Code Manual for CONTAIN 2.0 - Federation of American Scientists

conditions. If “citlex” does not, then the exit temperature is set to the closest temperature
satis@ing these conditions, if one exists. If the exit temperature leads to heating of the
melt/condensate, the heat and mass transfer processes responsible are assumed to occur in
the same proportion as the original heat and mass fluxes to the ice surface that caused the ice
to melt. Otherwise, the heating is ignored.
12.3 Containment Smavs
This section discusses the thermal-hydraulic modeling of containment sprays. The modeling of
aerosol removal by the sprays is not discussed here but in Section 7.5 and the modeling of the
depletion of gaseous fission product species by the sprays is discussed in Section 8.6.
The spray system provides a uniformly divided water spray to the containment atmosphere. As
previously shown in Figure 12-2, heat and mass transfer to the droplets provide a rapid reduction in
temperature, pressure, and fission product concentration. The sprayed water collects in a sump at
the bottom of the containment. Generally, the initial spray water is from the WST. When that
source is exhausted, water is pumped from the sump, through a heat exchanger, and to the spray
nozzles. A model has been developed that determines the heat transfer between the droplets and
atmosphere and the associated condensation of steam onto or evaporation of the droplets.
The explicit coupling between the spray model and the atmospheric thermal-hydraulics can lead to
oscillations in the atmospheric temperature and pressure when the system timestep is too large.
Though often small in amplitude, these oscillations can be detrimental; e.g., they can cause the
saturation ratio to oscillate back and forth across unity, which can in turn cause spurious
condensation on the aerosols and artificial enhancement of aerosol removal by the sprays. The best
means of testing for this condition is to check the saturation ratio for oscillatory behavior. The only
safe procedure is to reduce the system timestep until the oscillations go away, unless the user can
establish that they cause no harmfhl effects in the particular calculation at hand. The maximum
stable timestep decreases somewhat with increasing spray flow rate and, more noticeably, with
decreasing spray drop size. The increase in computer time from reducing the system timestep may
be partially recovered by reducing the number of cell timesteps per system timestep (i.e., increasing
“ctmfr”; see Section 14.2.8).
The containment spray must be used in either one of two engineered system combinations with the
input specified in the SPRAY input block (see Section 14.3.3.4). For the simplest system, the spray
is paired with an engineered system source table, and the spray is active as long as the source is
ftite. A more elaborate system maybe initiated using a containment pressure setpoint given by the
input parameter “spstpr.” In the latter system, the user must include a tank to supply an initial
amount of fresh water to the spray train (see Section 12.5.5). When the tank is empty, a pump
provides recirculated water, which goes through a heat exchanger and then to the spray trains.
Failure of recirculation maybe simulated by specifying zero flow for the pump or by drawing water
from a source cell “iclin” that contains no pool. Sample input for this system is given in Section
14.3.3.4.