Code Manual for CONTAIN 2.0 - Federation of American Scientists

of flow velocities in the cavity are presently available so that correlation of entrainment velocity
against exit velocity is not possible. The velocity of interest to the entrainment process is believed, ~
however, to lie somewhere between the blowdown velocity and the cavity exit velocity. Physically,
this is reasonable given that the blowdown gas picks up extra mass by entraining debris into the flow
field and that the momentum of the blowdown gas must be conserved between the entrance and exit
of the cavity. The gas is also heated, which acts to accelerate the flow. The ability to use either the
average gas velocity through the cavity or the exit gas velocity from the cavity is provided through
the USEVOUT keyword.
As debris is ejected from the RPV, it is transferred from the RPV non-airborne field to the cavity
non-airborne field. Debris in the non-airborne field is assumed to have one particle size associated
with it for purposes of interacting with the blowdown steam. As debris is entrained out of the cavity
non-airborne field, the drop size models are invoked to distribute the debris among the various
tibome fields. The distribution of entrained mass during a timestep into the airborne fields is done
assuming that the mass is distributed log-normally. The mass median particle size, ~, is assumed
to be equal to one half the maximum stable drop size given by Equation (6-72). The mass of debris
entrained into a given field during a timestep is given by
AMT Ii
AMi = Nkids
~ I.
j=l J
li = i ‘xp{-[1n(3Y2}d
(6-73)
where AMi is the mass of debris entrained into field i, AM~ is the total mass entrained into all the
fields during the timestep, Nfi.l~,is the number of airborne debris fields, and a~ is the geometic
standard deviation. The integration limits ~ and bi in Equation (6-73) are given by
ai=ddi>l G
ai = di/rnin5,a~
()
, i = 1
bi = ~~, i c Nfi~ld
bi = tin(5,G~)di, i = Nfi~l~
(6-74)
where di is the particle diameter assigned to field i. The geometric standard deviation o~ is controlled
by the user-specified parameter WESIG, which is the natural logarithm of o~. The default value of
o~ is 2; hence, WESIG = in(2) = 0.693 by default. In DCH experiments, the size distribution
observed is generally broader than this, with a~ = 4 being typical. However, the value of ~
calculated from Equation (6-72) will vary as the gas flow conditions in the cavity vary, which will
tend to broaden the size distribution obtained for the entire calculation.
Rev O 632 6/30/97