Abstract
Thermodynamic analyses were performed to evaluate recuperated open air Brayton cycles for nuclear microreactors operating with a power output of 3 MWe. Specifically, the efficiencies of the recuperated air Brayton cycles were compared under steady-state operating conditions for different climate conditions, reactor types, turbomachinery efficiencies, and recuperator performance. Recuperator minimum approach temperatures of 5, 10, and 15 °C were evaluated using an effectiveness-number of thermal units approach to encompass the expected range of different heat exchanger designs. Optimal compressor pressure ratio and optimum thermal efficiencies are presented for turbine efficiencies of 80%, 85%, and 90%; compressor efficiencies of 70%, 75%, 80%, and 85%; and turbine inlet temperatures of 500 °C, 650 °C and 850 °C corresponding to different reactor types. Effects of climate on the thermal efficiency of the recuperated air Brayton cycles show the largest effect on the recuperated cycle due to the change in ambient temperature, whereas the humidity of the ambient air has a negligibly small effect. An exergy analysis utilizing a high-performing compressor and turbine and a recuperating heat exchanger with a 10 °C minimum approach temperature showed that the compressor, recuperating heat exchanger, and the ambient heat rejection accounted for nearly 72% of the exergy destruction. The effect of pressure drop through the heat exchangers was quantified in terms of compressor pressure ratio and heat exchanger performance.
•Evaluation of recuperated open air Brayton cycles for 3 MWe nuclear microreactors.•Effects of turbine inlet temperature representative of different microreactor types.•Effects of climate, recuperator performance, and turbomachinery efficiencies.•Exergy destruction greatest for compressor, recuperator, and ambient heat rejection.•Second Law efficiency of the cycle is 63%.