Comparative analysis on high-efficiency energy conversion system with different working mediums matched with small lead-cooled fast reactor

Abstract

Nuclear energy is developing toward miniaturization, high security, and efficiency. A new compact and high-efficiency energy conversion system is being developed to match the integrated and natural-circulated lead-cooled fast reactor. This energy conversion system uses a closed Brayton cycle instead of a steam Rankine cycle for its high thermoelectric conversion efficiency and simple and compact cycle arrangement. A recompression cycle is adopted to solve the heat exchanger pinch point problem while maintaining a relatively simple and compact cycle arrangement. Many mediums are used in the various Brayton cycles, including carbon dioxide (CO2), air, nitrogen, and helium, for which qualitative, but rare quantitative, assessments have been performed. In this study, systematical analysis and quantitative comparison are performed. The efficiency of the system is investigated using various typical working mediums at various split and compression ratios within the parameters of the system. According to various comparisons, the highest system conversion efficiency of CO2 in recompression Brayton cycles is 39.36% within the working temperature range of 15–560 °C under three pressure conditions (8 MPa, 13 MPa, 20 MPa), while the efficiencies of air, nitrogen, and helium are only 32.74%, 32.77%, and 32.48%, respectively. However, the efficiency of these last three working mediums will be higher under the optimal conditions of a simple Brayton cycle, which are 32.97%, 33.22%, and 33.59%, respectively. Finally, this paper proposes an energy conversion system scheme for a lead-cooled fast reactor with supercritical carbon dioxide (S–CO2) as the working fluid, a compression ratio of 2.5, a split ratio of 0.65, a maximum temperature of 560 °C, a maximum pressure of 20 MPa, and a system efficiency of 39.36%.