Optimal Design Core Inlet Flow Field For A Small Solid Fuel Pebble Bed Reactor

In China,the research of thorium based molten salt reactor is at the early stage,which needs to be designed and analyzed in detail for each structure of the system.Thus,we can do some preparatory work and experience accumulation for its future development,Designing and constructing the solid fuel molten reactor is a part of this peculiar task.The core inlet design is one of the whole project design.It has a particularly important influence on stability of reactor structure and flow field distribution.Thus,it is necessary to design and optimize the reactor core inlet for the overall structure.In this paper,the research selects a small solid molten salt reactor(TMSR-SF2)as the research object,uses software tools of Gambit2.4.6 and ANSYS FLUENT16.0 to establish three-dimensional geometric model TMSR-SF2 and calculate and analyze results.This paper aims to research thermal-hydraulics behavior of the core inlet such as core temperature,flow field and pressure when the molten salt channel structure of reflection layer is changes.The specific research contents are as follows:Firstly,molten salt flow characteristics inner the core inlet is researched by changing the flow area of lower reflection.six different flow areas of the lower reflector structure are chose,respectively 15%,12.5%,10.02%,7.5%,5%,0%,to study flow field,temperature,pressure in the core.The results show that the maximum local hot spot temperature in the core active region increases,the pressure drop in the core inlet reduces with flow area of the lower reflection layer increasing,the smaller flow area of the lower reflection layer helps to flatten axial temperature distribution of the core active area,molten salt average rate remains stable in the core active area.Secondly,changing the channel diameter and space of lower reflection layer researches how to influence thermal hydraulic characteristics of the core inlet : four different channel diameters and spaces of the lower reflector structure are chose,respectively,1.0 cm?1.5 cm?2.0 cm?2.5cm,to study the effect,which is the flow characteristics and flow field of molten salt inner the core inlet.The results show that the the maximum local hot spot temperature decreases with the pore diameter size reducing,and the pressure drop in the core inlet decreases with the pore diameter size increasing,smaller pore diameter can make molten salt velocity gradient more uniform at the outlet of molten salt channels.Thirdly,Building local porous medium core model and local real pebble bed core model compares two models' molten salt velocity and momentum variation by 4 different channel diameters,further analysis their difference that simulates the local core flow field.The results show that After the molten salt flows from the flow channel into the core bed,the velocity field perturbation between the 1 to 4 layers of the ball flow is larger.When inlet flow velocity is constant,the average velocity and momentum of molten salt in the core increase with the increase of he pore diameter size.Under the same channel,average velocity of molten salt in the local pebble-bed core model is larger than that in the local porous medium model,Mainly at the condition of conservation of mass,as local real pebble bed core model has smaller flow area,its molten salt velocity is relatively larger.