Detailed knowledge about corrosion processes affecting the mechanical and chemical stability of metallic canisters containing nuclear waste is important input for the Safety Case. The goal of this project is to significantly improve the understanding of metallic corrosion under conditions representative of clay-based disposal sites for heat generating waste. This is achieved by combining in situ experiments in underground research laboratory and experiments in the laboratory under more defined conditions. Half-cell reactions are identified by applying electrochemical methods. The structure of the corrosion products and the morphology of the corroded surface are characterized by application of modern microscopic and spectroscopic techniques. The ultimate goal is to quantify and evaluate the degradation processes based on a reliable description of the underlying corrosion mechanisms.