基于替代材料的燃料棒熔化实验研究

为获得核反应堆燃料元件熔化以及熔融物扩展和消熔过程中的关键实验数据，本研究将典型压水堆中的燃料棒元件作为研究对象，在堆芯材料严重事故现象可视化研究实验装置FROMA上开展了低温条件下的燃料棒熔化实验。实验采用锌-铝的替代材料燃料棒，开展了单棒的熔化凝固可视化研究，获得了严重事故过程中燃料棒包壳的瞬态轴向温度分布特性以及熔融物扩展、迁移和再定位的动态过程。本研究基于实验数据对熔融物的流动、扩展和凝固、迁移等相关的物理现象和过程进行深入分析，为反应堆严重事故现象分析模型的开发提供了数据支持。

Experimental Study on Fuel Rod Melting Based on Alternative Material

The melting process of fuel elements is the crucial link of severe accidents. The phenomenon of melting of fuel rods and migration of molten materials involves complex physical and chemical transformation and they are coupled with great uncertainty and are difficult to predict accurately. Therefore, it is necessary to use advanced experimental method to conduct research to investigate the mechanism and behavior characteristics of the melting of fuel rods and migration of molten materials. In order to obtain key experimental data in the process of nuclear reactor fuel rod melting and the molten materials migration, the FROMA (fuel rod melting progression apparatus) was established and a series of experiments were carried out under low temperature. The experiments were carried out using zinc-aluminum structure fuel rods which focused on a series of key phenomena such as the possible damage and melting of fuel rods in severe accidents. The transient axial temperature distribution characteristics of the fuel rod cladding and the dynamic process images of melt expansion, migration and relocation during a severe accident were obtained. Based on the experimental data, an in-depth analysis of the physical phenomena and processes related to the flow, expansion, solidification and migration of the melt were conducted and the dynamic process law of the melt’s expansion and migration in the reactor during an accident was obtained. Rod melting and the flow, expansion, solidification and melting mechanism of the melt in the interstitial channels of the rod bundle were also revealed. The research results in this paper reduce the uncertainty of the existing severe accident analysis procedures and fill the insufficiency of domestic research on the severe accident of the fuel rod melting. The main conclusions are as follows. 1) The melting process can be divided into three parts: heating, melting and disintegration under the low heating power in the low temperature experiments. During the melting process, the test rod will appear some obvious phenomenon such as bubbling, cladding collapse, deformation displacement and molten materials drop. 2) FROMA can visualize the process of cladding bubbling, rupture and core material melting, migration and relocation. 3) Dynamic image parameters, temperature, power and droplet size are obtained in the experiment and it can be used for the preliminary verification and optimization of models in some programs such as MELCOR, MPS, and ABAQUS-FUEL. The experimental research will help reveal the mechanism of the key phenomena during severe accidents and reduce the uncertainty of existing severe accident analysis programs. It can also provide key data support for China’s independent development of related physical models. The date can be finally applied to the preliminary verification and optimization of the models which can be used to analysis nuclear reactor’s design and safety and it’s also significant for engineering application.