Experimental investigations on steam-air-hydrogen condensation and corresponding component separation phenomenon

Abstract

Under severe accident conditions of a pressurized water reactor, hydrogen will be released into the containment, forming a mixture of steam-air-hydrogen, and then transported to the surroundings. This process can be coupled with complex mass transfer behavior caused by wall condensation. Under the coupling effect of condensation and buoyancy introduced by hydrogen, the mixture gas will form different types of transport behaviors. This will be closely related to the stratification and flammability risk of high-concentration hydrogen. To quantitatively determine these phenomena and assess the potential causing reasons, experiments were performed with helium instead of hydrogen based on the COAST (condensation and species transport) facility. The tests cover a broad parameter range with steam concentrations of 8.4– 89%, helium concentrations of 10– 66% (XHe/XNon), and pressures of 0.4– 1.3 MPa. The phenomena of steam condensation induced component separation were firstly confirmed in the tests, and the component concentration threshold was clarified at XHe/XNon = 50%. The three flow patterns of steam-air- helium mixture gas was identified by Shapiro-Moffette ternary diagram. Moreover, the temperature inverse stratification caused by the high-concentration helium-air layer was discovered in the experiments, and its influence on heat transfer was clarified.