Supercritical CO$_2$ cycle coupling to sodium cooled fast reactors recent R&D achievements at CEA

Abstract : This paper highlights some recent achievements carried out at French Atomic and Alternative Energies Commission (CEA) in the framework of the R&D on the supercritical CO$_2$ (sCO$_2$) cycle for Sodium Cooled Fast Reactors (SFRs). We discuss the sCO$_2$ cycle thermodynamic potential and in-depth investigations of some connected thermal-hydraulic issues regarding compression performance modeling and cavitation phenomenology nearby the critical point. Outlines of these numerical studies are the followings: – Net efficiency of a condensing cycle could be up to 44% for a turbine inlet operating at (515°C, 25MPa). – A revised approach for compression performance maps representation is developed on a 2 input parameters basis which complies with current treatment by system codes. This methodology is shown, using CFD, to succeed in modeling the impact of the fluid compressibility change on compressor performance. This finding should also ease engineering work by reducing the required number of component qualification tests. In support, ability of CFD to provide a relevant database has been validated by confrontation with some experimental data from a test compressor. – Through analytical consideration of a characteristic parameter and further dynamic simulations, thermal regime is balanced to be the driving mechanism of bubble collapse near the critical point due to combined effects of liquid-like high density and low thermal diffusivity. A very slow contraction could therefore be foreseen, leading to the absence of noticeable pressure rise, in line with some experimental observations from the literature. Again, this outcome could support future engineering work on cycle thermodynamic and compressor thermal-hydraulic designs.