Progress in the initial design activities for the European DEMO divertor: Subproject "Cassette"

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J.H.

You

,

G. Mazzone

,

Ch.

Bachmann

,

D. Coccorese

,

V. Cocilovo

,

D. De

Meis

,

P.A.

Di

Maio

e

_,

_D.

_Dongiovanni

b

_,

_P.

_Frosi

b

_,

_G.

_Di

_Gironimo

d

_,

_S.

_Garitta

e

_,

_G.

_Mariano

f

_,

D. Marzullo

d

_,

_M.T.

_Porﬁri

b

_,

_G.

_Ramogida

b

_,

_E.

_Vallone

e

_,

_R.

_Villari

b

_,

_M.

_Zucchetti

g

a_Max_Planck_Institute_for_Plasma_Physics,_Boltzmann_Str._2,₈₅₇₄₈_Garching,_Germany

b_ENEA_Frascati,_Department_of_Fusion_and_Technology_for_Nuclear_Safety_and_Security,_via_E._Fermi_45,₀₀₀₄₄_Frascati,_Italy c_EUROfusion,_PMU_PPPT_Department,_Boltzmann_Str._2,₈₅₇₄₈_Garching,_Germany

d_{CREATE/University}_of_Naples_Federico_II,_Department_of_Industrial_{Engineering,Piazzale}_Tecchio_80,₈₀₁₂₅_Napoli,_Italy e_University_of_Palermo,_Department_of_Energy,_Viale_delle_Scienze,₉₀₁₂₈_Ediﬁcio_6,_Palermo,_Italy

f_Sapienza_University_of_Rome_Palazzo_Baleani,_Department_of_Energetics,_Corso_Vittorio_Emanuele_II,₂₄₄₋₀₀₁₈₆_Rome,_Italy g_Politecnico_di_Torino,_Department_of_Energy,_Corso_Duca_degli_Abruzzi₂₄₋₁₀₁₂₉_Torino,_Italy

h

i

g

h

l

i

g

h

t

s

•AbriefoverviewontheEuropeanDEMOdivertorcassettedesignstudiesispresented.

•Comprehensivecomputationalassessmentofmulti-physicalloadsisreported.

•Constraints,impactandimplicationsofpredictedloadingareexplained.

•Systemperformanceandrationalesoffurtherdesignoptimizationarediscussed.

a

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Articlehistory:

Received13September2016

Receivedinrevisedform26January2017 Accepted3March2017

Availableonline18March2017 Keywords: DEMO Divertorcassette Neutronics Cooling Thermohydraulics Electromagneticloads

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Since2014preconceptualdesignactivitiesforEuropeanDEMOdivertorhavebeenconductedasan integrated,interdisciplinaryR&DeffortintheframeworkofEUROfusionConsortium.Consistingoftwo subprojectareas,‘Cassette’and‘Target’,thisdivertorprojecthastheobjectivetodeliveraholistic pre-conceptualdesignconcepttogetherwiththekeytechnologicalsolutionstomaterializethedesign.Inthis paper,abriefoverviewontherecentresultsfromthesubproject‘Cassette’ispresented.Inthissubproject, theoverallcassettesystemisengineeredbasedontheloadanalysisandspeciﬁcation.Thepreliminary studiescoveredmulti-physicalanalysesofneutronic,thermal,hydraulic,electromagneticandstructural loads.Inthispaper,focusisputontheneutronics,thermohydraulicsandelectromagneticanalysis.

1. Introduction

Since2014preconceptualdesignactivitiesfordevelopingthe

divertorofEuropeanDEMOreactorhavebeenconductedinthe

framework of EUROfusionConsortium. The aimof the divertor

project(WPDIV) istodeliveraholisticdesign concepttogether

withthekeytechnologiesrequiredformaterializingtheconcept

preparingtheconceptualdesignphase. WPDIVisanintegrated,

∗ Correspondingauthor.Jeong-HaYou. E-mailaddress:[email protected](J.H.You).

interdisciplinaryR&Deffortwhere6researchinstitutesand3

uni-versitygroupsareinvolved.

WPDIVconsistsoftwosubprojectareas:‘Cassettedesignand

integration’(hereafter‘Cassette’)and‘Targetdevelopment’

(‘Tar-get’).Inthesubproject‘Cassette’,theoverallsystemofcassettebody

isengineeredwhereasinthesubproject‘Target’advanceddesign

conceptsandkeytechnologiesfortheplasma-facingcomponents

(PFCs)ofthetargetsaredeveloped[1,2].

ThisdesignstudyisbasedonthebaselineCADconﬁguration

modeloftheEuropeanDEMOplantissuedin2015[3].The

envis-agedfusionpoweris2037MW(netelectricpower:500MW).In

http://dx.doi.org/10.1016/j.fusengdes.2017.03.018

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Fig.1. (a)CADmodeloftheDEMOdivertorcassetteand(b)atargetPFCmock-upwithaschematicofthecrosssection[1].

thispaper,recentresultsfromtheWPDIVactivitiesarepresented

focusingonthesubproject‘Cassette’(Fig.1[1]).

2. Generaltechnicalinformation

IntheEuropeanDEMOplantdesign,thedivertorconsistsof54

separablecassettes.For eachsetofthreecassettes,alowerport

isassignedforremotemaintenanceoperation.TheDEMOdivertor

hasareducedsizecomparedtotheITERdivertor[4].

InFig.2thesectionalgeometryofthecurrentcassettemodel

(revisedin2016)isillustratedtogetherwiththedimensions.The

cassettebodyhasapoloidalextensionof3.02m,heightof1.97m

andtoroidalouterwidthof1.04m.Thenominalgapsizebetween

twoadjacentcassetteswillbebetween20and30mm.Themain

bodyofcassetteismadeofEurofer97,reducedactivationferritic

martensiticsteel.Itisdividedintochambersseparatedbystiffening

ribs.

Thein-andoutboardverticaltargetsareprotectedbyactively

cooledPFCscoveringthesurface.ThePFCsandmaincassettebody

arecooledbyseparatecoolingcircuitstoholddifferentcoolant

temperatureforeach.Theprimaryoptionforcoolantiswaterfor

thewholedivertorwhereasthefeasibilityofheliumcoolingisalso

exploredasalow-priorityoption.Thebaselinedesignoptionfor

water-cooledPFCsistheITER-typetungstenmonoblock(witha

reducedsize)withCuCrZrcoolingtube[4,5].Inaddition,novelPFC

designconceptsaredeveloped[2].

Itisnotedthatthedomeisstillregardedasoptionalandits

necessityiscurrentlyunderextensiveassessment.

3. Neutronicanalysis

BasedontheDEMO plantCADmodelof2015(with

helium-cooledpebblebedblanket),3Dneutronicsanalysiswascarriedout

usingtheMCNP5codeandJEFF3.2nucleardata[6].The

calcula-tionswerenormalizedtothegrossfusionpowerof2037MWwhich

wouldcorrespondtoaneutronproductionrateof7.232×1020_n/s.

Astheﬁnaldecisionisstillopenastowhetherthedomeshallbe

deployedornot,itwasassumedthattheentiresurfaceofthe

cas-settebodytotheplasmawascoveredwithPFCsofthesamekind

toshieldthewholecassettefromparticlesandradiation.Itisnoted

thatthisisatemporaryoptiontoavoidanyunrealisticneutronic

assessmentintheabsenceofadome.Aconsolidatedshielding

con-ceptiscurrentlydevisedwhichshallbeemployedincasedomeis

notadopted.

FortheneutronicsmodellingofPFCs,itwasassumedthatthe

sectionofthePFCconsistedof3homogenizedlayerswherethe

outermostlayersweretungstenandthemiddlelayerwasamixture

oftungsten(W:34vol.%),water(33vol.%),CuCrZr(18vol.%)and

copper(Cu:15vol.%)representingtheactualvolumefractionof

constituentmaterialsinthePFC.

Forthecassettebody,wateraswellasheliumwasassumed

ascoolant,forwhich3differentcasesofmaterialsmixturewere

consideredasfollows(volumepercent):

1)H2O-cooled:Eurofer(54%),H2O(46%)

2)He-cooled:Eurofer(50%),He(50%)

3)He-cooled:Eurofer(30%),He(50%),B4C(20%)

Inthecase3,B4Ccladdingwasassumedforneutronshielding.

ThechemicalcompositionofEurofer97steelisgiveninTable1.

Onlythemajoralloyingelementsandtheimpuritiesofhigh

radio-logicalimpactarelisted[7].

3.1. Neutronwallloading

Theneutronwallloadinthedivertorexhibitshighspatial

vari-abilityduetothecomplexgeometry.Themaximumvalueamounts

to0.53MW/m2_at_the_upper_surface_of_the_cassette_which_is_roughly

onehalfofthemaximumneutronwallloadattheoutboard

equa-torialﬁrstwall(1.33MW/m2_).

3.2. Nuclearheating

Fig.3showsthespatialdistributionsofnuclearheatingpower

densityinEuroferforthewater-cooled(left)andthehelium-cooled

(right)cases,respectively.ItshowsthatnuclearheatinginEurofer

wasconcentratednearthesurfaceofthecassetteanddecreased

rapidlyintheoutwardradialdirection(notabene:thecolorcode

scaleislogarithmic).Thevolumetricheatingpowerdensityranged

between0.1 and 6 MW/m3 _for _the_water-cooled _cassette_body

whereasitvariedfrom0.2to4MW/m3_for_the_{helium-cooled}_case

(0.1-3.5MW/m3_with_B

4Cshield).

Table1

ChemicalcompositionofEurofer97steel(wt.%)[7].

Fe Cr W Mn V Ta C Ni Mo Ti Nb Al B Co

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Fig.2.SectionalgeometryanddimensionsoftheDEMOdivertorcassettemodelasof2016.(a)toroidalmid-section,(b)radialprojectionview,(c)toroidalandpoloidalcross sections(d)outboardpartofatoroidalcutsectionshowingribs.

Fig.3. SpatialdistributionsofnuclearheatingpowerdensityinEuroferinthecassette(left:water-cooled,right:helium-cooledwithoutB4Cshield).

Table2

Totalnuclearheatingpowersinthemajorcomponents.

Nuclearheatingin54cassettes(MW) H2O-cooled(H2O:46vol.%) He-cooled(He:50vol.%) He+B4C(20%)(He:50vol.%)

Innerverticaltarget 5.4 4.9 3.8

Outerverticaltarget 8.1 7.0 5.4

PFCskinoncassettebody 16.7 14.0 11.3

Cassettebody(bulk) 96.1 47.0 55.6

Total 126.3 72.9 76.1

Thenuclearheatingpowerinthemajorcomponentsofdivertor (in54cassettes)issummarizedinTable2.Thetotalnuclearheating

powerintheentiredivertoramountsto126,73and76MWforthe

water-cooled,helium-cooledandhelium-cooledwithB4Cshield,

respectively.Thehigherheatingpowerinthewater-cooled

cas-settewasduetothepresenceofwaterwheresubstantialamount

ofpowerisdepositedcontrarytohelium.Fortheunderlying

vac-uumvesselmadeofSS316L,water-coolingprovidedmoreeffective

shielding(max.0.7MW/m3₎_compared_to_the_{helium-cooled}_cases

(max.1–1.8MW/m3_).

Inthehelium-cooledcases,thepresenceoftheB4Cshielddid

bringnotableshieldingeffectinthePFCs,butthiseffectwas

can-celedout by theincreased heatingpower in thecassettebody

resultinginonlyminutedifferenceinthetotalpower.

3.3. Latticedamagebyirradiation

Themaximumvaluesofdpa(displacementperatom)predicted

forthemajorcomponentsofthedivertorafter2fpy(fullpower

year)andforthevacuumvesselpartlocatingdirectlybehindthe

cassetteafter6fpyaresummarized inTable3.The2fpyisthe

envisaged period of continuous service before replacement for

maintenance(forvacuumvessel:6fpy).

Fig.4showsthespatialdistributionsofirradiationdamagerate

inthedivertorexpressedintermsofdpaperfpy(left:water-cooled,

right:helium-cooled).Thedpainthecopperheatsinkwasalways

higherthaninthetungstenarmorduetothelowerenergy

thresh-oldandhigherdisplacementcross-sectionofCucomparedtoW.

Thespatialvariationofdpadamageamountedtoafactoroftwofor

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Fig.4. Spatialdistributionsofirradiationdamagerate(dpaperfpy)inthedivertor(left:water-cooled,right:helium-cooledwithoutB4Cshield).

upperregionneartheblanketwhilethelowerdpaappearedinthe lowerpartofthetargetaroundthestrikepoint.Helium-coolingled toslightlyhigherdpadosethanwater-coolingduetomoderation ofneutronthroughthesteelbodyandwatercoolant.The maxi-mumcumulateddoseintheWarmorafter2fpy(speciﬁedPFC lifetime)reached3dpaforwater-and3.2dpaforhelium-cooling. IntheCuCrZrtube,themaximumdosewas12.8dpaforwater-and 14.2dpaforhelium-cooling.Accordingtothepreviousirradiation testdata,CuCrZrexhibitssaturationoftensilebehaviorinthedose rangeof0.5-2.5dpa[8]or1–10dpa[9]at150–300◦C.Thus,the

peakdpavalues(13–14dpa)mayprobablybeacceptable.

Themaximumaccumulateddamageinthesteelcassettebody

was6dpa(after2fpy)forwater-coolingwhereasitreached10

dpaforhelium-cooling(9dpawithB4Cshield).Ifthewatercoolant

temperatureiskeptabove180◦Cinthecassettebody,then6dpa

wouldbeacceptableforEurofersteelastheshiftofthefracture

toughnesstransitiontemperaturebyirradiationupto6dpastill

doesnot bringthesteelintofullyembrittledstate[10].Forthe

helium-cooledcase,theinletcoolanttemperaturewillhavetobe

higherthan210◦Ctoavoidfullembrittlementofthesteelbody

at9–10dpa.Thedpaproﬁlesexhibitedrapiddeclineintheradial

direction.Intheouterbottomregionthedosedecreaseddownto

0.02dpainthewater-cooledcassette.Inthehelium-cooledcase,

thedoseinthesameregionwasoneorderofmagnitudehigherdue

toreducedshieldingcapability.

Thecumulativedamageinthevacuumvessel(SS316L)after

6fpywas1.8,4.8and3.9dpaforthewater-andhelium-cooled

caseswithandwithoutB4Cshield,respectively.It isnotedthat

thealloweddpalimitspeciﬁedfortheausteniticstainlesssteelis

2.75dpaatwhichthefracturetoughnessisreducedbynomore

than30%[11].Water-coolingensuressufﬁcientneutronshielding

forthevacuumvesselwhileitdoesnotseemtobethecaseforthe

helium-coolingcases.

3.4. Heliumtransmutation

Formationofheliumbubblesbytransmutationcausessevere

embrittlementand swellingaffecting reweldabilityrequired for

remotemaintenance.Themaximumheliumproductioninthesteel

cassettebodyreached100appmafter2fpy.Theassumedboron

contentinEurofer97was0.002wt.%(Table1)whichisthe

max-imumallowableimpurity concentrationlimitfor borondeﬁned

intheF4Especiﬁcation[7].Theheliumconcentrationlimitbelow

whichreweldingusingelectronbeamissupposedtobepossible

is1–3appm[11]beingtwoordersofmagnitudelowerthanthe

predictedmaximumvalueontheplasma-facingsurface.For

ensur-ingreliablereweldingofcoolingpipes,thecuttingzonehastobe

locatedintheoutermostoutboardregionsufﬁcientlyshieldedby

theblanketsandcassetteitself.

3.5. Forthcominganalyses

Thenextneutronicsanalysiscampaignwillincludetheeffectof

thedome,realisticdistributionofmaterialsinareﬁnedCADmodel

andreviseddivertorcassettelayout(e.g.portplugin thelower

domainforshieldingthevacuumvessel).

4. Coolingschemeandthermohydraulicanalysis

4.1. Operationtemperaturerangeforthewater-cooledcassette

Thebaselinecoolingconceptisbasedonwater-coolingwhile

helium-cooling isconsideredasadvanceddesign option.In this

paper,discussionisfocusedonthewater-coolingcase.

Itis oneofthebasicdesignrequirementsthatthestructural

materialofthecassettebody(i.e.Eurofersteel)beoperatedinsuch

awaythatuncontrolledfastfractureisavoided.Inthisdesignstudy,

fracturetoughnesstransitiontemperature(FTTT)wasemployedas

measureofcriticaltemperaturebandacrosswhich thematerial

stateinthecrack-tipregionrapidlychangesfromductileto

brit-tle.AsFTTTismeasuredusingprecrackedspecimens,itisregarded

moreconservativecomparedtoDBTT(ductile-to-brittletransition

temperature)byimpacttests.Theloweroperationtemperature

limitofirradiatedEurofercanbedeﬁnedaccordingtotheFTTTdata

at6dpaasfollows[12]:>180◦C(withHeproduction)or>120◦C(no

Heproduction).TheupperservicetemperaturelimitofEurofer97

isknowntobearound550◦C,abovewhichthesteelrapidlyloses

strength.Thethermohydraulicdesignforcoolingthesteelcassette

bodyshouldrespectthesetemperatureconstraints.

4.2. Water-coolingofcassettebody

Theinteriorofthecassettebodyisdividedintomany

cham-bersseparatedbyribs(20mmthick)eachwithahole(diameter:

40–70mm)throughwhich thepressurizedcoolant isguided to

ﬂow. A schematicview of thecassette interior is illustratedin

Fig.5(a).Theoutletandinletcoolantfeedingpipesconnectedto

theoutboardedgefaceareshown.Thelayoutsofthefeedingpipes,

ribsandholeswereoptimizedonthebasisofiterativeCFD

simula-tions.Therectangularcrosssectionofthecassettebodyconsisted

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(right)wherethedirectionofcoolantﬂowisschematicallyillustrated.

Table4

InputparametersconsideredforCFDanalysisofthewater-cooledcassettebodyand thepredictedresultsofthermo-hydraulicperformance.

H2O-cooledcassette Pipedesign1 Pipedesign2

Coolantinlettemp.(◦_C) ₁₅₀ ₁₈₀

Coolantinletpressure(MPa) 3.5 3.5

Massﬂowrate(kg/s) 308 861

Coolantoutlettemp.(◦_C) ₂₂₀ ₂₁₀

Pressuredrop(MPa) 0.01 0.1

Pumpingpower(kW) 4 93

Coolantmax.temp.(◦_C) ₂₄₂_(at_the_wall) ₂₁₄_(at_the_wall)

Cassettebodytemp.(◦_C) _<330 _<330

Fig.6. Streamlinesandspeedofthewatercoolantﬂowinginthedivertorcassette (left).Twodifferentdesignconceptsofthecoolingpipeconnectionstothecassette body(right).

andoutletcoolantstreams(seeFig.5(b)).Theoutershellplateis

30mmthick.

Toassess thecooling performance of the water-cooled

cas-settebody,full3Dthermohydraulicanalysiswascarriedoutbased

onﬁnite volumemethodusingcommercialcomputationalﬂuid

dynamics(CFD)code,ANSYS-CFX(v16).Theinputcoolant

param-etersandtheresultsof3DCFDanalysisaresummarizedinTable4.

DetailsoftheCFDsimulationarefoundelsewhere[13,14].

InFig.6,thestreamlinesofwatercoolantareplottedtogether

withthespeed distributionincolorcode.In general,thewater

ﬂowexhibitsareasonablestreamlinepattern,buttwolarge

vor-ticesformedintheoutboardregionneedtobereducedbyfurther

optimizationoftheribstructure.

Itis foundthatthewater-coolingcase exhibitsa reasonable

thermalandhydraulicperformance.Particularly,water-coolingis

beneﬁcialintermsofthelowpumpingpower(4kWintotal)and

highheatcapacity.Themaximumtemperaturedevelopinginthe

steelbodywasfarbelowthemaximumallowableservice

tempera-turelimit(550◦C).Thewatercoolantbulkwasheatedupto220◦C

inthe outletregion.The maximumtemperature inthe coolant

reachedlocallyupto242◦Cinthethinboundarylayernearthe

innersurfacewhichwasclosetothevaporizationtemperatureat

Table5

Thermohydraulicperformanceofthewater-cooledtargetPFCpredictedforthree differentcoolingoptions.

percassette Option1 Option2 Option3

Massﬂowrate(kg/s) 60 110 60

Temperaturerise(◦_C) ₉ ₅ ₉

Pressuredrop(MPa) 1.4 1.5 1.8

Min.velocity(m/s) 17 15 15

Min.CHFmargin 1.6 1.6 1.4

thegivenpressure.Forincreasingthemargintoﬁlmboilingwater, massﬂowrateneedstobeincreased.

4.3. Water-coolingoftargetPFCs

Thethermohydraulicperformanceofthewater-cooled diver-tortargetPFCwasassessedbymeansof3DCFDsimulations.The targetPFCsareexposedtohighheatfluxloadsgeneratedby radia-tion(53MW),plasmabombardment(39MW)andnuclearheating (14MW).Thismeansthat54in-andoutboardtargetplateshave toexhaustthedeposited thermalpowerof106MWintotal.At theplasmastrikepointthemaximumpowerdensitywasassumed toreachabout20MW/m2 _during_slow_transients_(loss_of_plasma detachment)in2–3s.Duringaquasi-stationaryoperation(pulse duration:2h)theheatfluxdensityprofilewasassumedtorange

from1to10MW/m2_[15]_._The_power_exhaust_capability_has_to_be

assuredintermsofglobalenergybalanceaswellaslocalmarginto

criticalheatﬂux(CHF)atthetubewall.Tothisend,ahighlyefﬁcient

coolingschemeandtechnologiesaredemanded.

InWPDIV,threedifferentoptionsofcoolingcircuithavebeen

devisedandestimated(Fig.7).Followingcoolantparameterswere

assumedforthePFCsasCFDboundaryconditions[2]:

–Peakheatﬂuxdensityatstrikepoint:20MW/m2

–Heatﬂuxpeakingfactoratthetubewall:2

–Coolanttemperature:150◦C(PFCinlet)

–Coolantpressure:5MPa(PFCinlet)

–MassﬂowrateperpipeinPFC:1.67kg/s

TheresultsofthecomparativeCFDanalysisaresummarizedin

Table5.AllthreeoptionsallowsufﬁcientmargintotheCHFatthe

strikepointfortheappliedsurfaceheatﬂux.Itisnotedthatthe

recommendedmargintoCHFis1.4 atleast.Theriseofcoolant

temperaturelooksalsomoderateforallthreecases.

Ontheotherhand,pressuredropisquitesigniﬁcant,especially

foroption3.Anotherconcernisthehighcoolantspeedlocally

peak-ingupto20m/ssothatcorrosion-erosionofpipewallisfostered.

Theoutcomeof thisCFDanalysisimpliesthat thepeak coolant

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tempera-Fig.7. Threedifferentcoolingschemeoptionsconsideredforthethermohydraulicdesignofthedivertortargetplate.

tureand/orincreasingthetuberadius.Afollow-upinvestigationis

ongoingtargetingthecoolantspeedofabout10m/s,pressuredrop

below1.4MPaandCHFmarginhigherthan1.4.Here,the

oper-ationtemperaturerangerecommendedfortheirradiatedCuCrZr

heatsinktube(structuralmaterial)bythestructuraldesigncode

ITERSDC-ICimposesconstraintontheapplicablecoolant

temper-ature[16,17].Forrelaxingsuchconstraint,advanceddesignrules

basedonnon-ductilefracturemechanicscanbeemployedsothat

theuseoflow-temperatureoperationofdivertorPFCsisjustiﬁed.

5. Electromagneticforceanalysis

Globalplasmainstabilitiessuchasplasmadisruptionsand

ver-ticaldisplacementevents(VDEs)induceorgeneratehugetransient

electriccurrentsintheconductivesteelcassettebody.Disruptions

induceeddycurrentswhereasVDEsgeneratehalocurrents.The

interactionofthecurrentswiththemagneticﬁeldinducesLorentz

force(F=J× B)asimpactload.Particularly,theforceinducedbya

VDEcanimposeacriticalimpactonthedivertorduetohighcurrent

density.InWPDIV,ﬁniteelementmethod(FEM)-based3D

elec-tromagneticanalysiswascarriedouttoassesssuchimpactloads

assumingvariousparametriccombinations.Inthispaper,onlythe

resultforthemostcriticalcaseispresented(productofhalo

frac-tionand toroidal peaking factor:1, halocurrent partition ratio

betweenthemainbodyandotherparts:1).Thedurationtimeof

linearcurrentquenchwasassumedtobe50ms[18](ForDEMO,it

wasrevisedto70ms[19]).Itwasassumedthatplasmadisruption

began10saftertheinitiationoffastdischarge(characteristictime:

27s).Contactresistancewasneglected.Theradialdecayoftoroidal

magneticﬁeldrangedfrom8.3Tto5.6T(nominalBT:5.6T).

5.1. Halocurrent

Fig.8illustratestheelectricpotentialﬁeldgeneratedbyaVDE

incolor code(left) togetherwitharrowsindicating thecurrent

pathanddirection(right).Theelectricpotentialbuiltupalongthe

poloidaldirectionfromtheinboardtoptowardtheoutboardend

formingthehalocurrent path.Themaximumhalocurrent

den-sityreached2.2MA/m2_._{Concentration}_of_current_density_occurred

locallyattheshelledgesandcorners.

Fig.8.ElectricpotentialﬁeldgeneratedbyaVDE(left)andhalocurrentpath indi-catedwitharrows(right).

Fig.9.InducedLorentzforcesinthedivertorcassetteshellplate(left:vertical,right: radialcomponent).

5.2. Lorentzforcesandstresses

The induced Lorentz forces in the shellplate are plotted in

Fig.9(left:vertical,right:radialcomponent).Strongupward

verti-calforceappearedinthemiddlepartofthecassettebody(30MN)

anddownwardverticalforceintheinboardandoutboardwings

(10MN). Theupwardvertical forcecauses(elastic)deformation

ofthemiddlepartwherethedisplacementreachesupto1.4mm

upwards.

Fig.10showstheinducedstressﬁelds(vonMisesstress)inthe

outershellplate(left)andintheinternalribs(right).Thestressstate

intheentirecassettestructureremainedintheelasticregimeeven

inthemostsevereloadingcaseconsideredinthisanalysis.This

resultindicatesthatthecassettebodyisrobustenoughto

with-standthetransientelectromagneticimpactloadscausedbyplasma

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well.Examplesare:FEM-basedstructuralanalysisandcode-based

designstudy,optimizationofCADmodels,developmentofcassette

ﬁxationscheme,experimentalveriﬁcationofCFD,andfunctional

analysis,etc.(willbereportedelsewhere.)

7. Conclusions

Theinitialdesignexplorationstudyinthepreconceptualdesign

phase to develop European DEMO divertor has been recently

concluded.Inthesubproject‘Cassettedesignandintegration’,

fol-lowingresultsarethemajorachievements:

1CAD:complete3Dconﬁgurationmodelwascreated.

2Neutronics:theradiologicalimpactwasanalyzedforthecase

domeisnotdeployed.ArmoringofcassettesurfacewiththePFCs

similartothetargetnecessitatedimprovedshielding.

3Thermohydraulics:forbothtargetPFCsandcassettebody,the

currentdesignofwater-coolingcircuitsseemedadequate.

4Electromagneticanalysis:thecurrentcassettemodelseemedto

berobustenoughtoaccommodateVDEimpactloads.

[7]TechnicalspeciﬁcationsEUROFERmaterialdatabase,F4E-2008-GRT-010 (PNS-MD).

[8]W.Timmis,MaterialAssessmentReportontheUseofCopperAlloysinDEMO EFDAReportWP12-MAT02-M03,2013.

[9]P.Fenici,etal.,J.Nucl.Mater.212–215(1994)399–403. [10]E.Gaganidze,J.Aktaa,Fus.Eng.Des.88(2013)118–128. [11]V.Barabash,etal.,J.Nucl.Mater.367–370(2007)21–32.

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[13]P.A.DiMaio,etal.,FusionEng.Des.(2017),http://dx.doi.org/10.1016/j. fusengdes.2017.02.012.

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