Zircaloy-2 and -4, developed mainly in the United States, have been used in Germany for fuel rod claddings and in-core structural components from the beginning of reactor technology. Extensive studies of the material properties of the Zircaloys have been performed in Siemens laboratories since 1957. Irradiation testing was done in several test reactors. However, the combined effects of irradiation and real environmental conditions were determined through many experimental irradiations in existing power reactors. Elaborate examinations in the reactor pools of such experimental materials and of many standard fuel rods and assemblies after intermediate, full, and intentionally extended exposures were the main source of information and hard data. These programs were supported by several utilities and in certain areas carried out in cooperation with others.

Zircaloy-2 and -4 turned out to be very reliable materials that fulfilled all requirements for normal operation and likewise the requirements for postulated accidental conditions and for intermediate storage for many years. Optimization of Zircaloy-2 and -4 during recent years includes both optimization of microstructure and of chemical composition. BWRs and PWRs need differently optimized materials. Today's more demanding operation conditions and discharge burnups required a further optimization of the Zircaloys and for “hot” PWRs even the development of more corrosion-resistant Zr alloys. A significant improvement of PWR corrosion behavior can be achieved with Zr alloys using the alloying elements of Zircaloy with somewhat modified concentrations. Sn should be below or at least in the lower range of the ASTM specification range for Zircaloy-4, Fe and Cr should be somewhat higher, and Si should be specified as an alloying element rather than as an impurity.