Code Manual for CONTAIN 2.0 - Federation of American Scientists

The trapping rate for the different species in a given field and cell is assumed to be the same. The
trapping rate, ki,,, is also assumed to be constant over a calculational timestep. Therefore, the
trapping terms in the DCH mass and energy conservation equations in Section 6.2.2 are linear and
can be represented by a time-averaged removal rate that depends on the initial mass of airborne
debris for each material in a given field and cell. If the timestep is given by At,, then an average
trapping rate for material kin field n in cell i over the timestep is given by
[1
dm~i~~
,,, -m,i~,~l ‘exp(-ki,JIAt~)l
dt trap = “r AtC
The following subsections describe the equations used to calculate the trapping rate, A,,..
(6-76)
Special provisions are made in the trapping model for sending some fraction of the trapped debris
material to the intermediate material layer in the lower cell. In the present model, this fraction is
specified by the user. The addition of trapped debris to the lower cell is governed by:
(6-77)
where mwjx is the mass of material k in the uppermost intermediate layer of the cavity in cell i, and
fwj is the user-supplied fraction of trapped debris to deposit into the uppermost intermediate layer
of the cavity of cell i. This is specified using the COOLFRAC keyword in the DCH-CELL input
block.
The user-supplied fraction, fw,i, governs the fraction of the trapped debris that goes into the
uppermost intermediate layer of the lower cell. The remaining fraction, (1-fwj), of the trapped debris
will be placed in the non-airborne debris field. Note that this option is available in any cell, but is
most useful in the cavity cell. The CONTAIN lower cell layer system is described in Chapter 5. If
there is no intermediate lower cell layer, or if there is no lower cell defined at all, then all trapped
debris is placed in the non-airborne debris field regardless of the fm,i value. Trapped debris cannot
be passed into the CORCON layer system if CORCON is active. Therefore, fw,i will be ignored if
CORCON is active and all trapped debris will be placed in the non-airborne debris field. This is not
considered an important limitation because DCH calculations are typically performed only to predict
the peak short term containment load. The fwj parameter is used if CORCON is defined but has not
yet been activated; therefore, DCH can be used during the early phase of the accident and CORCON
used in a restart or in a new calculation using the trapping results from the DCH run.
Except for the debris that is optionally sent to the lower cell, the DCH model stores trapped debris
in the non-airborne debris field. This field also can be used to hold debris in the cavity that has not
yet been entrained by the blowdown gas. If debris is not sent to the lower cell, the mass of debris
in the non-airborne debris field is governed by the following equation
Rev O 634 6/30/97