Code Manual for CONTAIN 2.0 - Federation of American Scientists

Although the number of individual vents present maybe specified by the user in the dedicated
model, the vents are assumed to behave effectively as a single path. There is no provision for
modeling the clearing of vent rows at different elevations. However, the fact that the effective area
for gas flow may increase with pressure, as different rows are cleared, maybe simulated through
user-specifiable pressure-range parameters, corresponding to the difference between the pressure
required to initiate gas flow quasi-statically and the pressure required to keep the vents fully cleared.
11.1.2.1 Vent ClearimzTime. The suppression pool vent clearing time is based on the time required
for the liquid level on either side of the suppression pool to drop to the level at which the vent begins
to clear. The equation for the liquid level velocity is based on the Bernoulli mechanical energy
balance equation for quasi-steady flow. (Figure 11-4 displays the liquid level velocities for typical
BWR containment.)
The Bernoulli equation is
~[v:-v:)+m .,
PW - P~ + ptg(HW- H~) + z L (11-8)
where PWis the wetwell pressure; P~ is the drywell pressure; pt is the pool density g is the
acceleration of gravity (9.8 m/s2); HWis the wetwell liquid level; H~is the drywell liquid level; VW
is the wetwell pool rise velocity v~is the drywell-side fall velocity; and APLis the irreversible loss
in total pressure.
Also, the amount of liquid removed from the drywell side of the vent equals the amount of liquid
added to the wetwell side. Thus, flvd= v., where ~ is the ratio of the drywell vent area to the wetwell
pool area. Substituting this definition of VWinto Equation (11-8) produces
2
Pw - Pd + ptg(Hw - H~) + p$2 - l): +Ap~=O
(11-9)
For flow from the drywell to wetwell, APLin Equation (11-9) can be rewritten
APL = + p[K V: + &’L
~ir60] as follows,
(11-10)
where K is the sudden expansion loss factor in the turbulent flow regime and APLrepresents the
additional loss terms. For-sudden expansion, K = (1/~ - 1)2. Therefore, by substitution, Equation
(11-l l) becomes
- p)z v: + APL (11-11)
when expressed in terms of vd, and Equation (11-9) becomes
where AHdWequals HW– H~,and AP~Wequals PW- p&
(11-12)
Rev O 11 9 6/30/97