| Research Article |
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Features of transient power regulation by a bypass valve control for a Brayton space nuclear power system |
| MA Wenkui, YE Ping, QU Xinhe, YANG Xiaoyong |
| Key Laboratory of Advanced Reactor Engineering and Safety of the Ministry of Education, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China |
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Abstract [Objective] Long lifespan, compact, high-energy density, and efficient power systems are necessary to achieve future space exploration goals. The space reactor coupled Brayton cycle is high in energy conversion efficiency, small in volume, light in weight, and stable in operation, which is optimal for megawatt space power systems. The power control features are the key to the safe and efficient operation of a Brayton space nuclear power system. The reactor reactivity, inventory, and bypass valve are effective means of system power control. The bypass valve can change the local mass flow rate of a Brayton system and is expected to rapidly control system power to meet the frequently changing load of a space vehicle.[Methods] In this paper, a model of a Brayton space reactor system is established. A system power control simulation program is compiled based on the idea of modular modeling, each component of the system is solved independently, and the mass, momentum, and energy are transferred through data transmission between components. The calculation results of the model in this paper are compared with the simulation results of the startup process in the references, and the accuracy of the program and model is verified. The power-on and power-off transient performance of the system under the control of the bypass valve is investigated, and the effects of the bypass valve opening on system performance are studied.[Results] The power-on and power-off transient results of the system under bypass valve control indicated that bypass valve control could quickly change the pressure and distribution of mass flow rates in the system, the working conditions of the turbine and compressor, and the output power of the system, which could quickly respond to the power demand and load changes of a space vehicle. The change in the load led to a torque unbalance of the shaft, which could further induce rotating shaft overspeed accidents. The strong centrifugal force may damage the blades of the turbine and compressor. The bypass control adjusted the mass flow rate, pressure ratio, and output power of the turbine and compressor, controlled the shaft speed to operate near the rated value and simultaneously avoided the overspeed risk of the rotating shaft. Furthermore, the effect results of the bypass valve opening on system performance showed that the low-pressure side of the system and the radiant heat reject loop were sensitive to the parameter disturbance caused by the bypass valve control. The high-pressure gas at the compressor outlet mixed with the low-pressure gas at the turbine outlet through the bypass valve, and the pressure of the low-pressure side pipes and components increased. The elevated heat rejection power of the radiator increased the temperature of the heat reject loop, and the radiator needed greater heat rejection capacity.[Conclusions] Therefore, bypass valve control is an effective means to control the power and prevent shaft overspeed in a Brayton space nuclear power system. This study provides a reference for operating a Brayton space reactor system.
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| Keywords
space reactor
closed Brayton cycle
bypass valve
power control
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Issue Date: 22 July 2023
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2023,
Vol. 63
