Brittle destruction of carbon based materials under off-normal ITER-FEAT conditions

A numerical simulation model for brittle destruction of carbon based materials (CBMs) based on crack generation by thermal shocks was developed. Crack generation in heated graphite samples depends on the grain anisotropy, the grain size, the failure stress distribution of the bonds connecting adjacent grains and on the temperature and the temperature gradient in the sample. A realistic value for the mean failure stress was obtained from a numerical simulation of destructive compression tests and from a comparison of calculated and measured onset of brittle destruction for volumetric heating. Graphite predamaging due to crack propagation into the depth of the sample or due to volumetric heating might occur, resulting in an enhancement of brittle destruction under cyclic heat loads for typical ITER-FEAT off-normal events. Results of a consistent analysis of brittle destruction and of target screening by dust particles and of enhancement of brittle destruction under cyclic heat loads are presented.