[en] The Westinghouse Hanford Company program is investigating corrosion and stress corrosion cracking of Zircaloy-2 and 4 in two model tuff repository environments using an experimental approach in which the repository environment is reproduced as accurately as possible, including temperature, radiation field, water chemistry and materials associations. Post-experimental sample evaluation utilizes or will utilize sophisticated SEM/STEM, Auger surface analysis/ion milling, and trace element release to detect, locate and measure the effects of corrosion. The experiments themselves are being conducted using actual spent fuel and repository materials at repository conditions. The short experimental time (i.e., one year) is being compensated for by sensitive measuring techniques. Characterization of any corrosion found will be used to understand the mechanisms involved for extrapolation purposes. The initial evaluation of samples from two, six, and 12-month electrochemical corrosion experiments indicated no Zircaloy-4 corrosion at a detection sensitivity of 1 to 2 μm of corrosion per year. To improve the sensitivity of the experiment, baseline conditions (e.g., beginning with a polished metal surface) will need to be established that are expected to make it possible to resolve corrosion on the scale of hundreds of angstroms. Examples are the development of such measurements as film depth determination via Auger surface analysis/ion milling and Zr and ¹⁴C released into the aqueous corrosion environment. Characterization of any corrosion found will be used to understand the mechanisms involved. This will allow extrapolation of results to predict cladding lifetime under repository conditions. 3 refs