ORNL-1816 - the Molten Salt Energy Technologies Web Site

ANP QUARTERLY PROGRESS REPORT
were also followed so that the rate of reduction
could be determined. The results are presented
in Figs. 5.2 and 5.3. After 2.65 faradays had
passed, the HF level was below lo', mole/liter,
corresponding to fairly complete purification, and
the trial was terminated. Analysis of the filtered
melt showed 120 ppm Fe, 40 ppm Ni, and 13
ppm Cr. The results given in Fig. 5.2 show that
the rate of HF evolution with electrolysis is about
three times as great as without electrolysis during
the early stages of the purification. This factor
decreases unti I there is hardly any difference at
the end of the run. The decrease is considered
to be due to the gradual accumulation of UF, and
is reflected in Fig. 5.3, which shows the apparent
current efficiency in terms of equivalents of HF
per faraday as a function of the number of faradays
passed. The apparent efficiency varies from 3.5
to 0.5% for the UF4-containing melt as compared
with 32% in NaF-ZrF,. The cause
-
of the low
ORNL-LR-DWG 4527
1
k 6
5
2
-
x 5
u)
-
m 4
a
(3
c
z
Y 3
_J
LL
LL
W
E 2
LL
I
4
GAS SWEEP RATE: o 33 \iter/min
0
0 0 5 10 15 2.0 25 30
FARADAYS PASSED
Fig. 5.2. Rate of HF Removal During Electroly-
sis of NaF-ZrF,-UF, (53.5-40-6.5 mole X ) Under
H, at 800'C.
68
efficiency was apparent from the current-voltage
curves obtainedwhen UF, was present.
After electrolysis had proceeded for a short
time, decomposition potentials and "knees" were
not encountered. Plots of current against voltage
showed a sharp increase from the origin and thus
indicated that no overvoltages or decomposition
potentials need be exceeded to obtain large
currents. This increase was interpreted as being
due to the presence of UF, and a small amount
of reduced UF,. The primary electrode reactions,
reduction of UF, at the cathode along with oxi-
.dation of UF, at the anode, caused the over-all
changes in the melt to occur very slowly. No
appreciable amounts of precipitated metals were
found on the cathodes, and it was presumed that
the bulk of impurities such as Fett must have
been reduced in the melt as secondary reactions
rather than being deposited on the cathode. Such
behavior might result in metal "fogs," which
would be most undesirable.
Fluoride Production Facility ..
F. L. Daley J. P. Blakely
Mater ials Chemistry Division
A total of 1119.6 kg of processed fluorides was
produced in the 250-lb facility during the past
* ,
I
>
3.5
$ 3.0
LT
2
E
2.5
N
0
x
0 3.0
-
0
E
:
a
b-
z
W
;
LL
U
W
U
r
1.5
1.0
0.5
0
TOTAL FARADAYS PASSED, 2.646
esBE&l
ORNL-LR-OWG 4528
0 0.5 4.0 4.5 2.0 2.5 3.0 3.5
FARADAYS PASSED f -
Fig. 5.3. Apparent Current Efficiency for Re-
moval of HF While Electrolyzing NaF-ZrF4-UF,
(53.5-40-6.5 mole %) Under H, at 800%
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