Code Manual for CONTAIN 2.0 - Federation of American Scientists

CCIS are modeled through an embedded version of the CORCON Mod3 code. CORCON Mod3
includes an integrated version of VANESA for representing aerosol releases; therefore, in the ~
discussions that follow CORCON is used to refer to both the CORCON Mod3 and VANESA
models. When active, the CORCON model governs the processes occurring in the melt, which is
assumed to be located at the bottom the coolant pool, if it exists. Convective and boiling heat
transfer from the substrate can be modeled with either the CORCON model or the heat conduction
model. In most severe accident analyses, the user will invoke CORCON to represent CCIs and
related phenomena. In situations where concrete ablation is not expected to be important, the
simpler heat conduction model can be used rather than CORCON. The former model has the
advantages that it handles transient conduction in the concrete, is simpler to set up and use than
CORCON, and runs significantly faster than the CORCON module.
The coolant pool is the repository used for liquid coolant taken from or directed to the lower cell by
other modules. Such transfers can occur as the result of flow through pool-type engineered vents
(see Chapter 4), operation of engineered systems (see Chapter 12), condensate runoff from heat
transfer structures (see Chapter 10), coolant aerosol deposition (see Chapter 7), the flow DROPOUT
model (see Chapter 4), and the steam blowdown phase separation process (see Chapter 11) that is
modeled in conjunction with the safety relief valve (SRV) model. Note that if a coolant pool is not
defined, any liquid coolant directed to a cell will be lost from a problem, although its mass and
energy will be noted in the WASTE location of the mass and energy accounting output. To reduce
the number of pools required in a problem, condensate runoff from structures in a given cell (e.g.,
as a result of condensation) can be directed to the pool in another cell by using the cell OVERFLOW
keyword (see Chapter 10 and Section 14.3.1.12).
A number of models deal with the venting of gas/aerosol/fission-product mixtures under the pool
surface. The gases are partially or completely equilibrated with the pool, depending on the model,
as discussed in Section 4.4.7 and in Section 11.2.1. Also, the aerosols are scrubbed in a manner
discussed in Section 7.7. For example, such mixtures are vented into the coolant pool when the
downstream end of a gas-type engineered vent lies under the surface of the pool in the downstream
cell. Also, when CORCON is active, any such mixtures generated by CCIs are assumed to be
injected at the bottom of the coolant pool, if present. Otherwise, they are injected into the
atmosphere. In addition, the user can specify such mixtures as external sources to the pool through
the SRV model.
Convective, condensation, and radiative heat transfer between the pool surface and atmosphere is
modeled in a manner similar to that between heat transfer structures and the atmosphere, and is
therefore discussed in Chapter 10 rather than here. As with structures, the modeling of condensation
heat transfer for the pool-atmosphere interface requires the specification of CONDENSE option.
Convective heat transfer between the pool and the submerged portion of heat transfer structures is
also discussed in Chapter 10.
Boiling heat transfer correlations are also discussed in Chapter 10. Presently, boiling heat transfer
correlations are used only between the coolant pool and pool substrate. If CORCON is active, the
boiling heat transfer model of CORCON Mod3 is used. This model takes into account the effects
of gas barbotage and pool subcooling in the film boiling regime. If CORCON is not active and the
substrate is hotter than the pool, then the somewhat simpler boiling heat transfer model from _