The corrosion of zirconium under deep geologic repository conditions

Zirconium alloys are widely used in nuclear reactors as fuel cladding and as reactor structural elements (i.e., CANDU reactor pressure tubes), and are therefore a component of the waste materials that could be emplaced in a deep geologic repository. Therefore, the corrosion mechanisms and rates for relevant zirconium alloys under repository conditions have been reviewed. Since titanium and zirconium alloys have many similarities, and because the data base for the corrosion of titanium alloys under repository conditions is considerably more extensive than that for zirconium alloys, the electrochemical and corrosion behavior of both materials have been compared and evaluated. Although electrochemical studies suggest Zircaloy cladding could be susceptible to pitting, redox conditions within a failed waste container will remain reducing and unable to support pitting. This leaves passive corrosion as the only long-term corrosion mechanism. The available data indicates that the rate of passive corrosion will be very low. A rate of 20 nm/year would be a reasonable upper limit but it is likely the rate will be less than 1 nm/year.