Recent progress in the synthesis and characterization of uranium carbide compounds. SCR/CSM, Université de Rennes1, UMR CNRS 6226 Institut de Physique Nucléaire, IPN-Orsay, Université Paris-Sud ieme Journées des Actinides 2 nd Workshop an Actinide Targets Genève, 27mars -01 avril

Recent progress efforts on the synthesis and characterization sintering of uranium monocarbide compounds. SCR/CSM, Université de Rennes1, UMR CNRS 6226 Institut de Physique Nucléaire, IPN-Orsay, Université Paris-Sud ieme Journées des Actinides 2 nd Workshop an Actinide Targets Genève, 27mars -01 avril

Outline : Part I : Objective of the study A- Frame of the work (GFR-He, ISOL-target) B – Aim the study Part II : Synthesis of uranium monocarbide. A – Overview on the binary phases diagram U-C B – Melting of U and C using an arc furnace C – Carbothermal reduction at high temperature Part III : Sintering of dense UC pellets. A- Natural sintering B- Hot pressing of powder. Part IV : Conclusions and future work A- Synthetic routes B- sintering of carbides

Gen-IV : Gas-Fast Neutron Reactors (Allegro) (U, Pu, MA*)C/ SiC-SiCf WORKING CONDITIONS : GFR-He concept -T°:- working conditions : °C - incidental / accidental conditions : °C for one hour, without melting -η : - fast neutrons, fluence η/m 2, - Cycle - 3 years ASSEMBLY : Needle-like STRUCTRAL & MATRIX MATERIALS : SiC-based meterials LINER M : W, (W-Re) alloys FUEL : (U, Pu)C solid solution, with insertion of MA* - atomic ratio of the composition : U : Pu : MA* of : : compromise between high densification and porosity * Minor actinides : Np, Am, Cm Needle-like assembly Liner : M Improve the performance of reactors and fuel cycles with current nuclear system (security, resources sustainability, reprocessing,..)

Targets for Isotope Separation On Line (ISOL) facilities ISOL target of 3 rd generation (SPIRAL2) INCIDENT BEAM : -Energetic light (deutons) or heavy ions or thermal neutrons - Properly focused REACTIONS : -spallation, fission or fragmentation mechanisms EJECTION FROM THE TARGET : -ionized, accelerated, purified WORKING CONDITIONS -T° # 2000°C under high vacuum - heavy irradiation TARGET - composition : UC x Mixed UC / UC 2 or UC 2 + nC. - Compromise between density and open porosity Working temperature, T = 2000°C Production of rare-isotope beams for nuclear physics Pellets are pilled up in a graphite container

New generations of nuclear systems Gen IV – GFR-He reactors & ISOL facilities CHALLENGES : Comprehensive study Advanced materials working under extreme conditions (T°, η, D+, … long-time.) Stability / Evolution (Fuel or Target) under working conditions microstructure of the pellets : grain sizes, morphology porosity, distribution of the porosity Identify the main parameters which controlled the microstructure of UC pellets. Prospective works on : - synthetic routes, - microstructural parameters of the powder, - sintering mechanisms.

Binary phase diagram of U-C UC : - congruent melting compound T°f # 2530°C - solid solution UC-UC 2 at high T° - line compound at low T° - NaCl type of structure, a = (3) R. Benz, C.G. Hoffmann, G.N. Rupert, High Temp. Science, 1 (1969) 342.

Synthesis of uranium monocarbide Arc-melting : U + n C g UC n n = 1 T > 2600°C Easy to melt High purity of the product Reproducible Fast (20 min) Ingots of 0.5 – 3g Need to be grinded

Rietveld analysis of a samples with nominal composition UC 1.02 Detection limit below 1 wt % of a secondary phase, UC 2.

SEM observations of a UC Ingot SEM observations : - Dense materials, - Low porosity - Well crystallized sample : brittlee & easy to grind

Distribution of the grain size De0.375 à2000 Nombres100 Moyenne:1.594 Médiane:1.443 D(3,2):7.068 Moyenne/Médiane:1.105 Mode:1.204 Intervalle à 95%:0.544 Intervalle à 95%:4.671 Ecart-type:1.731 Variance:2.995 C.V.:0 Skewness:1.083 Kurtosis:1.498 Surface spécifique m 2.g -1 (BET)2.4 Grinded UC ingots

Carbothermal reduction of uranium oxide Reactions (1450 < T < 1900°C): UO C  UC + 2 CO ↑ - Reduction of U 3 O 8 under H 2 flux - Control of the stoichiometry of oxygen ! Experimental procedure : UO 2 + nC  pellets (  8, 10)  C graphite crucible n = 2, 2.5, 3, 3.5, 4, °C ( hours) 300°C/h High temperature furnace with C graphite resistor Influence of : Temperature initial composition (n)

Carbothermal reduction of uranium oxide - single phase of UC n = 3 T = 1700°C for 3h No significant diffrence on the XRD powder patterns between the arc-melting method and the carboreduction one Arc-melted sample T = 1900°C for 1h

SEM observations of a UC compact x 100 x 1000x 5000 Large cavities : gas released Grain sizes [1-5] µm UO 2 + 3C UC T = 1700°C, t = 3h Synthesis and sintering in one step impossible (mechanical properties)

Size of the UC particules ! De0.375 à2000 Nombres100 Moyenne: Médiane: D(3,2): Moyenne/Médiane: Mode: Intervalle à 95%: Intervalle à 95%: Ecart-type: Variance: C.V.:0 Skewness: Kurtosis: Surface spécifique m 2.g -1 (BET)2.5 No significant diffrence on the grain size and specific area of the powders obtained by arc-melting and by carboreduction.

Natural sintering of UC Pellets Sintering in a H.F. furnace 7,5 5,8 5,5 7,5 V = cm² d measured = g/cm3 d calculated = 13,68 g/ cm3 C = 75,0% Pellet n° 2 : cold pressing 5 tonnes/ cm² Densification about 75 % is a reproducible value over several experiments 1500 < T < 1900°C

SEM observations of a UC sintered pellet x 200 x 500 x 5000 Large cavities : Small single crystals # 50 µm T Solid state diffusion favor the grain growth T = 1900°C, 1 h

Hot press sintering of UC Pellets Sintering in a H.P. furnace Mold of C graphite Sintering conditions : 1500 °C for 2 h under rough vacuum with 80 MPa. Raw surface  = 10,3 mm h = 3,6 mm Densification ~ 85%

SEM observations of a H.P UC pellet x 200 x 2000 Black area : cavities Grain size about 5 µm x 5000 Lamellar morphology - free carbon - UC 2

Conclusion - Preparation of single phase UC powders : NaCl type, a = 4.951(2) Å, [0-5]µm, - arc-melting, n = 1, - carbothermic reduction, (T = 1700°C, n = 3, t =3h) -Sintering : competition between grain growth / porosity -Temperature favors the grain growth only -Pressure may help to limit the growth of the grain methodic procedures not easy task, refractory material Synthesis by carbothermic reduction Sintering of UC pellets Sintering of uranium carbides great challenge

Acknowlodgements GROUPEMENT DE RECHERCHE CNRS – CEA/DEN -EDF - ANDRA R. ELOIRDI F. de BRUYCKER S. MOREL D. MANARA E. COLINEAU B. FOUREST N. DACHEUX Merci de votre attention et de votre patience ! GROUPEMENT DE RECHERCHE CEA CNRS EDF AREVA-NP AREVA-NC