Research On The Granular Flow Of The Gravity Driven Dense Granular Flow Target(DGT) In Accelerator Driven Sub-critical System(ADS)

The Accelerator Driven Sub-critical System?ADS?is a nuclear device that the scientific community believes can be used to effectively transform nuclear waste and generate energy.At present,many technological powers are investing in this leading field with great manpower and material resources.As one of the three key components of ADS,spallation target is mainly used to generate neutron s with wide spectrum and large flux to drive the sub-critical reactor which transforms the nuclear waste,playing an important role in the whole system.This work is aimed at researching the granular flow in the target and the design of the gravity driven Dense Granular-flow Target?DGT?,which is proposed by the Institute of Modern Physics?IMP?,Chinese Academy of Sciences?CAS?.The DGT has advantages over the solid targets and liquid targets in terms of operation power,reliability,stability and radiochemical toxicity.First,the target material is in the form of grains,so the range of materials chosen as spallation reaction material is greatly increased compared to that in the liquid metal target?the liquid metal target needs material with low melting point.?.Since grains can flow under gravity in the target,which is better than the solid,it can be achieved that the grains can interact with the proton beam in the spallation region and doing the heat transfer in other area,namely offline.Consequently,the power upper limit that the target can bear is increased.As there is no recirculation zone in granular flow of the target?different from the liquid metal target?and flow stability is good,the DGT is more reliable.For the forthcoming DGT in the prototype,the research on the granular flow is one of the key issues.For granular flow,the flow rate and stability of the free surface are the key points to be studied.The full text of the above research is arranged as follows:The first chapter mainly introduces the development of ADS and spallation target,and the background of the DGT.It includes:1)the national research projects that put forward for the R&D of ADS and their current status,existing problems and corresponding solutions;2)the current development of the spallation target,the main target type,respective advantages and disadvantages,existing problems and corresponding solutions;the advantages of DGT;3)the status of research on the investigation of flow rate in a hopper;4)the status of research on the investigation of free surface in liquid metal target.The second chapter mainly introduces the methodology in this study.The Discrete Element Method?DEM?is very common in the simulation of a granular system.The first section introduces the history of DEM,as well as the characteristics of the soft-ball model and the hard-ball model.The second section focuses on the basic principle of the soft ball model and the method to be realized from the view of programing.The third section introduces the experimental platform which is used to verify the simulation results.The third chapter mainly introduces the research on the flow rate in a hopper with a pipe inside.It includes three aspects:1)the influences of distance from the end of beam pipe to the orifice of the hopper H₀,diameter of beam-pipe D₁,diameter of hopper D and diameter of the hopper's orifice D₀ to the flow rate;meanwhile,the effect of friction coefficient between particles and particles,friction coefficient between particles and wall of hopper,Young's modulus E,density?and the restitution coefficient?of the particle material on the flow rate;2)verifying the principles of the influence of above geometrical parameters on the flow rate through experiments;3)since wear is unavoidable in the granular flow in the hopper,this paper pays attention to the influence of the shape of the hopper's orifice on the flow rate.The fourth chapter mainly studies the shape and stability of the free surface under the beam pipe.It includes five aspects:1)through observation on simulation results,free surface shape were fitted with given formula under different conditions;2)the formation and development of the free surface;3)analysis of fluctuation of the free surface;4)verifying the correctness of the simulation results through the experiments to some degree;5)the model used to calculate the duration of grains on the free surface under the beam pipe.The fifth chapter is the summary of all the relevant work in this paper and the prospect of the future work.