Nuclear Engineering and Design 185 (1998) 153 – 172 Experimental analysis of heat transfer within the AP600 containment under postulated accident conditions Mark H. Anderson a , Luis E. Herranz b , Michael L. Corradini a, * a Department of Engineering Physics, Uniersity of Wisconsin, 1500 Engineering Drie, Madison, WI 53706, USA b Department of Nuclear Fission, Centre for Energy, Enironment and Technology Research, CIEMAT, Ada. Complutense, 22, 28040 Madrid, Spain Received 29 July 1997; received in revised form 8 April 1998; accepted 1 May 1998 Abstract 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 been 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 walls has been investigated in two scaled vessels with similar aspect ratios to the actual AP600. The heat transfer degradation in the presence of noncondensable gas has been analyzed for different noncondensable mixtures of air and helium (hydrogen simulant). Molar fractions of noncondensables/steam ranged from (0.4 – 4.0) and helium concentra- tions in the noncondensable mixture were 0 – 50% by volume. In addition, the effects of the bulk temperatures, the mass fraction of noncondensable/steam, the cold wall surface temperature, the pressure, noncondensable composition, and the inclination of the condensing surface were studied. It was found that the heat transfer coefficients 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 but could result in stratification at higher concentrations. The complete study gives a large and relatively complete data base on condensation within a scaled AP600 containment structure, providing an invaluable set of data against which to validate models. In addition, specific areas requiring further investigation are summarized. © 1998 Published by Elsevier Science S.A. All rights reserved. 1. Introduction Since the inception of the nuclear industry, nuclear safety has been one of the major issues for the nuclear fuel cycle. As a result, a large amount of work has been conducted and significant achievements have been realized, particularly in the area of understanding phenomena during acci- dents. This work has led to major improvements in the next generation reactor designs which in- corporate new safety features. The improvement in these safety systems generally involves the use of natural forces to provide containment cooling and are referred to as passive containment cooling systems (PCCS). One of the reactor concepts that * Corresponding author. Tel.: +1 608 2652001; fax: +1 608 2626400; e-mail: corradini@engr.wisc.edu 0029-5493/98/$ - see front matter © 1998 Published by Elsevier Science S.A. All rights reserved. PII S0029-5493(98)00232-5