计算流体动力学在燃料组件热工水力性能分析和格架研制中的应用

国外使用商用计算流体动力学(CFD)软件分析燃料组件中流体的三维流场和温度场，并将验证的方法用于燃料组件格架设计，获得了成功。中国核动力研究设计院空泡物理和自然循环重点实验室用CFX程序对带格架棒束内流场进行了计算，解决了小尺寸复杂结构几何体的模拟，边界条件的选取和CFX计算能力的评价，然后完成了单相，空气一水两相流场和流动特性的计算分析及试验对比验证。已完成的研究表明，尽管CFX程序目前在计算两相流动和传热方面还存在不足，但通过比较单相流场的湍流，旋涡和棒束附近流体温度分布基本可以评价格架对流体的交混性能；格架上的弹簧和刚突对于流动有相当的作用，对其进行模拟是必要的。研究还建议在使用CFD方法进行燃料组件格架热工水力分析前要先进行基准练习以保证分析结果的正确性。

Application of Calculation Fluid Dynamic in Thermal Hydraulic Analysis of the Fuel Assembles and Design of the Spacer Grid

The time and cost for the analysis and design can be decreased greatly by using of Calculation Fluid Dynamic (CFD) methodology in thermal performance analysis of fuel assemble and the design of spacer grid. In the middle of 1990s, the commercial CFD code has been used to analyze the 3D flow and temperature fields of the fuel in foreign countries. It was successful to design the spacer grid with the verified methodol-ogy. In the Laboratory of Bubble Physics and Natural Circulation, the CFX code was employed to calculate the fluid field of a rod bundle with spacers in the end of 1990s. The structure simulation of complex small size geometry, the selection of the proper boundary conditions and the evaluation of CFX applicability have been studied and problems were solved. Then the calculation of flow field of the single-phase and air-water two-phase has been carried out and compared with experiment results. The steam-water two-phase flow has been studied and the design of new spacer has been carried out. It is desired to develop a CFD analysis and design methodology, which can predict not only the flow and temperature fields in rod bundle with spacers, but also the surface temperature of the rods. The results show that it can compare the turbulence, eddy and fluid temperature near rod of single-phase flow to evaluate the mixing characteristics of a spacer to fluid. The spring and dimple of the spacer have evi-dently effect on flow and it is necessary to simulate. In order to ensure the correctness of prediction results, it suggests to take a benchmark exercise before the analysis of CFD thermal hydraulic analysis for a fuel assem-ble with spacers.