Modified log-activity diagrams as a tool for modelling corrosion of nuclear waste container materials, with particular reference to copper

Abstract

Abstract Thermochemical data are used to construct a modified log-activity diagram for the system Cu H O Cl (CO 2). This diagram, restricted to standard state of pressure and temperature, serves as a complement to Pourbaix diagrams for the study of equilibria appropriate to solid phases and aqueous ionic species of copper in chloride-bearing waters. Coordinate axes represent activities of chloride and aqueous copper species; other thermodynamic variables are collapsed onto the diagram. Equilibria involving chlorination reactions, some of which cannot be displayed on a Pourbaix diagram, are presented. Also displayed are the various permissible geometric relationships of lines on a Pourbaix diagram. Modified log-activity diagrams may be used to model localized corrosion of copper and are potentially useful for the analysis and prediction of failure mechanisms in high level waste packages.