Program Brief

Statement of Problem: Localized corrosion limits the performance of container materials designed to isolate radionuclides in a high-level waste repository. Predicting the long-term occurrence of localized corrosion from short-term experiments is a significant challenge.

Approach and Accomplishments: Localized corrosion and stress corrosion cracking were shown to be triggered when the corrosion potential exceeds the repassivation potential. Experiments were performed to elucidate the mechanism of repassivation of stainless steels and nickel-based alloys through the use of Raman spectroscopy, microelectrodes, and thermodynamic modeling. The repassivation potentials of a number of alloys were measured as a function of environmental variables. The corrosion potential was modeled using well established electrochemical kinetic laws. These parameters were then incorporated in the total system performance assessment code to obtain a probabilistic estimate of container life.

The applicability of repassivation potential to long-term prediction continues to be verified by experiments conducted at controlled potentials and various redox conditions. In addition, the predicted behavior of various alloys was verified against industrial experience with these alloys in different applications such as off-shore oil and gas components and chemical process industry systems.

Client Benefits: The repassivation potential methodology provides a powerful and flexible approach for localized corrosion prediction. The approach has been determined to be applicable for a variety of systems by investigators involved in many high-level waste disposal programs. It is an abstracted model that has a sound mechanistic basis and permits evaluation of a variety of design options.