ID 14

Flash-boiling atomization of water in vacuum: application for ITER safety

 

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 in the coolant system pipe 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 but, as the vaporization will only be partial, some water will rain on the vacuum chamber walls which could lead to re-suspension through surface boiling. Therefore, the analysis of the characteristics of the two-phase flow generated by the flashing liquid jet due to water leakage is an important issue to identify the main physical phenomena involved in the aerosol particles re-suspension. Preliminary flash-boiling experiments were conducted under rough 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 backlit shadowgraphy, qualitative and quantitative information were obtained on the spray geometry and droplets velocity for different superheats and mass flow rates. This study is the first step toward dust re-suspension experiments from flash-boiling and surface boiling.