Ab initio modeling of the behavior of helium and xenon in actinide dioxide nuclear fuels

By means of an ab initio plane wave pseudopotential method, the behavior of helium in UO2, PuO2, AmO2 and (Am0.5Pu0.5)O2 and of xenon in UO2 is studied. We first show that a pseudopotential approach in the generalized gradient approximation (GGA) can satisfactorily describe the cohesive properties of these actinide dioxides. We then calculate the formation energies of point defects (vacancies and interstitials), as well as the incorporation and solution energies of helium in UO2, PuO2, AmO2 and (Am0.5Pu0.5)O2, and of xenon in UO2. The results are discussed according to the incorporation site of the gas atom in the fluorite lattice and according to the dioxide stoichiometry.