Code Manual for CONTAIN 2.0 - Federation of American Scientists

Specifically, for DFB to occur, the incoming diluent to combustible mole fraction must be below
“shratio,” the receiving cell oxygen mole fraction must be above “mfocb,” the receiving cell diluent <
mole fraction must be below “rnfscb,” and the combustible mass inflow rate (kg/s) must be above
“h2flow.” In addition, a user-specifiable fraction “cfracb” of the inflowing combustible gases is
burned if these conditions are met, subject, of course, to there being sufficient oxygen. The ignition
criteria are based on temperature thresholds such that the combustion will occur only if the entering
gas temperature exceeds the threshold. Two such thresholds are provided. The first can be set by
specifying the keyword DITEMP, and applies during the bum window defined by the values of
TACTIV and TDEACT (see Section 14.3.1.7). The default value of DFTEMP is OK and hence this
threshold has no effect unless the user provides a value. Outside the bum window, the threshold is
controlled by DFAUTO and the default value is effectively infinite (1020K). Hence the user must
specify a value of DFAUTO in order for DFB combustion to occur outside the burn window, except
that combustion will still occur when the receiving cell is sufficiently hot or contains sufficient hot
debris that ignition is assumed to occur on the basis of BSR existence criteria, as discussed in
Section 9.3. DFTEMP and DFAUTO may be used to simulate autoignition of hot incoming jets in
the absence of a nearby ignition source. Note, however, that combustion in this model will terminate
as soon as the jet temperature drops below the relevant threshold temperature. In reality, once the
jet is ignited, combustion could continue even if the incoming gas temperature falls to lower values,
provided the conditions for a stable flame are met. The CONTAIN model does not take this
possibility into account.
The DFB temperature thresholds are applied independently to each unsubmerged gas flow path, and
the dedicated suppression pool vent if not submerged. Therefore, hot combustible gases entering
a cell through one path may bum via the DFB model, while cooler combustible gases entering the
same cell through other paths may not bum. This will occur if the temperatures of some upstream
cells are above the threshold, while the temperatures of other upstream cells are below the threshold.
Combustion of user-specified sources or of gas flows evolving from the surface of the coolant pool
in the DFB model is modeled but is not subject to the temperature criteria defined by DFTEMP and
DFAUTO. These flows always behave as if DFTEMP = Owere specified within the bum window
and as if DFAUTO = w were specified outside the burn window. In applying the DFB composition
criteria, all user-specified sources within a given cell are combined and treated assuming that they
represent a single stream of incoming mixed gas. The same is true of gas flows evolving from the
pool surface.
The DFB model is based on the nominal amounts Njc~Wand Nj~~co$of Hz and CO, respectively, over
the flow timestep A~ that are burned in diffusion flames
(9-28)
‘JeH2=+[fcbYTH21A
‘JecO=*n[dfcb%:?cOIA
Rev O 918 6/30/97