不同燃料球排布方式下熔盐堆堆芯流动和换热特性研究

Characteristic of core flow and heat transfer of different fuel ball arrangement modes in molten salt reactor

固态燃料熔盐堆(Thorium Molten Salt Reactor-Solid Fuel,TMSR-SF)的堆芯是由燃料石墨球随机堆积而成的,在分析中建立随机堆积的小球模型存在较大困难和不确定性,通常假设为规则的排布方式。利用计算流体力学分析程序,选取了面心立方和体心立方两种规则的小球排布方式进行建模,分析不同排布方式下堆芯流动和换热的特性。结果表明,面心立方排布下的流线呈现出周期性弯曲,小球中心最高温度为1 153 K,总压降为1 323 Pa,体心立方排布下的流线大体呈直线,小球中心最高温度为1 155 K,总压降为574 Pa,面心立方排布的流动压降明显大于体心立方排布。对于单个中间小球,面心立方排布的小球表面温度分布更均匀,热点温度更低,但熔盐从燃料球底部流动到顶部的压降更大。

Background： Thorium-based molten salt reactor nuclear power system project is one of the leading science and technology projects of Chinese Academy of Sciences, its strategic goal is to develop the fourth generation fission reactor nuclear power system. The core of solid fuel molten salt reactor is constructed of the random pileup of fuel graphite balls, which brings difficulties and uncertainties in the establishment of the pebble bed model for simulation analysis. Purpose： This study aims to analyze the influence of two modes of fuel ball arrangement on the core flow and heat transfer in the molten salt reactor, which are face centered cubic （FCC） and body centered cubic （BCC） arrangement mode. Methods： Based on the computational fluid dynamics （CFD） program, two computational models based on the FCC and BCC arrangement modes are established respectively. The re-normalization group （RNG） k-ε turbulence model is selected with constant velocity and temperature as the inlet boundary conditions and constant pressure as the outlet boundary condition whilst the gauge pressure is assumed to be zero. Results： Compared to the BCC arrangement mode, the streamline under the FCC arrangement mode is more complex, the flow pressure drop is larger, the fuel ball surface temperature distribution is more uniform, and the hot spot temperature is lower. Under the FCC arrangement mode, the maximum temperature of the ball center is 1 153 K, the total pressure drop is 1 323 Pa; under the BCC arrangement mode, the maximum temperature of the ball center is 1 155 K, the total pressure drop is 574 Pa. Conclusion： The streamlines under the FCC arrangement mode are periodically curved and the streamlines under the BCC arrangement mode are generally straight. Under FCC arrangement mode, the surface temperature distribution of a single intermediate fuel ball is more uniform and the hot spot temperature is lower, but the pressure drop from the bottom of the fuel ball to the top is larger than that of BCC arrangement mode.