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Containment
Thin liquid film
Severe Accident
Systems behaviour
The physical phenomena, occurring during postulated accident scenarios in the containment of a Light Water Reactor (LWR), associated with liquid film formation by steam condensation and liquid film re-evaporation have safety relevance because affect the overall containment pressure and the distribution of gases (air, steam, hydrogen) and radioisotopes within the containment compartments.
The heat/mass transfer processes associated with the flow of the liquid film in the wall are not properly addressed in most of the LWR containment codes, including advanced Lumped Parameters (LP) codes, where the film dynamics is treated in a very rudimental way and using empirical parameters. Moreover, mechanistic treatment of film tracking is still difficult even within the two-fluid model approach used in the modern Computational Fluid Dynamics CFD codes, as thin liquid film flow (and hold-up when the film is thinner than a certain limit), depends on surface irregularities and wetting dynamics, and the numerical resolution of a thin film (thinner than 0.5 mm) would be computationally too expensive. Indeed, the thickness of the film, its velocity under transient conditions, the partition of the wall between wet and dry portions, the heat transfer between the structures and the film, etc. are all variables which should be included in the physical models for representing the basic phenomena of condensation and re-evaporation.
The main objectives of the research program proposed here are to advance the knowledge on liquid film dynamics with condensation and re-evaporation phenomena taking place and to develop physical models suitable for improving advanced LP and CFD codes used for nuclear safety analysis. The advanced LP ASTEC code is chosen as reference code for assessing the new models analyzing experimental cases. The CFD-type GOTHIC code will be used for identifying the experimental conditions which would allow the correct representation of the investigated phenomena.
