Code Manual for CONTAIN 2.0 - Federation of American Scientists

The intercell flow of pool coolant maybe treated either implicitly or explicitly. Pool flow paths
defined in terms of engineered vents are treated implicitly, in a manner similar to that for gas flow ~
paths. The flow of pool coolant may not be as strongly coupled to pressure heads as the gas, so that
an explicit treatment maybe feasible. The liquid transport system components associated with the
engineered safety features and discussed in Section 12.5 maybe used to treat interpool transfers in
an explicit manner. In some cases, use of an explicit model for pools will significantly reduce the
overhead of the implicit solver.
A simple containment-oriented gas-pool flow hierarchy establishes which type of flow (i.e., gas or
pool or both) is allowed when flow paths are submerged. The flow of the atmosphere and pool fields
within their respective paths is taken to be independent in the sense that interracial shear and void
fraction effects are not taken into account. However, effects related to the coverage of the inlet or
outlet of a gas path by pool coolant are taken into account. These include gas-pool equilibration,
blockage of gas flow path inlets by the pool, liquid head terms, and scrubbing effects. A discussion
of flow path configurations and the pool-gas hierarchy for the flow paths is given in Section 4.2.
Key elements of atmosphere/pool thermodynamics and intercell flow models are illustrated in Figure
4-1.
Section 4.3 gives a summary of the modeling options available for the gas and pool flow paths, as
well as the suppression vent flow path. The governing equations for the flow path models are given
in Section 4.4. The latter section discusses the three basic models for intercell flow, i.e., the inertial
flow model, the quasi-steady flow model, and user-specified flow rates, as well as the formulations
for critical or choked flow, gravitational heads, pool boiling, gas-pool equilibration, the velocity of
gas evolution from the pool, and the FIX-FLOW option for overcoming the gas Courant limit in ~
certain situations. As discussed in Section 4.4.5, the CONTAIN formulation of gas gravitational
heads has been revised completely in CONTAIN 1.2 to satisfy three important criteria regarding the
treatment of stratifications. As a consequence, the strong cautionary statements made with respect
to previous code versions regarding convective overmixing are no longer necessary. However, the
user should consult the guidance given in Section 13.3.1.3 with respect to avoiding certain situations
that may lead to excessive stability of stratifications.
Section 4.5 discusses the momentum, mass, and energy conservation equations used by the intercell
flow model and summarizes all contributions to the conservation equations, except the DCH ones.
This section also discusses the gas and pool thermodynamic state calculations.
4.1 The CO NTAIN Cell
The fluid control volumes, or cells, in CONTANN are partitioned into two parts: the atmosphere and
the coolant pool. A horizontal interface between the pool and atmosphere is assumed to be present
at the collapsed hydrostatic level of the pool, an assumption that neglects possible level swell due
to boiling and gas injected below the pool surface through submerged gas flow paths and other
sources. Use of the collapsed level is consistent with the fact that although the equilibration and
scrubbing of such injected gas are taken into account, a separate bubble field is not modeled in the
pool. Instead, the injected gas is assumed to immediately become part of the atmosphere field of the
downstream cell, without holdup in the pool.
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