Code Manual for CONTAIN 2.0 - Federation of American Scientists

13.3.2.5.11 ENTFR. The parameter ENTFR is the entrained fraction of debris. If the user wishes
to specifi an entrained fraction of debris, but does not want to invoke a model to calculate a value, ~
an entrained fraction can be specified directly by using this parameter in the input.
13.3.3 Heat and Mass Transfer
13.3.3.1 @txoximatiniz the Uchida Heat Transfer Data. Uchida et al. [Uch65] presented
experimental data for condensation on a small vertical plate in the presence of air. The experiments
were conducted in a vessel initially filled with 1 bar of air at 17 degrees C (ambient air density).
Steam was injected at increasing rates while the cooled plate was maintained at a constant
temperature. Data for the total heat transfer coefficient, including both sensible and latent heat
transfer, was correlated as a function of the air/steam mass ratio. Peterson [Pet96] has presented a
diffision layer model of the condensation process investigated experimentally by Uchida. Using this
model, Peterson was able to explain the theoretical basis for the Uchida correlation. Good agreement
between theory and data was shown by Peterson for conditions of naturil convection in the
experimental vessel. More importantly, this theory indicates that a scale dependency based on the
initial air density is present but not reflected in the Uchida correlation. Since the Uchida data is used
extensively in the nuclear industry to predict condensation rates on containment structures, it is
useful to establish the relation between the CONTAIN method of calculating condensation rates and
the data presented by Uchida.
The diffusion layer theory described by Peterson is essentially identical to the heat and mass transfer
analogy method modeled in the CONT~ code. Therefore the agreement between the theoretical
estimates of Peterson and the Uchida data represent an independent verification of the heat and mass
transfer modeling approach in the CONTAIN code. Figure 13-7 shows the CONTA.IN-calculated
heat transfer coefficients under natural convection conditions for three initial air inventories
represented by initial pressures of 0.5, 1, and 2 bars. As indicated, the CONTAIN predictions for
a l-bar initial condition (ambient air density) are in good agreement with Peterson’s fit of the Uchida
data. The agreement confii that the Uchida data can be reproduced with the CONTAIN heat and
mass transfer model under natural convection conditions. The film resistance in the Uchida
experiments is essentially zero due to the small dimensions of the condensing plate. In the
CONTAIN results shown in Figure 13-7, the fdm resistance is zero since the results are reported at
the fmt timestep in the calculation prior to condensate build-up. In actual containment calculations
where a film does develop, agreement with Uchida can be presemed by using the MINDEPTH
keyword to specify a small depth (on the order of 50 ~m) for the film. This input effectively
minimizes the film resistance in comparison to the gas boundary layer resistance.
Consistent with the conclusions of Peterson, the comparisons in Figure 13-7 also show that when
the initial air density varies from the ambient, condensation is not well represented by the Uchida
data. Thus, the data are not applicable to cases in which significant air density gradients exist in the
containment, such as those resulting from steam stratification. From the above results, it is
Rev O 13 60 6/30/97