A role of electrons in zirconium oxidation

Abstract

Growing the oxide scale on the zirconium cladding of fuel elements in pressured-water reactors (PWR) is caused by the current of oxygen anions off the waterside to the metal through the layer of zirconia and by the strictly equal inverse electronic current. This process periodically speeds up the corrosion of the zirconium cladding in the aqueous coolant due to the breakaway of the dense part of oxide scale when its thickness reaches 2 mkm. It is shown that the electronic resistivity of zirconia is not limiting the zirconium oxidation at working temperatures. For gaining this limitation, a metal of lesser valence than zirconium has to be added to this oxide scale up to 15%. Then, oxygen vacancies arise in the complex zirconia, increase its band-gap, and thus, sharply decrease the electronic conductivity and form the solid oxide electrolyte whose growth is inhibited in contact with water at working temperatures of PWR.