Experimental analysis of heat transfer within the AP600 containment under postulated accident conditions

The new AP600 reactor designed by Westinghouse uses a passive safety system relying on heat removal by condensation to keep the containment within the design limits of pressure and temperature. Even though some research has b een done so far in this regard, there are some uncertainties concerning the behavior of the system under postulated accident conditions. In this paper , steam condensation onto the internal surfaces of the AP600 containment wa lls has been investigated in two scaled vessels with similar aspect ratios to the actual AP600. The heat transfer degradation in the presence of nonco ndensable gas has been analyzed for different noncondensable mixtures of ai r and helium (hydrogen simulant). Molar fractions of noncondensables/steam ranged from (0.4-4.0) and helium concentrations in the noncondensable mixtu re were 0-50% by volume. In addition, the effects of the bulk temperatures, the mass fraction of noncondensable/steam, the cold wall surface temperatu re, the pressure, noncondensable composition, and the inclination of the co ndensing surface were studied. It was found that the heat transfer coeffici ents ranged from 50 to 800 J s(-1) K-1 m(-2) with the highest for high wall temperatures at high pressure and low noncondensable molar fractions. The effect of a light gas (helium) in the noncondensable mixture were found to be negligible for concentrations less than approximately 35 molar percent b ut could result in stratification at higher concentrations. The complete st udy gives a large and relatively complete data base on condensation within a scaled AP600 containment structure, providing an invaluable set of data a gainst which to validate models. In addition, specific areas requiring furt her investigation are summarized. (C) 1998 Published by Elsevier Science S. A. All rights reserved.