advanced materials for fuel cladding in sodium fast reactors in ...

ADVANCED MATERIALS FOR FUEL CLADDINGIN SODIUM FAST REACTORS(and an insight into Lead Fast Reactors)Marion LE FLEM,With the help of Yann DE CARLAN, Laurent CHAFFRON and Jean-Louis SÉRANPhénixCEA-Saclay CenterNuclear Energy DivisionNuclear Material DepartementSection for Applied Metallurgy ResearchASTRIDMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 1

Introduction – SFRIn-service condition for the cladding material• Temperature : 400°C-650°C (700°C)• Ultimate target dose : up to 180-200 dpa~ Comparable to LFR but dose (400-550°°C, C, 100dpa)Main functions of the pin (critical component)• Welcoming MOX fuel (confinement of fuel and fission products)• Providing heat exhange between fuel and NaSodium-Cooled Fast ReactorRequired properties• Compatibility with Na and with fuel (kinetics) + reprocessing• Compatibility with rapid neutron spectrum (activation, transparency)• Mechanical integrity in any condition (cladding = 1st barrier of confinement) Appropriate mech. strength, ductility (>0,2%), toughness (>20 MPa.m 1/2 ) Good dimensional stability (clad diameter, elongation) Resistance to irradiation swelling (

Introduction – SFR Fuel claddingReference Materials for SFR = steelsAustenitic steels 15/15 TiSwelling must be decreased• Appropriate mechanical properties and also for LFR• But swelling worries resulting in embrittlement Incubation time and life time restriction to dose lower than 130dpaFerritic steels (9-12%Cr, T91, EM10)• OK in SFR as wrapper tube and also in LFR• Too weak for SFR claddingMechanical properties must be enhancedBefore irradiationPhénixSwellingEmbrittlement limit15/15 TiAfter irradiation130dpa maxFerritic-martensitic steelsRapsodieMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 3

Introduction – SFR Fuel claddingLow swelling and appropriate mechanical properties Advanced materials for SFR1- Advanced austenitic steels2- Ferritic/martensitic ODS Steels (Oxide dispersed strengthening)3- Refractory metals4- Ceramics ?Melting temperature ↗Innovation ↗And for LFR ?• Main drawback is compatibility with Pb need of coatings or new alloys Also need of materials with higher performances (cfSFR)Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 4

1- Advanced Austenitic Steels (1/3)Improvement of resistance to swelling= Combination of benefic parameters- High Ni content 15-30% inhibitor in solid solution- Stabilisation by Ti (even by Ti + Nb + V) + cold work (25% CW) carbide precipitation- Use of Si + P enhancement of precipitation under irradiationSSmall level of CW cavities in the cells15/15Ti ,100dpa, 560°C20% CW Dislocations pinned by TiCBenefic effect of Ni(swelling inhibitors in solid solution)Narrow specifications to fulfil the requirements…Impact on chemical composition, homogeneity, process…Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors5

1- Advanced Austenitic Steels (2/3)Mechanical properties – Out of pile propertiesTensile testsYield Stress (MPa)[CEA]Ti+Nb+V stabilized700Ti+Nb stabilized[CEA]600500Ti stabilized400300minimum of 15/15 Ti20 200 400 500 600 700Test temperature (°C)• Advanced austenitic steels exhibit comparableproperties to 15/15Ti• To be determined after irradiation…Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 6

1- Advanced Austenitic Steels (3/3)Swelling resistance – Supernova experience in Phénix (1988-2005 89dpa)Confirmation of improvement in swelling resistance via Ti+Nb stabilization ofaustenitic steels[CEA]normalized flux10.9Volume swelling (%)Reference15/15 Tinon-optimized 15/15 TiAdvanced austeniticTi stabilized0.80.70.60.50.40.30.2• Possible optimisationof 15/15 Ti• Stability to be provedabove 150dpa0.10Advanced austeniticTi+Nb stabilizedIrradiation temperature (°C)Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 7

2- ODS Steels (1/6)Introduction – Low swelling of ferritic/martensitic steelsBut need of improvement in mechanical properties (creep)ε (%)Principle of ODS (Oxide Dispersed Strengthening) :Reinforcement of ferritic/martensitic steels by homogeneous distribution of nanosize oxides(e.g. Y 2 O 3 ), stable in temperature and under irradiationFerritic Fe 14Cr 1W 0,3Mn 0,3 Si 0,2 Ni Ti + Y 2 O 3Fe-18Cr650°C180 MPaODS Fe-18Cr 0,5 Y 2 O 3Time (h) Fe 18Cr 1W 0,3Mn 0,3 Si 0,2 Ni Ti + Y 2 O 3 Fe 14Cr 2W Ti + Y 2 O 3- Anisotropic- Possible embrittlement under irradiation- Recrystallization difficult to control- Good corrosion resistanceMartensiticODS:Low deformation +Increase in rupture timetime Fe 9Cr 1W 0,3Mn 0,3 Si 0,2 Ni Ti + Y 2 O 3 Fe 9Cr 2W 0,3Mn 0,3 Si 0,2 Ni Ti + Y 2 O 3- Isotropic- Easier to manufacture- T < 750°C- Questionnable corrosion resistanceMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors8

2- ODS Steels (2/6)Fabrication – Powder metallurgy (≠ melting of basic steels)Broyage mécaniqueMechanical alloyingGainageCanningHot extrusionFilage à chaudAlloyed Poudre pré-alliée powderpowder PoudreYPoudre Y 2 O 2 O 3 powder 3Matériau extruded final steelBars, tubesCEA/ SRMA/LTMEXMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 9

2- ODS Steels (3/6)Microstructure – What happens during fabrication ?Before MAFe-9/18Cr-Ti (Ø = 100 µm)10 % Y 2 O 3 (Ø = 1 µm)After MA100 µm200 µmFe crystallite (15 nm)Amorphousphases(10 nm)Fe crystallite(100 nm or more withnano YTiO particles)(Y, Ti, O)Y 2 Ti 2 O 7YTiO 310 nmAfter MA + Annealing100 µmMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors[M. Ratti, thèse CEA 2009]10

2- ODS Steels (4/6)Mechanical properties – Tensile testsODS 14Cr steel0,3 Y 2 0 325201210Energy (J)151058642000 200 400 600 800 -150 -100 -50 0 50 100 150 200 250 300 350Temperature (°C)Temperature (°C)• Anisotropy• Ductility depends on orientation, and object• Influence of fabrication routeMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 11

2- ODS Steels (5/6)Mechanical properties – Creep resistance650°CMA 957250 MPaCEA 14 Cr ODSCEA 18 Cr ODS250 MPa300 MPa• MA ODS >> conventionnal Ferritic/Martensitic steels (EM12)• Austenitic 15/15Ti remains better than ODS BUT could be comparable for long time• Low intragranular deformation of ODS large secondary creep domain BUT no tertiary creep domain•Need to understand deformation and damage occurrence (failure) dislocation/precipitates interactionMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 12

2- ODS Steels (6/6)Stability under irradiationMechanical properties (on grade DY = preliminary ODS grade Fe13 Cr2Ti1,5 Mo + 0,5 Y 2 O 3 -TiO 2 )4 Elong. (%)3unirr.Before irradiation484°C - 76 dpa21UE = TE0-300 0 300 600 900RuptureDuctile "Cleavage"DuctilePresent grades (e.g. developed at CEA) stableLarge (Y,Ti) 2 O 3 – Ø > 10-100 nm• Occurrence of damage with dose but remain crystalline• Slight dissolution under irradiationNano-sized (Y,Ti,O) oxides – Ø < 10 nm• No obvious evolution in size… High embrittlement…Need of optimized gradesand dedicated R&D programup to 45 dpa at 500°C(in situ TEM)[Lescoat JNM 2011]Fe18Cr1W0.4Ti + 0.6 Y 2 O 3Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 13

ODS = present reference for future evolution ofASTRID core (SFR prototype).First Cores ASTRIDAIM1 (15-15 Ti)One ODS sub assemblyASTRID prototypeOther innovations are under investigation inparticular in terms of margin to melting and stabilityof the core in case of accidental scenario (high T°C) Refractory materials (Metals ? Ceramics ?)Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 14

3- Refractory metals (1/7)IntroductionV• Nb, Mo, Ta and W are not acceptable in terms of neutron compatibility (absorption…)• Only semi-refractory V, Cr and Zr exhibit enough neutron transparency• Only V exhibits• appropriate strength at high temperature• AND widely known behavior under irradiationIs vanadium a good candidatefor SFR fuel cladding ?Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 15

3- Refractory metals – Vanadium alloys (2/7)V-4Cr-4Ti = reference gradeMost of the investigations were performed on the V-Cr-Ti system (fusion application)• Cr in solid solution increases hardness and mechanical properties• Ti in solid solution allows ductility and limits irradiation swelling[Smith 1995]V-4Cr-4TiV-4Cr-4Ti• Occurrence of maximum swelling with dose• Swelling increse with Cr%• Very low swelling of V-4Cr-4Ti optimized gradeMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors

3- Refractory metals – Vanadium alloys (3/7)Mechanical properties[Smith 2000]• V-4Cr-4Ti exhibits stable UTS up to 700-750°C• Comparable to 15/15Ti at 600°C• Preliminary calculations suggest V-4Cr-4Ti is OK for SFR cladding• ODS steels are stronger BUT…… effect of Cr on creep resistance V-15Cr-5Ti ~ ODS steelsMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 17

3- Refractory metals – Vanadium alloys (4/7)Mechanical properties : V is ductile ![Chung 1996] [Gentzbittel 2012]DBTT = -200°C• low DBTT (-200°C) compared to ODS steels (~-100°C at best)• limited primany and secondary creep• ductile behavior (≠ ODS)Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 18

3- Refractory metals – Vanadium alloys (5/7)Mechanical properties : V is ductile ! Even after irradiation• Embrittlement at low irradiation temperature but recovery above ~400°C• Basically, total recovery at 0.3×Tm = 650°C• Detrimental effet of O and high Cr (more pronounced embrittlement)Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 19

3- Refractory metals – Vanadium alloys (6/7)Keypoint = compatibility with environment…• Diffusion of O in the V substrate below theoxide layer embrittlement• Need of canning during fabrication• Need of strong atmosphere control during hightemperature tests (creep…)[M. Fujiwara 2002]Need of external protection…Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 20

3- Refractory metals – Vanadium alloys (7/7)Need of external protection - example :• V-4Cr-4Ti with silicide coating at 650°C in He + 5ppmO 2∆m/S (mg.cm -2 )6543210V-4Cr-4Ti (GfE)V(Cr)Si 2V(Ti)Si 20 100 200 300 400temps (h) [Chaia 2012]• Very low weight gain in air and in He + 5 ppm O 2• No dissolution in impure liquid NaMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors21

3- Ceramic cladding ? (1/3)Introduction – Numerous advantages for SiC f /SiC• Intrinsic properties for SiC– Irradiation resistance– Heat resistance, heat transfer– Thermo-chemical stability– Neutron transparency– Low activation• Main features of SiC/SiC– Non catastrophic failure– Stable mechanical properties up to 1000°C at least– Anisotropic but tailorable properties– Stability under irradiation if appropriate fibersCVI SiC/SiC3 rd generation SiC/SiC(TSA3, Hi-Nicalon S)1 st and 2 nd generation SiC/SiC(Nicalon, Hi-Nicalon)[Jones 2002]CEA, "Science as art " 1st place,MRS Fall meeting 2009Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 22

3- Ceramic cladding ? (2/3)Mechanical properties – SiC f /SiC = Elastic damageable materialNon linear response to thermomechanical sollicitations dependant on the SiCf/SiC (architecture,constituents, type of sollicitation…).3 domains related to damage occurrence in the compositeElestic domainMatrix cracking Fiber ruptureQuestionnable points :Damageable elastic material !cracks, change in propertiesloss of gas-tighness, design ?CMC are challengingmaterials for nuclearapplicationMatrix crackingTensile Test on a minicomposite[El Yagoubi 2011]Guillaumat, LCTS 1994Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 23

3- Ceramic cladding ? (3/4)Matrix cracking – impact on thermal conductivity (key point)• SiC/SiC exhibit low and scattered conductivity (10 W/m.K max)• It drops with irradiation• It drops with matrix cracking[Hegeman 2005][El Yagoubi 2011]Matrix crackingFiber ruptureat 900Elestic domain~40%irradiationMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors

3- Ceramic cladding ? (4/4)Matrix cracking – impact on leaktightness• When cracks occur, there is a loss of leak-tighness (fission products) = « leak before break »• Need of gas-tight systems abble to sustain strain in operating conditions CEA sandwich concept with inner metallic liner (CEA Patent)~100µmWinded 2D braid 3D braidHorizontal 3D braiding machineExamples of SiC braids [CEA]5 mmExamples of sandwich cladding prototypeSiC/SiC + metallic liner + SiC/SiC• Gastightess even when cracked SiC/SiC (OK up to 300 MPa at least !)• Mechanical properties to be assessed (e.g. inner pressure…)• Chemical compatibility beween SiC and liner to be checked (very good preliminary results with Ta and Nb)Marion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors 25

4- Conclusions1- Advanced Austenitic steels☺ • Very good and achievable response to irradiation swelling of 15/15 Ti• Mechanical properties to be confirmed• Need of additional irradiation experiments to high dose (200dpa)CEA new specificationsby the end of 20122- ODS steels☺• Very good resistance to swelling•Complex processing of powder metallurgy•Almost no tertiary creep domainStability to be assessed in Pb…Limited Cr% is the key point Coating ?3- Vanadium alloys☺• V-Cr-Ti alloys seem very appropriate ☹• Mechanical properties >700°C• Improvement of alloys for SFRs ?3- Ceramic cladding – SiC/SiC : technological challenge☺• Almost no deformation (expansion, swelling)• High temperature strength (>800°C)•Complex and expensive but achievable fabricationProtection for chemical compatibility R&D + complex fabricationWrapper in SFRCladding in PWR• Gas-tighness solutions Long term R&DMarion LE FLEM, Advanced Materials for Fuel Cladding in Sodium Fast Reactors26