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In nuclear decommissioning and dismantling operations, a dynamic confinement is applied to all openings in order to prevent the transfer of pollutants outside depressurized enclosures and to insure the safety of workers. To guarantee an efficient dynamic confinement, ISO 16647 and ISO 17873 recommend to maintain a constant value for inward inflow velocity near the opening depending on the level of radioactive pollution hazard. The main purpose of this work is to identify possible conditions under which flow inversions near the opening may lead to gaseous pollutant leakage and then failure of the dynamic confinement. We aim at quantifying the amount of this backflow. Leakage from an experimental ventilated enclosure with a small opening on its frontal wall has been investigated. Laser flow visualizations and Particle Image Velocimetry (PIV) measurements showed that the presence of an additional turbulent jet flow in competition with the inward confinement flow is among the main causes leading to leakage through opening. The gas tracing technique has provided experimental data to quantify the pollutant backflow and allowed us to compare different scenarios. We conclude that a new criterion based on local aeraulic conditions near the opening is relevant to guarantee an efficient confinement.

Experimental study of backflow air leakage through an opening from a depressurized enclosure