Irradiation-enhanced diffusion and diffusion-limited creep in U3Si2
MWD Cooper and KA Gamble and L Capolungo and C Matthews and DA Andersson and B Beeler and CR Stanek and K Metzger, JOURNAL OF NUCLEAR MATERIALS, 555, 153129 (2021).
U3Si2 is an advanced fuel candidate due to its relatively high fissile density and attractive thermal properties. Compared to standard UO2 fuel, there are significant data gaps for the thermophysical and thermomechanical properties of U3Si2. Point defect concentrations and mobilities under irradiation govern a number of important fuel performance properties, such as creep and fission gas release. In this work, we utilized density functional theory (DFT) data to inform a cluster dynamics framework to predict point defect concentrations in U3Si2 under irradiation. Molecular dynamics (MD) simulations were used to examine the contribution of atomic mixing during ballistic cascades to diffusion, as well as the diffusivity of U and Si at grain boundaries. These atomic scale models for diffusivity were then used to inform a creep model based on bulk (Nabarro-Herring) and grain boundary (Coble) diffusional creep, and climb-limited dislocation creep. The model compares well against available experimental data and has been implemented in the BISON fuel performance code. A demonstration case using simple power profiles has been carried out, showing that negligible creep occurs due to the low temperatures experienced by U3Si2 in-reactor, a consequence of its high thermal conductivity. Published by Elsevier B.V.
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