Study of the U3Si5, USi2-x and USi2 phases stability due to the incorporation of aluminium in solution by the use of Differential Scanning Calorimetry (DSC) technique

ABSTRACT U(Mo) alloys are being studied to be applied as a fuel for research and test reactors. When U(Mo) particles are dispersed in an Al matrix, it is known that an interdiffusion during fabrication process and / or irradiation. In this sense, irradiation tests have shown that this IL has a bad behavior under irradiation coming up the addition of Si to Al as one of the most promising solutions. Several out of pile experiences have been performed with U(Mo)/Al(Si) diffusion couples in which U(Al,SI)3, U3Si5, USi2, USi2-x, Al20Mo2U and/or Al43Mo4U6 are the phases identified as conforming the IL. In some cases, U3Si5 was identified considering modified lattice parameters, which can be justified assuming that the U3Si5 phase would accept a small amount of Al in solution. However, although the Al-Si-U ternary system has been extensively studied, there are no previous experimental results to correlate lattice parameters modification with Al solubility in U3Si5, USi2 y USi2-x phases. From previous paragraphs, it is important to study the Al-Si-U ternary system especially in the environment of U3Si5, USi2 and USi2-x phases. With this aim, ten alloys were fabricated. Nine of them were isothermally treated at 550 ºC and microstructurally characterized. The Main results show the presence of needle-like morphology in the alloys with concentrations around that of the U3Si5 phase. From th fact that this kind of morphologies is characteristic of a displacive transformation, which occur during cooling process, the use of a dynamic identification transformation technique (as differential scanning calorimetry) came up as mandatory in this research In this new stage, nine alloys were studied with the calorimeter using two heating/coolig rates (± 1 ºC/min and ± 10 ºC/min). Transformation temperatures and enthalpy of formation of compounds were determined. The samples were also microstructurally characterized after testing.