Interdiffusion behavior of U₃Si₂ with FeCrAl via diffusion couple studies

Uranium silicide (U₃Si₂) is a candidate to replace uranium oxide (UO₂) as light water reactor (LWR) fuel because of its higher thermal conductivity and higher fissile density relative to the current standard, UO₂. A class of Fe, Cr, Al alloys collectively known as FeCrAl alloys that have superior mechanical and oxidation resistance are being considered as an alternative to the standard Zirconium based LWR cladding. The interdiffusion behavior between FeCrAl and U₃Si₂ is investigated in this study. Commercially available FeCrAl, along with U₃Si₂ pellets were placed in diffusion couples. Individual tests were ran at temperatures ranging from 500 °C to 1000 °C for 30 h and 100 h. The interdiffusion was analyzed with an optical microscope, scanning electron microscope, and transmission electron microscope. Uniform and planar interdiffusion layers along the material interface were illustrated with backscatter electron micrographs and energy-dispersive X-ray spectroscopy. Electron diffraction was used to validate phases present in the system, including distinct U₂Fe₃Si/UFe₂ and UFeSi layers at the material interface. U and Fe diffused far into the FeCrAl and U₃Si₂ matrix, respectively, in the higher temperature tests. No interaction was observed at 500 °C for 30 h.