[en] The initiation of iodine-induced corrosion cracking (SCC) in zircaloy sheet and tubing at approximately 600 K was investigated by scanning electron microscopy and energy dispersive X-ray microanalysis. Two distinct types of SCC nuclei were observed: small cracks occurred in all samples deformed in iodine vapor, and in occasional samples relatively large cracks were also formed that were always associated with local concentrations of impurities or alloying additives in the metal surface. No evidence was found that the small crack nuclei were capable of propagating, but it was shown that the condition required for the formation of the large crack nuclei coincided with those required for iodine-induced failure of pressurized zircaloy tubing specimens. Models are proposed for the formation of both types of crack nuclei in the surface of stressed zircaloy exposed to iodine vapor at about 600 K. (Auth.)