Abstract
Analysis of microstructure evolution in irradiated Zr and Zr alloys based on the modern radiation damage theory suggests some important features of self-interstitial atoms (SIAs). Alignment of vacancy loops and voids along basal planes requires anisotropic interstitial transport with a dominant contribution along the basal plane. Under neutron irradiation this can be explained by one-dimensional mobility of SIA clusters but experiments under electron irradiation indicate unambiguously that even the single SIA should exhibit anisotropic diffusion. No experimental information is available on SIA properties in Zr and the data obtained by ab initio calculations within the last decade reported stable SIA configurations that should provide essentially three-dimensional diffusion. To clarify this issue, an extensive investigation of SIAs in Zr has been performed from first principles using two different codes. It was demonstrated that simulation cell size, type of pseudopotential, the exchange-correlation functional, and the c/a ratio are crucially important for determining the properties of interstitials in hcp Zr. The most stable SIA configurations lie in the basal plane, which should lead to SIA diffusion mainly along basal planes. The results provide a confirmation of basic mechanisms for microstructural evolution under irradiation.
