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This paper summarizes the results from over 300 fracture toughness tests on compact specimens taken from zirconium alloy pressure tubing, primarily Zircaloy-2 and cold-worked Zr-2.5Nb. Test conditions include temperatures from 20 to 300°C, varying hydrogen concentrations and hydride orientations, irradiation at several temperatures, and irradiation times up to ten years. A thorough analysis of the results shows that strength and hydride orientation are the principal factors affecting toughness. An extremely steep ductile-brittle transition is observed in alloys containing hydride platelets in the radial (through-wall) orientation.
Annotation The 41 papers of this proceedings volume were first presented at the 13th symposium on Zirconium in the Nuclear Industry held in Annecy, France in June of 2001. Many of the papers are devoted to material related issues, corrosion and hydriding behavior, in-reactor studies, and the behavior and properties of Zr alloys used in storing spent fuel. Some papers report on studies of second phase particles, irradiation creep and growth, and material performance during loss of coolant and reactivity initiated accidents. Annotation copyrighted by Book News, Inc., Portland, OR.
Tubes of 2.5Nb zirconium alloy were fatigued in the tension-tension mode by cyclic internal pressures to cause axial crack growth and unstable fractures at room temperature. Pressure-cycle rates ranged from 400 to 3000 cph. Both the cold-worked and heat-treated conditions, before and after hydriding (200 to 300 ppm H2), were investigated. Exploratory tests were done to determine the effect of the axial length of the surface-stress-intensifying defect on fatigue-crack initiation, growth, and critical length at unstable fracture.
An R-curve approach was investigated with the aim of establishing a means of predicting critical crack lengths in Zr-2.5Nb pressure tubes using small fracture-mechanics specimens. Because of the elastic-plastic nature of the fracture process and limitations on the maximum specimen size, conventional R-curve methods were not applicable. The crack growth resistance was therefore expressed in terms of the crack opening displacement (COD) and R-curves were plotted for several sizes of specimens and crack lengths at 20°C and at 300°C. The effect of hydrogen on R-curve behavior at these two temperatures was investigated as well.