Dynamic Monte-Carlo modeling of hydrogen retention and chemical erosion from Tore Supra deposits

摘要

A multi-scale model has been developed to study the hydrogen retention [A. Rai, R. Schneider, M. Warrier, J. Nucl. Mater. 374 (2008) 304] and chemical erosion of porous graphite. To model the chemical erosion process due to thermal hydrogen ions,Küppers cycle [J. Küppers, Surf. Sci. Rep. 22 (1995) 249; M. Witt-mann, J. Küppers, J. Nucl. Mater. 227 (1996) 186] has been introduced. The model is applied to study hydrogen transport in deposits collected from the leading edge of neutralizers of Tore Supra. The effect of internal structure on chemical erosion is studied. The MD study [E. Salonen et al., J. Nucl. Mater. 290-293 (2001) 144] shows that the experimentally observed decrease of erosion yield at higher fluxes is due to the decrease of carbon collision cross-section at a surface due to shielding by hydrogen atom already present on the surface. Inspired by this study, a simple multi-scale model is developed to describe the flux dependence of chemical erosion. The idea is to use the local chemistry effect from the Küppers model to calculate the hydrocarbon molecule formation process and then to find the release probability of the produced hydrocarbon based on the purely geometrical constraints. The model represents quite well the trends in experimental data.