竖直锡包壳熔化过程的实验分析和数值模拟

发布时间：2018-02-05 17:00

本文关键词： 熔化实验包壳熔化单根燃料棒破裂失效凝固/熔化　出处：《中国科学技术大学》2017年硕士论文　论文类型：学位论文

【摘要】：核反应堆严重事故的研究是近几十年来核安全领域的重要课题。自三哩岛事故后,世界多国的多个组织或者机构分别进行了不同类型的大型实验,探究严重事故中出现的各种现象和机理,同时也发展了如SCDAP/RELAP5和MELCOR等多种严重事故系统分析程序。单根燃料棒的熔化过程作为严重事故中堆芯损坏的重要环节,决定着事故的发展走向和严重程度。然而,现有的对堆芯熔化中燃料棒的熔化的相关认知依然缺乏,严重事故分析程序对这一过程的处理也多做工程简化或忽略。以单根燃料棒的熔化过程为研究目的,本文通过实验模拟和数值计算的手段对锡包壳的熔化过程进行详细的研究。模拟实验采用低熔点金属锡作为熔化对象,通过重铸和再加工,形成不锈钢加热棒外裹特定厚度的锡包壳。通过改变加热功率、包壳厚度以及环境条件等影响条件,分析对包壳的熔化过程的影响。实验采用可视化,并用DV机记录熔化过程中的形态变化。实验结果归纳了熔化过程中的三个阶段:加热阶段、熔化阶段和解体阶段,其中的熔化阶段根据出现的现象分为液滴析出、肿胀变形和"熔孔"三个环节。针对其中的肿胀变形和"熔孔"现象,引入圆柱壁应力模型进行定性分析,得出肿胀变形程度取决于包壳厚度。对包壳出现的"熔孔"现象进行定量分析和预测,得出包壳"熔孔"破裂失效高度随着加热功率升高而降低,而且与加热功率和熔化时间呈函数关系。最后,本文对比了不同的环境条件对熔化过程产生的影响。数值计算采用成熟CFD软件ANSYS FLUENT,利用其中的凝固/熔化模型与VOF耦合对实验进行二维计算。与实验结果类似,计算过程分为加热、熔化、破口和再凝固等4个阶段。熔化阶段中存在加热棒加热和高温液体向下汇聚的两种热量传递过程。通过提取原形状区域的固相分数为参考量,定量分析了破口产生、加热功率和环境温度对熔化的影响。结果表明,破口的产生对熔化的过程具有转折性的意义,破口高度与环境温度存在较大的依赖关系。
[Abstract]:Study on severe accident of nuclear reactors is an important research topic in the field of nuclear safety in recent decades. Since the Three Mile Island accident, many countries in the world a number of organizations or institutions were large different types of experiment, various phenomena and mechanism in case of a serious accident inquiry, has also developed such as SCDAP/RELAP5 and MELCOR and other serious accident system analysis program. The melting process of single fuel rod as a serious accident in the reactor core damage important link, determines the development trend and the severity of the accident. However, the existing of melting of fuel rods and core melt in the cognition is still lacking, analysis procedures of the process is more simplified or ignore the serious accident. In the melting process of a single fuel rod for the purpose of the study, through experimental simulation and numerical calculation method of tin cladding melting process of detailed research . simulation experiment with low melting point metal tin melting as object, and then processing by recasting and forming stainless steel heating rod coated with a specific thickness of the tin cladding. By changing the heating power, cladding thickness and environmental conditions affect the conditions, influence analysis of melting process of cladding. The experimental visualization, and morphological changes the DV record in the melting process. The experimental results are summarized in three stages: the stage of heating in the melting process, melting stage and disintegration stage, the melting stage according to the phenomenon of droplet is divided into precipitation, swelling and "melt hole" three links. The swelling deformation and "melt hole" the phenomenon, introducing cylinder wall stress model and qualitative analysis, the swelling deformation depends on the cladding thickness of cladding. The "melt hole" phenomenon for quantitative analysis and prediction, the shell of "melt hole" with the height of fracture failure The heating power is increased, and the function relation with the heating power and the melting time is. Finally, this paper compares the effects of different environmental conditions on the melting process. The numerical calculation of the mature CFD software ANSYS FLUENT, by which the solidification / melting model coupled with VOF on experimental two-dimensional calculation. Similar to the experimental results, calculation the process is divided into 4 stages of heating, melting, solidification and then break. There are two kinds of heat heating and high temperature liquid downward collection melting stage transfer process. Through the solid fraction extract the original shape as a reference, quantitative analysis of the breach, effect of heating power and environmental temperature on the melting results. That breach of melting process of turning the meaning of existence depends greatly on the gap height and ambient temperature.

【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TL364

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