带7道格架的5×5棒束两相性能CFD分析

CFD Analysis for Two Phase Performance in 5×5 Rod Bundle with 7 Spacer Girds

采用两相计算流体动力学(CFD)方法进行带7道格架的5×5棒束两相性能研究,其中结构搅混格架(MG)和跨间搅混格架(MSMG)交替布置,计算考虑汽泡合并与破裂、热量传递,但不考虑相间的质量传递。为选择合理的两相模型参数,首先以带2道格架(MG、MSMG)的AFA3G燃料组件5×5棒束架为研究对象,对最大气泡直径、汽泡合并破裂系数、非曳力模型及曳力模型、入口气泡直径、入口空泡份额分布等进行了敏感性及不确定性分析。此后采用该两相模型设置,针对带7道格架的AFA3G燃料组件进行了两相性能研究,计算结果显示格架间的各项参数不存在完全一致的周期性,但同种格架上游的空泡份额分布具有一定的相似性,因此用于两相性能评价可计算带2~3道格架的棒束,该研究可用于带格架棒束两相计算的模型设置与几何规模选择,为下一步采用两相CFD计算建立燃料组件热工水力性能评价准则奠定了基础。最后比较了AFA3G燃料组件及改进型燃料组件两种格架的空泡分布特性,并从提高燃料组件临界热流密度(CHF)特性的角度对其进行评价,获得与实验一致的结论,证明了评价方法的正确性。

A 5×5 rod bundles with 7 spacer girds which structure mixing gird(MG)and mid span mixing gird(MSMG)are arranged alternant are studied by two phase computational fluid mechanic(CFD),and bubbles coalescence and breakup,and heat transfer are considered in the calculation,but not the interface mass change.In order to choose the reasonable two phase model parameters,5×5 rod bundles with 2 spacer girds(MG and MSMG)based on AFA3 G fuel assembly isstudied by two phase CFD,and the sensitivity and uncertainty analysis is conducted on max bubble size,bubbles coalescence and breakup model parameters,non-drag force model,drag force model parameters,inlet bubble diameter and inlet void fraction distribution.Use this model setting,the study of the two phase performance is conducted on AFA3 G fuel assembly with 7 spacer grids.The calculation shows that the bubble through the spacer grid is without periodicity,but the void fraction fields of every MSMG upstream are similar and the MG upstream shows the same situation.This research is useful to choose the model setting and geometry size for the rod bundle with spacer girds in the two phase calculation,for geometry size it is possible to analyze the two phase performance on rod bundle with 2 or 3 spacer grids.Finally,the void fraction distribution of AFA3 G fuel assembly and advanced fuel assembly are compared,and evaluated in terms of the improvement of the CHF.It agrees well with the experiment,which verifies the evaluation method,the research is the base for the establishment of the evaluation guideline for the thermal hydraulic performance of the fuel assembly by two phase CFD calculation.