Visual investigation on the breakup of high superheated molten metal during FCI process

Highlights: • Visual investigation on the breakup process of high superheated molten metal was carried out. • The mechanism of the breakup process was analyzed in detail under different working conditions. • Two dimensionless parameters were proposed to predict the occurrence of the breakup process. - Abstract: A visual experimental investigation was carried out to study the breakup process as high superheated molten metal falling into the subcooled coolant during the severe accident of a nuclear reactor, namely the FCI (fuel coolant interaction) process. Deionized water was used as the coolant, and the aluminum, lead, and bismuth were used as the metal samples. In this study, the characteristics of FCI process with different molten metals, different molten metal mixtures, different coolant depths, different coolant temperatures and different initial molten metal temperatures were analyzed in detail. The molten metal breakup process was observed by a high speed camera during this experimental study. It was found that the breakup process was restricted significantly by the high melting point of the metal, large surface tension, large viscosity, high thermal conductivity, and low specific heat of the molten metal. Meanwhile, increasing the coolant temperature and the temperature of molten lead could obviously restrict or prevent the breakup process. Finally, two dimensionless parameters were proposed to predict the occurrence of the breakup process.