Study on gas entrainment evaluation method from free liquid surface in a sodium-cooled fast reactor; Evaluation of gas entrainment phenomena under the different outlet conditions

Endo, Kazuki*; Kobayashi, Shunsuke*; Jasmine, H.*; Takeda, Jotaro*; Sakai, Takaaki*; Matsushita, Kentaro  ; Ezure, Toshiki 

When the gas entrainment (GE) phenomenon occurs, where argon (Ar) cover gas is entrained in the coolant at the liquid surface in the reactor vessel of a sodium-cooled fast reactor, Ar bubbles may cause reactivity disturbances when they pass through the core. In this study, the number and type of GE events were measured under different outlet shapes in a rectangular open channel GE test section with a bottom slit, and the effect of change in downward flow velocity gradient on GE was analyzed by numerical analysis. The outlet shapes were two types: one with an outlet only below the slit (Outlet channel 1) and one with an outlet both above and below the slit (Outlet shape 2). As a result, it was confirmed that the number of GE events tends to increase with increasing inlet velocity in Outlet channel 1 while is significantly reduced in Outlet channel 2. The numerical analysis revealed that the decrease in the downward flow velocity gradient to the bottom suppressed GE in Outlet channel 2.