Code Manual for CONTAIN 2.0 - Federation of American Scientists

not taken into account.) Aerosol deposition processes are assumed to occur on the surfaces of heat
transfer structures not submerged in the coolant pool in a cell. Aerosols and fission products
deposited on structure surfaces are assumed to transfer to the pool in proportion to the structure
surface area that is subsequently flooded. (This process should not be cotised with the wash-down
of deposited aerosols with condensate runoff from unsubmerged surfaces, discussed above.) As in
prior versions, deposition may also occur on the surface of the coolant pool. Such deposition
requires the definition of a coolant pool in the cell, as discussed in Section 5.4, but no longer requires
the use of the SETTLE keyword that is required in code versions prior to CONTAIN 1.2. This
deposition occurs on a surface area equal to the cell cross-sectional area at the pool height, if coolant
is present; equal to the lower cell cross-sectional area, if the coolant pool is dry and CORCON is not
active; or equal to the CORCON upper surface area, if the pool is dry and CORCON is active. As
discussed in Section 7.2.3, pool deposition is offset by gas convection from the pool surface. Such
gas convection takes into account evaporation, boiling, and any venting of noncondensable gases
below the surface of the pool. It should also be noted that, as discussed in Section 7.7, aerosols and
any attached fission products are completely removed from the gas vented under the surface of a
coolant pool through the submerged end of a gas flow path. These aerosols and fission products are
subsequently placed in the pool. This is the result of an incomplete implementation of aerosol
scrubbing models for submerged gas flow paths and does not apply to the dedicated suppression pool
vent flow path, for which scrubbing models are in place.
7.1 Aerosol Size Distribution
In CONTAIN, the aerosol particle size distribution is represented by a number “nsectn” of particle
size classes called sections. The section boundaries are based on a compact spherical-equivalent
diameter d (the diameter of a fully dense spherical particle with the same density and mass as the
particle in question) and are distributed between user-specifiable minimum and maximum diameters
for the particle sizes considered in the calculation. The minimum and maximum diameters are
specified by the spherical equivalent diameters “diaml” and “diam2,” respectively, in the AEROSOL
input block (see Section 14.2.5). The “nsectn” + 1 size class boundaries are determined by
partitioning the interval [“diaml, ““diam2”] geometrically; that is, the interval [ln(’’diaml “),
ln(’’diam2”)] is divided evenly. The default values of “diaml” = 10-7m and “diam2” = 10-4m give
satisfactory results in a number of containment situations. The user is cautioned that a value smaller
than 10-7m for “diaml” may introduce stiffness into the calculation and increase the execution time
considerably.
The CONTAIN aerosol module is designed to use a small number of sections for computational
efficiency. A sensitivity study has shown that the default particle diameter range between 10-7and
10-4 m can be handled adequately by ten sections in a typical case. [Lei84] However, it is
recommended that no fewer than 20 sections be used without testing. On the other hand, one must
avoid using so many sections that the geometric constraint that particle volumes must increase by
a factor of two or more from section to section (see Equation (7-4) below) is violated.
Upper and lower accounting bins have been added to keep track of aerosol paticles that may become
larger than the maximum diameter or smaller than the minimum diameter, respectively. (Such
masses are referred to as “mesh’ losses in the following discussion.) Aerosol particles can become
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