This section presents the performance of cladding in aqueous disposal environments and dry storage environments. Hydrogen-induced cracking of cladding may be a major detrimental degradation mechanism for both disposal and storage conditions. Crack opening area allows radionuclide release under both conditions. Oxidation (or general corrosion) of cladding is very slow and localized corrosion is unlikely to occur in near-neutral pH disposal environments (Ahn, 1996b). Oxidation of cladding is only possible in the presence of residual water and/or oxygen in dry storage canisters. Initially defective cladding may be further cracked (unzipped) by the pres­sure imposed on it by corrosion products of the SNF matrix or zirconium
itself. Longer longitudinal cracks that develop from the initial cracking/ unzipping will increase radionuclide release under both conditions.