Code Manual for CONTAIN 2.0 - Federation of American Scientists

material definitions are given in the Sequoyah sample problem discussed in Section 15.3. Use of
the mass and energy accounting scheme is discussed in Section 3.4 and 14.2.2.
2.4 Atmosp here/Pool Thermal-Hydraulics and Intercell Flow
The atmosphere/pool thermodynamics and intercel.1 flow models deal with the thermodynamic state
of the bulk fluids in a cell and the intercell flow of the atmosphere and pool fields. As discussed in
Section 2.1 the bulk fluids are of two types: the atmosphere bulk fluid, consisting of the
noncondensable gases, coolant vapor, and any homogeneously dispersed liquid coolant in the cell
atmosphere, and the pool bulk fluid, consisting of the coolant in the pool. Besides the bulk fluids,
a number of other fields are associated with the atmosphere and pool, including aerosols, fission
products, and dispersed core debris in the atmosphere and deposited aerosols and fission products
in the pool.
The treatment of intercell flow is typical of a control volume code. The cell fluids are assumed to
be stagnant and well-mixed. Flow is assumed to occur between cells through junctions, called flow
paths, that essentially determine the exchange of mass and energy between the cells. The momentum
equation in this framework is actually a lumped-parameter equation for the junction flows that
assumes that the flow is controlled by a fluid slug with an effective length specified by the user. The
flow paths are not repositories and do not have an actual inventory associated with them. The
material flowing into a flow path is placed immediately in the downstream cell without regard to the
holdup of the material in the flow path.
Note that the pool tracking modifications implemented in CONTAIN 1.2, as well as the hybrid ~
gravitational head formulation discussed below, have radically changed the treatment of intercell
flows. In CONTAIN 1.2, both the atmosphere fluid and the pool fluid, if present, are treated as bulk
fluids on the same footing. Within this dual fluid treatment, the atmosphere and pool are assumed
to be able to occupy the same physical volume within a cell, with the pool completely displacing the
atmosphere below the pool surface elevation in the case of a partially fdled cell. In conjunction with
this new volume-filling assumption, the effects of submergence on flow paths and heat transfer
structures are now treated. In addition, the pool thermodynamic state is now calculated by the
implicit flow solver, and a new type of implicit pool flow path, with features comparable to those
of gas paths, is available. In order to define the CONTAIN cell geome~ more precisely than in
prior versions, the cell geometry has been generalized, as discussed in Section 4.1.
In contrast, in code versions prior to CONTAIN 1.2, a single bulk fluid, the atmosphere fluid, is
treated implicitly with respect to intercell flow. In addition the pool is considered to occupy a
volume that only partially overlaps that of the atmosphere, and while volumetric displacement effects
are taken into account, the effects of submergence are not generally considered.
Flow paths modeled within the recommended implicit flow solver may now transport either the
atmosphere fields or the pool fields. These fields may flow only in a path of the appropriate type,
a situation requiring the definition in general of both types of CONTAIN flow paths for each
physical flow path. For generalized flow paths specified through the engineered vent input, the type
is defined by the user to be either GAS or POOL, respectively. The specialized flow path
Rev O 212 6/30/97