Study of bubble migration characteristics in downward flow under SGTR accidents of LFR with similarity experiments.

• The bubble migration behavior in flowing liquids is studied with similarity experiments. • Visualization of migration behavior of bubbles in size of 1∼8 mm in downward flow. • The bubble theories in stagnant liquids are applicable for bubbles in downward flow. • The empirical correlations of slip velocity and drag coefficients are established. Under the Steam Generator Tube Rupture (SGTR) accident scenario of Lead-cooled Fast Reactor (LFR), the second loop coolant pressurized water interacts vigorously with the primary loop coolant LBE, resulting in the generation of a large number of bubbles. These bubbles may migrate to the core along with the flowing liquid metal, causing reactive disturbances and even deterioration of core heat transfer. Aiming at the bubble migration issue in the flowing liquid under SGTR accident conditions, several similarity experiments are performed by injecting gas into downward flow by utilizing visualization technology to simulate the bubble migration behavior in flowing Lead-Bismuth Eutectic (LBE). The bubbles with diameter of 2 ∼ 8 mm are injected into downward flows with flow velocities from −350 to −235 mm/s, and their migration process are captured by the high-speed camera. The comparison of the existing bubble rising theories in stagnant liquid and experimental results shows that the basic research methods for bubble terminal velocity and drag coefficient are applicable for the bubble in downward flow with certain errors. An empirical modified correlation is recommended for bubbles with equivalent diameters from 2 mm to 8 mm in downward flow based on experimental data and dimensional analysis. These data can provide a reference on analyzing bubble migration process in flowing liquid under SGTR accidents. [ABSTRACT FROM AUTHOR]