Evaluation of anisotropic elastic and plastic parameters of zircaloy-4 fuel cladding from biaxial stress test data and their application to a fracture mechanics analysis

Abstract

ABSTRACT The mechanical properties of fuel cladding near the elastic limit are essential in considering its failure limit during a pellet-cladding mechanical interaction phase under reactivity-initiated accident (RIA) conditions. The mechanical properties of a Zircaloy-4 cladding tube, such as orthotropic elasticity and anisotropic constants for Hill’s plasticity law, were evaluated based on the biaxial stress test data, focusing on the equivalent plastic strain up to ~2.5%. Samples with various fabrication conditions, such as cold-worked, recrystallized, and stress relieved after cold-work with Q-factors of 2, 3, and 4 were investigated. The evaluation revealed noticeable difference in the elastic and plastic properties between cold-worked, recrystallized and stress relieved samples, including their anisotropic feature, while the impact of Q-factors was minor. The derived mechanical properties were applied to calculation of the fracture mechanics parameter, J-integral, which was found sensitive to the mechanical property differences. Critical J-integral values were then estimated by comparing the calculation and failure limit data from biaxial-expansion-due-to-compression tests on precracked tubes. This produced systematically lower J-integral values of the stress relieved tube than those previously evaluated based on the failure limit data from in-pile RIA-simulated tests.