Studies of Electrochemical Corrosion Processes of UO2 and Mixed Oxide Fuels in Aqueous Solutions in the View of Final Storage of Spent Nuclear Fuel - JRC-ITU-TN-2008/55

This research work was carried out in the Nuclear Chemistry Unit of the Institute for Transuranium Elements (ITU) at the European Commission, Joint Research Centre in Karlsruhe, Federal Republic of Germany, from 1st of July 2004 until 15th of April 2008 with a grant from the European Commission. The possible release of toxic and radioactive species from spent nuclear fuel in contact with water in a deep geological repository is expected to depend mainly on the rate of dissolution of the UO2 matrix. At the depth of the repository very low oxygen concentrations are expected. Moreover, large amounts of hydrogen are expected to be generated from the corrosion of iron containing canisters and containers. In this reducing groundwater environment UO2 has very low solubility. However, radiolysis of the ground water will produce reactive radicals and molecular products and can thereby alter the redox conditions. In this work different electrochemical techniques were used to study the corrosion behaviour of UO2 based materials in aqueous solutions in anoxic and reducing conditions. The possible influence of hydrogen on the corrosion mechanism of UO2 was investigated. In order to study the importance of the alpha activity level on the corrosion of the matrix, UO2 electrode samples doped with different concentrations of short-lived alpha emitters were used. In the frame of ACTINET Network of Excellence the collaboration between Institute for Transuranium Elements (ITU) in Karlsruhe, Germany and The Centre for Studies and Research by Irradiation (CERI) in Orléans, France made possible the use of a cyclotron generated He2+ beam to simulate high levels of alpha activities. Impedance Spectroscopy, together with potentiostatic polarization and cyclic voltammetry measurements were used on a variety of materials, ranging from depleted UO2 to 10% 233U doped UO2. A comparison was made between the electrochemical results and the results provided by the solution analysis and surface characterization. The good concordance of the results shows that the electrochemical techniques can be taken into consideration for the safety assessment of the final spent nuclear fuel repository.

ALECU Catalin; 

2008-12-16

European Commission - Joint Research Centre - Institute for Transuranium Elements

JRC49450