Characterization of (Th,U)O 2 pellets made by advanced CAP process

Abstract

Coated Agglomerate Pelletization (CAP) process is being developed by Bhabha Atomic Research Centre (BARC) for the fabrication of ThO 2–UO 2 mixed oxide fuel pellets. In order to improve the microstructures with better microhomogeneity, a study was made to modify the CAP process. The advanced CAP (A-CAP) process is similar to the CAP process except that the co-precipitated powder of mixed oxide, ThO 2–30%UO 2 or ThO 2–50%UO 2, is used for coating instead of U 3O 8 powder. The choice of ThO 2–UO 2 powders as the coating material is advantageous compared to U 3O 8, since the presence of large quantities of ThO 2 in UO 2 powder gives better self-shielding effect. In this paper, ThO 2 containing 4%UO 2 (% in weight) was prepared by the A-CAP process. Property measurements including microstructure and microhomogeneity were made by optical microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), etc. It was found that the pellets sintered in air at 1400 °C showed a duplex grain structure and those sintered in Ar–8%H 2 at 1650 °C showed a very uniform grain structure with excellent microhomogeneity.