2012:21 Technical Note, Initial Review Phase for SKBs Safety Assessment SR-Site: Corrosion of Copper

The uniform and localized corrosion treatments as well as stress corrosion cracking positions currently considered by SKB have been examined with the objective of identifying key unresolved issues or gaps, needs and opportunities. In conjunction with the review of the SKB reports listed in Appendix 1, there has been some consideration of the broader literature.  This summary highlights the main review findings.

Current experimental evidence for spontaneous copper corrosion in O2 free waters lacks corroborating diagnostics and broad consensus from multiple investigators. Therefore, it is the opinion of this review that the matter is unresolved. Further diagnostic experiments are recommended in O2 free waters. Experiments could also confirm thermodynamic predicts of conditions where spontaneous corrosion processes cease. There is also evidence to support the concern for spontaneous copper corrosion in oxygen free situations at high Cl- concentrations, when low Cu cation concentrations and elevated temperatures are present. These conditions should be further explored to define under what conditions spontaneous corrosion occurs. The likely transition from spontaneity to non-spontaneity upon changes in certain parameters could be experimentally confirmed.

Assuming that O2 uniform corrosion is spontaneous, kinetic models have been developed for formation of CuOH in pure water and Cu2S in sulfide containing waters. These kinetic models for spontaneous uniform corrosion rates are non-conservative as currently composed and rely on key tenets that create low rates. Either evidence supporting these key tenets and assumptions should be strengthened or upper bound rates should also be established. For instance Cu2S in sulfide containing waters restricts copper corrosion to rates governed by HS- concentration and mass transport. This assumption eliminates the option for copper corrosion after HS- consumption (perhaps catalyzed by S-2 regeneration and re-adsorption). This assumption of HS- sequestering could be strengthened.