Susceptibility of copper to general and pitting corrosion in saline groundwater

In Sweden and Finland the spent nuclear fuel is planned to be encapsulated in cast iron canisters that have an outer shield made of copper, which is responsible for the corrosion protection. In this work the susceptibility of Cu OFP to general and pitting corrosion was investigated in saline (1.45% Cl-) groundwater at T = 80 deg C and p = 14 MPa using electrochemical techniques and weight loss measurements in autoclave conditions. The results were compared with earlier results gained in similar conditions but in highly saline (5.4% Cl-) groundwater. The conclusions presented here are strictly applicable only for the present case, where the groundwater was deoxygenated with nitrogen bubbling (ensuring dissolved oxygen level of lower than 5 mg/l) and where there was almost no mass transfer limitation for the corrosion products away from the surface. The main observations made are: The corrosion potential of Cu OFP in all test runs was in the range of -0.10 VSHE < Ecorr < 0.05 VSHE, i.e. about 0.1 V higher than in the highly saline groundwater; At the corrosion potential active dissolution (corrosion) of Cu OFP takes place, as was the case in highly saline groundwater. However, the corrosion rate based on weight loss measurements of corrosion coupons was 0.014 mm/y, about 30% lower than in the highly saline groundwater. (orig.)