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Contribution à l'étude des propriétés mécaniques du combustible nucléaire : Modélisation atomistique de la déformation du dioxyde d'uranium

Abstract : Mechanical properties of nuclear fuel are a complex problem, involving many coupled mechanisms occurring at different length scales. We used Molecular Dynamics models to bring some light on some of these mechanisms at the atomic scale. We devised a procedure to calculate transition pathways between some UO2 polymorphs, and then carried out dynamics simulations of these transitions. We confirmed the stability of the cotunnite structure at high pressure using various empirical potentials, the fluorite structure being the most stable at room pressure. Moreover, we showed a reconstructive phase transition between the fluorite and cotunnite structures. We also showed the importance of the major deformation axis on the kind of transition that occur under tensile conditions. Depending on the loading direction, a scrutinyite or rutile phase can appear. We then calculated the elastic behaviour of UO2 using different potentials. The relative agreement between them was used to produce a set of parameters to be used as input in mesoscale models. We also simulated crack propagation in UO2 single crystals. These simulations showed secondary phases nucleation at crack tips, and hinted at the importance thereof on crack propagation at higher length-scales. We then described some properties of edge dislocations in UO2. The core structures were compared for various glide planes. The critical resolved shear stress was calculated for temperatures up to 2000 K. These calculations showed a link between lattice disorder at the dislocations core and the dislocations mobility
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Paul Fossati. Contribution à l'étude des propriétés mécaniques du combustible nucléaire : Modélisation atomistique de la déformation du dioxyde d'uranium. Autre. Ecole Centrale Paris, 2012. Français. ⟨NNT : 2012ECAP0045⟩. ⟨tel-00780059⟩

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