High-Performance Supercritical Carbon Dioxide Cycle for Next-Generation Nuclear Reactors

TLDR

Supercritical CO₂ cycles are a promising power conversion option for future nuclear reactors operating at 550–650 °C, but their real‑gas behavior that improves efficiency poses challenges for part‑load operation. Because traditional inventory control used for helium Brayton cycles is infeasible, bypass control is the preferred strategy for part‑load operation, though it reduces efficiency compared to base‑load. A recompression cycle operating at ~20 MPa turbine inlet pressure attains cycle efficiencies comparable to helium Brayton cycles at ~250 °C higher turbine inlet temperature, offers greater simplicity by eliminating intercooling, and its high operating pressure shrinks plant component sizes, making it a cost‑effective option for modular nuclear power plants despite a minor part‑load efficiency penalty that is mitigated by the predominance of base‑load operation.

Abstract

Supercritical carbon dioxide cycles are a promising power conversion option for future nuclear reactors operating with a reactor outlet temperature in the range of 550 to 650°C. The recompression cycle version operating with ~20-MPa turbine inlet pressure achieves similar cycle efficiencies as helium Brayton cycles operating at ~250°C higher turbine inlet temperature. The simplicity and high efficiency of the recompression cycle makes it a prime option from among the family of supercritical carbon dioxide cycles. The elimination of the need for intercooling due to the small required compressor work (because of the high density close to the critical point) makes the recompression cycle even simpler than helium Brayton cycles, which require intercooling to achieve attractive efficiencies. The high operating pressure reduces the size of the plant components significantly, making it a promising power cycle for low-cost modularized electricity-generating nuclear systems. However, the real gas behavior that improves the cycle efficiency presents a challenge for part-load operation. The traditional inventory control used for helium Brayton cycles may not be feasible. Bypass control is thus the prime option for part-load operation, making the cycle less efficient than during base-load operation. Since nuclear power plants are operated almost exclusively in base load, this drawback is not a disqualifying blemish.