A multi-scale model for particle diffusion in porous structures was used to study the effect of the internal structure of graphite on atomic hydrogen transport and inventory in graphite. The diffusion of trace amounts of atomic hydrogen were modelled as a trapping-de-trapping mechanism within the porous network typical in graphites. Activation energies for the different traps were taken from experiments and from molecular dynamics simulations. Different diffusion mechanisms dominate at different graphite temperatures. It was seen that the trace diffusion coefficient of hydrogen scales as the square of the jump lengths of the dominant mechanism. Depending on the de-trapping mechanism and on the internal structure of graphite, the jump lengths after each de-trapping event could vary over a few orders of magnitude. This gives rise to the possibility of anomalous diffusion in graphite. The effect of closing the pores of graphite on atomic hydrogen diffusion was also presented

Effect of the Porous Structure of Graphite on Atomic Hydrogen Diffusion and Inventory. Warrier, M., Schneider, R., Salonen, E., Nordlund, K.: Nuclear Fusion, 2007, 47[12], 1656-63