Fuel-matrix chemical interaction between U-7wt.%Mo alloy and Mg

A solid-to-solid, U-7wt.%Mo vs. Mg diffusion couple was assembled and annealed at 550°C for 96 hours. The microstructure in the interdiffusion zone and the development of concentration profiles were examined via scanning electron microscopy, transmission electron microscopy(TEM) and X-ray energy dispersive spectroscopy. A TEM specimen was prepared at the interface between U-7wt.%Mo and Mg using focused ion beam in-situ lift-out. The U-7wt.%Mo alloy was bonded well to the Mg at the atomic scale, without any evidence of oxidation, cracks or pores. Despite the good bonding, very little or negligible interdiffusion was observed. This is consistent with the expectation based on negligible solubilities according to the equilibrium phase diagrams. Along with other desirable properties, Mg is a potential inert matrix or barrier material for U-Mo fuel alloy system being developed for the Reduced Enrichment for Research and Test Reactor (RERTR) program.