Validation of gasification model for NBG-18 nuclear graphite

This paper introduces a chemical kinetics model and compares its calculations with reported measurements of weight loss and total gasification rate for different NBG-18 nuclear graphite specimens in experiments performed at 876–1226 K. Results show that the gasification rate is chemical-kinetics limited at low and intermediate temperatures and diffusion-limited at high temperatures. At high temperatures, the model calculates the diffusion velocity of oxygen through the boundary layer using a developed correlation for Reynolds numbers of 0.006–1000. The agreement of the calculations with reported measurements of the total gasification rate and transient weight loss confirms the soundness of the chemical kinetics approach and validates the developed model and the multi-parameter optimization algorithm for determining the chemical kinetics parameters, based on reported measurements. These parameters are the values and Gaussian-like distributions of the specific activation energies for oxygen adsorption and desorption of CO, the specific activation energy for desorption of CO2, the initial surface area of free active sites and the rate constants for the four elementary chemical reactions in the model. The performed parametric analyses for NBG-18 nuclear graphite specimens investigated the effects of temperature and oxygen partial pressure on total gasification rate and production rates of CO and CO2 gases, for wide ranges of temperatures and oxygen partial pressures.