Conductivity of UO2 ceramics: effect of a weakly to strongly branched pore network up to 500°C (exp) and numerical simulations beyond
Résumé
We consider in this study three uranium dioxide ceramics whose porous network varies noticeably according to the manufacturing conditions. This porous network is made up of a fine and elongated porosity which is called inter-granules pores but also of occluded pores which can be highlighted at a much smaller scale.
Thermal diffusivity measurements have been performed by a flash laser method on these ceramics at 50°C under different atmospheres but also up to 500°C conditions under an argon and dihydrogen atmosphere. These measurements have shown marked differences in the thermal conductivities of these three ceramics, in particular a sharp degradation when the open porosity increases is reported.
To understand the influence of these two families of porosity on the effective conductivity, a double-scale model has been developed. The effect of occluded porosity is approximated using the Maxwell (1873) model. The effect of the inter-granules porosity is evaluated by full-field numerical simulations performed on synthetic microstructures generated by the optimization process described in Moutin (2023) .
Comparisons of model predictions to experimental results confirm the predominant role of the inter-granules porosity on the effective conductivity. Besides, it is shown that the Knudsen effect must be taken into account to accurately predict environment effect at 50°C. Finally, the simulated conductivity of the ceramics are shown to predict temperatures effects up to 500°C
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