Experimental studies and two-fluid numerical approach for underexpanded CO₂-Gas jet into liquid-sodium

Daniele Vivaldi (1) , Frédéric Gruy (2, 3, 4) , Nicole Simon (1)

1 DTN - Département Technologie Nucléaire
2 SPIN-ENSMSE - Centre Sciences des Processus Industriels et Naturels
3 PROPICE-ENSMSE - Département PROcédés Poudres, Interfaces, Cristallisation et Ecoulements
4 LGF-ENSMSE - Laboratoire Georges Friedel

Sodium-cooled Fast Reactors (SFRs) represent one of the most promising technologies in the context of generation IV nuclear power reactors. In order to improve electric efficiency and to avoid a reaction between Sodium and water when Rankine cycles are used, the concept of Brayton cycles using supercritical CO₂ is being investigated as alternative energy conversion cycle. However, an accidental scenario must be evaluated, since a leakage inside the CO₂-sodium heat exchanger would cause a reactive underexpanded CO₂-into-Sodium jet, which in turn could lead to mechanical and thermal problems. A two-fluid approach has been investigated for the modelling of the two-phase jet. According to available flow maps, mist flow has been assumed at the leak exit, where high gas volume fraction and high interfacial slip velocity exist, and bubbly flow has been assumed for lower gas volume fraction and slip velocity. An interfacial friction model has been developed. Droplet and bubble diameters have been estimated following literature experimental results and using critical Weber number. For the drag coefficients, consistent correlations have been developed. A two-phase mixture turbulence model has been added. The interfacial friction approach has been implemented into the two-fluid model of the CFD software Ansys Fluent 14.0. Experimental gas-into-water tests have been realized in order to obtain visual information and to perform void fraction measurements through optical probe: numerical results are consistent with experimental ones in terms of void fraction profile during the injection transient and axial and radial void fraction profile at steady-state conditions. The two-fluid approach presented here will be the base for the implementation of a chemical reaction model, in order to account for the exothermic chemical reaction between the CO₂ and the sodium.

Mots clés: Sodium-cooled Fast Reactor; SFR; generation IV nuclear power reactors; supercritical CO₂; interfacial friction model

Domaines: Génie des procédés

Daniele Vivaldi, Frédéric Gruy, Nicole Simon. Experimental studies and two-fluid numerical approach for underexpanded CO₂-Gas jet into liquid-sodium. NURETH-15. The International Topical Meeting on Nuclear Reactor Thermal-Hydraulics., May 2013, Pise, Italy. pp.029. ⟨hal-00929885⟩