A numerical model for the CO2-sodium chemical interactions in sodium fast nuclear reactors
Résumé
Supercritical CO2 (sCO2) Brayton cycles have gained interest in the frame of Sodium-cooled nuclear Fast Reactors (SFRs), as an alternative to the conventional water Rankine cycles. If CO2 leaks inside the CO2-Na heat exchanger, an underexpanded CO2-into-liquid-sodium jet is formed. CO2 chemically reacts with sodium, following an exothermic reaction which forms mainly solid products. In order to develop a model to numerically reproduce the jet development, a detailed description of the CO2-Na chemical reaction mechanism must be investigated. In this paper, a chemical reaction model at the dispersed phase scale between CO2-sodium, inside an underexpanded CO2-into-sodium jet, is presented. The model considers the reaction between a sodium droplet with the surrounding CO2 environment for the region close to the leakage, where mist flow is supposed to exist, and between a CO2 bubble with the surrounding liquid sodium environment for the region further downstream the leakage, where bubbly flow takes place. The depletion rate for a single particle (droplet or bubble) is determined, as a function of the main influencing parameters, such as temperature, droplet slip velocity, bulk mass fractions, and the chemical kinetics.