Synthesis, design and operation optimisation of a marine supercritical CO2 cycle for nuclear propulsion

Supercritical CO₂ Brayton cycles coupled with advanced Molten Salt Reactors offer a promising zero-GHG propulsion alternative for large ocean-going vessels. Their high power density, favourable part-load performance, and compatibility with compact heat-exchanger technologies make them strong candidates for deep-sea decarbonisation. The main objective of this study is to identify optimal sCO₂ cycle and powertrain configurations for marine nuclear propulsion through integrated thermoeconomic optimisation, using a very large ore carrier as a representative application case whose scale and operational regularity render it particularly suitable for nuclear propulsion. A comprehensive thermoeconomic modelling framework is formulated, encompassing multiple sCO₂ cycle variants and three shafting configurations (electric, mechanical, hybrid). Detailed design and off-design component models are combined with energy, exergy, and cost correlations within a generic super-configuration, enabling unified synthesis, design, and operational thermoeconomic optimisation. The optimal solution achieves a design-point efficiency of approximately 45%, comparable to modern large two-stroke diesel propulsion systems, while eliminating direct GHG emissions. Optimisation results reveal two dominant configurations depending on the objective: a fully electric recompression cycle for maximum efficiency, and a hybrid mechanical–electric arrangement for minimum annualised cost. Reactor-cost sensitivity shows that recompression cycles remain optimal across a wide cost range, confirming their structural robustness. Part-load optimisation demonstrates high efficiencies down to 50% load and yields optimal operating set-points for future control development. A preliminary operational lifetime comparison with a conventional diesel-based ship indicates that, despite much higher capital expenditure, the nuclear sCO₂ system achieves a lower annualised cost and becomes economically favourable after approximately ten years of operation. Overall, the results highlight the technical and economic viability of nuclear sCO₂ propulsion for large commercial vessels and provide a rigorous framework for future component design, integration, and assessment. • A thermoeconomic optimisation framework is developed for MSR-driven sCO₂ cycle applied to a marine propulsion system. • A generic super-configuration enables unified optimisation of cycle synthesis, component design, and shafting arrangements. • Optimal solutions achieve about 45% efficiency and identify electric and hybrid powertrains as the best-performing configurations. • Sensitivity and lifecycle analyses show the recompression cycle's robustness and the economic competitiveness of nuclear sCO₂ propulsion. • The nuclear sCO₂ system achieves a lower annualised cost and becomes economically favourable after approximately ten years of operation.