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Etudes rheologiques de pates ceramique pour la mise en forme de combustible nucleaire par extrusion

Abstract : Nuclear MOx -(U,Pu)O2- fuels, are shaped into pellets by dry-pressing a mixture of UO2/PuO2 . This process relies on several steps, among which the materials are powdered (crushing, mixing, sieving, pressing). It presents proven benefits, such as ease of implementation and high production rates. Alternative shaping processes based on materials in a wet or liquid state, are interesting alternatives for the mixing steps. Indeed, they reduce the dust accumulation due to dry-powder processes. Moreover, such processes should enable a better control over the fired fuel microstructures, through a more homogeneous mixing in the first steps. Extrusion processes could prove useful to engineer fuel rods. This work is focused on understanding the rheology of ceramic pastes, to be able to control its extrusion. Yttrium oxide and titanium dioxide, acting as plutonium dioxide and uranium dioxide, were selected for their respective proximity regarding morphology, granulometry and electric neutral point. Criteria believed to be the main parameters physically dictating the agglomeration and flow of the ceramic pastes. The pastes were obtained with a 30cm3 roller blade mixer (Brabender). Organic additives were added to enable the extrusion of non-model, highly charged systems. A capillary rheometer (RH2000, Malvern Panalytical) and less-conventional squeeze test flows were used to study the rheology of such pastes. A ram-extruder was built and mounted on an electromechanical testing machine (Instron). Ceramic pastes, shaped into 20cm rods, without surface defect and withstanding the specifications for nuclear fuels (fired density, mechanical strength, roughness, dimensions, purity and composition and microstructure) were further characterized. Six parameters fitted Benbow-Bridgwater’s equation to predict the extrusion pressure when changing geometry and speed. Constitutive modelling has been carried out on the forces obtained from squeezing test set-ups. The compressive forces were found to be dependent on sample deformation, compressive speed and volume fraction of ceramics. Friction seems to play an important role in flows of the system studied. Traditional capillary experiments have also been found to be poorly reliable to successfully characterize the rheological behaviour of these complex systems. Extruding highly charged ceramics rods, respecting nuclear specifications, is challenging. Modelling such flows requires reliable rheological flow-configurations. Squeezing tests and modified models successfully predict these pastes behaviour under controlled flow conditions. Further work will focus on applying these revisited models on extrusion flows. The final goal will be to transpose the study on ceramic pastes with nuclear oxides.
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https://hal.archives-ouvertes.fr/hal-02411053
Contributor : Bibliothèque Cadarache <>
Submitted on : Saturday, December 14, 2019 - 12:43:02 PM
Last modification on : Wednesday, October 14, 2020 - 3:52:29 AM

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  • HAL Id : hal-02411053, version 1

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P.-F. Mougard Camacho, A. Poulesquen, F. Doreau, Romain Castellani, Rudy Valette. Etudes rheologiques de pates ceramique pour la mise en forme de combustible nucleaire par extrusion. Congress of European Ceramic Society, Jun 2019, Turin, Italie. ⟨hal-02411053⟩

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