Code Manual for CONTAIN 2.0 - Federation of American Scientists

the effects of the perpendicular component of the settling velocity, leading in some flow geometries
to deposition within the path, are not modeled. In the explicit flow option, aerosol slip or
decontamination effects are not considered.
The time-dependent evolution of aerosol masses is calculated in two steps. First, the effects of
aerosol agglomeration, deposition, and condensation are calculated within a cell, neglecting the
effects of flow. Second, the effects of flow on the airborne aerosol mass ~,,,i,~ of component kin
section i and cell n are then calculated from
(7-50)
where the sum extends over all gas flow paths connecting cell j to n and the suppression pool vent
path, if present; A;. is the effective flow path area as defined in Table 4-2; u denotes the upstream
or donor cell; VUis the cell free volume of donor cell u; and Fi,j~is the attenuation factor for the jn
path, which depends on flow direction. The aerosol velocity v~J~,i= v~j.- v,Jnj is equal to the gas
velocity v~jnminus the aerosol gravitational settling terminal velocity v,J~j= v,,icos ej~. In the latter
expression, V,jis the settling velocity as defined in Equation (7-17), but logarithmically averaged
over the particle diameters in size class i, and cosejnis the cosine of the angle of the flow path with
respect to vertical. This cosine is set through the VCOSN keyword for a gas flow path within the
implicit flow option and is zero for a gas flow path by default or for the suppression pool vent path
or within the explicit flow option. The attenuation factor Fj~,is set to 1 for outflows or for inflows
from gas flow paths or the suppression pool vent flow path, if they are not submerged; is set to
inftity for inflows through a submerged gas flow path; and is determined by the DFs calculated in
the SPARC or SCRUB scrubbing model for inflows through a submerged suppression pool vent
flow path (F= UDn. The aerosols removed from the gas flow for an smaller than unity are placed,
along with any associated fission products, in the coolant pool in the downstream cell.
The user should be aware that problems may arise with respect to the problem splitting that is used
to handle aerosol agglomeration, deposition, and condensation on the one hand and the intercell flow
of aerosols on the other. To account for the effects of aerosol agglomeration, deposition, and
condensation (in the case of the fixed-grid option), a Runge-Kutta method, with automatic timestep
control, is used. This calculation disregards flow. To account for the effects of flow, aerosols are
redistributed with the atmosphere gases every flow timestep. During the redistribution process, the
aerosol distribution is assumed not to evolve except through the flow process. The flow of the
atmosphere gases is calculated with automatic timestep control. The aerosol distributions from each
of these separate calculations are updated every system timestep. However, the timestep controls
for each calculation individually may not ensure that the coupled problem is described adequately.
The user is warned that no check is made on the adequacy of the update interval. In general, the user
should check the sensitivity of the calculation with respect to the system timestep whenever both
aerosol processes within a cell and intercell flow result in large effects on the aerosols within a cell
during a timestep.
O 739 6/30/97