For the next generation of nuclear reactors, High Temperature Gas-cooled Reactors specifically, an unlikely air ingress is an important consideration in the license applications of many international regulators. A significant amount of research on oxidation rates of various graphite grades under a number of conditions has been undertaken to address such an event. However, consequences to the reactor result from the microstructural changes to the graphite rather than directly from oxidation. The microstructure is inherent to a graphite’s properties and ultimately degradation to the graphite’s performance must be determined to establish the safety of reactor design. To understand the oxidation induced microstructural change and its corresponding impact on performance, a thorough understanding of the reaction system is needed.
This presentation will focus on a concerted effort over the past five years at Idaho and Oak Ridge National Laboratories to develop a universal oxidation model for graphite. Various features of this model will be discussed including experimental determination of intrinsic kinetic parameters, ongoing efforts to characterize microstructurally dependent properties, and the implementation of these parameters into a mass and heat transport finite element model to blindly predict the oxidation rates of various grades of graphite.