Anisotropic biaxial creep of textured zircaloy: Application to in-reactor life prediction

Zirconium alloys are commonly used in light water reactors as thin-walled tubings to prevent coolant-fuel contact and to retain fission gases. These alloys have hexagonal close-packed crystal structure with low c/a ratio at and below the reactor operating temperatures and exhibit preferred orientations or textures. The anisotropic mechanical properties in turn affect their in-service behavior such as in-pile creep-down of the cladding tubes. Creep anisotropy was characterized using biaxial creep tests and the creep-loci constructed at constant energy dissipation deviated from isotropy. The anisotropy parameters derived from the loci agreed with those obtained from the strain-rate ratios at varied stress ratios. Effects of cold work were clearly revealed in that the relatively strong hoop direction for the recrystallized (Rx) material became far weaker