Assessment of positrons for defect studies in CeO₂ materials

Disposal of spent nuclear fuel poses significant challenges, as the UO₂ and fission products are under constant irradiation and must be safely stored for millennia. CeO₂ is a non-radioactive analog for UO₂ for studying microstructure and its evolution. Many techniques have been applied to uranium and cerium oxides to investigate point defects. Positron annihilation spectroscopies (PAS) are sensitive to neutral and negatively charged vacancy-like point defects and impurity vacancy complexes. PAS has been applied previously to UO_2+x to investigate nuclear fuels, but virtually no PAS work exists on CeO₂. Here, the basics of positron annihilation spectroscopy is reviewed, and preliminary work on undoped and doped CeO₂ is shown and compared to the literature results from UO₂. To simulate fission product incorporation in spent nuclear fuels, CeO₂ samples were doped at different concentration with yttrium. Select samples were irradiated with heavy ions at different doses. Doping and irradiation are shown to give rise to different defect characteristics.