Melt jet-breakup and fragmentation phenomena in nuclear reactors: A review of experimental works and solidification effects

During severe accidents at Nuclear Power Plants (NPPs), fuel-coolant interaction (FCI) is a critical event in which the melt released from the core region comes into contact with the coolant. The melt may eject in the form of a melt jet and threaten the integrity of the NPP. Therefore, fragmentation of the melt jet and quenching of particulate fragments from the melt jet are invaluable from the viewpoint of safety assessment. To assess the integrity of an NPP, melt fragmentation phenomena that affects quenching and sustainable cooling of the debris bed are important factors that must be predicted and evaluated precisely. The present review summarizes experimental works on the FCI phenomenon, especially, fragmentation of a melt jet during a severe accident in an NPP. In addition, special attention is paid to solidification effects. Based on the literature survey, we discussed the dominant factors governing the fragmentation mechanisms. Furthermore, we discuss the applicability of various models for estimating these phenomena.