On the U-Fe-C Isothermal Section at 1100 °C

The energy crisis and climate change have promoted a growing interest in non-fossil sources, such as nuclear, with uranium carbides being seen as potential fuel candidates for Generation IV nuclear reactors. However, the need of accurate thermophysical data for the fuel and its compatibility with core materials during the extreme fission conditions is still an issue. Here a study of the ternary uranium-iron-carbon system performed at 1100 °C using powder x-ray diffraction and Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry is presented. The U-Fe-C isothermal section is characterized by two ternary compounds, thirteen 3-phase regions and five 2-phase regions. UFeC₂ and ~ U₁₁Fe₁₂C₁₈ were confirmed to be present at 1100 °C and crystallize in structures related to the binary uranium carbides. UFeC₂ crystallizes in an original structure type, a distorted variant of the UCoC₂ structure, with space group P4/n and a = 3.503(5) Å and c = 7.405(5) Å lattice parameters. ~ U₁₁Fe₁₂C_18, has a crystal structure related to the Th₁₁Ru₁₂C₁₈ structure-type (space group I \(\overline{4 }\) 3m) with the lattice parameter a ≈ 10 Å. Furthermore, an island of a α-UC₂-based phase with 32U:4Fe:64C composition was found in the 1100 °C isothermal section, indicating the inclusion of Fe in the α-UC₂ binary compound.