Effects of Neutron Irradiation on the Flow and Fracture Behavior of Zircaloy-2

Abstract

This paper deals with the effects of cold-work and neutron irradiation on the deformation and fracture behavior of Zircaloy-2, a zirconium-tin alloy. Both annealed and cold-worked specimens were given fast neutron exposures over the range 1019 to 1021 neutrons/cm2 at irradiation temperatures of 60 and 280 C. Specimens were taken both from the transverse and rolling directions of sheet containing 0, 10, 20, 40, and 70 per cent cold-work. The preferred orientations imparted by cold-rolling were characterized by X ray diffraction. The effects of preferred orientation on tensile properties are modified by neutron irradiation. However, variations in the nonhomogeneity of deformation with stress direction are as dominant after irradiation as before. Although modes of fracture and void formation in smooth tension specimens are unchanged by irradiation, the deformation during necking in the transverse direction is more confined to shear zones. This greater confinement of necking deformation plus the decrease in strain hardenability account for a large decrease in fracture energy with irradiation. Data showing the effect of irradiation temperature on tensile properties and the effect of neutron exposure on notch strength are presented. At high neutron doses, damage accumulation with irradiation near 300 C is greater than at lower temperatures. Neutron irradiation alone to about 3 X 1020 neutrons/cm2 does not embrittle annealed Zircaloy-2 but can cause notch sensitivity in material containing sufficient cold-work. Hydrogen pickup during exposure in an in-reactor loop is greater than in an ex-reactor loop and might contribute to embrittlement.