High resolution crystallographic and chemical analysis has been performed on iodine-induced stress corrosion crack tips taken from irradiated and non-irradiated zirconium alloys. Defuelled cladding tubes were subjected to mandrel testing and subsequent analysis of the crack tip region showed the predominance of transgranular cracking on non-basal planes for the first time in irradiated material. In a separate mandrel-tested crack tip sample, iodine
was unambiguously identified in the crack tip region using both STEM-EDX and NanoSIMS. For comparison, non-irradiated C-ring samples were subjected to testing in iodine-ethanol solution, subsequent crack tip analysis showed large levels of intergranular attack and no significant iodine segregation.