压水堆燃料棒流致振动非线性复杂响应研究

Flow-induced vibration of fuel rods caused by the coolant flow is the key factor which affects the operation safety and stability of reactors. It is also a technique problem concerned by the scientists in the field of reactor structure mechanics analysis as well. The flow-induced vibration can cause the grid-to-rod-wear and even lead to structural damage in severe cases. Analysis methodology of refined flow field characteristics of fuel assembly has not been formed and the flow-induced vibration mechanism of fuel rod has not been specified so far. The fuel assembly in the Pressure Water Reactor is taken as the research objective in the project, and the study contents are as follows: building the refined fuel assembly model for the flow field characteristics analysis to obtain accurate flow-induced vibration excitation force for the fuel rod, and establishing the nonlinear dynamics model of fuel rods subjected to coolant flow considering loose of the supports, analyzing the flow-induced vibration stability and dynamic characteristics, exploring the effects of variation of flow field and structure design parameters on the fuel rod vibration behavior. Research achievements in the project will provide preconditions for flow-induced vibration abrasion study of the fuel rods and theoretical basis for optimization for structure design of the fuel assembly.

冷却剂流动引起的燃料棒流致振动是影响反应堆运行的安全性与稳定性的重要因素，也是从事核反应堆力学分析的专家学者们长期关注的难题。燃料棒的流致振动会引起的包壳磨蚀，严重时甚至会导致结构的直接破坏。目前，精细化燃料组件的流场特性分析方法尚未形成，燃料棒的流致振动机理尚不明确。本项目以压水堆燃料组件为研究对象，拟开展以下研究：建立精细化燃料组件的流场特性分析模型，获得准确的燃料棒流致振动激励力；建立考虑支撑松动的燃料棒在冷却剂作用下的非线性动力学模型，进行流致振动稳定性和动力学特性研究，探索流场参数、结构设计参数对燃料棒流致振动行为的影响。本项目的研究成果为燃料棒的流致振动磨蚀研究提供前提条件，为实现结构设计的优化提供理论依据。

核反应堆冷却剂的流动会引起燃料组件中的燃料棒与格架的相对位移，进一步导致燃料棒的包壳磨损，从而引起燃料的熔融甚至核泄漏等严重的核事故。由冷却剂流动导致的燃料棒振动不可避免，因此，揭示流场、结构等参数与燃料棒流致振动的影响规律，明确燃料棒流致振动的深层机理，从结构和流场设计以及材料选型方面降低磨损量是专家学者们关注的重点。本项目以压水堆燃料棒为研究对象，构建了冷却剂冲刷下，频域和时域的燃料棒流体激振力计算方法，提出了考虑格架支撑失效的燃料棒非线性动力分析模型，发展了针对湍流激振、涡激振动和流弹失稳的燃料棒流致振动幅值及风险预测方法。在此基础上，分析了结构设计和流场参数对燃料棒流致振动响应的影响，突破了燃料棒的流体载荷计算、流致振动风险快速评价等关键问题。本项目的研究成果可用于同类型的（棒束或管束）结构的流致振动分析评价，为结构设计提供有力支撑。