With nuclear graphite IG-110, we measured various kinetic parameters and reaction rates of the C/CO2 reaction. As a result, its activation energy is 295 +/- 8 kJ/mol and the order of reaction is 0.9. It turns out that the rate of C/CO2 reaction is much smaller than the rate of the C/O-2 reaction which is dominant in HTGR air-ingress below 1400 degrees C. Finally, we propose the following rate equation for the C/CO2 reaction of IG-110: r(C-CO2) (kg/m(s)(3)) = 3.95 x 10(3) . exp (-290000/R.T) . (p(CO2))(0.9).