Stress-corrosion crack initiation and propagation behavior of Zircaloy-4 cladding under an iodine environment

Iodine-induced stress-corrosion cracking (ISCC) properties and the associated ISCC process of Zircaloy-4 fuel cladding were evaluated. Cladding was heat-treated to have either stress-relieved (SR) or recrystallized (RX) microstructures, and then an internal pressurization with a smooth and pre-cracked specimen was performed at 350 °C, in an iodine environment. The results showed that the threshold stress-intensity factor (KISCC) of the SR and RX Zircaloy-4 claddings were 3.3 and 4.8 MPa m0.5, respectively. The crack propagation rate of the RX Zircaloy-4 was 10 times lower than that of the SR one. Crack initiation and propagation mechanisms of Zircaloy-4 claddings, which had different microstructures, were proposed by a grain-boundary pitting model and a pitting-assisted slip cleavage model; they showed reasonable results.