压水堆乏燃料单棒冷却液膜流动特性实验研究

为避免在极端事故工况下，乏燃料水池会长期失去补水和冷却，第3代核电站如AP1000和CAP1400，引入了喷淋冷却系统。在喷淋条件下，乏燃料棒上液膜流动特性是影响冷却效果的重要因素，国内外学者还未对其做过详细的研究。本文使用光学法研究了在不同雷诺数(Re)条件下，对单根乏燃料棒进行喷淋冷却所形成的液膜厚度随时间和空间的变化。利用CCD相机采集液膜图像，并经过处理得到了清晰的液膜厚度图像和与图像吻合良好的数据。实验结果表明：当Re为608～7 538时，瞬态液膜厚度最大值出现在Re=7 085的条件下，其值为2.36 mm；随着Re的增加，时均液膜厚度会随之增加，并且液膜波动的振幅也会随之增加；在沿棒方向上，随着距棒顶距离的增加，液膜厚度会逐渐减小并趋于平稳，并且随着Re的增加，平稳部分会出现在距棒顶更远的位置。对乏燃料单棒冷却液膜流动特性的研究，为确定具有有效冷却能力的最小喷淋流量奠定了基础。

Experimental Study on Flow Characteristics of Coolant Film of Single Spent Fuel Rod in PWR

After the Fukushima nuclear accident, the safety of spent fuel pool has attracted much attention. Under extreme accident conditions, the spent fuel pool may lose make-up water and cooling for a long time, causing the water level in the spent fuel pool to drop, resulting in excessive temperature of spent fuel rods, even damage to fuel assemblies and leakage of radioactive substances, come into being serious safety problems. In order to avoid this safety problem, the third generation nuclear power plants, such as AP1000 and CAP1400, introduced spray cooling system. Under the condition of spraying, the liquid film flow characteristics on spent fuel rods is an important factor affecting the cooling effect, which has not been studied in detail by domestic and foreign scholars. Too large or too small spray flow rate may lead to the rupture of the liquid film on the spent fuel rod. Therefore, it is necessary to study the flow characteristics of the liquid film on the spent fuel rod. In this paper, optical method was used to study the time and space variation of liquid film thickness formed by spray cooling of single spent fuel rod at different Reynolds numbers. The liquid film image was captured by CCD camera, and the clear liquid film thickness image and good coincidence data were obtained after processing. Using the obtained data, the fluctuation images of liquid film at different Reynolds numbers at fixed positions of spent fuel rod and at different positions of spent fuel rod at fixed Reynolds numbers were drawn. In addition, the variation trend of time-averaged liquid film thickness on spent fuel rod at different Reynolds numbers was obtained. The experimental results show that when Reynolds number is in the range of 608-7 538, the maximum value of transient liquid film thickness is 2.36 mm, which occurs when Reynolds number is 7 085. With the increase of Reynolds number, the time mean liquid film thickness will increase, and the amplitude of liquid film fluctuation will also increase. Along the rod direction, with the increase of the distance from the top of the rod, the liquid film thickness will gradually decrease and become stable, and as the Reynolds number increases, the stable part will appear farther from the top of the rod. The research on the flow characteristics of single rod coolant film of spent fuel lays a foundation for determining the minimum spray flow rate with effective cooling capacity.