EXPERIMENTAL STUDY OF BUBBLE MIGRATION CHARACTERISTICS IN MCCI MOLTEN POOL

When the molten core-concrete interaction (MCCI) occurs in a reactor, the high-temperature melt may melt through the concrete bottom plate and form a molten pool. At the same time, due to the heat generated by decay heat and chemical reactions, the concrete will decompose and produce a large amount of water vapor and carbon dioxide and other gases. After entering the molten pool, these gases will migrate within it and have a stirring effect on the molten pool. This study focuses on the phenomenon of gas migration in MCCI molten pool, and establishes an experimental platform for studying the migration characteristics of gas in MCCI. A 25% glycerol aqueous solution was used as a substitute fluid for the melt, and helium gas was used as a substitute gas to study the migration characteristics of gas in the molten pool. The experimental platform has 49 ventilation holes, which can simulate the migration of bubble groups in the molten pool, and each ventilation hole can adjust the apparent gas velocity separately. The experiment mainly measured the migration velocity, equivalent diameter, and aspect ratio of bubbles. By adjusting the gas flow rate, the changes in these three parameters were studied to obtain the migration characteristics of bubbles. Through this study, it was found that with the increase of apparent gas velocity, the equivalent diameter of bubbles increases, the aspect ratio of bubbles decreases, and the final stable velocity of bubble migration increases. Through this study, the variation patterns of bubble size, shape, and velocity under different gas flow rates were obtained, which can provide support for systematic calculation programs to calculate chemical reactions, fission product release, and molten pool stratification in MCCI processes.