Properties of hexagonal Zr and tetragonal ZrO2 low index surfaces from DFT calculations.

ABSTRACT The use of nuclear reactor as a source of electric energy has been extended and consolidated during the second half of last century and the beginnings of XXI century. The continuity of this resource relies on the reliability and security of nuclear plants, requiring the improvement of all features related to their operation. Among them, the structural elements integrity that depends strongly on the mechanical stability of protective oxides must be taken into account. Zircaloy-4 (zirconium based alloy with Sn, Fe and Cr additions) is used for the coolant channels at CNA I and CNA II plants. However, this alloy suffers corrosion problems which have caused, for example, the replacement of coolant channels at CNA I in 1988. In this work we analyze from functional density theory (DFT) the properties of low index hexagonal Zr surface and of the experimentally observed (001) tetragonal ZrO2 surface. Our results predict Zr (1120) and O terminated ZrO2(001) with Zr subsurface, as the surfaces with the lowest superficial energy. The Zr(1010) surface exhibits the most inhomogeneous charge density. This feature could favor oxygen adsorption and then the oxide growth, in agreement with the experimentally observed Zr(1010)/ZrO2(001) interface.