EFFECTS OF IODINE CONCENTRATION ON IODINE-INDUCED STRESS-CORROSION CRACKING OF ZIRCALOY-4 TUBE

Iodine-induced stress corrosion cracking (I-SCC) experiments on Zircaloy-4 tube were undertaken in the iodine concentration range of 0-4 mg/cm**2, the temperature range of 330-400 degree C and a nominal hoop stress of 475 MPa, using the internal pressurization method. The time-to-failure, failure strain and strain rate were measured as a function of the iodine concentration. An apparent activation energy for I-SCC was calculated from the temperature dependence of I-SCC. A fractographic interpretation was also made through scanning electron microscopic examination. The results suggest that the iodine concentration has an influence on the crack propagation step to increase the propagation rate of I-SCC, promoting the I-SCC susceptibility. The I-SCC behavior of Zircaloy is discussed from the viewpoint of the crack initiation and propagation process.