An optimized power conversion system for a stellarator-based nuclear fusion power plant

Fusion is a candidate base-load and load-following energy source for the future carbon-free energy mix, and stellarators are promising magnetic fusion reactors. Unlike all other fusion devices, which are pulsed, the stellarator is inherently steady-state. Thus it requires a different downstream power conversion system compared to tokamaks. In this paper, we conceive and optimize such a system for a stellarator power plant equipped with plasma-facing liquid metal walls in the 700–900 °C temperature range. We rely on a supercritical CO2 Brayton–Rankine Combined Cycle, and optimize the power plant via a genetic algorithm. We also compare the effect of the characteristic parameters on the stellarator performance. The efficiency of the power conversion system is 51% and net electrical efficiency of the complete plant (including reactor auxiliaries) is 34%. Such figures are remarkably higher compared to the state-of-the-art designs in the field of thermo-nuclear fusion plants, considering that the most optimistic and recent estimate foresee a heat-to-power conversion efficiency of about 34% for tokamak-like reactors. Finally, we discuss the technical feasibility of the two most critical components for operations: (i) the large-scale supercritical CO2 Gas Turbine, and (ii) the compact heat exchanger for the Brayton cycle. We obtain compact machines since the maximum diameter calculated for the s-CO2 compressor is about 1.2 m with a rotational speed of 3000 rpm, and the volume required to accommodate the heat exchange surface could achieve 40 m3 with an area density of 7900 m2/m3.