenbythepressuregradient generatedbetweenthetwosidesofthemembrane,itisneededto achieveagoodvacuuminordertoaccomplishwithahigh extrac-tionrate.ThevacuumvolumeinTRITONisabout16liters.Ahigh vacuumlevelisaccomplishedbytheuseofaturbomolecularpump TheHiPace500®,fromPfeifferVacuumGmbH,givesapumping speedupto445l/sforH2,enoughforthisapplication

5.2 Heatingsystem Sincetheexperimentsshouldbeperformedathigh tempera-ture,theintegrationof aheating systemis essential.A mineral insulated electrical resistance, from Thermocoax, will be used for that purpose It is made of an Inconel alloy sheath with a nickel/chromiumcoreaptforworkinginahighvacuum environ-mentandupto1000◦C.Itwillbeinstalledinthelateralfaceofthe PAVstructure,whereazig-zagslotwillhostthecable

5.3 Instrumentation Additionalinstrumentationisneededtocontrolthefluid tem-peratureandvacuumpressure:

• Type N- Nicrobell D sheath thermocouples, from TCDirect, installedintovacuumchannelstomeasuretheinternal temper-atureofthepermeatoralongitslength

• Pirani/cold cathodefull range gauge,from Pfeiffer-Vacuum,to controlthevacuumlevelanddisposedintheoppositefaceof thepumpconnection

6 Conclusions

Asmall-scaleprototypeofPAV,TRITON,hasbeendesignedto validateexperimentallythepermeationagainstvacuumtechnique

inflowingPbLiathighvelocity

Specificrequirementsformanufacturing,assemblyandtesting havedrivensomedesignchanges.Initially,theuse␣-Femembrane wasenvisioned.However,duetostructuralandmachiningissues

arearrangementwasintroducedinordertosimplifyandimprove thedesignwiththeuseofmoreadequatematerials.Thefinaldesign consistsonvanadiummembranesintoastainlesssteelstructure ThetargetefficiencyoftheDCLL-TEShasnotbeenfullyassessed; though a conservativevalue of 80% hasbeen established for a properoperationof the powerplant Since it wasnot a target drivingtheprototypedesign,theevaluationofoperational con-ditions(temperatureandmassflow rate)resultedina rangeof efficienciesbetween5and39%forVmembranesconsideringtwo valuesofSieverts’constant.AtrelevantDCLLconditionsan effi-ciencybetween24and27%isexpected

Theimplementationofauxiliarysystemshasalsobeenincluded

inordertokeepanadequatevacuumlevelandtherequired tem-peraturebothcontrolledwiththecorrespondingsensors

Acknowledgments

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

donotnecessarilyreflectthoseoftheEuropeanCommission.This workhasbeenpartiallyfunded by theMINECOMinistryunder projectENE2013-43650-R.B.Garcinu ˜noacknowledgesapre-PhD contractoftheSpanishMINECO

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