Use of UO2 films for electrochemical studies

UO2 films have been prepared by dc reactive sputtering of a uranium metal t arget in an Ar/O-2 atmosphere. We have used the films deposited on gold sub strates, as working electrodes for electrochemical investigations as simula ting the surfaces of fuel pellets. Film composition was determined by photo electron spectroscopy (XPS and UPS) and X-ray diffraction (XRD). The oxide stoichiometry as a function of deposition conditions was determined and the appropriate conditions for UO2.0 formation established. AC impedance and c yclic voltammetry measurements were performed. A double RC electrical equiv alent circuit was used to fit the data from impedance measurements, similar to those used in unirradiated UO2 or spent fuel pellets. However due to th e porosity or adhesion defects on the thin films that permitted a direct co ntact between the solution and the gold substrate, we were obliged to add a contribution simulating the water-gold system.,Cyclic voltammetry measurem ents show the influence of pH on the dissolution mechanism. Alkaline soluti ons permit the formation of an oxidised layer (UO2.33) which is not present in the acidic solutions. In both pH = 2 and pH = 6 solutions, a U-VI speci es layer is formed. (C) 2001 Published by Elsevier Science BY.