Abstract
Dust re-suspension inside the vacuum vessel is one of the safety issues of ITER (International Thermonuclear Experimental Reactor). Plasma interaction with the PFCs (Plasma Facing Components) leads to their erosion, generating dust. One of the accident scenarios leading to dust re-suspension is the Ingress of Coolant Event (ICE) where a leak of the coolant pipes inside the vacuum vessel leads to flash atomization of the cooling water. The steam flow from the leak is considered to be the main source of dust re-suspension. Therefore, experimentations about the two-phase flow generated by the flashing liquid jet due to water leakage is important to identify the main physical phenomena involved in the aerosol particles re-suspension at low pressure. Flash-boiling experiments were conducted under primary vacuum conditions to investigate the flow behavior and structure of a superheated water (20°C to 140°C) injection into vacuum (1 mbar to 10 mbar). Using high speed dual-frame backlighted shadowgraphy and high speed PIV, qualitative and quantitative information were obtained on the two-phase flow such as spray geometry, droplets and gas velocities for different superheats and injected water mass flow rates. A transparent nozzle was also designed to better understand the phase change before the injection upstream the leak of coolant.
