带交混翼定位格架5×5棒束通道单相流场结构演化机制研究

High-cost fuel assemblies are continually consumed and supplemented in nuclear reactors. The world major nuclear power vendors and research institutes have long been devoted to developing and improving advanced fuel assemblies, which have high economy and reliability. In recent years, our country has attached great importance to the independent research and development of advanced fuel assemblies in order to overcome the limitations induced by foreign intellectual properties and to reduce the operating costs of nuclear power plants. Thermal-hydraulic performance is an important evaluating index of advanced fuel assemblies. Precise measurement and analysis of the flow field inside a rod bundle fuel assembly has become one of the key fundamental scientific problems, which is commonly concerned at home and abroad in the development of advanced fuel assemblies. And it is also an important technological breakthrough of our own advanced fuel assemblies. Hence, we intend to carry out a basic visualized experimental investigation of the 5×5 rod bundle full flow field with dynamic PIV measurement techniques. Precise and intensive quantitative experimental data of the rod bundle flow field will be gained through the measurement. Meanwhile, CFD simulation of the 5×5 rod bundle flow field and simulation model verification will be carried out on the basis of visualized experimental data. The proposed investigation will provide an insight into the flow field evolution characteristics of the rod bundle with spacer grids and the fluid-solid interaction mechanism of the interaction between the grid components and the local single-phase flow, which could be a valuable reference for both single-phase heat transfer and two-phase flow characteristics research in rod bundles. This study will offer crucial basic data and valuable theoretical guidelines to the breakthrough of advanced fuel assembly development in our country.

燃料组件在核反应堆中不断消耗和补充且成本较高，世界各大核电公司和研究机构一直致力于高经济性和可靠性的先进燃料组件研发与改进，目前国家为了突破国外知识产权带来的限制并降低核电站运营成本，高度重视先进燃料组件的自主研发。热工水力性能是先进燃料组件的重要评价指标，其中棒束燃料组件中流场的精确测量与分析是目前国内外先进燃料组件研发中共同关注的关键基础科学问题之一，也是我国先进燃料组件研发的重要技术突破口。本项目拟采用PIV动态测量技术开展5×5棒束全场可视化基础实验研究，获得棒束通道内单相流场定量精细测量实验数据，并进行5×5棒束流场特性的CFD理论模拟与模型校验，从微观角度深入认识定位格架作用下棒束通道内流场演化特性与结构部件的局部流固间作用机理，为棒束通道内单相传热和两相流场特性研究提供重要参考，最终为我国先进燃料组件研发获得突破提供关键性的基础实验数据和有价值的理论指导。

燃料组件是压水堆(PWR)和沸水堆 (BWR)核电站的消耗性核心部件，先进燃料组件研发是改善核电站安全性、 可靠性和经济性的有效手段，也是目前我国核电国产化的关键技术。本项目主要通过开展5×5棒束单相流场PIV可视化实验研究、5×5棒束单相流场CFD数值模拟，掌握带交混翼定位格架5×5棒束通道内的单相流场结构特性及其演化机制。.本项目建立了用于带定位格架5×5棒束通道可视化测量的实验装置、实验本体、PIV测量系统，完成了5×5棒束通道单相流场结构可视化测量实验（获得39组数据）、单孔发泡两相流场可视化拍摄拓展实验（获得92组数据），构建了适用于复杂棒束通道流场模拟计算的单相、两相（拓展）CFD模型，并对湍流模型进行了对比验证。研究结果表明，定位格架的搅混翼排列是横向流场分布模式（曲线形状、峰值位置）的决定性因素，入口流量则决定着棒束通道内横向速度的幅度大小；实验格架的横向搅混幅度沿轴向先迅速衰减，后基本维持恒定，横向搅混幅度的影响距高可到格架下游13D位置；棒束通道流速是影响子通道内汽相分布的主因，高流速下搅混翼后的背压区会出现持续的气柱，从而影响棒束流动传热与临界热流密度特性；对比发现，不同CFD湍流模型的计算结果区别不大，均适用于实验格架棒束通道流场预测。.本项目研究为认识棒束流场结构、设计棒束临界热流密度实验用定位格架提供了重要的基础实验数据和有价值的理论指导。为燃料组件子通道程序验证和先进燃料组件研发提供了实验平台和 CFD计算工具，具有一定的工程应用价值。