The effect of nitrite ion on the electric properties of oxide films on copper

The spent nuclear fuel is planned to be stored in steel canisters that have an outer shield made of copper. The copper shield is responsible for the corrosion protection of the canister construction. General corrosion of the copper will not be the limiting factor in the waste repository environment when estimating the life-time of the canister construction. However, localised corrosion, i.e. pitting and stress corrosion cracking (SCC), may destroy the construction. Nitrites, chlorides, sulphides and carbonates has been suggested to promote the localised corrosion of copper. The effect of nitrite on the electrical and electrochemical properties of surface films on copper was studied in this work in oxidising 0.1 M borate buffer and in 0.1 M borate buffer + 0.3 M NaNO2 solution in pH 8.9 at 80°C. The film growth rate of Cu2O is decreased in the presence of nitrite ions in the solution. The film resistance growth rate of Cu2O + CuO/Cu(OH)2 films at open circuit potential increased in the presence of nitrite ions in the solution. Nitrite ions do not affect the electrical properties of Cu2O and Cu2O + CuO/Cu(OH)2 films. According to the polarisation curve measurements performed using Cu2O and CuO/Cu(OH)2 films, nitrite affects the electrochemical reactions taking place both in the solution and on the oxide surface. The applicability of SCC models on the explanation of nitrite induced SCC of copper is discussed. A more comprehensive study is needed in order to quantitatively determine the amounts of Cu(I) and Cu(II) ions dissolving on copper in the presence of nitrites