Effects of agitation in a shallow pool on atomization behavior of a jet

Masaki, Naoto*; Kaneko, Akiko*; Horiguchi, Naoki   ; Yoshida, Hiroyuki  

During a severe accident in nuclear reactors, melted fuel rods and other materials may fall as liquid jets into the pool of cooling water remaining in the lower head of the pressure vessel. From the viewpoint of preventing accident development, the clarification of cooling and solidification mechanisms with atomization in the cooling water is essential. Many researchers performed experimental and analytical work to understand jet behavior and atomization in a deep pool. In the case of insufficient water depth, i.e., shallow water pool, there are a few reports in both experimental and analytical approaches. The reports of shallow pools show that atomization occurs even after the jet has impacted the bottom wall. However, the mechanism has not been understood. In this study, we assumed that instability due to velocity difference affects the atomization in a shallow-water pool and tried to give a velocity difference to the interface as an agitation using a vortex provided by a stirrer to examine whether the agitation affects atomization. We conducted visualization and measurement experiments using a simulated liquid-liquid two-fluid system in the shallow pool. As a result, an agitation using a vortex occurred in the pool. The number of droplets and the rise time of the number changed increasing the stirrer frequency. This result suggests that the agitation contributed to the atomization.