(A) conceptual study of using an isothermal compressor on a supercritical $CO_2$ cycle for various nuclear applications

Abstract

The state-of-the-art nuclear designs have received attention for their potential to surpass their conven-tional PWR predecessors. Among various concepts for improving the current reactors through the development of power conversion systems, the supercritical carbon dioxide ($s-CO_2$) Brayton cycle has received a lot of atten-tion for its potential to replace the conventional steam Rankine cycles. In order to further improve upon the technology, the use of an isothermal compressor in place of a conventional compressor is suggested. The iso-thermal compressor is a particularly more attractive option for $s-CO_2$ power cycle applications due to the nature of the working fluid. Because the $s-CO_2$ Brayton cycle gains advantage in efficiency by reducing compression work near the critical point, the use of an isothermal compressor can further maximize the advantage of com-pressing near the critical point. The main goal of the research is to evaluate the potential of using the isothermal compressors in the $s-CO_2$ cycle layout by suggesting a new thermodynamic framework and analyzing their performance parameters. This theoretical study presents how the use of the isothermal compressor can diversify the cycle layout optimi-zation and contribute to surpassing the current maximum limits of the $s-CO_2$ Brayton cycles. To explore the improvements of the $s-CO_2$ cycle through the use of isothermal compressors, three sets of reactor design condi-tions, SMART, SFR, VHTR, are selected as reference points. Under these sets of conditions, the $s-CO_2$ Brayton cycle layouts adopting the isothermal compressors, namely, iso-Brayton cycles, are optimized and evaluated for the maximum cycle net efficiency, and their total conductance (UA) values that compares the estimated size of heat exchangers are summed up for comparison among different cycle layouts. In addition, the re-search assesses the physical feasibility of different compressor concepts to enable the isothermal compressor in the fundamental level, by estimating the required cooling flux profiles.