Multicomponent analysis of the carbon/water equilibria in the HTGR primary coolant system

A thermodynamic equilibrium approach has been used to examine the limits of impurity composition of helium coolant in a high-temperature gas-cooled reactor (HTGR). Complex equilibria codes (CECs), which assume thermodynamic equilibrium and use free energy minimization techniques, have been developed to calculate coolant compositions following various amounts of steam ingress, and steam ingress in the presence of other impurities. In general, the results indicate that the most likely species, H2, CO, and CO2, dominate the chemistry in the coolant. Analytical treatments based on this conclusion are shown to give good agreement with CEC results. The CECs have proved useful for defining limits of coolant impurity reactions and for predicting possibly important chemical species in the HTGR coolant system