Power Conversion System Evaluation for the Next Generation Nuclear Plant

A study was performed to examine power conversion system (PCS) options for the next generation nuclear plant, a very high temperature gas-cooled reactor. The purpose of the study was to provide insight into which PCS should be used and how should it be coupled to the reactor: direct or indirect. Seven PCSs were examined: direct helium Brayton, indirect helium Brayton, supercritical CO₂ (SCCO₂), cascaded SCCO₂, combined-cycle gas turbine (CCGT), subcritical steam-Rankine, and supercritical steam-Rankine with double reheat. The results of the study show that the SCCO₂ cycles are very promising and warrant further development, but the relative immaturity precludes it as a short-term option. Further, the results show a relative unattractiveness of the Brayton cycles when compared to the SCCO₂ cycles. The best short-term options were the steam-Rankine cycles. The supercritical steam-Rankine cycle gave the best performance of the two. The CCGT was the most costly and provided little performance advantage over the supercritical steam-Rankine cycle. Issues associated with closed-loop operation, high-temperature compressor inlet temperature, and potential nitriding from the He/N₂ working fluid cast uncertainty on the maturity of this cycle.