Code Manual for CONTAIN 2.0 - Federation of American Scientists

Aeff =4 for AP > APU
where ~ is the total vent area, AP is equal to P~- PWfor flow from drywell to wetwell and is equal
to PW- P~for flow from wetwell to drywell, APti~is the minimum pressure difference to support the
liquid head at opening, based on the current pool inventory, and ~~u is the pressure diff~~ence at
maximum area, defined as:
AP~a = Aptin + Apd (for flow from drywell to wetwell)
APm = APti + APW (for flow from wetwell to @well).
In the expressions, AP~is the user-specified pressure range over which the effective vent gas flow
area goes from zero to its maximum value for flow from the drywell to wetwell (“dpdry”), and APW
is the range for the pressure difference analogous to AP~but referring to flow from the wetwell to
the drywell (“dpwet”).
In the submerged case, the flow Wijis defined as the gas flow entering the vent and the downstream
pool. Gas-pool equilibration processes will in general alter the composition of the flow entering the
atmosphere of the downstream cell. Such processes are modeled for flow from drywell to wetwell
but not flow from the wetwell to drywell, for reasons discussed below. The equilibration modeling
in the former case is described in Section 4.4.7, with the equilibration length Aij=O.
Gas-pool equilibration is ignored in submerged flow from wetwell to drywell because of the
limitations of the single-pool approximation used with the dedicated model. The problem is that the 4
pool conditions on the drywell side of the vents could be different from those in the main pool but
are not calculated within the single-pool approximation. Reverse flow should occur only under two
circumstances: during wetwell pressurization events, in which case the wetwell loads are the
principal concern, or during suction conditions in the drywell resulting from failure of the drywellwetwell
vacuum breakers after a blowdown. Under the former conditions, assuming that main pool
conditions exist on the drywell side of the vents could be nonconservative. Thus, it is probably
better to ignore the equilibration. Under the latter conditions the drywell loads presumably have
mitigated substantially, and in addition the wetwell atmosphere and pool maybe reasonably well
equilibrated as a result of the equilibration that previously occurred in forward flow. Thus, the
modeling of equilibration effects in flow from wetwell to @well may not be important. If gas-pool
equilibration in such flow could be important, a two-pool segmented suppression pool vent model
such as that discussed in Section 11.1.1 should be used to investigate the sensitivity to equilibration
effects.
The flow equation in Table 4-2 is used to calculate the suppression pool vent gas flow Wij for vents
in the bypass (uncovered) state. CR in this case is taken to be unity. Aijand L,j are interpreted as
the total vent area and vent inertial length, respectively, in the SPVENT input block. Finally, the
pressure difference Nij used is that between the drywell and the wetwell, but gas gravitational head
corrections are not taken into account.
Rev O 11 18 6/30/97