In the event of a severe accident, past experiences such as Three Mile Island and Fukushima Daichi have shown that the reactor core of a light-water nuclear reactor, if not properly safeguarded, could go through a meltdown. This will be followed by the formation of a corium, a mix of molten fuel elements, and liquid metals from the Reactor Pressure Vessel (RPV). In the worst-case scenario, a melt through from the RPV can occur and lead to the spreading of the corium, in the form of a molten element’s jet impinging on a flat concrete structure of the Primary Containment Vessel (PCV). To enhance the decommissioning and the safety procedure, scope of the present article is to deepen the understanding of the phenomena involved in the mentioned scenario, mainly jet-instability and molten material spreading. In the present study, experiments were carried out, by using corium simulant materials such as Copper and Tin, to investigate the link between the instability of the gravity-driven molten metal jet and the impinging followed by its spreading over a flat area.

在发生严重事故的情况下，诸如三哩岛和福岛第一核电站等过去的经验表明，如果没有适当保护，轻水核反应堆的反应堆芯可能会发生熔毁。随后将由反应堆压力容器（RPV）形成皮质，熔融燃料元素和液态金属的混合物。在最坏的情况下，RPV可能会发生融化并导致皮质扩散，其形式是熔融元素的射流撞击到主安全壳（PCV）的扁平混凝土结构上。为了增强退役和安全程序，本文的范围是加深对涉及上述场景的现象的理解，主要是射流不稳定和熔融材料扩散。在目前的研究中，