Multi-objective optimization and evaluation of supercritical CO2 Brayton cycle for nuclear power generation

The supercritical CO2 Brayton cycle is considered a promising energy conversion system for Generation IV reactors for its simple layout, compact structure, and high cycle efficiency. Mathematical models of four Brayton cycle layouts are developed in this study for different reactors to reduce the cost and increase the thermohydraulic performance of nuclear power generation to promote the commercialization of nuclear energy. Parametric analysis, multi-objective optimizations, and four decision-making methods are applied to obtain each Brayton scheme's optimal thermohydraulic and economic indexes. Results show that for the same design thermal power scale of reactors, the higher the core's exit temperature, the better the Brayton cycle's thermo-economic performance. Among the four-cycle layouts, the recompression cycle (RC) has the best overall performance, followed by the simple recuperation cycle (SR) and the intercooling cycle (IC), and the worst is the reheating cycle (RH). However, RH has the lowest total cost of investment (C-tot) of $1619.85 million, and IC has the lowest levelized cost of energy (LCOE) of 0.012 $/(kWh). The nuclear Brayton cycle system's overall performance has been improved due to optimization. The performance of the molten salt reactor combined with the intercooling cycle (MSR-IC) scheme has the greatest improvement, with the net output power (W-net), thermal efficiency eta(t), and exergy efficiency (eta(e)) improved by 8.58%, 8.58%, and 11.21%, respectively. The performance of the lead-cooled fast reactor combined with the simple recuperation cycle scheme was optimized to increase C-tot by 27.78%. In comparison, the internal rate of return (IRR) increased by only 7.8%, which is not friendly to investors with limited funds. For the nuclear Brayton cycle, the molten salt reactor combined with the recompression cycle scheme should receive priority, and the gas-cooled fast reactor combined with the reheating cycle scheme should be considered carefully.