Numerical modeling of two-phase underexpanded reactive CO$_2$-into-sodium jets in the frame ofSodium nuclear Fast Reactors

Abstract

International audienceSupercritical CO$_2$ (sCO$_2$) Brayton cycles have gained interest in the frame of Sodium-cooled nuclear FastReactors (SFRs), as an alternative to the conventional water Rankine cycles. If CO$_2$ leaks inside the CO$_2$-Na heat exchanger, an underexpanded CO$_2$-into-liquid-sodium jet is formed. CO$_2$ leaks at sonic velocityand chemically reacts with sodium, through an exothermic reaction. The consequences of such a scenariomust be investigated, in order to predict the temperature increasing inside the heat exchanger and on thetube walls, due to the exothermic chemical reaction, as well as the reaction products distribution insidethe 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 theCO$_2$-gas and the sodium-liquid phases. The model allows to predict the most relevant information, such astemperature distribution, the jet penetration length and the reaction products distribution downstream theCO$_2$ leakage. Some experimental studies on underexpanded gas-into-sodium reactive jets, available inliterature, have been compared to our numerical results. It is found that the numerical temperature profilesare consistent with the ones experimentally measured