Thermodynamic analysis and optimization of the combined supercritical carbon dioxide Brayton cycle and organic Rankine cycle-based nuclear hydrogen production system

The Supercritical Carbon Dioxide Brayton Cycle (SCBC) with high efficiency is a very promising thermodynamic cycle to replace the Steam Rankine Cycle (SRC) as the power cycle of a Nuclear Hydrogen Production (NHP) system. However, detailed research on the NHP system using SCBC as a power cycle has not been carried out so far and the system's thermodynamic characteristics are not well known. To fill this research gap, three promising very high-temperature gas-cooled reactor and copper-chlorine cycle-based NHP systems using different power cycles including SRC, SCBC, and combined SCBC and Organic Rankine Cycle (ORC) are proposed and studied in this work. The energy and exergy analysis method and the particle-swarm optimization algorithm have been used respectively to model and optimize the system. In addition, a parametric analysis based on two typical reactor concepts has been performed to comprehensively investigate the system's thermodynamic characteristics. Finally, a performance comparison of three systems under different hydrogen production loads has been conducted. Major results show that under different hydrogen production loads, the variations in the thermodynamic performance of the SCBC-based NHP system are sensitive to the reactor inlet temperature. Under low reactor inlet temperatures (≤587°C), the thermal efficiency of the SCBC is less than 37%. Besides, increasing the compressor pressure ratio of SCBC can enhance the system's thermodynamic performance, and the system's thermal and exergy efficiencies are improved by about 0.7% to 3.7% and 1.0% to 5.3% respectively by using ORC. Highlights: Three VHTR and Cu-Cl cycle-based nuclear hydrogen production systems are studied. Three systems are modeled based on the energy and exergy analysis method. Parametric analysis and optimization under two reactor concepts are conducted. SCBC's thermal efficiency under low reactor inlet temperatures is less than 37%. System overall thermal efficiency is improved by about 0.7% to 3.7% through using ORC.