Optimization Of The First Wall Of WCCB For The CFETR And Research On The Performance Of The Breeding Pebble Bed

The blanket,one of the key components of CFETR,performs the functions of energy transfer,tritium breeding and radiation shielding of other key components,such as superconducting magnet.The first wall of the blanket directly faces the plasma and takes most of the heat flow from plasma to the blanket,and the particle pebble bed inside of the blanket is used for tritium breeding.Therefore,Researches on the first wall and pebble bed performance are essential for the entire blanket design,and important for reliable and safe operation of blanket.In this dissertation,the optimization of the first wall of WCCB to the CFETR and the studies of the performance on the breeder pebble bed are carried out,according to the design parameters of the CFETR project.Firstly,the turbulent flow and heat transfer process in the complex structure are numerically solved by the Reynolds-averaged RANS method,and the first wall is optimized with the consideration of different amounts of surface heat flows.In order to reduce the thermal stress in the first wall,a copper transition layer is arranged between the tungsten armor and the first wall,and 16 stress relief grooves are evenly set in the tungsten armor and the copper transition layer.FeCrAl alloy is coated on the inner surfaces of the first wall cooling channel,which effectively reduces the penetration of tritium.Secondly,based on the threedimensional smooth square tube,the square tube with straight rib and the square tube with V-shaped rib,the thermal wall structure of the channel has been studied using the enhanced heat transfer analysis.Using the turbulent heat transfer theory,the flow field analysis and thermal analysis of the channel are carried out.The heat-line and field synergistic analysis methods are used to conduct an in-depth analysis of the enhanced heat transfer mechanism of the first wall.From the perspectives of entropy production and entransy dissipation,the efficiency of enhanced heat transfer by adding fins are analyzed.The methods and principles of enhanced heat transfer are further supplemented to optimize the heat transfer of the first wall channel of the water-cooled solid blanket.According to the optimization studies of the first wall of the CFETR water-cooled solid blanket,the thermodynamic properties of the breeder pebble bed are analyzed using the discrete element method.The characteristics of the breeder pebble bed under different temperatures and pressure perturbation are also studied.In addition,according to the characteristics of the water-cooled solid blanket in a background magnetic field,a coupling program was further developed to study the perturbation of the neutron multiplier particle pebble bed in the magnetic field.Meanwhile,the flow characteristics of the particle pebble bed are analyzed based on the coupling of EDEM and CFD.The pressure drop of the particle pebble bed is further analyzed,and the empirical relationship is fitted from the calculations.Following conclusions could be drawn from the optimization results of CFETR first wall and the studies on the particle pebble bed performances:1).the thickness of the front edge of the first wall is fixed as 3 mm,and the thickness of the tritium blocking layer FeCrAl is fixed as 0.5 mm.The heat exchange efficiency is significantly improved by adding the fins and will be improved further by increase the fins height.The design of first wall with V shape fins shows the better overall thermal dynamic performance;2).The packing factor of the particle pebble bed will be increased under the perturbation of temperature,pressure and magnetic field.The basic rules under such perturbation are obtained according to our studies.The rules of the pebble bed flow performance changing over the temperature,the ratio of the particle radius and the friction forces of the particles are also obtained.The research methods and results presented in this dissertation could be used for the comprehensive performance analysis of the first wall,provide the theorical basics for the first wall optimization,and provide important references for the related components thermal analyses in future.The obtained changing rule of the pebble bed under various disturbances provides the basics for the reliable and safe design of the blanket,and also provides the references for the future CFETR blanket construction.