Code Manual for CONTAIN 2.0 - Federation of American Scientists

13.3.2.2.2 Standard Prescription Input and Model Choices. Thepresent discussion will delimited
tothefinal version thatwas recommended for NPPanalysis. Itisimportant tounderstand thatthis ~
version is still considered applicable to experimental analysis; in fact, the modifications introduced
would make very little difference in the analysis of any of the experiments considered in the
CONTAIN validation effort. The experimental validation presented in Reference Wi195 and
summarized in Figure 13-3 is therefore considered equally applicable to the present prescription.
The principal reason for the modifications was the recognition that NPP analyses may encounter a
wider range of conditions than any studied experimentally, and that the prescription used in the
experimental analysis could encounter pitfalls under some conditions even though problems did not
arise for the conditions of the experiments. In addition, the NPP prescription includes a few
simplifications; e.g., elimination of some nondefault parameter specifications now considered to be
unnecessary.
The current standard input prescription for DCH analysis is summarized in Table 13-1. All
parameters and model options not given in the table are left at the CONTAIN default values.
In the analyses of the experiments, parameters describing vessel blowdown, the fraction of the debris
dispersed from the cavity (f&,P),and the time-dependence of the debris source rate [S~(t)]were based
upon experimental results. This approach is obviously inapplicable for scenarios not studied
experimentally, including NPP analysis. Hence semi-empirical means of providing this information
are adopted. These will be described next.
Melt Characteristics and Vessel Failure Size. In any CONTAIN DCH analysis, definition of the melt
characteristics (total mass ~, composition, initial temperature T$ must be obtained from an invessel
analysis or some other information source; CONTAIN has no models for calculating these
quantities. The diameter of the hole in the vessel head, d~,likewise must be determined by the user,
except that the effect of ablation on the hole size can be calculated by the RPV models if these are
used.
Blo wdown. In the standard prescription, the blowdown of steam from the primary system can be
modeled by defining one or more cells to represent the primary system. The initial conditions for
these cells should be specified to correspond to the gas composition (steam plus any hydrogen
present), temperature, and pressure of the primary system immediately prior to vessel breach. If the
ideal gas equation of state for steam is being used, the volume specified for the primary system
should be increased so that the code will calculate the correct mass of steam for the specified
conditions; if the real equation of state is used, the volume specified should correspond to the actual
free volume of the primary system.
The blowdown is calculated by opening a flow path from the primary system cell(s) to the cell
representing the cavity. Let t: represent the time the blowdown begins; it corresponds to the time
of gas blowthrough in the melt ejection process, not the actual moment of vessel breach. Rather than
opening the flow path area abruptly to its final size, & = nd~4, it is more realistic to specify a flow
path area that increases linearly with time over an interval of duration z~given by the semi-empirical
relation ~i195]
Rev. O 13-28 6/30/97