Generation de microstructures de combustible nucleaireheterogene et homogeneisation mecanique

National audienceCertains combustibles nucleaires sont constitues d'un melange d'UO2 et de PuO2 ; ils presentent une microstructure heterogene complexe. Des cartographies de la teneur en Pu (plutonium)obtenue par mesure microsonde exhibe des amas respectivement riches et pauvres en Pu, inclus dans une matrice a teneur Pu intermediaire.Dans les codes combustibles, cette heterogeneite est traitee en considerant une repartition du Pu en une, deux ou trois phases a teneur homogene. Pour valider cette hypothese simplificatrice etameliorer la precision des calculs, l'effet d'une distribution heterogene de teneur est maintenant etudie. Pour cela, il faut pouvoir generer des microstructures 3D, sur lesquelles seront realises des calculs thermiques, neutroniques, mecaniques, etc

Assessment of Cold Composite Fuels for PWRs

This study is devoted to the evaluation of a new innovative micro structured fuel for future pressurized water reactor. This fuel should have the potential to increase the safety margins, lowering fuel temperatures by adding a small fraction of a high conductivity second phase material, the matrix, in the oxide fuel phase. After matrix selection, two different composite fuels were studied: first, a CERCER (CERamic = UO2-CERamic matrix made of silicon carbide, SiC) fuel type has been investigated, the advantages of a ceramic being generally its transparency to neutrons and its high melting temperature. The study then focused on CERMET fuels (CERamic-METal). Several materials have been considered such as zirconium alloys, austenitic and ferritic stainless steels and chromium based alloys. The behavior of this fuel in a standard rod has been modeled with finite element codes and was assessed for different aspects of the cycle as neutronic studies, thermal behavior in normal, incidental and accidental conditions. Feasibility of fuels has been investigated with the fabrication and characterizations of the microstructure of composite fuels with powder metallurgy and HIP processes. Finally, a global evaluation is given

A study of xenon aggregates in uranium dioxide using X-ray absorption spectroscopy

International audienceX-ray absorption spectroscopy experiments were performed on a set of xenon implanted uranium dioxide samples. Results indicate that the gas forms highly pressurised inclusions as a result of temperature anneals or an external ion irradiation. Estimated bubble pressures were found to be in the region of 2–5 GPa at low temperature. The consequences of such high pressures developing within intra-granular bubbles in irradiated fuels are discussed. A model is given enabling the computation of the sink strengths of bubbles as a function of the pressure of the rare-gas they contain. The model predicts that for pressure values found in the experiments, fission gas bubbles do not act as sinks for diffusing rare-gas atoms