Short communication: Spark plasma sintering as an innovative process for nuclear fuel plate manufacturing

International audienceIn this paper, we propose an alternative process based on spark plasma sintering for the manufacture of nuclear fuel plates for research reactors. This process presents significant flexibility to control manufacturing parameters such as fuel meat geometry and porosity according to the designer specifications. Furthermore, it allows to increase uranium loading up to 7.3 gU cm−3, exceeding the current requirements for high performance MTRs. With this process neither dogbone, fishtail nor sharp particles penetrating the cladding are observed. The potentialities of this approach are illustrated with the manufacturing of a high loaded (5.6 gU cm−3) U3Si2/Al mini-plate. © 202

Géopolymères à base de métakaolin : impact de l’addition d’acide orthophosphorique dans le mélange réactif

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Metakaolin-based geopolymer: Formation of new phases influencing the setting time with the use of additives

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From arc-melted ingot to MTR fuel plate A SEM/EBSD microstructural study of U3Si2

International audienceU3Si2/Al fuel plates are widely used in Material Testing Reactors (MTRs) as Low Enriched Uranium driver fuel. In this paper, a reinvestigation of the microstructure of U3Si2 particles is proposed to take full advantage of the new capabilities offered by Electron BackScattered Diffraction (EBSD) techniques. Using EBSD we demonstrate that most particles are single crystalline in as-fabricated plates. To understand this characteristic, linked to the microstructure of the starting material, an in-depth study of U3Si2 ingots produced by arc-melting was performed at a laboratory scale; they were extensively characterized by EBSD, scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. It is shown that U3Si2 grain may be large (up to several thousands of micrometers) and that they exhibit a strong preferential orientation, linked to the axial thermal gradient created in the arc-melting chamber. A significant impact of the cooling rate after arc-melting on the ingot microstructure is noticed grains are smaller and more columnar when the cooling rate is high. A deviation from 3U/2Si stoichiometry caused for example by impurities induces the formation of a secondary phase, which exhibits a square spiral morphology. We then demonstrate that the cooling rate of U3Si2 ingots has a direct influence on the characteristics of the powders obtained by crushing these ingots. Indeed the powder obtained from “slow” cooled ingots is found very close to the powder used for industrial MTR plates. On the contrary particles obtained from “fast” cooled ingots, are polycrystalline and more resistant to crushing. Thus, this work provides significant advances both in the characterisation of technological products like U3Si2/Al MTR plates and in more basic knowledge about the U3Si2 phase formation

Microstructural characterization of atomized U 3 Si 2 powders with different silicon contents (7.4-7.8 wt%)

International audienceAtomization processes are used to produce uranium-based powders for the manufacturing of dispersion fuel for nuclear research reactors. Whereas this process is considered worldwide as a reference for U-Mo powder production, its use for U 3 Si 2 is still limited. In this paper, the microstructure of as-atomized nearly stoichiometric (7.4 wt% Si) and hyperstoichiometric (7.6 and 7.8 wt% Si) U 3 Si 2 powders is studied in detail. A wide range of analytical techniques were applied: X-ray diffraction (XRD), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM), electron backscattered diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS) at both micrometer (SEM) and nanometer (STEM) scales. These analyses lead to an original description of the microstructure of these as-atomized U 3 Si 2 particles. It is shown that most of atomized particles contain only a few U 3 Si 2 grains, some being even monocrystalline. The main secondary phase present in hyper-stoichiometric batches is an U 20 Si 16 C 3like phase. Other minor phases are also encountered, some of them containing metallic impurity elements. These features are attributed to the uranium raw material composition and to a slight contamination by carbon during the powder synthesis. The nature and morphology of secondary phases present in U 3 Si 2 atomized particles appear thus to be linked not only to the silicon excess but also to the presence of impurities which probably strongly segregate during the very fast solidification of the alloy droplets. A slight superficial oxidation of particles also occurs and induces a local redistribution of silicon

Mat-O-Covid : comment l’utiliser ?

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