A nuclear-driven combined cooling and power system based on supercritical and transcritical CO₂ cycles: energy, exergy, and exergoeconomic analysis, multi-objective optimization and reactor startup analysis

Energy cascade utilization is deemed as one of the most efficient paths to cope with energy crises and improve energy efficiency. To further analyze the application and performance of the multi-generation system in nuclear energy cascade utilization, this paper establishes a combined power and cooling system comprising a supercritical CO₂ Brayton cycle with a transcritical CO₂ refrigeration cycle. The energy, exergy, and exergoeconomic (3E) analyses of the combined system are conducted and multi-objective optimization is carried out to examine the optimum system performance. A startup strategy for the supercritical CO₂ direct-cooled reactor is proposed and the reactor's startup transient process is analyzed to examine the coupling characteristics between the reactor and its secondary circuit coolant system. The results show that the increasing the main compressor and throttle valve outlet pressure as well as turbine inlet temperature are conducive to the thermodynamic and exergoeconomic performance of the system. When the reactor thermal power is 5 MW, the maximum system thermal efficiency is 42.50 %, while COP and total product unit cost are 3.53 and 14.01 $·GJ⁻¹, respectively. The comparative analysis with a similar system reveals the superior performance of the combined system. Under identical operating conditions, the thermal efficiency and exergy efficiency of the combined system are 2.50 % and 3.36 % higher, respectively, compared to the reference system, with the total product unit cost being 11.62 % lower. Moreover, the response time for the reactor to reach low power steady state and full power steady state is about 487 min and 236 min, respectively.