Molecular dynamics simulation of the effect of sub-surface helium bubbles on hydrogen retention in tungsten

Nanometer-sized bubbles in tungsten containing various concentrations of helium and/or hydrogen gas were studied using molecular dynamics simulations. Bubbles of different sizes and compositions were relaxed and evolved at temperatures from 300 K to 2100 K. Helium atoms are evenly distributed inside the bubble at all temperatures, while the hydrogen tends to diffuse to the bubble periphery. In all cases a large amount of hydrogen is bound within the first 1-2 layers of the tungsten matrix surrounding the bubble, though clear dependencies on temperature and bubble composition were found. (C) 2013 Elsevier B. V. All rights reserved.