Advanced graphite oxidation models

Graphite oxidation must be carefully considered in safety analyses for modem energy systems such as HTRs or fusion reactors. Restrictions of actual oxidation models and their improvement are discussed and some experimental data and calculation results concerning these subjects are presented. Advanced graphite oxidation models should solve the diffusion/reaction equation for in-pore diffusion controlled conditions (regime II), provided that burn-off dependent reactivities and diffusivities are known. It is suggested that a reasonable agreement between experimental rate data and calculation results is obtained only if graphite removal by erosion is considered in addition to gasification. Further, for high-temperature oxidation of graphite by oxygen, in regime III the increase of the mass transfer rate by a two-reaction mechanism should be taken into account. Finally, changes in geometry and configuration of carbon components induced by oxidation in regime III have to be considered. (authors)