Fracture mechanics analysis on stress corrosion crack growth in Zircaloy-2

To predict the response of Zircaloy-2 cladding tube in an iodine environment, a model of the stress corrosion cracking (SCC) process has been developed based on fracture mechanics. At first, SCC tests of Zircaloy-2 plate were performed at 250∼390℃ in iodine vapor to measure the crack growth rate da/dt and the threshold stress intensity factor for SCC growth K_ISCC. Tests were carried out using a WOL (Wedge Opening Loading) fracture mechanics specimen. The da/dt was shown to be da/dt=CKⁿ, where K is the stress intensity factor and C and n are experimental constants. C,n and K_ISCC could be expressed as a function of temperature. Secondary, internal gas pressurization SCC tests for Zircaloy-2 cladding tubes were performed at 400℃ to measure time to failure at various hoop stresses. The stress intensity factor of semi-elliptical cracks, which were produced in the cladding tubes, was calculated by a three-dimensional FEM (Finite Element Method) to analyze the crack growth rate as a function of K. Comparison of experimental results with those calculated using the developed SCC fracture process model showed good agreement. (author)