Core-shell (kH)@Be-n (k = 1-3, n = 6-11) systems are studied computationally. The smallest system with endohedral hydrogen is H@Be-6 with a central H anion, thermodynamically stable to dissociation into H + Be-6. Larger structures are constructed by merging a few such units and have reduced stability. Potential energy barriers to hydrogen exit from the cage assemblies are estimated. Face- and edge-sharing combinations of the structural units are considered. The extrapolated upper bound for the potential 'nanofoam' material storage capacity is 10 weight-% of hydrogen. The changes in shape and electronic properties of the Ben cages upon insertion of hydrogen are also analyzed. (C) 2012 Elsevier B.V. All rights reserved.