Modeling and Simulation of a Supercritical CO2-Liquid Sodium Compact Heat Exchanger for Sodium Fast Reactors

The study focuses on modeling and simulations of sodium-sCO2 intermediary compact heat exchangers for sodium-cooled fast reactors (SFR). A simplified 1-D analytical model was developed in companion with a 3-D CFD model. Using classic heat transfer correlations for Nusselt number, some simulation results using the 1-D model have achieved reasonable match with the CFD simulation results for longer channels (i.e., 40 cm and 80 cm). However, for short channel (10 cm) when axial conduction within the sodium fluid is significant, the 1-D model significantly over-predicted the heat transfer effectiveness. By incorporating the temperature-jump model, the 1-D model can extend its predictive capability for low-Prandtl number fluid/Peclet number flows. The results can help improve the understanding of heat transfer for sodium and low-Prandtl number fluids in general and improve designs of sodium-sCO2 compact heat exchangers. The results also confirmed that the sCO2 side dominates the overall heat transfer for Na-sCO2 heat exchangers. A preliminary attempt of optimizing the channel geometry shows mixing results – while heat transfer effectiveness was significantly increased for the wavy channel, much greater pressure drop was also predicted by the simulations

Power Cycle Selection and Optimization for a Small Modular Reactor

As a way to improve safety and economics, one area of research and commercialization of new nuclear power plants has focused on the development of small modular reactors (SMRs). NuScale Power has developed a 50 MWe natural convection cooling SMR coupled with a regenerative Rankine cycle. Current estimates place the NuScale SMR plant at a competitive levelized cost of electricity (LCOE), but there is continued interest to improve the economics of the system. This paper provides a research review and analysis of alternative power cycle designs well suited for the NuScale SMR. Alternative cycles are analyzed for overall cycle efficiency, 2nd law exergy efficiencies, capital cost, and plant (LCOE). These results are compared to the baseline regenerative Rankine cycle via optimization techniques. Results reveal two cycles, regenerative reheat Rankine and transcritical ethanol, have promise as alternative cycles. While both cycles had higher estimated capital costs, the additional power produced reduced the LCOE by 5.1 ± 4.0% for the regenerative reheat Rankine cycle and 4.8 ± 4.8% for the transcritical ethanol cycle, when compared to the regenerative Rankine cycle. The regenerative reheat Rankine cycle would be the simplest cycle to integrate into the NuScale SMR as it is similar to the baseline regenerative Rankine cycle. Conversely, the transcritical ethanol cycle would require more research to assess the viability, but has greater potential to improve the economics of the system