A Study Of The Influence Of Dense Granular Target Geometry On The Fluidity

The development of spallation neutron source has a very important influence on the development of modern nuclear energy engineering and materials science.In different engineering applications,the requirements of spallation neutron source are different according to the purpose and environment.Nuclear fission reactor is one of the most important components of energy in the world,but its spent nuclear fuel reprocessing is still a problem to be solved.The accelerator driven subcritical system,ADS,is one of the most efficient methods for future spent nuclear fuel disposal.The ADS system uses the spallation target to generate neutrons to drive the back-end subcritical fission reactor to transmute spent nuclear fuel and provide energy.According to the existing problems of solid target and liquid target,the concept design of dense granular target was proposed innovatively by the Institute of modern physics,which integrated the advantages of solid target and liquid target.In addition,nuclear fusion energy is the future energy solution for human beings,but the huge energy and extreme environment generated by nuclear fusion put forward very strict requirements for the nuclear fusion device.In order to carry out the international test,the IFMIF project was proposed,and China also proposed the research plan of deuterium beryllium neutron source for the research of small high energy and high flux fusion materials,using the accelerator driven neutron source to provide a detection environment,which puts forward higher requirements for the performance of spallation target.Based on the experience of CIADS dense granular flow target,the research team proposed the concept design of dense granular flow chute flow target.Neutrino physics plays an important role in particle physics.Neutrino physics experiments need high energy muon beams.China has put forward its own high-intensity frontier experiment: MuOn-decay MEdium baseline NeuTrino beam experiment(moment),which is the next generation of neutrino experiment in China after the JUNO,and will keep China in the leading position in the field of neutrino physics.In order to improve the accuracy of measurement,the best way is to improve the intensity of the beam.Moreover,the main goal of the MOMENT target is to obtain secondary particles,so the working environment of the MOMENT device's spalling target and station is more complex than that of other traditional high-power spalling neutron sources.Under the same power requirement,the thermal power density of the target of MOMENT will be two orders of magnitude higher,which puts forward extremely high requirements for the design of the target scheme.Based on the experience of CIADS's dense granular flow target,the research team put forward a concept of no container granular waterfall flow target.Dense granular flow target can transfer heat off-line and avoid instability,damage to material,leakage and other problems of liquid target.It is a kind of very potential target design scheme.As a new design,the primary consideration is its flow stability.This paper mainly studies the influence of geometry of the target on granular flow fluidity by means of simulation and experiment and evaluates the feasibility of the target system design.This article mainly includes three parts:(1)we investigated the influence of a beam tube on a granular flow in a rectangular bin experimentally.the varying of the height of the bar results in the transitions from clogging to a dense flow via a surface flow regime.Below the bar,the free surface of flow can be described as a slope.It seems that the change of flow rate from clogging to surface flow is a jump.In dense flow regime,the Beverloo scaling law will be valid under the existence of the bar.The slope of surface will saturate with increasing flow rate.The velocity distribution was analyzed and is consistent with that in a heap flow.To ensure the connectivity of the flow,the allowable distance between bar and sidewall can be slightly less than the outlet size.And we produced a heap flow in this bin and confirmed a linear dependence of flow rate on the slope of surface.(2)Here the flowability of an accelerating inclined dense granular flow was investigated by simulations.It was found that in this accelerating flow there were slight fluctuations of velocity and density and no surface wave was observed.Furthermore,the stability of the flow was studied by using linear stability analysis and calculating Lyapunov exponent.All the results demonstrated the constancy and stability of the accelerating flow and supported the availability of this flow to be a proposal design of high-power target.(3)numerical simulation is carried out for the waterfall granular flow of different sizes target.The spatial distribution of granular velocity and volume fraction in funnel and jet is studied.It shows when the slot width is small,the velocity is nearly constant with the time going by and the distribution can be predicted with a Gaussian-like function.However,the prediction fails when the slot is wide and the flowrate is higher than the predicted value from Beverloo law.There is a high fluctuation of vertical velocity at the rim of outlet.The volume fraction in the hopper flow is also constant but decreases above the outlet.In the granular jet beneath the hopper,the volume fraction will drop with height rapidly because of the dispersion of granular jet if the slot width is small.In contrast,there is a dense core in granular jet if the slot width is large.The fluctuations of velocity and volume fraction in this core are relatively small.At last,the whole paper was summarized and the further work plan was suggested.