Diffusivity of hydrogen and properties of point defects in beryllium investigated by DFT

Beryllium will be one of the plasma-facing materials for ITER. It will have to sustain high fluxes of hydrogen isotopes and as a consequence significant amounts of tritium can be retained in the wall. For safety and operational reasons, the deuterium and tritium inventory in the vacuum vessel must be limited. As a consequence, hydrogen diffusion, trapping and solubility are of vital importance in assessing and modeling the plasma fuel retention into the wall. In order to understand these issues, point defects and the behavior of hydrogen in beryllium are investigated based on Density Functional Theory calculations. Although some data have already been acquired in the past, some of them disagree, which motivates further investigations. To do so, the formation energy and diffusion properties of point defects are investigated in the first part of this paper. In a second part, the solubility and diffusivity of hydrogen in beryllium are calculated. A diffusion coefficient is established in order to be used in Rate-Equation and Kinetic Monte-Carlo Kinetic models and to allow for comparison with experimental measurements.