Thermodynamic and exergy analysis of a multi-source TES-coupled Rankine cycle for EU DEMO with DCLL blanket

To address the periodic thermal-power fluctuation and multi-temperature heat-utilization characteristics of pulsed tokamak fusion reactors, a multi-source thermal-energy-storage (TES)-coupled Rankine-cycle system is investigated for EU DEMO with a dual-coolant lithium-lead (DCLL) blanket. Three high-temperature TES topologies, namely parallel, hybrid, and three-tank configurations, are compared in terms of temperature matching, storage requirements, circulation characteristics, and exergy destruction. Non-reheat, steam-reheating, and molten-salt-reheating Rankine cycles are further evaluated, together with continuous utilization of low-grade vacuum-vessel heat through an independent thermal-oil TES subsystem. The results show that cascade organization of the multi-temperature heat sources improves high-temperature heat preservation and reduces the required molten-salt inventory, with the hybrid configuration selected as the representative TES topology. The three-tank configuration further reduces local heat-transfer irreversibility, but requires a larger active molten-salt inventory and higher pumping energy than the hybrid configuration. Among the Rankine-cycle configurations, molten-salt reheating provides the best thermodynamic performance by increasing the steam temperature before the subsequent expansion stages. For the 2.04 GWth DCLL fusion DEMO reactor considered in this study, the molten-salt-reheating configuration achieves a cycle-averaged system net power output of 618.04 MW and a system energy conversion efficiency of 37.79%. System-level exergy analysis identifies the evaporator, low-pressure turbine, condenser, and TES heat exchangers as the principal sources of irreversibility.