板状燃料元件堆芯传热稳定性特征研究

Plate type fuel element is widely used in integral and test reactor cores , for it can allow higher power density, deeper fuel burnup and smaller core volume because of its compact structure. In the semi-closed narrow gap rectangular channel, physics-structure coupling effect under low pressure condition will lead to very complex coolant flow and heat transfer phenomena. In this project, the thermal-hydraulic phenomena of coolant in channel of the fuel assembly of NP engineering will be studied. The characterized relationships among the Onset of Nucleate Boiling, the Onset of Significant Vaporization and the Onset of Flow Instability will be explored, as a result, the precondition, judgment method and evolutionary character about flow excursion can be obtained. And the effects of thermal hydraulic parameters on the pressure drop and heat transfer characteristics of coolant will be studied systematically. And, the pressure drop and heat transfer models in the narrow gap rectangular channel will be proposed. On these bases, combining numerical simulation and experimental study, by the investigation of effects of thermal hydraulic parameters on the pressure drop and heat transfer, complete two-phase flow instabilities classification, criterion and improvement measures can be obtained. It is believed that all the achievements will not only provide basis for fuel assembly flow channel design and optimization of thermal hydraulics, but also enrich the flow and heat transfer theories of coolant in the narrow gap rectangular channel.

板状燃料元件因结构紧凑，有利于提高堆芯功率密度、更深的燃耗深度、减小堆芯体积等特点而被广泛应用在一体化反应堆和实验堆芯中。半闭式窄间隙矩形通道在低压运行下的物理-结构耦合效应给冷却剂带来了异常复杂的流动和传热现象。本项目立足于NP工程反应堆中的板状燃料组件，围绕窄通道内传热稳定特性开展研究。主要研究核态沸腾起始点、净蒸汽产生点与流动不稳定起始点的特征关系，获得冷却剂流量漂移的前提条件、判定方法和演化特征；同时系统研究冷却剂热工参数对压降和换热特性的影响规律，给出窄间隙矩形通道内两相流压降与换热模型；在此基础上，采用数值模拟和实验相结合的手段，研究冷却剂热工参数对流动不稳定性的影响规律，从而获得完备的两相流不稳定性分类方法、判别准则和改善措施。本项目的完成将为板状燃料组件流道设计及热工水力学优化提供依据，同时在学术上将丰富冷却剂在窄间隙流道内的流动理论和传热机制。

板状燃料元件因结构紧凑，有利于提高堆芯功率密度、可以增强换热、减小堆芯体积等特点而被广泛应用在小型反应堆和实验堆中。窄间隙矩形通道在低压运行下的两相沸腾流动带来了异常复杂的流动和传热现象。本项目立足于NP工程反应堆中的板状燃料组件，围绕窄通道内传热稳定特性开展研究。. 本项目首先开展了窄矩形通道内的流动传热特性研究。根据NP反应堆的尺寸和热工参数，自主设计并搭建了一套完整的窄矩形通道热工水力实验回路，实验测量了窄矩形通道内冷却剂流动传热过程中的温度、压力、流速等热工水力学参数，并对传热特性和压降特性进行了研究。并基于CFD和相变模型，实现了窄通道内流动沸腾的数值模拟，计算了不同工况下的ONB点以及传热系数。. 在流动不稳定性方面，实验研究了不稳定性起始点的影响因素，并提出了预测OFI点的经验关系式。结合可视化实验装置，对流动不稳定性发生过程中的气泡行为和流型变化进行了观察和记录，发现了不同种类的不稳定性流型转变特征类型，并提出了一个划分准则。利用系统程序实现了并联通道不稳定性边界的计算。完善了系统不稳定性的影响因素分析，并提出了抑制流动不稳定性的方法。. 本项目获得的研究成果在一定程度上掌握了板状燃料元件堆芯传热及流动不稳定性的基本特征，为板状燃料组件的反应堆安全设计提供参考和指导，同时在学术上也丰富了冷却剂在窄间隙流道内的流动理论和传热机制。