Optimal design of supercritical CO2 power cycle for next generation nuclear power conversion systems

Most generation IV (Gen IV) nuclear reactors have high operating temperatures to increase power plant efficiency and to allow for hydrogen production. The widely used steam Rankine cycle is not suitable for Gen IV reactors because of high turbine inlet temperature with extremely high pressure by using ultra-supercritical (USC) steam cycle. The supercritical CO2 (S-CO2) recompression cycle can achieve a competitively high thermal efficiency with turbine inlet temperature at 500-600 °C and turbine inlet pressure at 20 MPa. However, the operating pressure of the heat source is still too high to promote its application and impede the licensing of using S-CO2 cycle for nuclear power plant. The aim of this work is to reduce the operating pressure of heat sources in the S-CO2 cycle, since the heat sources are usually accompanied by high radiation or high temperature environment. A combined recompression cycle and dual expansion turbine technology is first recommended to reduce the operating pressure of heat source for nuclear power plants and maintain high thermal efficiency. Additionally, sensitivity analysis is performed for three types of S-CO2 power cycles to compare the merits and faults. An optimization analysis is also presented. The results show that the combined recompression cycle and dual expansion turbine technology is effective and suitable for Gen IV reactors with a relatively low heat source operating pressure and high thermal efficiency. This kind of S-CO2 cycle can be coupled with different kinds of heat sources to reduce their operating pressure.