A Review and Case Study of the Susceptibility of Zircaloy-4 Sheathing as a Function of their Metallurgical History in Fabrication

Abstract

This experimental programme has primarily focused on determining the dependency of Pellet-Cladding Interaction (PCI) conditions and the resulting Iodine Stress Corrosion Cracking (ISCC) failures on residual stresses within a wide range of manufactured CANDU Zircaloy-4 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 is provided, in terms of more recent and vintage Zircaloy-4 sheathing samples and their associated post-production stress state from two independent sources. 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 (10g.L^-1) at room temperature. Results indicate that a residual tensile stress state of the sheathing above a certain threshold (~100 MPa) is strongly correlated to the failure in the ISCC process.