ORNL-4191 - the Molten Salt Energy Technologies Web Site

I-
92
-Clt
NO ClRCUl ATING BUBBLES
et- -1
I
I
0 R N L-- DWG 67- .I 18 1 3
1.0 3000
1.0 3000
2.0 3000
4.0 3000
OlFFUSlON COEFFICIENT OF Xe IN GRAPHITE 47 1200°F (tt‘/hr)
-PERMEABILITY OF He IN GRAP!ilTE AT ROOM TEMPERATURE (cm2/sec)
Fig. 7.1. Effect of Diffusion coefficient in Graphite on 13’Xe Poison Fraction.
is used as a parameter. Numerically, this is approximately
equal to the permeability of helium
in graphite at room temperature with units of
cm2/sec, if Knudsen flow prevails. Knudsen flow
should be the dominant flow character for permeabilities
less than lo-’ cm2/sec. For permeabilities
greater than lop5 cm2/sec, viscous flow
becomes important and this direct relationship
does not exist.
The gas circulated through the system is handled
in these calculations as two groups of bubbles.
The first group, referred to as the “once-through”
bubbles, is injected at the bubble generator and
removed with 100% efficiency by the gas separator.
The second group, referred to as the “recirculated”
bubbles, is injected at the bubble generator, completely
hypasses the gas separator, and recirculates
through the system until the bubbles are
removed with 100% efficiency on their second pass
through the gas separator. In the accompanying
plots the bubble surface area is the quoted parameter.
For proper orientation, note that 3000 ft2 of
bubble surface aiea corresponds to an average void
fraction of 1% in the stripper region of the fuel loop
with bubbles 0.020 in. in diameter, and also corresponds
to a gas flow rate of about 40 scfin.
Figure 7.1 shows the ‘35Xe poison fraction as a
function of the diffusion coefficient in graphite.