Mathematical modeling of oxidation behaviour and burn-off in nuclear graphite of high temperature gas-cooled reactors

Abstract

We investigated the oxidation of nuclear grade graphite IG-110 in HTGRs, which is influenced by boundary layer conditions and in pore diffusion of oxygen. After exposure to oxygen the concentration profile and the total mass transfer rate of oxygen in a IG-110 cylinder was calculated by modeling with Shell mass balance and solving the resulting differential equation. The concentration profile of oxygen and effectiveness factor were estimated using experimental data. It turns out that the oxygen concentration profile is nearly uniform when the graphite temperature is lower than 700℃. In addition, variation of concentration of oxygen in a IG-110 cylinder with respect to temperature was also calculated. It shows that oxygen concentration reduces to zero at a distance from the exterior surface less than radius of the cylinder (r) above 900℃. Finally, a model for predicting burn-off behaviour is obtained through the investigation of the variation of interfacial area density with burn-off.