Numerical modeling of two-phase underexpanded reactive CO2 into sodium jets in the frame of sodium nuclear fast reactors
Résumé
Supercritical CO2 (s CO2) 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 leaks at sonic velocity and chemically reacts with sodium, through an exothermic reaction. The consequences of such a scenario must be investigated, in order to predict the temperature increasing inside the heat exchanger and on the tube walls, due to the exothermic chemical reaction, as well as the reaction products distribution inside the heat exchanger. This article presents a numerical approach for modeling such a two-phase reactive jet. A two-fluid multi-component CFD approach is employed, with a heterogeneous reaction between the CO2-gas and the sodium-liquid phases. The model allows to predict the most relevant information, such as temperature distribution, the jet penetration length and the reaction products distribution downstream the CO2 leakage. Some experimental studies on underexpanded gas-into-sodium reactive jets, available in literature, have been compared to our numerical results. It is found that the numerical temperature profiles are consistent with the ones experimentally measured.