First principles study of point defect effects on iodine diffusion in zirconium

Abstract

The formation energies, diffusion barriers, and vibration frequencies of complex iodine defects in zirconium are calculated with first principles calculations and nudged elastic band method. The effective diffusion rates of these complex defects are evaluated in the temperature range from 300 K to 2000 K. The iodine interstitial diffusion and the iodine diffusion via IZr−VZr are the dominant diffusion mechanisms. The vacancies may be traps for iodine diffusion and they can slow down the diffusion of iodine atoms. For the zirconium cladding materials in light water reactors, various point defects may be generated. Our calculated effective diffusion coefficients agree with the experimental data well and it indicates that bulk diffusion may be a main diffusion mechanism for the iodine diffusion in zirconium alloy. Keywords: Diffusion, Iodine, Zirconium, Point defects, First-principles calculations, Nudged elastic band method