Evaluation of sensors to monitor the effect of bentonite on the corrosion rate of copper in Olkiluoto-type saline groundwater

This work concerns the effect of bentonite and groundwater on the corrosion of copper ina closely simulated final disposal vault environment of radioactive waste. The feasibilityof two sensors—an on-line corrosion rate monitoring sensor and a modified referenceelectrode, has been tested with respect to Cu corrosion in MX80 bentonite saturated withhighly saline groundwater in conditions closely simulating those in a nuclear wasterepository. As a result, it can be stated that both sensors showed the expected stability atleast up to 150 h of operation. Thus it is expected that they can be used for reliable long-term corrosion rate and electrode potential measurements in the presence of wettedbentonite. In addition, it has been demonstrated that after an initial transient period ofca. 5–8 h, Cu corrosion in bentonite saturated with highly saline groundwater becomesundetectably low probably because of the anoxic conditions reached in the free ground-water. At the same time, the corrosion potential of Cu is still in the active corrosion regionaccording to thermodynamic calculations. Furthermore, redox potentials in the wettedbentonite remain significantly higher than in the free groundwater. This may indicatethat the decomposition of the oxygen contained in the pores of the bentonite is a processoccurring in a time scale larger than that of the present experiments.