Oxidation of Pu alloys stabilized in δ–phase: Study of Ga alloying element behavior by using EXAFS analysis and Reverse Monte Carlo simulation

Studies were performed to improve the knowledge about Ga behavior during oxidation of Pu alloys stabilized in δ–phase. The coupling of EXAFS experiments with Reverse Monte Carlo (RMC) simulation of 3D material structure has achieved the characterization of the atomic local environment around Pu and Ga atoms in the outer PuO ₂ layer formed on a δ−PuGa 1 at% alloy. No formation of Ga aggregates or Ga oxides was detected. The RMC analysis of experimental data has revealed the presence of Ga atoms within the lattice of the oxide scale in Pu substitutional sites or octahedral sites. Nevertheless, this incorporation leads to a large local disorder with a displacement of Ga atoms from their initial high symmetry crystallographic site. Finally, the results obtained bring new insights explaining the destabilization of the δ−phase by the diffusion of Ga atoms likely into Pu vacancies in PuO ₂ lattice during oxidation.