Non-stoichiometry in U3Si2

Uranium silicides, in particular U3Si2, are being explored as an advanced nuclear fuel with increased accident tolerance as well as competitive economics compared to the baseline UO2 fuel. Here we use density functional theory calculations and thermochemical analysis to assess the stability of U3Si2 with respect to non-stoichiometry reactions in both the hypo- and hyper-stoichiometric regimes. We find that the degree of non-stoichiometry in U3Si2 is much smaller than in UO2 and at most reaches a few percent at high temperature. Non-stoichiometry impacts fuel performance by determining whether the loss of uranium due to fission leads to a non-stoichiometric U3Si2±x phase or precipitation of a second U-Si phase. We also investigate the U5Si4 phase as a candidate for the equilibrium phase diagram.