Code Manual for CONTAIN 2.0 - Federation of American Scientists

5.0 LOWER CELL AND CAVITY MODELS
The lower cell system of models provide for the representation of processes in the lower regions of
a cell. The principal uses of the lower cell models include the modeling of coolant pools and the
underlying substrates and of core concrete interactions (CCIS). The lower cell includes models for
heat conduction between the pool and substrate layers, CCIS, volumetric and radionuclide decay
heating, and mass and energy sources to the pool and substrate layers. As discussed in Section 5.7.1,
the CONTAIN lower cell model for radionuclide decay heating utilizes the ANSI-standard decay
power curve [Ame79] and is used in conjunction with the decay heating from explicit fission
products that is discussed in Section 8.5. Other models for decay heating are imbedded in the
CORCON module and are discussed in Section 5.3.2.
A coolant pool, if present, is assumed to occupy the lower regions of the CONTAIN cell as depicted
in Figure 4-4. The cell geometric shape (i.e., the cross-sectional area as a fi.mction of height) is
defined by the cell GEOMETRY input discussed in Section 14.3.1.1. The pool is assumed to fill this
cell from the bottom up, with a horizontal free surface dividing the pool and atmosphere volumes.
Heat transfer structures and the pool substrate are assumed to be excluded from the user-specified
cell volume.
If CORCON is not active, a conduction model solution for the heat transfer between the pool and
the layers in the pool substrate is carried out. For purposes of the conduction solution, the substrate
area is defined through the lower cell GEOMETRY area discussed in Section 5.1 below and in
Section 14.3.2.1. (The use of cell GEOMETRY input for the pool cross-sectional area as a function
of height is a non-upward compatible change from versions prior to CONTAIN 1.2, which assume
a constant pool cross-sectional area given by the lower cell GEOMETRY area.) The substrate is
considered to be either composed of “intermediate” and “concrete” layers, as discussed below, or
represented by a basemat temperature boundary condition.
Note that a lower cell substrate is not the only way to define the region below the pool. As discussed
in Chapter 10, the pool may also be in contact with the face of a submerged slab-type floor heat
transfer structure, which can be at any elevation equal to or above the bottom of the pool. The
bottom of the pool may also be a virtual flow boundary, characterized by a pool-type engineered vent
to the cell below, in which case the pool is considered to be in contact with the pool in the cell below
rather than a substrate. In the latter two cases, a lower cell GEOMETRY area for the pool substrate
must still be defined but should simply be set to a negligible value.
The changes in CONTAIN 1.2 to allow the pool to flood the lower regions of a cell, including the
heat transfer structures, have resulted in non-upward compatible changes with respect to aerosol
deposition onto the pool surface (which is typically dominated by settling). This deposition is
modeled if and only if aerosols are defined and a coolant pool is defined in the cell. The lower cell
SETTLE keyword is no longer required for such deposition to occur. In addition, the aerosol
deposition velocity is now offset by any gases evolving from the pool free surface. In contrast,
deposition does not occur on the part of a heat transfer structure that is submerged below the pool
surface.