CORRELATION OF FAILURE TIMES FOR IODINE SCC OF ZIRCALOY

A crack-growth model of stress corrosion cracking has been successfully applied to predict times-to-failure of zircaloy specimens exposed to iodine vapor. Data for two types of tests were analyzed using the model. The first was a variable loading experiment in which failure occurred after the specimen had been subjected to two distinct stresses in succession. The second was a series of tests in which surface roughness, and probably residual stress as well, was reduced by chemical polishing of the specimens. The success of the crack growth model in dealing with these situations suggests that crack propagation rather than crack initiation is the rate-controlling step in iodine stress corrosion cracking of zircaloy. Furthermore, the metal in the vicinity of the growing crack is apparently so embrittled by iodine that a model originally intended for ceramics applies