Zircalloy (also called zircaloy) is a metal alloy that consists of more than 90 percent of zirconium. Zirconium is mainly used in chemical equipment construction (spray heads, pump parts, pipes and valves) because the element has very high corrosion resistance. In addition to zirconium, the alloy contains a small amount of tin (about 1.5 percent) and other metals such as iron, nickel, chromium or niobium.
Due to the small working diameter for neutrons or the high permeability of neutrons, zircalloy is used for the cylindrical sleeves of fuel rods in nuclear reactors. In these sleeves is the nuclear fuel, usually uranium dioxide or MOX fuel, in the form of pellets. To achieve the highest possible heat conductivity, helium is squeezed into the space between the zircalloy sleeve and the nuclear fuel.
Generally, corrosion of zircalloy components in a nuclear reactor is inevitable. The corrosion, and thus the thickness of the oxide layer, increases over time. The extent of corrosion is mainly determined by the quality of the material, the casing temperature and the chemical composition of the surrounding cooling water. The radiation in a reactor also affects the structure of the sleeve material. Corrosion is the main reason that the life span of fuel elements in a nuclear reactor is limited to about three to five years.
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