Observations of chemical inhomogeneity sites of possible importance in stress corrosion cracking of Zircaloy using scanning Auger microscopy

Sparsely-distributed chemical inhomogeneities are thought to be important in stress corrosion cracking of Zircaloy nuclear fuel cladding by fission products. In previous work, SCC resistance of the three lots of cladding for which data were available was found to correlate very strongly with their average chemical inhomogeneity size. SEM and Auger analyses now reveal that many of the chemical inhomogeneities appear to be thin flakes of carbon (typical size 50 mm long and wide by 1-10 μm thick), incorporated into the surface of the Zircaloy cladding near pre-existing small particles of Al2O3 and SiO2. Speculations are presented concerning the possible origins of the chemical inhomogeneities. (orig.)