Thermodynamic modeling of thermal processes involving actinides (U, Am, Pu) in the course of heating radioactive graphite in steam

Abstract

The behavior of actinides (U, Am, Pu) in the course of combustion of radioactive graphite in steam was studied by thermodynamic modeling. Thermodynamic modeling was performed using TERRA program in the temperature interval from 373 to 3273 K to determine the possible composition of volatile actinide species formed in the course of graphite utilization by heating in steam. The modeling shows that the actinides at high temperatures are present in the following forms: U, as UO₃ and UO₂ vapors and as UO₃^– and UO₂⁺ ions; Am, as Am vapor; and Pu, as PuO₂ and PuO vapors and as ionized PuO⁺. The main reactions within separate phases and at the interface were revealed, and their equilibrium constants were determined.