Thermodynamic Analysis and Optimization of Nuclear Closed Air Brayton Cycle

Abstract

In order to improve the flexibility and adaptability of micro nuclear power systems, air is considered as an optional working fluid of nuclear Brayton cycle. It has ability to avoid shortage of working fluid under extreme conditions, and ensure the system operating with tight supply. Compared with the traditional open cycles, the closed cycle has advantages of higher cycle efficiency, smaller equipment size and higher power density. Few of closed air power cycle in nuclear power system has been studied by now. In this paper, cycle parameters were analyzed and designed, and optimal cycle performance was compared between cycle constructions. Four closed air Brayton cycles are proposed and modeled in EBSILON 15.0, including simple regenerative cycle (SRC), intercooling regenerative cycle (IRC), reheat regenerative cycle (RRC) and intercooling-reheat regenerative cycle (IRRC). Thermodynamic analysis of the key parameters is conducted, including pressure ratio, turbine inlet temperature, compressor inlet temperature and pressure. In addition, the genetic algorithm (GA) is applied for multi-parameters optimization for the maximal cycle efficiency. Result shows that with the increase of pressure ratio, the efficiency of SRC increases firstly and then decreases. With the increase of turbine inlet temperature, the pressure ratio corresponding to the maximal cycle efficiency increases gradually. Specific work gradually increases with pressure ratio. In higher turbine inlet temperature, the rising velocity of specific work is faster. Cycle efficiency increases with compressor inlet pressure, and this trend tend to be slower in high pressure region. With the increasing of compressor inlet pressure, optimal pressure ratio decreases and finally approaches to 2.0. The cycle minimal cycle pressure was selected as 6 MPa. Maximal efficiency and corresponding pressure ratio increase with turbine inlet temperature increasing and decrease with compressor inlet temperature increasing. Comparing with SRC, RRC brings 1.16% cycle efficiency promotion, and IRC presents significant specific work increasing. In cycle efficiency distribution contour map of pressure ratio-middle pressure ratio, design point should be selected in high efficiency area. IRRC reaches 39% maximal cycle efficiency and maximal specific power 0.118 MW/(kg/s) of CABC.