Euler-Euler CFD simulation of high velocity gas injection at pool scrubbing conditions

Pressure relief by blowdown is one of the most important measures to prevent excessive pressures in the primary circuit or containment in the event of severe nuclear accidents. Pool scrubbing can significantly reduce the release of radioactive materials, e.g. aerosols, to the environment during the pressure relief. The decontamination factor indicating the particle retention efficiency depends, among other factors, on the hydrodynamic conditions of the gas-liquid two-phase flow inside the pool. In the present work, the hydrodynamics in two typical pool scrubbing experiments is investigated with the two-fluid bubbly flow model, and the influence of some key factors including bubble diameter, nozzle submergence as well as interaction models is analysed. One case is a rectangular pool and the other is a cylindrical column, and their injection Weber number is around 2×103 and 4×105, respectively. The numerical results show that the void fraction and velocity field expand from the central region where the nozzle is located to the whole cross section, as the distance from the nozzle exit increases. The profile as well as its development depends largely on the bubble size and the interaction force model. It reveals that in the monodisperse simulation the tuning of bubble diameter is necessary for achieving good agreement, which is however awkward for high velocity gas injection. More information is required for properly describing the bubble size distribution as well as its evolution in pool scrubbing conditions. Furthermore, the experimental data show clear drag reduction in the bubble swarm generated by the gas jet, and further investigations on the mechanism and model improvement have to be done.