Morphology is a fundamental attribute when investigating voids and bubbles in UO 2 . This study uses molecular dynamics and Monte Carlo simulations to predict the lowest energy shapes for voids and bub- bles in UO 2 . The energies of the { 100 } , { 110 } and { 111 } surfaces have been calculated and used to predict the equilibrium void shape from Wulff construction. This equilibrium shape is compared to low energy faceted voids exhibiting different relative proportions of each family of terminating surfaces. It is found that the equilibrium Wulff shape does not represent the lowest energy morphology for nm void sizes at temperatures between 30 0 K and 120 0 K. Furthermore, the lowest energy faceted voids are slightly more energetically favourable than spherical voids, and as Xe is added, and bubble pressure increases, the faceted morphology becomes even more favourable than the spherical shape.