Study of the Susceptibility of Oxygen-Free Phosphorous Doped Copper to Corrosion in Simulated Groundwater in the Presence of Chloride and Sulfide

Abstract

Copper of the quality oxygen free and high conductivity, doped with phosphorus (Cu OFP) has been chosen as the material for the fabrication of high level nuclear waste containers in Sweden. This material will be the corrosion barrier for spent fuel in the environment of a deep geological repository. It is planned that the service life of this container will be 100,000 years. During this time water with high concentration of chloride ions might come in contact with the copper surface. If pH conditions are appropriate, this might cause pitting corrosion. This work reports a study of the susceptibility of Cu OFP to corrosion when chloride ions are present, both deionized water (DW) and in standard synthetic underground water (SUW). The techniques used were electrochemical methods such as corrosion potential evolution and Tafel curves. In addition, this system was studied with Electrochemical Impedance Spectroscopy (EIS). We also used characterization techniques such as Scanning Electronic Microscopy (SEM), Energy Disperse Spectroscopy (EDS) . The main conclusions are that copper is more susceptible to corrosion at high chloride ion concentration. Additionally, when the chloride concentration is low, it is possible to form copper chloride crystals, but at the highest concentration, copper chloride complexes are formed, leaving the copper surface without deposits. When the chloride concentration is low (<0.1 M) the corrosion process is mainly controlled by diffusion, while at higher concentrations (0.1M to 1M) corrosion is controlled by transport processes. At low concentration of sulfide ( <3*10-5M), copper corrosion in the presence of chloride is controlled by diffusional processes.