Code Manual for CONTAIN 2.0 - Federation of American Scientists

where k is the thermal conductivity, At is the shortest time scale of interest, p is the density, and CP
is the specific heat of the material. The surface nodes that are in contact with the gas or pool should ~
be a small fraction of this length, if accuracy in the heat transfer is desired. The user should also take
care not to change the node thicknesses too abruptly from one node to the next. (Generally, any
change in thickness by a factor of two or less should be acceptable.) The user should also consider
stability in defining total structure thicknesses, as discussed in Section 2.2.2.2.
10.5.1.2 Lower Cell Lavers. The second type of heat sink in CONTAIN arises in modeling of the
lower cell, which is intended to represent processes involving deep pools, core debris layers, and
concrete-lined sumps. Lower cell modeling options are discussed in detail in Chapter 5, and the
details of the lower-cell interlayer heat transfer modeling are discussed in Section 5.5. In contrast
to the film modeling for heat transfer structures, the pool is allowed to develop internal boundary
layers at the top and bottom and is otherwise assumed to be well-mixed. When core-concrete
interactions are not being modeled, a one-dimensional heat conduction model is used to calculate
heat transfer between the various lower-cell layers. The conduction algorithm is identical to that
used for slab-shaped heat transfer structures.
Note that a number of options available for heat transfer structures are not available for lower cell
layers. Those options not available include forced-convection heat and mass transfer modeling, the
modeling of concrete outgassing, and all external boundary conditions available for heat transfer
structures but the specification of surface (i.e., basemat) temperature. However, models not
available for structures are available for the lower cell, including the ability to treat (1) nodes with
varying masses, which may be comprised of a mixture of materials in any node but that of the pool,
(2) convective heat transfer for pool nodes, (3) boiling heat transfer between the pool and a substrate _
comprised of lower-cell layers, as discussed in Section 10.4, and (4) fission product decay heating
and/or user-specified heating rates in any layer.
The nodalization requirements for the modeling of conduction in the lower-cell layers are similar
to those for a heat transfer structure. The user should be forewarned, however, that the lower cell
input is designed to produce relatively coarse nodes. Nodalizations for accurate solution of the
interlayer conduction equation, however, can be produced through use of a large number of concrete
layer nodes and multiple intermediate layers to resolve transient conduction effects.
10.5.2 Connected Structure Boundary Condition
The connected structure option allows the user to model heat transfer structures requiring inner
surface models at each exposed face as well as the modeling of conduction heat transfer between the
two faces. A typical example would be a model for a containment shell that has condensation heat
transfer occurring on the interior surface, evaporative heat transfer occurring on the exterior surface,
and substantial heat conduction through the shell. Such situations can be treated in terms of two
structures defined in two different cells and connected at their outer faces through a conduction
boundary condition. The connected-structure boundary condition in effect forces time-averaged
agreement of the heat flux at the outer surfaces of the two connected structures. In the algorithm
developed to implement this boundary condition, conductive outer surface boundary conditions are
O 10 54 6/30/97