The evaluation of thermal conductivity in UAl2 rod manufactured by powder metallurgy method

The structures of UAl2 and UAl3 are isotropic just like a MgCu2 face centered cubic and AuCu3 Cubic structures with relatively high melting temperatures of 1590 .deg. C and 1350 .deg. C, respectively. However, UAl4 is anisotropic with an orthorhombic structure with a low decomposition temperature of 731 .deg. C. Uranium densities of UAl2 and UAl3, which are 6.64 g-U/cc and 5.08 g-U/cc, are considered to be applicable for reactor fuels. In addition, UAl2 and UAl3 does not have a solid solution range, while UAl4 has a small solid solution range. From the above aspects, monolithic UAl2 is considered to be the most valuable, so an effort has been made to develop the relevant fabrication technology. Monolithic UAl2 has been reported as being fabricated by an arc-melting method, which is difficult when producing a rod type fuel. KAERI has developed a rotating disk atomization process to fabricate a uranium alloy powder. So the utilization of an atomized uranium powder has been pursued by using powder metallurgy technology. Relatively fine uranium powder was used. Blending, compaction, and extrusion were implemented in the same manner as the HANARO fuel fabrication process. In this study a SEM observation of the cross section of the UAl2 specimen was conducted to observe the fabrication voids and cracks as well as the remaining uranium phases in the monolithic UAl2 rod. The densities of the formed UAl2 rods were measured by the immersion method. The presence of the UAl2 phase was confirmed for the annealed specimen through an X-ray diffraction analysis. Thermal conductivities were measured and discussed from the viewpoint of nuclear fuel candidates. This study also focused on an examination of the soundness of the formed UAl2 specimen and the feasibility of a monolithic UAl2 fuel for nuclear reactors