Study On Fragmentation Behavior Of Lead-Bismuth In Contact With Water During SGTR Accident In The Lead-based Reactor

Lead-Bismuth Eutectic (LBE) has been chosen as the promising candidate materials for primary coolant of China LEAd-based Reactor (CLEAR) due to its favorable thermal-physical properties. In the pool-type structure design of CLEAR, steam generator units (SGU) are directly placed inside the reactor vessel to conduct the heat exchange between the highly pressurized water and molten LBE. When the steam generator tube rupture (SGTR) accident happens, a sudden vaporization of the discharged highly pressurized water will be induced and a steam explosion phenomenon will be initiated in the accident, and the strong impact pressures could evoke structure risks. At present, the experiments focused on the study of SGTR accident in lead-based reactor are rare. In particular, the knowledge of the phenomena of fragmentation and steam explosion induced by the interaction of LBE and water in the initial phase of the accident was limited. Moreover, the theoretical models were still in debate. Hence, it is particularly important to carry out the experimental study in this field.An observable experimental facility was designed and built to study the interface behaviors during the contact of molten LBE and water. In this paper, it is necessary to conduct the LBE droplet/water contact interaction which focuses on the fragmentation procedure to reveal the original process of the SGTR accident. Based on these experiences, the molten LBE jet and water interaction has been further performed to investigate the accident phenomenon when a larger contact interface has occurred. Besides, the energy of the strong impact pressure induced by the steam explosion in this paper has been assessed, and the physical mechanism of this interaction has been explored. The primary contents and results are summarized in the following text:1. A series of experiments of molten lead-bismuth alloy droplet with water interaction have been conducted. The results showed as follows:the fragmentation of molten LBE was accleratecd by the increase of molten LBE temperature (250～500℃) and water temperature (25～80℃). There was a thermal interaction zone (TIZ) exsited in the fragmentation process of molten LBE alloy droplet in water, in which the phenomenon of violent boiling could be easily happened.2. A series of experiments of eutectic lead-bismuth alloy jet with water interaction have been carried out and the effect of temperatures, the falling heights and the released diameters of molten LBE jet, as well as the water temperatures were investigated in the experiment. The results were follows:1) with the increase of the temperatures (300℃ ～600℃), falling heights (210mm～450mm) and the released diameters (5mm-8mm) of molten LBE as well as the increasing of water temperatures (20℃～80℃), the fragmentation behaviors were more fully and completely.2) The well-known theory of underwater explosion shock wave was used to evaluate the explosion energy induced by the steam explosion in the experiment.3) Comparison of the debris size of molten LBE obtained with fragmentation theory showed that the debris size was closed to the Kelvin-Helmholtz (K-H) instability theory and critical Weber number theory, so it was regarded as the dominant physical mechanism of the molten LBE fragmentation in the present study.In summary, the experiments were carried out to investigate the interaction of high temperature molten lead-bismuth alloy in water in this research. Some fundamental experimental data and rules about the interaction of lead-bismuth and water were obtained. It provided valuable data to estabilish the integral theoretical model of lead-bismuth alloy/water interaction, and also supplied some theoretical and data supports for the safety analysis of SGTR accident in CLEAR reactor.