Following an accident, the gas speeds induced by natural convection inside a nuclear power plant containment can be of the order of several tens of cm/s, i.e. two orders of magnitude greater than the settling velocities of the generated aerosols. Accordingly, the airborne fission product particles will most of the time follow the streamlines rather than uniformly settle under the lone influence of gravity, as is traditionally modeled in lumped-parameter containment codes. As a result, the controlling phenomena for aerosol removal need to be assessed using a more rigorous treatment of the forces acting on the particle. The CFD code CFX4.4 is used for to compute the flow field and particle tracks in the Phebus containment during steady state conditions. It is found that the calculated half-lives of the aerosols are within 25% of the experimental values. In addition, 80 to 90% of the particles deposit on the bottom section of the containment, which is also consistent with experiments findings. In stark contrast to the classical treatment, it is found that the aerosol decay constant is a much weaker function of particle size.

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