The incorporation of xenon at point defects and bubbles in uranium mononitride

Uranium mononitride (UN) has been proposed as an accident tolerant fuel for nuclear fission reactors and offers enhanced performance during accident scenarios relative to the current fuel, uranium dioxide. However, its performance in reactor is significantly less well understood than for the oxide. Therefore, this work explores incorporation of Xe into UN using density functional theory to understand the early stages of fission gas evolution. These results are used to derive a new potential for Xe in UN, which is then employed to simulate the growth of xenon bubbles in spherical voids of various sizes at 300 K and 1200 K. At sufficiently high gas densities, the xenon was found to mainly crystallise in an fcc arrangement. Loop punching was observed at 10.2 GPa and above for larger bubbles of 4.8 nm radius, significantly so for higher temperatures. This work suggests that no Xe undergoes thermal resolution at temperatures up to 1200 K and that the UN lattice prefers to undergo deformation instead.