Localized Ductility of Irradiated Zircaloy-2 Cladding in Air and Iodine Environments

Abstract

A laboratory testing method which is capable of imposing plane-stress and localized plane-strain loading conditions on tubing specimens was used to examine effects of annealing temperature and test environment on the strength and ductility of neutron irradiated Zircaloy-2 tubing. Tests were performed at 350°C in both air and iodine environments on specimens previously irradiated at 327°C in a helium atmosphere to fluences ranging between 1.26 and 1.60 × 1021 neutrons (n)/cm2 (E > 1 MeV). The tensile ductility under plane-strain loading conditions depended on preirradiation annealing temperature, with recrystallized specimens showing the largest plastic strain at maximum load (6 to 10 percent) in air. By way of comparison, stress-relieved specimens showed the largest plastic strain at maximum load (4 to 5 percent) under conditions of plane-stress loading in air. An iodine environment reduced the load-carrying capacity of the cladding (plane-strain loading) and lowered the strain at maximum load to near the detection limit of the test technique (approximately 1 percent), regardless of prior heat treatment. A change in failure mode from dimpled ductile rupture to quasicleavage and fluting accompanied this loss of ductility.