Thermomechanical Performance Analysis And Failure Study Of Tritium Breeder Pebble Bed For Fusion Reactor Blanket

The tritium breeder blanket system is one of the key systems of the fusion reactor.Its main function is to multiply and extract tritium in the fusion reactor and realize tritium self-sustainment.In solid tritium breeder blanket of fusion reactor,lithium ceramic pebble bed is generally used as tritium carrier.During the operation of the blanket,the temperature of the pebble bed can reach 350℃-800℃.The lithium ceramic pebble bed is easy to interact with the blanket structural steel under the cyclic thermal stress,which not only directly affects the mechanical properties of the blanket,but also may cause the crush of lithium ceramic particles,affecting the proliferation and extraction of tritium.Therefore,this paper aims to carry out experimental research on the thermo-mechanical properties and crushing characteristics of the pebble bed,and provide relevant experimental data for the design and development of the solid blanket.Firstly,based on the thermal mechanical experimental device of the Institute of Plasma Physics,Chinese Academy of Sciences,the uniaxial compression experiment of Li₂TiO₃ pebble bed was carried out.The mechanical properties of Li₂TiO₃ pebble bed under RT-800℃and cyclic loading were studied,as well as the effects of particle size and bed height on the mechanical properties.The stress-strain curve of Li₂TiO₃ pebble bed was obtained,and an empirical formula for residual strain was obtained based on the stress-strain curve.Research has found that during the first loading cycle,the pebble bed exhibits significant irreversible residual strain.As the number of loading increases,the residual strain decreases.Under the same mechanical load,the 0.47mm Li₂TiO₃pebble bed produces higher residual strain than the0.99mm Li₂TiO₃ pebble bed.In high-temperature uniaxial compression experiments,the strain of the pebble bed continuously increases with the increase of temperature.After 100 loading and unloading cycles at 800℃,the strain of the pebble bed is almost 10%.The mechanical experiments on different heights of pebble beds at 500℃and 6MPa show that the height of the pebble bed has a significant impact on the mechanical behavior.Secondly,the crush load of Li₂TiO₃ particle of different sizes and the Li₂TiO₃ pebble bed crush rate were characterized.Based on the single particle crush load experimental device,The crush load of 0.99mm Li₂TiO₃ particles after cyclic loading at 500℃have no obvious changes compared with the original particles.And,the average crush load of 0.47mm particles is 8.23N,significantly lower than that of the 0.99mm large particles,33.85N.In addition,according to the crush rate test of the pebble bed after the high temperature cyclic load,it is found that the crushing rate of 0.99mm Li₂TiO₃ pebble bed at 500℃is 0.61%,0.74%and 1.01%,respectively under the maximum mechanical load of 4,6 and 8MPa.In this paper,the thermo-mechanical properties of Li₂TiO₃ pebble bed with solid blanket for fusion reactor have been tested,and the relevant experimental studies have been carried out on the fragmentation of Li₂TiO₃particles,and the relevant mechanical properties of Li₂TiO₃pebble bed have been obtained.The experimental results provide relevant data for the design and development of solid blanket.