Development of fuel-model interfaces: Characterization of Pd containing UO2 thin films

The presented work aims to reproducibly prepare UO2–Pd thin film model systems for spent nuclear fuel in order to further investigate surface reactions of these films under relevant redox conditions. The sputter co-deposition of U and Pd in the presence of O2 results in the homogeneous distribution of Pd in a crystalline UO2 matrix. Hereby, Pd is found to be oxidized and to form PdOx. Heating the films after deposition causes the diffusion of film components and induces a change in surface morphology. Independent of the heating temperature initial UO2+x transforms into UO2. This is different for the noble metal. At high temperatures (550–840 °C) Pd diffuses into the Si-wafer substrate and forms mixed Pd–Si–U alloys. At moderate temperatures (150–200 °C) Pd solely diffuses within the film matrix and forms micrometer sized metallic particles. These particles are further characterized as being an agglomeration of small nanometer sized spheres.