TMSR-SF球床随机堆积结构的离散元模拟

Discrete element simulation of random packing structures in TMSR-SF

中国科学院上海应用物理研究所设计的10 MW固态燃料钍基熔盐实验堆(Thorium-based Molten Salt experimental Reactor with Solid Fuel,TMSR-SF)是一种球床型氟盐冷却高温堆,其三维球床随机堆积结构对于堆芯反应性变化和换料分区方案以及热工水力分析中的流动传热都具有重要的影响。为了研究TMSR-SF堆芯球床随机堆积规律,基于PFC3D(Particle Flow Code 3 Dimensional)程序,分别计算并分析了填充颗粒球大小、颗粒间摩擦系数以及填充颗粒球数对球床稳态堆积结构的影响。结果表明:填充直径小的颗粒球,可使球床孔隙率振荡减弱,有利于堆芯功率密度分布的展平;通过减小颗粒间摩擦系数能较好地模拟振动压实效果,压实过程中颗粒间摩擦系数与稳态堆积球床孔隙率和配位数满足负指数关系。当填充颗粒球数超过约8 000个后,球床平均孔隙率和配位数变化趋于恒定,分别稳定在0.43和5.6左右;此时颗粒球数量对球床稳态堆积结构的影响降至最低,可被用来代替满装堆时的球床用于TMSR-SF自然循环的热工水力数值分析,达到节省计算资源的目的。本研究对理解TMSR-SF堆芯球床结构特性与堆积规律具有参考价值。

[Background] The 10 MW thorium-based molten salt reactor with solid fuel (TMSR-SF), designed by Shanghai Institute of Applied Physics, is a pebble bed fluoride salt cooled high temperature reactor in the world. The three-dimensional random packing structure has an important influence on the reactivity and fuel management scheme in the neutron physics as well as the heat transfer in thermal-hydraulic analysis.[Purpose] This study aims at the simulation analysis of the structural characteristics of the random packing pebble bed in TMSR-SF by discrete element method (DEM).[Method] The particle flow code 3 dimensional (PFC3D) was employed to simulate the particle motion under buoyancy effects of particle size, friction coefficient, and number of particles on the steady state packing structures. Radial porosity distribution of stochastic accumulation pebble bed generated by DEM was verified.[Results and Conclusion] The simulation results show that packed bed with smaller particle diameter can weaken the oscillation of the axial and radial porosity, which will help to smooth the power distribution in the reactor core. By reducing the friction between particles, the vibration process can be well reflected. The relationship between the friction coefficient and packing porosity as well as the coordination numbers of the filler is in accordance with the negative exponential distribution. When the filled particles number exceeds 8 000, the bed average porosity and coordination numbers tend to be constant with the value of 0.43 and 5.6 respectively, the influence of particle number was minimized. Then the packing bed with 8 000 filled particles can be used as a representative of the full packed pebble bed to study the thermal-hydraulic numerical analysis of the natural circulation in TMSR-SF, which will help saving the computational resources.