Development of graphite oxidation model for air-ingress analysis in HTGR

One of the most critical event expected in high temperature gas-cooled reactors (HTGR) is an air-ingress accident caused by a pipe break. When air ingresses into the reactor core following the accident, the graphite material consisting of reactor moderators and reflectors suffers from chemical reactions with gases. Such a situation would cause serious consequences increasing temperature, damaging structural integrity and accumulating toxic gases. In this study, the main focus has been on the rate of reaction among the various topics concerned with the oxidation of graphite during the air-ingress. The followings are the main parameters that affect the rate of oxidation and product gases: (1) Kinetics, (2) Mass Diffusion, (3) Combined Effect of Kinetics and Mass Diffusion, (4) Moisture, (5) Shape and Size, and (7) Degree of Burn-off. Until recently, many researchers have studied this field, but there is still no good model that covers all these effects. In the present study, we experimentally investigated various effects related to the graphite oxidation, and developed theoretical models. Finally, we validated the models by comparison with the experimental data. Conclusively, the present study recommends the following graphite oxidation models : [Table inserted]