PORE-SIZE DISTRIBUTIONS IN URANIUM-DIOXIDE AND URANIUM DIOXIDE-GADOLINIUM OXIDE FUEL KERNEL PRODUCED BY SOL-GEL TECHNIQUE

Small kernels of UO2-Gd2O3 were produced from their nitrate solutions by the application of sol-gel process in place of the more conventional process of mixing powders. The sol-gel method consisted of the following steps: sol preparation, sol drop dispersion, gellation, washing of gelled microspheres, aging, drying, calcination, reduction, and sintering. The effect of reduction temperature (873, 1073 and 1773 K) under a reducing gas mixture of 50% H-2 + 50% N2 on pore volume and pore size distribution, was studied both for UO2 and UO2-Gd2O3 containing microspheres. The results indicated decreasing pore volume with increasing temperature as expected. However, the incorporation of Gd2O3 into UO2 in the sol had a retardation effect in sintering which resulted in higher pore volume than that of UO2-only microspheres. Mean pore diameter also remained small (about 950 nm) for UO2-Gd2O3 samples after reduction (sintering at 1773 K) when compared to 1400 nm for UO2-only samples. X-ray diffraction studies showed uniform distribution of Gd2O3 with no phase separation as well as a decrease in lattice parameter of UO2 indicating incorporation of Gd2O3 into UO2 lattice structure.