Volume 2, Issue 2 (February 2005)
ZIRLO™ — An Alloy Development Success
Significant data and milestones in the development of the ZIRLO alloy for PWR applications are reviewed. From humble beginnings as an R&D program, an approach to improving the corrosion resistance of zirconium-based alloys was developed. The corrosion resistance of dilute alloys is controlled by the microstructure, and both solid solution and precipitate effects impact corrosion performance. Several transition metals are beneficial for corrosion at low concentrations, but the most favorable alloy system is zirconium-niobium, because it offers flexibility in processing options. Strength of the binary alloys can be improved by additions of tin, which, in combination with low levels of iron, provide corrosion resistance in lithium hydroxide solutions. Numerous experimental ingots, thermo-mechanical processing routes, corrosion tests, and materials characterizations were performed along the path to the final alloy composition. The resulting material, ZIRLO, has proven itself as a successful alloy for PWR fuel cladding and structural applications.