The natural circulation cooling transient process for the spent fuel assembly in sodium-cooled fast reactor was investigated by Fluent code. The thermal-hydraulic phenomena and their change trends in the spent fuel assembly internal coolant channel and external flow field were acquired.The results show that the method dividing the grids of spent fuel rod gap into winding wire grids and flow field grids around winding wire is able to generate high quality structured grids in the region of spent fuel assembly.In natural circulation cooling transient process with Ar,the increase of argon flow velocity in inner sub-channels is lagged behind wall sub-channels,and the tempera-ture of inner sub-channels rises faster consequently.The axial temperature distribution of spent fuel assembly is characterized with the higher temperature in the central region and the lower temperature near the edge region.The time should not be more than 6 minutes after the spent fuel assembly is placed in argon,in order to avoid the tempera-ture of spent fuel assembly shell exceeding the design value.%应用Fluent程序,对处于氩气中的钠冷快堆乏燃料组件自然循环冷却瞬态过程进行了三维数值模拟.计算获得了乏燃料组件内部冷却剂通道和外部区域的热工水力学现象及变化规律.结果表明:利用标记区域分割方法,将燃料棒间隙网格划分为绕丝网格和绕丝周边流体域网格,能在棒束区生成高质量结构化网格;在氩气自然循环冷却瞬态过程中,棒束区内子通道氩气流量增加速度落后于边子通道,内子通道升温更快;乏燃料组件棒束区温度在轴向呈现中心高、边缘低的分布特征;为避免包壳温度超过设计值,乏燃料组件处于氩气中的时间不宜超过6 min.
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