(A) study on the high density U alloy fuel prepared by centrifugal atomization

Abstract

The characteristics of high density U-Mo alloy powders solidified rapidly by the centrifugal atomization process have been examined. The thermal compatibility between centrifugally atomized particle and aluminium matrix in U-Mo alloy fuels has been studied. In addition, the characteristics, that is, morphology, size distribution, alloy phase and microstructure of $U_3Si_2$ powders solidified rapidly by a centrifugal atomization process have been investigated. It has been carried out a comparison test for two kinds of rod type fuels prepared with atomized spherical $U_3Si_2$ powder and comminuted irregular $U_3Si_2$ powder for the purpose of increasing U loading density. Also, thermal compatibility of atomized $U_3Si_2$ dispersed fuel meats has been characterized, and compared with comminuted $U_3Si_2$. In chapter Ⅲ, most of atomized U-Mo alloy particles have a smooth surface and near-perfect spherical shape. The atomized powder irrespective of particle size is found to be single phase γ-U alloy with isotropic structure and non-dendritic grain. The continuous cooling DSC trace of U-5at.% Mo alloy shows a small, broad endothermic peak originated from the formation of α-U phase and $U_2$ Mo phase, whereas that of U-22at.% Mo alloy shows no peak over all temperature ranges associated with the decomposition of α-U phase. The γ-U phase of U-5at.% Mo powder is decomposed as the α-U phase and the $U_2$ Mo phase after an annealing treatment at 400℃ for 100 hours. But the γ-U phase of atomized U-22at.% Mo powder remains as it was. In chapter Ⅳ, extruded dispersion fuels of 24 vol.% spherical U-2wt.% Mo and U-22at.% Mo powders in an aluminum matrix have been annealed for over 2000 hours at 400℃. No significant dimensional changes occurs in the U-22at.% Mo/aluminum dispersions. The U-5at.% Mo/aluminum dispersion, however, increases in volume by 26% after 2000 hours at 400℃. This large volume change is mainly due to the formation of voids and cracks resulting from nearly ...