Experimental investigation on trigger dynamics of molten droplet under external disturbance pressure during fuel coolant interaction

摘要: Fuel-coolant interaction (FCI) remains one of the most complex challenges in severe accident research, with the triggering process being a key aspect that may govern subsequent fine fragmentation and potential steam explosions. In this study, the evolution characteristics of droplet–water interactions under external disturbance conditions were investigated using a self-designed FCI experimental setup. Analysis of the experimental observations reveals that cavity formation helps reduce the drag force on the droplet, thereby increasing its peak velocity. However, external disturbance pressure can disrupt the cavity, leading to a reduction in the droplet’s peak velocity. Furthermore, it was found that an increase in external disturbance pressure tends to raise the peak value of the droplet expansion rate, thereby promoting the fine-fragmentation process. This effect holds regardless of the initial droplet temperature, coolant temperature, or even when using droplet materials such as lead, which are generally considered unfavorable for steam explosions. Comparative analyses indicate that higher external disturbance pressure may shorten the triggering time of the droplet surface and enhance the trigger intensity. These findings provide important phenomenological insights for further investigation of the triggering mechanisms in the initial stage of fuel-coolant interactions.