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 oC) Pd diffuses into the Si-wafer substrate and forms mixed Pd-Si-U alloys. At moderate temperatures (150-200 oC) 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.