Code Manual for CONTAIN 2.0 - Federation of American Scientists

4.0 ATMOSPHERIVPOOL THERMODYNAMIC AND INTERCELL FLOW MODELS
The atrnosphere/pool thermodynamics and intercell flow models deal with the thermodynamic state
of the bulk fluids in a cell and with 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. The effects of the coupling
of the aerosol and fission product fields to the bulk fluids are discussed elsewhere. For aerosols and
fission products attached to aerosols, such effects are discussed in Section 7.8. For fission products
attached to the atmosphere gas and in the pool, such effects are discussed in Section 8.8. Ztshould
be noted that the ojlen substantial effects of dispersed core debris are also not discussed in the
present section. The required modifications and additions to the equations in this section to include
the latter fields are presented in Chapter 6 on the direct containment heating (DCH) models.
It should be noted that sweeping changes were made in CONTAIN 1.2 with regard to treating the
pool bulk fluid on the same footing as the atmosphere bulk fluid. Jn CONTAIN 1.2 and later
versions, 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 filled cell. Note that pool level swell from
trapped gas in the pool is not modeled. 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 geometry more precisely than in prior code 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.
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 representing the dedicated
suppression pool vent model for boiling water reactors (BWRs) is also available, although its
thermal-hydraulic modeling in some respects has been made obsolete by the generalized flow paths.
A detailed discussion of the dedicated model is given in Section 11.1. The differences between the
generalized flow path modeling and the dedicated suppression pool vent modeling are also discussed
as necessary below. Note that the definition of flow paths within the FLOWS input block, as
opposed to the engineered vent input block, is now considered obsolete, but if present such flow
paths will be treated as gas flow paths.
Rev. O 4-1 6/30/97