Code Manual for CONTAIN 2.0 - Federation of American Scientists

where NtOti= N~ + N~o + ~ is the total moles of reactant gas adjusted for flows but excluding the
moles represented by Nj~~,mand Nj~~,coand 6 is a small number. N,,w is the moles of hydrogen to ~
entrain into the jet from the cell atmosphere, and N “
e,co 1S the moles of carbon monoxide to en~~n
into the jet from the cell atmosphere. The user can disable entrainment of pre-existing combustible
gases in the DFB model by speci~ing the keyword NOBURNEN in the CONTBURN input block.
If that keyword is not specified, any hydrogen or carbon monoxide pre-existing in cells will be
subject to inclusion in the burning jet as described above.
As noted previously, the DFB threshold and ignition criteria are applied independently to each inflow
from another cell. However, the sources (input tables) into a cell are combined into only one inflow,
which is then evaluated relative to the DFB criteria to determine if this inflow will experience a
DF33. The same is true of gas flows evolving from the surface of the coolant pool. Thus, a very high
source of steam could preclude the DFB of a combustible-gas source (into the same cell). Note that
the amount of combustible gas that is burned is not affected by flame speed or bum time, since the
DFB model simply recombines the combustible gas with oxygen in the receiving cell, if the
appropriate criteria are met.
The average molar rates of burning in difision flames for the entire cell and “flowtimestep are given
by
NH* =
Nco =
+Ne~ /@ P jet,H2 , )
P
+N
je4C0 )
e,co/Atf
(9-32)
provided the burning is not oxygen-limited. In the oxygen-limited case, these molar rates are
reduced to correspond to the oxygen available for burning. The contributions to WC~,and qC~~in
Tables 4-3 and 4-4 from diffusion flames are identical to Equations (9-26) and (9-27) for the case
of deflagrations, and the equations will not be repeated here.
9.3 Bulk SPOntaneous Recombination (BSR)
In a direct containment heating (DCH) event, large increases in the containment gas temperatures
are predicted to occur as well as the possibility of hot debris particles being dispersed throughout the
containment. It is possible that these conditions may cause the hydrogen to bum in the absence of
any deliberate ignition system or accidental ignition, even if the gas composition lies outside the
normal flammability limits. The BSR model was developed to treat this mode of combustion in a
parametric (as opposed to mechanistic) way. Typically, the BSR model has been used in DCH
calculations although, in principle, it could be applied to other accident scenarios in which hightemperature
combustible mixtures exist. Thus, the BSR model allows combustible gas and oxygen
to recombine volumetrically if one of the following spontaneous recombination conditions is
satisfied:
1. The bulk gas temperature exceeds a minimum spontaneous recombination temperature
“srtemp.”
Rev O 920 6/30/97