Nuclear damage parameters for SiC composites in fusion system
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Nuclear damage parameters for SiC composites in fusion system

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Nuclear damage parameters for SiC composites in fusion system

Nuclear damage parameters for SiC composites in fusion system

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    Nuclear damage parameters for SiC composites in fusion system Nuclear damage parameters for SiC composites in fusion system Presentation Transcript

    • Nuclear damage Parametersfor SiC/SiC Composite inFusion SystemsMohamed SawanFusion Technology InstituteThe University of Wisconsin-MadisonInternational Symposium on Silicon Carbide and Carbon-BasedMaterials for Fusion and Advanced Nuclear Energy applicationsJanuary 19-22, 2009Daytona Beach, FLYutai Katoh, Lance SneadMaterials Science and Technology DivisionOak Ridge national Laboratory
    • Much Harder Neutron Spectrumin Fusion Compared to FissionM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, Vienna10510710910111013101510-2100102104106108Fission ReactorFusion Reactor FWNeutronFluxperGroup(n/cm2s)Neutron Energy (eV)46 Energy Group StructureNeutron spectra normalized to1015n/cm2s total fluxAverage EnergyFission 0.7 MeVFusion 2.7 MeVFusion 14.1MeV PeakFusion LacksSignificant ThermalComponentHe/dpa ratio is significantly higher than in a fissionreactor nuclear environment (~10 vs. ~0.3 for FS)Effect more pronounced for SiC (~90 vs. ~1 for SiC)
    • Application of SiC/SiCComposites in Fusion SystemsSiC/SiC composites have been considered for use in fusion systemsBecause of their low induced radioactivity and high temperatureoperation they represent an attractive candidate for structural materialThey have been proposed as structural material for FW and blanket inseveral MFE and IFE designsSiC/SiC composite is the preferred structural material for FW andblanket of the HAPL IFE design with magnetic interventionSiC/SiC composites are considered for use as flow channel inserts (FCI)in dual coolant lithium lead blanket (DCLL). They provide electricalinsulation to mitigate MHD effects and thermally isolate the hightemperature LiPb from the low temperature helium cooled FSLifetime of SiC/SiC composites in fusion radiation environment is amajor critical issueRadiation effects in fiber, matrix, and interface components representimportant input for lifetime assessmentImpact of radiation on insulating properties of FCI is also a critical issueM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, Vienna
    • High Average power Laser(HAPL) Conceptual DesignM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, Vienna• Direct drive targets• Dry wall chamber• 40 KrF laser beams• 367.1 MJ target yield• 5 Hz Rep Rate• 6 MW/m2 peak NWLDry wall must accommodate ion andphoton threat spectra from targetExtreme flux of intermediate energyions pose a significant issue ofextremely high pulsed temperaturesand erosion/ablation of FWMagnetic intervention used to steerions away from chamber wallLarge fraction of magnetic energy canbe dissipated in chamber walls if anelectrically resistive structural materialis used (SiC/SiC)LiPb or Flibe self-cooled blankets used1 cm Be insert used in FW coolantchannel with Flibe for tritium self-sufficiency
    • Nuclear Analysis for SiC/SiC inFusion EnvironmentM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaRadiation parameters determined for SiC/SiC composites for MFE andIFE systemsConfigurations of ARIES-AT advanced tokamak and HAPL laser fusionconceptual designs were usedARIES-AT HAPL
    • Calculation of damageParametersRates of dpa, He production, H production, and % burnup calculatedfor both sublattices of SiC fiber/matrix and interface materialThe cross section library includes all partial reaction cross sectionsrequired to determine gas production and transmutationsThe library includes the damage energy cross sections needed todetermine the atomic displacementsUsed recommended displacement energies for SiC, namely 20 and 40eV for the C and Si sublattices, respectivelyLeading interface material candidates are graphite and multilayer SiCDamage parameters for the SiC interface material are identical tothose for the SiC fiber/matrixDamage parameters for the graphite interface material are same asthose for C sublattice of SiC except for dpa due to the higher (30 eV)displacement energyM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, Vienna
    • Peak Damage Parameters inOB SiC/SiC FW of MFE SystemM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaFlibe BlanketLiPb Blanket
    • Observations on Peak DamageParameters in MFE Systemdpa rates in C and Si sublattices of the SiC fiber/matrixare comparabledpa rate in graphite interface is 33% lower than in Csublattice of SiCHe production rate in C sublattice of SiC and graphiteinterface is about a factor of 4 higher than in Si sublatticeof SiC and is dominated by the (n,n´3 ) reactionHe production rate in graphite interface is 60% higherthan average He production rate in the SiC fiber/matrixSignificant hydrogen production occurs in Si with anegligible amount produced in CBurnup rate of Si sublattice is twice that for C sublattice ofSiC fiber/matrix and graphite interfaceM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, Vienna
    • Comments on Burnup of SiCBurnup of Si sublattice is about a factor of 2 morethan that for C sublatticeThe burnup is equivalent to introducing impurities inthe sublattices of the SiCProperty degradation depends on the kind ofimpurities introducedTransmutation of Si produces primarily Mg and Alwith smaller amount of P and main transmutationproduct for C is Be with smaller amount of B and LiNonstoichiometric burnup of Si and C is expected tobe worse than stoichiometric burnups and could bean important issue for SiCM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, Vienna
    • Impact of Breeder/Coolant onSiC/SiC Damage Parameters10-310-210-11001011021031040 10 20 30 40 50 60 70 80dpa/FPY in PbLi blanketHe appm/FPY in PbLi blanketdpa/FPY in Flibe blanketHe appm/FPY in Flibe blanketDamageRateinSiCDepth in Blanket (cm)Outboard in MFE ReactorNeutron Wall Loading 6 MW/m2M. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaPeak dpa values with Flibe areabout half those with LiPbPeak gas production andburnup rates with Flibe arehigher by 3-10% than withLiPbdpa values with Flibe havesteeper radial drop comparedto that in LiPb blanket whilegas production and burnuprates have slightly less steepradial dropFlibe is more effectiveattenuating intermediateenergy neutrons while LiPb ismore effective attenuatinghigh-energy neutrons
    • Neutron Energy Spectra at FWfor LiPb and Flibe BlanketsM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaHarder spectrum with FlibeLarger total neutron flux with LiPbdue to increased secondary neutronproduction from Pb that are mostlyin the 10 keV to 2 MeV rangeThese intermediate energy neutronsresult in higher dpa with LiPbHigh energy flux (E>2 MeV) is muchsmaller with LiPb resulting in lowergas production and burnup rates10410610810101012101410-2100102104106108PbLi BlanketFlibe BlanketNeutronFluxperEnergyGroup(n/cm2s)Neutron Energy (eV)Energy spectrum at first wallOB in MFE reactor6 MW/m2neutron wall loading175 Energy Groups
    • Different Features of IFE SystemsM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaSignificant geometrical, spectral and temporal differencesbetween IFE and MFE systems affect radiation damage levels withimpact on lifetime assessmentGeometrical differences:Point source in IFE Source neutrons in IFE chambers impinge onthe FW/blanket in a perpendicular direction For same NWL,lower radiation effects at FW with smaller radial gradient in blanketPointsource attargetFWFWVolumetricsource inplasmaIFEChamberMFEChamber
    • Different Features of IFE SystemsM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaEnergy Spectrum forNeutrons Emittedfrom HAPL TargetCombined geometrical andspectral differences impacttime-integrated radiationdamage parametersSimple scaling of radiationeffects with neutron wallloading between IFE and MFEsystems is inappropriateSpectral differences:• Fusion neutron interactions in compressed IFE target result inconsiderable softening of neutron spectrum incident on the FW/blanket in IFE chambers• Softened source neutron spectrum with 10-13 MeV average energydepending on target R with some neutron multiplication (~1.05)
    • Peak Damage Parameters inSiC/SiC FW of HAPLM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaFlibe BlanketLiPb Blanket
    • Comparison between FWNeutron Spectra in IFE and MFECalculated total neutron flux values at FW are nearly identicalin both systems for the same NWLSpectrum is softer in IFE system with average energy of 1.66MeV compared to 2.67 MeV in MFE systemM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, Vienna10410610810101012101410-2100102104106108IFEOB in MFENeutronFluxperEnergyGroup(n/cm2s)Neutron Energy (eV)Energy spectrum at first wallPbLi blanket6 MW/m2neutron wall loading175 Energy Groups101010111012101310141015106107IFEOB in MFENeutronFluxperEnergyGroup(n/cm2s) Neutron Energy (eV)Energy spectrum at first wallPbLi blanket6 MW/m2neutron wall loading175 Energy Groups
    • Comparison between FW DamageParameters in IFE and MFE• Peak values for the same neutron wallloading are significantly different• Gas production and burnup rates are about afactor of 2 lower in IFE system compared tothat in MFE system with the same NWL• The peak dpa rate in IFE is lower than that inthe OB region of MFE by ~7% for LiPbblanket and ~20% for Flibe blanket• These differences are due to geometrical andspectral differences between IFE and MFEsystemsM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, Vienna
    • Pulsed Effects in IFE SystemsM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaIn IFE chamber neutron source has a pulsednatureEnergy spectrum of neutrons from target resultsin time of flight spread and backscattering fromblanket extends period over which a particularradiation effect takes placeTime spread is larger for radiation effectsproduced by lower energy neutrons (time spreadof dpa larger than that for gas production andtransmutation)
    • Pulsed Effects in IFE Systems(Cont’d)M. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaPeak instantaneous damage rates in IFE FW/blanketare ~5 to 8 orders of magnitude higher than steadystate damage rates produced in MFE systemsDifference in time spread results in higherinstantaneous He/dpa ratios in IFE systemscompared to MFE systemsTime dependent neutronics analysis is necessary forsubsequent microstructure evolution analysisAnalysis is underway to determine pulsedinstantaneous damage parameters in SiC/SiC FW ofHAPL and couple results with microstructureevolution analysis
    • Pulsed Damage parameters inHAPL SiC/SiC FWM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaTemporal peaking factor is significantly higher for He production thanfor atomic displacement (8.7x107 vs. 1.1x107)Peak instantaneous He/dpa ratio is much higher than that determinedfrom the temporal average (cumulative) values (368 vs. 47)
    • Use of SiC FCI as Insulator inDCLL Blanket• The Dual Coolant Lithium Lead (DCLL) blanket concept is thepreferred US blanket concept for commercial fusion plants• It provides a pathway to high outlet temperature with currentgeneration structural materials• A key element is use of SiC (foam or composite) flow channelinserts (FCI) for electrical and thermal insulationM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, Vienna
    • Peak Damage Parameters inSiC FCI of DCLL BlanketNeutronics calculations for the DCLL concept in OB region ofMFE system with a NWL of 6 MW/m2M. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaRelative values for different constituents are similar to thoseobtained for the SiC/SiC FW of self-cooled LiPb blanketDamage parameter values are lower by ~40% due toattenuation in the 3 cm thick He-cooled ferritic steel FW
    • Metallic TransmutationProducts in SiC FCIM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, ViennaFCI is not a structural element and main concern is degradation in its primaryrole as electrical and thermal insulatorDegradation in resistivity results from introduction of metallic transmutationproductsTransmutation calculations using the ALARA code determined rate of build-upof different metallic transmutation products00100020003000400050000 0.5 1 1.5 2 2.5 3 3.5LiBeBMgAlPTTransmutationProduction(appm)Operation Time (FPY)6 MW/m2Neutron Wall LoadingFront Layer of SiC FCIin DCLL BlanketDominant metallic transmutationproduct is Mg that builds up to~0.43 at% concentration at theexpected lifetime of a DCLLblanket in a fusion power plantIt is essential to assess impact ofthese levels on electrical andthermal conductivities of FCI todetermine if it will restrictlifetime of the DCLL to less thanthat determined by radiationdamage to ferritic steel FW
    • Conclusions• Radiation damage parameters in SiC/SiC composite have strong dependenceon the blanket design (coolant,breeder) and plasma confinementapproach (MFE, IFE)• Input needed from materialscommunity regarding appropriatelifetime criterionM. Sawan1st RCM on “Nuclear Data Libraries for Advanced Systems- Fusion Devices”2-5 Dec 2008, IAEA, Vienna