环形燃料棒束再淹没行为实验研究

环形燃料是一种可在维持或提升安全裕度的前提下大幅提高反应堆经济效益的新型压水堆燃料，由于其双面冷却的特点，环形燃料在LOCA再淹没阶段的热工水力行为与传统实心燃料存在显著差异。现有关于环形燃料再淹没行为的实验研究鲜有报道。本研究基于自主设计的高温环形电加热棒建立了环形棒束再淹没实验装置，开展了3×3环形棒束底部再淹没实验研究，探究了环形棒束再淹没典型物理过程及不同工况下再淹没关键参数的变化规律。结果表明，环形棒束再淹没物理过程与传统实心棒束类似，且内外通道的骤冷前沿推进和传热模式变化趋于同步。在同一时刻下，环形棒内外壁面间存在温度梯度。骤冷前沿推进速度随再淹没速度和过冷度的增大而增大，随峰值包壳温度和线功率密度的增大而减小。此外，定位格架在低流速、低过冷度与高壁温工况下能显著提升下游的骤冷前沿推进速度。

Experimental Investigation on Reflooding Behavior in Annular Rod Bundle

The internally and externally cooled annular fuel is one of the innovative fuel geometry proposals for advanced PWR, which could provide a substantial increase of power density while maintaining or improving safety margins. The quenching behavior of annular fuel during reflood stage in LOCA is significantly different from that of cylindrical solid fuel, owing to the coupling effect of dual-cooling. However, the experimental study focusing on quenching characteristics in annular fuel geometry is very little. In the present study, a bottom reflood experimental study on quenching behavior in a 3×3 external and internal cooled annular rod bundle was carried out by using self-designed indirect-heating annular rods to set up the experimental apparatus. The typical physical process and the effects of key parameters on quench during reflooding were studied in detail. The results show that the flooding process in annular rod bundle is similar to that of cylindrical solid rod bundle. The quench front propagation and the variation of heat transfer mode of both external and internal surfaces are almost synchronous. However, it is observed that there is a temperature gradient between internal and external sides of annular rods at the same time. The quench front propagation velocity increases with reflood velocity and inlet subcooling, while decreases with the increase of peak cladding temperature and linear power density. In addition, the quench front propagation velocity at the downstream of spacer grid is found to increase under the conditions of low reflood velocity, low subcooling and high cladding temperature.