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Airborne particles produced by droplet collision in spray systems used for nuclear reactor applications



Congress title :CFA 2007/2008 - 23ème Congrès Français sur les Aérosols
Congress location :Paris
Congress date :16/01/2008

Summary

During the course of a hypothetical severe accident in a Pressurized Water Reactor (PWR), hydrogen can be produced by the core oxidation and distributed into the whole containment. In order to limit the risk of detonation, spray systems can be put at the top of the containment to ensure a mixing of the atmosphere, to reduce the total pressure, to cool down the containment walls, and to wash-out the eventually existing airborne fission products. The efficiency of the spray system depends on the evolution of the droplet size distribution along the height in the containment, linked to gravity drag forces, heat and mass transfers with the surrounding gas, and droplet coalescence. Spray system in reactor applications is composed of over 500 interacting water droplet sprays. Droplets are between 100 and 1000 µm large, and are used under pressure (2-3 bar) at temperature between 20 and 60 °C, and under gaseous mixture composed of water steam, hydrogen and air, with airborne particles. In this work, droplet collisions, with diameter between 200 and 700 µm, for Weber number from 20 up to 2600 have been studied. Experiments have been performed with water for different impact parameters and different droplet sizes. Both classical outcomes, described in literature and new outcome regimes, for higher impact velocity, have been observed and could lead to airborne particles generation as microdroplet, after collision.

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