Preliminary thermodynamic design and optimization of a steam Rankine cycle for CFEDR

The China Fusion Engineering Demonstration Reactor (CFEDR) serves as a vital bridge toward commercial fusion energy, necessitating a highly efficient Power Conversion System (PCS) to manage its multi-grade heat and pulsed operation. This study presents the thermodynamic design and optimization of a steam Rankine cycle integrated with Thermal Energy Storage (TES) for the CFEDR. Based on a continuous high-temperature thermal input of 1081.5 MW and a low-temperature input of 276.75MW, thermodynamic models were established to evaluate different cycle configurations and parameter sensitivities. Among the two complete candidate engineering schemes considered, the subcritical three-cylinder Rankine cycle scheme exhibited better overall thermodynamic performance under the adopted design conditions, achieving a net electrical power output of 487.53 MW and a cycle efficiency of 45.08%. Parametric analyses yielded optimal main steam and exhaust pressures of 17MPa and 5kPa, respectively, balancing thermal efficiency, component stress, and cooling water demands. Furthermore, the integration of low-grade waste heat into the feedwater preheating system was investigated. While replacing low-pressure regenerators with a low-grade heat preheater is thermodynamically viable, terminal temperature difference constraints restrict the maximum utilizable low-grade heat to approximately 220MW. A counter-case analysis confirmed that drastically adjusting main steam parameters to accommodate total low-grade heat absorption significantly penalizes overall net power. Consequently, this study establishes an optimized Rankine cycle baseline and highlights the necessity for complementary bottoming cycles to fully exploit residual low-grade thermal energy.