Optimization of the supercritical CO2 power conversion system based on the net efficiency under conditions of the pulse-operated fusion power reactor DEMO

Abstract

Fusion power plants represent a new energy technology with specific features including multiple heat sources with different outlet temperature and power, fluctuating high self-consumption, and in the case of the demonstration fusion power plant, the pulse operation of the heat sources. The supercritical CO2 (S-CO2) Brayton cycle was applied and optimized under DEMO conditions with the nuclear net efficiency as the main optimization criterion. The optimization was performed for helium-cooled and water-cooled reactor blanket concepts, and for simple and recompression S-CO2 cycle layouts with four heat sources. The optimization process used a brute-force search problem-solving technique applied to multiparametric space. The model data was taken from the European model of the fusion power plant DEMO1 2019. When applying the simple S-CO2 cycle, the net efficiency of the model power plant with the helium-cooled and water-cooled blanket was found to be 19.5% and 12.3%, respectively, whereas when applying the recompression S-CO2 cycle, the net efficiency was found to be 16.4% and 8.1%, respectively. The simple S-CO2 cycle provided higher net efficiency for the model fusion power plants with the given configuration of multiple heat sources than the recompression S-CO2 cycle, and the model power plants using the helium-cooled blanket achieved higher net efficiency compared to the power plants using the water-cooled blanket despite significantly higher self-consumption. The application of the simple S-CO2 cycle allowed the model fusion power plant with the helium-cooled blanket to achieve the net efficiency higher than the reference net efficiency of 17.9% of the current DEMO model using the steam cycle. For the power plants with the water-cooled blankets, S-CO2 cycles were found to be less efficient than the steam cycles.