A chemical-reaction kinetics model of nuclear graphite gasification has recently been developed and successfully validated with gasification rate measurements for nuclear graphite grades of IG-110, IG-430, NBG-18 and NBG-25. The model employs 4 elementary chemical reactions with applicable parameters, including the values and Gaussian-like distributions of the specific activation energies, the pre-exponential coefficients for adsorption of oxygen and desorption of CO and CO 2 gases, and the surface area of free active sites. These parameters are determined from the reported measurements of the total gasification and transient weight loss using a multi-parameter optimization algorithm. The determined chemical kinetics parameters for IG-100 and NB-25 are nearly the same, but slightly different from those for NBG-18 and IG-430. The initial specific area of free active sites is inversely proportional to the square root of the mass or volume of the graphite specimens used in experiments. The recommended chemical kinetics parameters in this paper for these grades of nuclear graphite should be applicable to future safety analysis of high-temperature gas cooled reactors in the unlikely event of a massive air ingress accident.