Fatigue Properties of Zirconium and Zirconium Alloys and Their Application in Design and FFS

Abstract A concern for fatigue in a Zirconium-clad reactor vessel was identified. To assess certain design details, elastic-plastic finite element analysis (FEA) can be performed. However, such analysis requires cyclic stress-strain properties along with strain-life properties for the material of interest, to establish an allowable number of cycles. The authors performed a literature review to produce a database of cyclic stress strain (CSS) and strain-life fatigue data for commercially pure Zirconium (Zr) and some Zirconium alloys. The effects of oxygen, niobium, other alloying elements, and certain corrosive environments on the response of the Zirconium alloys under cyclic loading were considered. Compiled cyclic stress-strain data demonstrated that under most conditions, a stabilized hysteresis loop emerged which satisfied the twice-yield model (Masing behavior). Strain-life fatigue data for Zirconium and Zirconium alloys from ambient temperature up to 360°C were collected and regressed to produce a mean strain life curve in the format of the UML. Various methods to establish lower bound fatigue curves for design and fitness-for-service (FFS) purposes are explored. Approaches for addressing welded structures of these materials are suggested, in light of the limited data currently available for welded joints. A brief discussion on fatigue crack growth in Zirconium/Zirconium alloys is provided.