A multidimensional model for the description of the fluid-dynamic behaviour of the atmosphere inside the reactor containment when spray systems are used is presented. The model accounts for the presence of a condensable specie, a noncondensable specie and water droplets. Both the gas and the dispersed phase have been considered as continua. The dynamic, thermal and mass interactions between the gas and the dispersed phase have been modelled referring to the correlation for an isolated particle flowing in a gas at rest. The model has been validated concerning the dynamic interactions on the basis of a comparison with experimental tests. A satisfactory agreement has been observed between experimental and numerical data.