Simulation of backflow during the dynamic containment of airlocks

Abstract

Decontamination processes in nuclear facilities require the implementation of ventilated airlocks around the contaminated equipment to prevent leakage of radioactive materials toward the surrounding environment. To ensure compliance with the recommendations of an efficient dynamic containment in nuclear facilities, which are provided by the ISO 17873 standard depending on maintenance and dismantling sites in nuclear facilities, depression must be ensured in the room where the contaminated equipments installed by using exhaust fans. This study focuses on two main objectives: first, identifying and comprehending the physical phenomena and geometric or dynamic parameters involved in the appearance of backflow of pollutants during the dynamic confinement on nuclear sites by air transfer mechanisms through openings; second, investigating and simulating the configurations and aerodynamic conditions in the vicinity of the openings that may result in the phenomenon of backflow in the case of a gaseous pollutant. Numerically simulating this occurrence will improve our capacity to comprehend, predict, and thus prevent it. The openings in which we are interested are those likely to be encountered in the airlocks of nuclear sites. These are rectangular slots with thin rigid or flexible walls. To illustrate this phenomenon, a numerical simulation is performed using the ANSYS Fluent commercial calculation code, a dynamic mesh is used to simulate a moving plate which consists in generating disturbances in the flow. The comparison of the experimental and numerical results confirms the leakage of the pollutant through the opening outside the depressurized airlock, and this only for well defined extraction velocities. HIGHLIGHTS Comprehension of the physical phenomena involved in the appearance of backflow of pollutants during dynamic confinement; Investigation and simulation the configurations and aerodynamic conditions in the vicinity of the openings that may cause a phenomenon of backflow in the case of a gaseous pollutant; Increasing the capacity for comprehension and prediction in order to prevent the phenomenon of backflow gaseous pollutants through simulation.