A Case Study of the Susceptibility of Zircaloy-4 Sheathing to Iodine Stress-Corrosion Cracking as a Function of Their Metallurgical History in Fabrication

This experimental undertaking has primarily focused on determining the dependency of Pellet-Cladding Mechanical Interaction (PCMI) conditions and the resulting Iodine Stress-Corrosion Cracking (ISCC) failures on residual stresses within a wide range of manufactured CANDU Zircaloy-4 cladding (sheathing). ISCC failures remain a fuel performance concern for water-cooled reactors, including CANDU reactors, accommodating a multitude of power maneuverability events, at high discharge burnups. A multi-year examination of more recent and vintage Zircaloy-4 sheathing samples and their associated post-production stress state from two independent sources is provided. A relationship between the residual stress history in manufacturing processes of Zircaloy-4 and ISCC has been investigated, by static loading of slotted ring samples in iodine-methanol solutions (10 g·L−1) at room temperature. Results indicate that inherent residual tensile stress state of the sheathing above a certain threshold is strongly correlated to the failure in ISCC process.