Stress corrosion cracking of hydrided zircaloy-4 claddings in iodine containing environments

To evaluate the susceptibility to SCC of hydrided Zircaloy-4 in iodine vapours, some C-rings samples with different contents of hydrogen (100-500 ppm) were prepared using electrolytic method. The mode of stressing chosen in this work was C-ring method. The equivalent stress on the inner surface was estimated using ANSYS code (480 MPa at room temperature and 300 MPa at 320 C). With the aim to study the susceptibility of hydrided Zircaloy-4 at localised corrosion, we used the potentio-cyclic method. The samples were exposed at 85 C in a KI solution (0.55 g/l) with adjusted pH at 10.5 by LiOH addition. To establish the SCC behaviour of hydrided Zircaloy-4, the stressed C-rings were exposed 320 C in iodine vapours. The experimental results showed that the susceptibility to SCC increases with the increasing of the hydrogen content. The incipient SCC cracks were detected by metallography. The SEM investigations relieved the presence of microcracks in the oxide layer, which can promote the SCC cracks. (authors)