The phase equilibria of advanced technology nuclear fuel candidates and interactions with alternate options to zirconium-based cladding is being explored. Uranium silicide (U3Si2) and silicide nitride (U3Si2-UN) composite fuels are the most promising contenders for the future, whereas ferritc alloys such as FeCrAl and SiC/SiC composite materials are under investigation for the cladding. The uranium density of the silicide and U-Si-N composite is advantageous in overcoming the neutron penalty imposed by the FeCrAlY material. This work focuses on thermochemical modeling and experiment to explore current limitations within the literature concerning the U-Si-N and U-Si-FeCrAlY phase space. Experimental techniques to investigate the U3Si5-USi2 region include arc-melting and characterization by SEM-EDS and XRD, which is also extended to ternary nitride compositions. A multiscale modeling approach is used to explore the U-Si phase space including DFT, evolutionary algorithms and cluster expansion to identify stable structure types. Density functional theory is also utilized for formation energies of the U-Si-N ternary as well as the U-Fe-Si phase space to include FeCrAlY cladding compositions. These first principal calculations support thermodynamic CALPHAD assessments these ternary systems, with the cumulative results serving as input for higher order fuel peformance evaluation.
This research is being performed using funding received from the DOE Office of Nuclear Energy's Nuclear Energy University Programs