Characterization of the interaction layer grown by interdiffusion between U-7wt%Mo and Al A356 alloy at 550 and 340 deg C

U(Mo) alloys are under study to get a low-enriched U fuel for research and test reactors. Qualification experiments of dispersion fuel elements have shown that the interaction layer between the U(Mo) particles and the Al matrix behaves unsatisfactorily. The addition of Si to Al seems to be a good solution. The goal of this work is to identify the phases constituting the interaction layer for out-of-pile interdiffusion couples U(Mo)/Al(Si). Samples gammaU-7wt%Mo/Al A356 alloy (7.1 wt%Si) made by Friction Stir Welding were annealed at 550 and 340 deg C. Results from metallography, microanalysis and X-ray diffraction, indicate that the interaction layer at 550 deg C is formed by the phases U(Al,Si)3, U3Si5 and Al20Mo2 U, while at 340 deg C it is formed by U(Al,Si)3 and U3Si5. X-ray diffraction with synchrotron radiation showed that the Si-rich phase, previously reported in the interaction layer at 550 deg C near U(Mo) alloy, is U3Si5.