Mitigation of gas entrainment in swirling free surface flows

Abstract

Gas entrainment presents a safety challenge within sodium-cooled fast reactors. This problem is similar to two-phase free surface interactions in a Taylor–Couette flow characterized by a large annulus gap (small radius ratio, η≈0.333) and highly turbulent swirling flows (Re≈105). The aim of the current work is to test strategies that could mitigate this phenomenon. A three-dimensional numerical model of the primary sodium pump annulus region involved in gas entrainment due to shaft rotation was developed, and turbulent swirling flow that occurs in the annular gap between the vessel and the shaft is investigated. The influence of baffle plates mounted on the stationary vessel with and without porosity was examined during the study. The simulation results revealed that submerged porous plates placed on the outer cylindrical wall both delayed vortex breakdown and suppressed shear waves near the surface. Both these effects substantially delayed gas entrainment into the liquid.