Computational Studies of Amorphous UO2 for Grain Boundary Behavior

Fission products at the point of contact between the pellet and the cladding contribute to the ultimate failure of the cladding through stress corrosion cracking (SCC). Gaseous fission products navigate along the grain boundaries after formation and eventually reach the plenum. To better understand fission product behavior at fuel grain boundaries, we generated random amorphous UO2 structures, as highly disordered grain boundaries exhibit the fastest kinetic properties. These structures were then optimized using ab initio methods and the most stable structure was selected for defect calculations. We have compared the atomic structure of UO2 structures with and without antiferromagnetism and calculated the incorporation energies of I, Te, and Xe in the grain boundaries of UO2. Each of the studied fission products favored the O-poor boundary. The grain boundary itself showed changes in lattice parameter lengths and angles after both vacancy formation and fission product incorporation.