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Assessment of the ternary phase diagram on the stoichiometric and hypo-stoichiometric U-Nd-O system

Abstract : This thesis concerns the experimental study and thermodynamic modeling of the behavior of advanced fuels used in current and future generation nuclear power plants. The subject of the thesis is more precisely the study of the ternary system (U-Nd-O) and for comparison purposes of (U-Ce-O). This system is particularly representative of the fission products accumulated in the fuel for high combustion rates but also of the initial atomic substitutions in the fuel by neutron poisons, used in nuclear fuels with high enrichment levels and capable of spacing out nuclear reactor outages. The study of this system presents significant challenges due to the open conflict between thermodynamic and kinetic phenomena. It is indeed an out of equilibrium system where the long-range ordering of local structures is frustrated by the negligible of atomic transport in the cation sublattice in the range of temperatures of interest for applications. During this thesis, a review of the existing literature motivated the manufacture of samples with well-defined characteristics by powder metallurgy methods and by soft chemistry methods leading to a control of dopant distributions. The results obtained by numerous characterization techniques (XRD, SEM, TEM, XAS) on samples treated thermally under oxidizing or reducing conditions have allowed a critical re-evaluation of the phase diagrams currently used. We have modelled a new phase diagram that includes new experimental results. This allows a better knowledge of the limits of use of nuclear fuels respecting optimal safety conditions.
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Submitted on : Wednesday, July 8, 2020 - 11:51:18 AM
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  • HAL Id : tel-02893429, version 1

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Bernardo Herrero Bocco. Assessment of the ternary phase diagram on the stoichiometric and hypo-stoichiometric U-Nd-O system. Materials and structures in mechanics [physics.class-ph]. Université Paris-Saclay, 2020. English. ⟨NNT : 2020UPASC008⟩. ⟨tel-02893429⟩

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