Code Manual for CONTAIN 2.0 - Federation of American Scientists

The condensation
Reference Pru78:
rate is calculated from a simplified version of the Mason equation presented in
G= (7-15)
where dPis the particle diameter, pcis the density of water, awis the activity of water, and a is the
surface tension specified by the keyword SURTEN. The remaining terms in Equation (7-15) are
previously defined in Equation (7-14). Note that Equation (7-15) includes solute and Kelvin effects,
whereas Equation (7-14) does not. Simplifications have been made in Equation (7-15) with respect
to the vapor diffusivity and gas conductivity: these are not corrected for finite gas mean free path
effects, as they are in the original expression in Reference Pru78.
The activity can be expressed as
[1 Ev~m~MW
aW=exp -
s m$%
(7-16)
where v~is the volubility factor of the salt, given by the SOLUBLE keyword discussed in Section
14.2.5, rnsis the mass of salts on the particle, and M, is the molecular weight of the salt.
After the particle growth calculation is completed the aerosol is remapped from this moving grid
formulation to the fixed-grid for calculation of aerosol agglomeration and deposition effects. The
remapping is performed by approximating the particle mass distribution as being constant with
respect to the logarithm of particle diameter.
7.2.3 Deposition
Containment aerosols can deposit or settle onto the surfaces of heat transfer structures and onto the
coolant pool in the lower cell. Deposition on such surfaces occurs through four processes:
gravitational settling, diffusion to surfaces, thermophoresis, and diffusiophoresis. Of these natural
depletion processes, gravitational settling is often the dominant mechanism, although phoretic effects
may be significant in some cases. In general, particle diffusion is considered to be a relatively
unimportant deposition process. The velocities for each of these deposition processes are defined
below. Note that deposition with respect to engineered systems is modeled somewhat differently
from that for structures and pools and is discussed in Sections 7.4 through 7.6.
Gravitational Settling. The gravitational deposition removal mechanism is governed by the
following particle settling velocity:
Rev O 720 6/30/97