Study On Physical And Safety Characteristics Of Open Cycle Reactor

Near-space is an important part of the national security system.Near-space vehicles have the advantages of fast deployment,good mobility and long continuous working hours,which have become the focus of extensive attention in recent years.Nuclear aero-engine uses nuclear fuel with high energy density,which can break through the limitation of volume and weight and provide a longer time of stagnation.It has incomparable strategic advantages.In this paper,based on the background of nuclear aero-engine,a 50MW open reactor system design was carried out.Based on the physical and thermal numerical simulation software,the reactor physical and safety characteristics were studied.In this paper,the design criteria and scheme selection of 50MW open reactor are firstly determined based on the summary of historical experience.On this basis,the inlet conditions and other parameters of the reactor are calculated to provide a basis for the calculation of flow heat transfer in the following paper.Based on the system scheme,this paper preliminarily established an open reactor physical model,and studied the effects of Density of TRISO particles,axial reflection layer and Gd₂O₃ addition ratio on physical characteristics by using Monte Carlo software Serpent,thus preliminarily mastered the basic mesophytic physical characteristics of a 50MW open reactor.Through comparative analysis,it is found that the initial reactivity of the reactor needs to be greater than 500pcm to meet the life of1000 days of full power operation.The addition of Gd₂O₃ into the fuel can effectively absorb thermal neutrons in the water flooding accident,but it will also seriously affect the initial reactivity of the reactor.The optimized control strategy can ensure that the reactor is in subcritical state under various working conditions and can meet the requirements of safe operation of the reactor.Thereafter,the safety characteristics of the designed open reactor were studied,and the core shielding and flow heat transfer were studied by using Monte Carlo software MCNP and CFD software respectively.It is found that:（1）Li H,Be O and B4C are the three shielding materials suitable for this scheme.Through studying the influence of the thickness on the shielding effect and the combination mode,the shielding system scheme in this paper is obtained.（2）In the fully developed section of the typical channel,the heat transfer remains stable,the fluid temperature and velocity increase steadily,and the temperature difference between the fluid and the wall surface is constant,which conforms to the heating law of equal heat flux.At the same time,it can be obtained that the maximum velocity at the fluid outlet is about 220m/s,and the maximum temperature in the solid domain is about 940K,which is far less than the temperature limit required for solid fuel.To sum up,this paper establishes a set of open reactor system scheme,which meets the requirements of the life of 50MW full power operation for 1000 days,and the shielding and thermal calculation results show that it meets the safety design criteria,which provides important reference significance for the system design of nuclear aero-engine.