Copper Corrosion in Bentonite: Studying of Parameters (pH, Eh/O2) of Importance for Cu Corrosion

The report describes the development of methods and equipment for studying the parameters (pH, Eh/O2) of importance for copper corrosion. The work involved the fabrication of electrodes for determining Eh and pH in compacted water-saturated bentonite. MX-80 and the Indian Asha 505 bentonites were used in the study. The redox-measurements were carried out by using electrodes prepared of Au and Pt wires. The pH measurements were carried out by using solid IrOx electrodes. The report describes testing of electrodes in different solutions and in bentonite. A destructive method for determining oxygen content in compacted bentonite was tested, too. The electrodes were used in measurements inside compacted bentonite with about the same density as is intended to be used in the Finnish repository for spent nuclear fuel. The results indicate that Au and Pt redox-electrodes and IrOx pH electrodes function in
compacted bentonite. The oxygen measurement in bentonite seems to work, too, and can complement the Eh measurements. Eh-values in originally aerobic bentonite samples having a dry densitiy of 1.5 g/cm3, exhibit mostly a decrease during the first days, which may mainly be ascribed to the depletion of oxygen. The Eh-decrease thereafter is probably associated with redox-reactions involving other species than oxygen. In samples with a dry density of 1.8 g/cm3, the observed Eh-decrease is mostly slower. No significant difference between the Eh and pH measurements in MX-80 and Asha 505 could be observed.