Off-design performance and control characteristics of space reactor closed Brayton cycle system

Abstract

The closed Brayton cycle system is a potential choice for the power conversion system for future space nuclear reactors owing to its high energy-conversion efficiency and compact configuration, especially with regard to high power demand. The load change requires a rapid and safe adjustment of the power generation unit. Thus, the off-design features are key for understanding and designing the control schemes of the space nuclear Brayton cycle. In this study, a cycle’s model is established and three independent variables are derived from the model with constraints. The corresponding control methods in theory are envisaged based on the model: inventory control, bleed control, and rotating speed control. The control mechanism and system performance under off-design conditions with these three methods are investigated, and it is observed that inventory control can maintain high efficiency when the electric load changes in a large scope. Bleed control can adjust output power in a relatively narrow range but can be used to prevent the over-speed of a turbomachine in case of a load rejection accident. The reduction in the rotating speed can decrease the output power to match the change in electric load quickly. It is an effective and important control method for the space Brayton cycle system. The results are helpful for the design and operation of space Brayton cycle system.