Optimal cycle scheme of direct cycle supercritical CO2 gas turbine for nuclear power generation systems

A supercritical CO2 turbine cycle can achieve a considerably high cycle thermal efficiency at medium turbine inlet temperatures of 500-650 degrees C at high pressure such as 20 MPa, which is too high to produce a reactor pressure vessel within the existing fabrication limits. To solve this problem, a dual expansion turbine cycle is effective; its application was examined for both the fast reactor (FR) of 527 degrees C and 12.5 MPa and a high-temperature gas-cooled reactor (HTGR) of 650 degrees C and 8 MPa. Results showed that, in the case of FR, the cycle thermal efficiency became 42.6%, 44.0%, and 45.1 %, respectively, for the 12.5 MPa cycle, the dual expansion cycle, and the 20 MPa cycle. Therefore, the dual expansion cycle is effective. On the other hand, for HTGR, the cycle thermal efficiency became 47.5%, 48.5%, and 50.3%, respectively, for the 8 MPa cycle, the dual expansion cycle, and 20 MPa cycle. In this case, the cycle efficiency advantage becomes smaller than that for the FR, but a 1.0% advantage is obtainable.