Power Conversion System Point Design for Molten - Salt - Cooled Fission and Fusion Energy Systems

This report describes three 2400-MW(t) reference point designs for the moltencoolant gas cycle (MCGC), based on the current power conversion unit (PCU) designs for the GT-MHR. A very-high-temperature helium cycle with a 900°C turbine inlet temperature achieves a thermodynamic efficiency of 54% and net electric output of 1300 MW(e), while a low-temperature helium cycle with a 600°C turbine inlet temperature achieves a thermodynamic efficiency of 44%. Design parameters for intermediate temperatures can be estimated by interpolation between these very high and low temperature designs. A third reference case, using nitrogen with 10 weight percent helium with a 900°C turbine inlet temperature also achieves a thermodynamic efficiency of 54%, with a PCU volume 40% larger than the helium-cycle. The reference MCGC designs have substantial maturity because the helium-cycle turbo-machinery, intercoolers, and recuperators are close derivatives of the GT-MHR PCU. The MCGC flow configuration keeps the entire pressure vessel boundary in contact with compressor outlet gas, keeping the vessel temperatures below 150°C. The nitrogen MCGC compressor inlet pressure is 0.7 MPa, compared to the 0.1 MPa that combustion turbines must work at to take in air and to discharge combustion products and pollutants back to the atmosphere. The nitrogen (and helium) cycles thus operate at a much higher average gas pressure, and thus higher power density compared to current large combustion turbines. This fact creates the theoretical potential for future advanced high-temperature fission and fusion reactors to have comparable, or lower, total capital costs compared to current natural-gas combined cycle power plants.