Preliminary design and optimization of sCO2 nuclear-powered merchant vessel propulsion systems for the Northern Sea Route

This study investigates the potential of supercritical CO2 (sCO2) power cycles as alternatives to conventional steam Rankine cycles for the nuclear propulsion of commercial vessels operating along the Northern Sea Route (NSR). A numerical model is developed to simulate the performance of both a simple recuperative cycle (SRC) and a reheated recuperative cycle (RRC), using a pressurized water reactor (PWR) as the heat source, and to size the system heat exchangers. A preliminary sensitivity analysis is carried out to identify the most influential design parameters, which are then used in a multi-objective optimization employing the NSGA-II algorithm to maximize thermal efficiency and minimize the total heat exchanger volume. The resulting Pareto fronts are evaluated using the TOPSIS method, and the optimal solutions are further analyzed through a preliminary 1-D design of the turbomachinery. The results highlight that the RRC outperforms the SRC in both efficiency and compactness, achieving up to 30.1% efficiency with significantly reduced heat exchangers overall volumes. An additional analysis incorporating the reactor pressure vessel (RPV) volume indicates a moderate reshaping of the Pareto front, not significantly modifying the optimal design selection. Compared to conventional steam Rankine cycles, the sCO2-based systems demonstrate over 25 times higher volumetric power density, highlighting their substantial space-saving potential for marine propulsion applications.