Large pools may have a very wide spectrum of geometric configurations. Heat transfer in one very limited zone in terms of volume (e. g. by condensing injected steam or by heat transfer from a passive containment cooler) does not imply homogeneous or nearly homogeneous temperature in the pool. Many containment phenomena require steam-liquid interface. Steam discharge into a suppression pool of boiling water reactor is a good example of this case. After break-up of the originally created bubbles in the suppression pool, the subsequent formation of bubble plumes takes place. Consequently, complete condensation occurs and this induces mixing in the pool, the process is being determined by single and two-phase natural circulation. It is important to understand the break-up and plume-stirring process and mechanisms, because the system pressure ultimately controlled by the pressure in the vapour space above the water surface in the suppression chamber. This pressure is the sum of the partial pressures of steam and gas, the former controlled by the temperature at the pool surface. In turn, the pool surface temperature depends on the efficiency of steam condensation in the pool, and the degree of mixing in the pool.

The following is a listing of the steam-liquid interactions related phenomena:

• Direct contact condensation of steam in pool water

• Bubble formation and break-up and the subsequent formation of bubble plums

• Break-up and plume-stirring process and mechanisms inducing mixing in the pool

As example for steam-liquid interactions can be given passive containment cooling (PCC) venting into the suppression pool of ESBWR and also injection of steam-gas mixture through a downcomer vent line into the suppression pool.