Pre-calculations have been performed for the spray experiments that are planned to be performed with the PPOOLEX test facility at the Lappeenranta University of Technology (LUT). PPOOLEX is a downscaled model of a BWR containment, which has pressurized drywell and wetwell compartments. Installation of sprays in the wetwell has been studied. The main interest was their interaction with the stratified pressure suppression pool.
The mixture of gas and liquid-water was described with Euler-Euler two-phase model, where the Discrete Particle Model (DPM) was used for spray droplets. The interaction of the droplets with the wetwell water pool was described with User-Defined Functions, where mass, momentum and enthalpy sources from the droplets to the water pool were modeled.
Initially, the water pool was assumed to be thermally stratified. Four spray nozzles installed close to the ceiling of the wetwell were considered. Each spray nozzle injected a mass flow rate of 17.8 liters/min, which corresponds to the rise of the water level by 1.5 cm within 60 s.
In the CFD simulation, the cooling of the water surface by the spray droplets was resolved. According to the simulation, the pool is partially mixed and the temperature at the pool bottom increases slightly. According to the simulation, it seems that the cooling of the pool surface by spray may eventually mix the pool. The length of the simulation is, however, only 60 s, which is fairly short. Longer simulation would be needed to see full mixing of the pool. In addition, grid sensitivity study should still be performed in order to rule out the role of numerical diffusion in the simulation result.