Zirconium Dioxide as a Protective Layer of Zirconium Fuel Cladding

Zirconium is important because of its mechanical and neutronics properties combined with its extraordinary resistance against corrosion. It’s mainly usage in nuclear engineering is as a nuclear fuel cladding. Even though Zr layers are very resistant to neutron fluence at reactor operating temperatures, high pressure and high radiation doses, exothermic Zr oxidation in accident scenario still occurs. Hydrogen, and a newly created layer of zirconium dioxide, are undesirable products of the high temperature steam oxidation. ZrO₂ adopts a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at higher temperatures. The volume expansion caused by the cubic to tetragonal to monoclinic transformation induces large stresses and these stresses cause ZrO₂ to crack upon cooling from high temperatures. To stabilize ZrO₂ other oxides may be added. Therefore ZrO₂ with its high ionic conductivity makes it one of the most promising ceramics to protect fuel cladding and the paper focuses on properties of ZrO₂ used on Zr fuel cladding of common power reactors.