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sec (50 hr). These latter residence times are
rough estimates, and as better information becomes
available from fission product behavior in the
MSKE, more reliable estimates of the residence
times for these elements will be possible. This
lowest solid curve in Fig. 23.1 is shown only to
suggest the general range of conditions under
which the fuel processing plant may operate.
The dashed curves in Fig. 23.1 were obtaincd
from the same reactor calculations, but some fis-
sion products were assumed to be removed in the
fluorinator. The elements Xe, Kr, Rt, I, Mo, Tc,
Te, and Se were considered to be completely re-
moved, and 15% of the Ru, Rh, Nb, and Sb were
removed. After fluorination, however, these
elements may “grow’’ back into the system.
HEAT GENERATION IN A MOLTEN-SALT STILL
Buildup of heat generation in a molten-salt
distillation system was calculated using the heat-
generation data given in Fig. 23.1. The reactor
and that part of the processing system prior to the
still were assumed to be at steady state, although
the transient associated with buildup of fission
products in the still was considered. Fuel salt
containing fission products remaining after
fluorination was fed to a distillation system, and
complete retentjon of fission products was as-
sumed. The fuel salt was assumed to have been
held up 24 hr in processing prior to entering the
still (12 hr before fluorination and 12 ht after).
The heat-generation data from Fig. 23.1 was
fitted by the method of least squares to the rela-
tion
247
where
H(t) == heat-generation rate at time t (Htu
hr- 1 ft.-’3
),
A,, k. ::: constants,
1 1
t ::: time after salt leaves fluorinator (days).
The rate of heat generation in the still is then
given as
where
Q(r) = heat generation in still after operating
for a time t (Wtu/hr),
F - fuel salt processing rate (ft3/day),
t - length of time still has operated (days).
Calculated heat-generation ratcs in the still are
shown in Fig. 23.2 for a piocessing rate of 15
ft3/day for several assumed removal efficiencies
(the same assumptions noted for Fig. 23.1) in
processing steps prior to the still. The still
system will be near steady state in two to three
years, and heat generation rates as high as 3.0
Mw can be expected. Removal of fission products
by gas stripping, plating on metal surfaces, and
formation of volatile fluorides during fluorination
will reduce this rate to about 2.2 Mw,
ORNL-DWG 67-9/38A
Fig. 23.2. Fission Product Decay Heat in MSBR Still and Accumulation Tank.