Graphite Oxidation Simulation in HTR Accident

of nuclear graphite in Generation-IV, prismatic Very High Temperature and High Temperature gas cooled Reactors (VHTRs and HTRs) in the unlikely event of a massive air ingress accident. The completed research tasks include: (a) Developing and validating a modeling capability, based on chemical reactions kinetics, for the gasification rates of nuclear graphite as functions of temperature, oxygen partial pressure and fractional weight loss. The developed capability has been reported in both the 1 st and 2 nd year technical reports. (b) Developing and implementing a multi-parameter optimization algorithm for obtaining the chemical-reactions kinetics parameters of different grades of nuclear graphite from reported experimental measurements of transient weight loss and total gasification rate as functions of temperature. Results show excellent agreement of the predictions using the obtained chemical-reactions kinetics parameters with reported measurements for different grades of nuclear graphite. Most comparison results are included in the 2 nd year technical report. Results of remaining comparisons are included in this report. (c) Comparing chemical-reactions kinetics parameters of nuclear graphite grades of IG-110, IG-430, NB-18, and NBG-25. These parameters include: (i) specific activation energies of adsorption of oxygen and desorption of CO gas and their Gaussian-like distributions and the corresponding rate constants; (ii) specific activation energy and the corresponding rate constant for the desorption of CO 2 gas; (iii) specific activation energy and corresponding rate constant for the formation of stable [CO] surface complexes; and (iv) initial surface area of free active sites. The values of the chemical reactions kinetics parameters are almost independent of the size of filler particles, but depend on materials of the particles. Nuclear graphite grades with petroleum coke filler particles (IG-100 and NBG-25), regardless of their size (medium of super fine), have similar chemical kinetics parameters. They are different from those of nuclear graphite grades with coal coke filler particles (IG-430 and NBG-18). The initial specific surface area of free active sites of nuclear graphite grades of IG-110, IG-430, NB-18, and NBG-25 decreases inversely proportional to square root of the initial mass of specimens in experiments (0.25 – 50 grams). Further work is needed to examine this finding for larger masses of nuclear graphite. (d) Developing a Sherwood number correlation for calculating the oxygen diffusion velocity in the boundary layer at high temperatures. At such temperatures, graphite gasification solely at the external surface is limited by oxygen diffusion in the boundary layer. At low and intermediate temperatures, gasification …