螺旋十字形燃料组件棒束通道旋流流动结构基础研究

The helical cruciform fuel (HCF) is an innovative nuclear fuel which utilizes 4-petalled, twisted Fuel rods. The helical cruciform fuel (HCF) geometry uses the strategy of fins to increase the heat transfer area and essentially turns the entire fuel column into a mixing vane to increase the swirl and cross-mixing in sub-channels. The HCF rods are in contact at every 1/4th (e.g. 90 degree) twist pitch and do not require spacer grids as they support each other. Nowadays the knowledge of the complex swirling flow inside the sub-channel of HCF is very limited. In this project, refractive index matching of experimental FEP rod and water enabled the use of an optical measurement technique. The velocity and turbulence distribution in a 5*5 rod bundle modeling HCF is measured by the PIV measurement system. The wire-mesh sensor technique is employed to characterize the progress of the cross-mixing along the flow direction and the degree of cross-mixing assessed using the quantity of tracer arriving in the neighboring sub-channels. Numerical models for single phase swirling flow and cross-mixing between the sub-channels are developed. The WMS demonstrates the three dimensional flow structures, i.e. void fraction, phasic velocity, sauter mean diameter and interfacial area concentration distributions. Acquired data exhibits the swirling two-phase flow dynamics in the HCF rod bundle. The two-phase Eulerian approach with interfacial area transport model is developed to predict the swirling two phase flow in the HCF rod bundle. The objective of the research is to develop the knowledge of flow structure in HCF rod bundle and present the analysis model for the HCF development.

螺旋十字形燃料(HCF)组件采用四叶螺旋燃料棒，实现了无格架自定位。螺旋形外包壳结构显著增加换热面积并在通道内形成持续的旋流流动，显著提高功率密度和热工安全裕度，是一种极具工程应用前景的创新型燃料组件设计。目前针对HCF组件棒束通道内的旋流结构及其对棒间交混和两相结构影响的认识十分有限。本项目采用PIV测试技术结合折射率补偿方法获取HCF棒束通道内单相旋流场的精细流动结构。基于实验数据，建立描述棒束通道内单相旋流和棒间交混的数值模型和计算方法，揭示棒束通道内旋流场的形成机制和棒间交混机理。采用丝网电导探针(WMS)系统获得棒束通道内旋流场中气液两相相态空间分布和界面输运特性。结合界面浓度输运方程，构建描述复杂棒束通道内气液两相流动结构的数学模型。揭示HCF棒束通道内旋流场中气液两相相态分布及其演化规律。本项目的研究旨在揭示棒束通道内的旋流结构，为HCF组件的设计和分析提供理论模型和分析手段

螺旋十字燃料（HCF）组件是由十字形横截面的旋扭燃料棒紧密排布构成的革新燃料组件，相邻燃料棒在不同高度平面接触形成支撑。HCF组件具有比换热面积大、无格架、自定位、强搅混的特点，在高功率密度下仍能保持较高的热工安全裕量，可在减小堆芯尺寸的同时提高堆芯输出功率。目前，俄罗斯已经成功将HCF组件用于核动力破冰船，实现了高安全、高紧凑和高功率密度的船用核动力系统。鉴于螺旋燃料的独有优势，美国也积极推进HCF组件相关的基础和应用研究，已经完成先导组件的设计和制造，计划近期进行堆内性能考核试验。然而，由于燃料组件的敏感性，公开发表的研究成果极少。我国螺旋十字燃料相关的研究尚处于起步阶段，对该型燃料流动传热和交混特性的认知仍存在较大不足。.本项目针对HCF棒束通道内的单相和两相流动结构开展基础性的实验和数值分析。通过流场可视化技术，获得棒束通道内单相旋流流场特性、两相相场结构和子通道间隙的交混机理，发现HCF棒束通道内的交混机制为流动后掠交混，湍流交混可忽略，建立HCF棒束组件通道的子通道交混理论模型。通过三维数值模拟研究，获得全流域单相、两相相场的时空结构分布和加热面单相对流传热、沸腾传热特性，开发单相/两相流动阻力和传热定量预测模型。建立适用于HCF组件持续变流通截面形状、变间隙宽度的子通道分析模型，基于本项目开发的流动传热和交混模型，改进子通道分析程序CTF，使其适用于HCF棒束通道单相、两相流动传热和交混特性研究，支撑HCF燃料组件设计和安全分析。