脉动流下棒束通道内相位差及瞬态流场研究

事故条件及海洋条件下反应堆处于非稳态工况，堆芯燃料组件内热工水力行为具有瞬变及多因素耦合特性，对反应堆的安全提出更高挑战，因此有必要对燃料组件内瞬态特性进行研究。本文通过测量棒状燃料组件内压降和流量之间延迟时间开展棒束通道脉动流条件下相位差研究，对比了相位差在不同振幅、不同流动状态下的变化特性，并分析了定位格架对脉动流相位差的作用特点。另外，基于粒子图像测速（PIV）技术开展了脉动流条件下棒束通道内流场分布特性研究，对比了相同流量条件下稳态工况与瞬态工况下流场分布差异，分析了主流具备不同加速度时棒束通道内流场分布特征。实验结果表明：定位格架可减小脉动流下棒束通道内相位差；棒束通道内流场演化滞后于主流量变化。实验结果有助于揭示燃料组件在非稳态条件下瞬态特性，并为燃料组件的设计和优化奠定基础。

Study on Phase Difference and Transient Flow Field in Rod Bundle under Pulsating Flow

The thermal-hydraulic behaviors in fuel assembly of reactor core have transient coupling characteristics under unsteady conditions including possible accident scenarios and ocean conditions, thus the study of transient characteristics in fuel assembly is necessary to improve the reactor safety. In this paper, the response time between frictional pressure drop and flow rate in a rod bundle was measured to perform the study of phase differences under the pulsating flow. A comparison of phase differences under different amplitudes and periods was conducted and the function of spacer grid for phase difference was also analyzed. In addition, the distribution characteristics of the flow field in the rod bundle under pulsating flow were studied based on the particle image velocimetry (PIV) technique. The differences of flow fields under steady conditions and transient conditions were compared. The flow fields of rod bundle under different accelerations were analyzed. The experimental results show that the spacer grid can reduce the phase difference of pulsating flow in the rod bundle and the flow field evolution in the rod bundle lags behind the variation of main flow. The experimental results are helpful to reveal the transient characteristics of the fuel assembly under unsteady conditions and provide a foundation for the design and optimization of the fuel assembly.