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Recent progress in the synthesis and characterization of uranium carbide compounds.

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 11. . 40 ieme Journées des Actinides 2 nd Workshop an Actinide Targets.

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Recent progress in the synthesis and characterization of uranium carbide compounds.

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  1. 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 11. 40ieme Journées des Actinides 2nd Workshop an Actinide Targets Genève, 27mars -01 avril

  2. Recent progressefforts on the synthesis and characterizationsintering of uranium monocarbidecompounds. SCR/CSM, Université de Rennes1, UMR CNRS 6226 Institut de Physique Nucléaire, IPN-Orsay, Université Paris-Sud 11. 40ieme Journées des Actinides 2nd Workshop an Actinide Targets Genève, 27mars -01 avril

  3. 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 Outline :

  4. Improve the performance of reactors and fuel cycles with current nuclear system (security , resources sustainability , reprocessing ,..) • WORKING CONDITIONS : GFR-He concept • -T°: - working conditions : 500-1000°C • - incidental / accidental conditions : 1600 -2000°C for one hour, without melting • -η : - fast neutrons , fluence 1.1027η/m2, • - 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 80-85 : 10-15 : 0-5. • compromise between high densification and porosity Gen-IV : Gas-Fast Neutron Reactors (Allegro) (U, Pu, MA*)C/ SiC-SiCf Liner : M Needle-likeassembly * Minor actinides : Np, Am, Cm

  5. Production of rare-isotope beams for nuclear physics ISOL target of 3rd 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 : UCx • Mixed UC / UC2 or UC2 + nC. • - Compromise between density and open porosity Targets for Isotope Separation On Line (ISOL) facilities Workingtemperature, T = 2000°C Pellets are pilled up in a graphite container

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

  7. UC : - congruent melting compound T°f # 2530°C - solid solution UC-UC2athigh T° - line compound atlow T° - NaCl type of structure, a = 4.9510(3) Binary phase diagram of U-C R. Benz, C.G. Hoffmann, G.N. Rupert, High Temp. Science, 1 (1969) 342.

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

  9. Rietveld analysis of a samples with nominal composition UC1.02 Detectionlimitbelow 1 wt % of a secondary phase, UC2.

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

  11. Grinded UC ingots Distribution of the grain size

  12. Reactions (1450 < T < 1900°C): UO2 + 3 C  UC + 2 CO ↑ ! • Reduction of U3O8 under H2 flux • Control of the stoichiometry of oxygen Carbothermalreduction of uranium oxide Experimental procedure : UO2+ nC pellets ( 8, 10)  Cgraphitecrucible n = 2, 2.5, 3, 3.5, 4, 4.5 1450 - 1900°C (0.5- 6 hours) 300°C/h High temperature furnace with C graphite resistor Influence of : Temperature initial composition (n)

  13. Arc-melted sample T = 1700°C for 3h Carbothermalreduction of uranium oxide T = 1900°C for 1h n = 3 • single phase of UC No significantdiffrence on the XRD powder patterns between the arc-meltingmethod and the carboreduction one

  14. T = 1700°C, t = 3h UO2 + 3C UC SEM observations of a UC compact x 1000 x 5000 x 100 Large cavities : gas released Grain sizes [1-5] µm Synthesis and sintering in one step impossible (mechanical properties)

  15. Size of the UC particules ! No significantdiffrence on the grain size and specific area of the powdersobtained by arc-melting and by carboreduction.

  16. Sintering in a H.F. furnace Natural sintering of UC Pellets 1500 < T < 1900°C 7,5 V = 0.2496 cm² d measured= 10.26 g/cm3 d calculated= 13,68 g/ cm3 C = 75,0% Pellet n° 2 : cold pressing 5 tonnes/ cm² 5,5 5,8 7,5 Densification about 75 % is a reproducible value over several experiments

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

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

  19. SEM observations of a H.P UC pellet x 200 x 2000 x 5000 Black area : cavities Grain size about 5µm Lamellar morphology - free carbon - UC2

  20. 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 Synthesis by carbothermic reduction Sintering of UC pellets methodic procedures not easy task, refractory material Sintering of uranium carbides great challenge

  21. Acknowlodgements 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 RECHERCHECNRS – CEA/DEN -EDF - ANDRA GROUPEMENT DE RECHERCHECEA CNRS EDF AREVA-NP AREVA-NC MATINEX PARIS

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