First-principles study of the stability and migration of Kr, I and Xe in ZrO2

The stability and migration of Kr, I and Xe in bulk ZrO2 and on the ZrO2 (1 1 1) surface have been studied by standard density functional theory (DFT) and the DFT-D2 method that corrects for the van der Waals interaction. Both methods show that Kr and Xe prefer to incorporate in the bulk phase rather than adsorb on the surface, and Xe is very mobile in the bulk state. For Kr and Xe adsorption on the surface, van der Waals interaction dominates, causing the weak interaction between the adsorbate and substrate. Iodine is found to have comparable stability in both phases and forms I O bonds with strong covalency. It exhibits higher mobility on the surface than in the bulk ZrO2, and diffusion from bulk-like state to surface state is an exothermic process. The fission product behavior in ZrO2 is shown to be a complicated synergetic effect of fission product atomic size, electron negativity, occupation site and phase structure of the host.