ORNL-1816 - the Molten Salt Energy Technologies Web Site

ANP QUARTERLY PROGRESS REPORT
Consequently, experiments were run with mixtures
prepared without the preliminary HF treatment, and
the resulting batches were studied closely for
such contaminants as oxides, sulfur, iron, chromium,
and nickel. In all cases the oxide content
was not detectable, and the sulfur content well
below 100 ppm. Comparison with HF-treated
batches showed no detectable differences. The
iron, chromium, and nickel concentrations were,
in general, lower than those resulting from HFtreated
batches. In an attempt to produce the
NaF-KF-LiF eutectic (1 1.5-42.0-46.5 mole 7%) plus
14 wt % UF, without the preliminary HF treatment,
it was found that the previous difficulty of inconsistent
results still remained.
A study of the reaction
F, --+ 4UF,
ali-metal fluorides has shown
that potassium fluoride has a strong inhibiting
completion of the reaction. It was
the KF concentration of the eutectic
mixture (NaF-KF-LiF, 11.5-42.0-46.5 mole %), a
little better than 50% conversion of the UF, to
UF, could be expected. With this in mind, new
attempts were made to produce consistent batches,
and it soon became evident that the handling
technique was quite important. After several
changes in processing techniques were tried, the
most promising method was chosen as a standard
procedure. Briefly, this method utilizes separate
purification steps for the main constituents involved.
The eutectic (NaF-KF-LiF, 11.5-42.0-46.5
mole %) is first heated and stripped with H,. The
melt is cooled and the UF, is added, after which
the melt is again heated and stripped. The melt
is then cooled, and uranium metal is added. The
final heating and stripping are then carried out,
and the batch is transferred to a storage can.
In this manner, drying and purification of the
alkali metal fluorides are accomplished without
danger of hydrolyzing or oxidizing the UF,; also,
thorough mixing of the UF, is provided before the
ranium metal is added. A further advantage is
that the batch is well purified and miscellaneous
side reactions of impurities with the uranium metal
are kept to a minimum.
A series of batches was processed to demonstrate
producibility of this method. In previous
ts the U3' concentration ranged from 0.5 to
6 wt %. The new series of preparations, listed in
able 5.6, shows a fair degree of consistency, and
TABLE 5.6. RESULTS OF ANALYSES OF
NaF-KF-Li F EUTECTIC*-UF3
PREPARATIONS
Uranium Content lmpuri ties
(wt W) (PPm)
U3' Total U Fe Cr Ni
5.39 8.09 155 70 45
4.83 10.9 95 30 85
6.63 12.5 220 30 75
4.92 12.3 60 25 35
5.60 10.5 145 50 1510**
5.02 11.5 140 30 45
5.86 11.2 80 25 25
5.08 11.4 150 30 60
5.70 10.6 430** 28 18
5.47 10.9 215 30 135
*(11.546.5-42.0 mole W).
**Note: to be rechecked.
such material will be accepted for corrosion studies.
Since it was known that the reaction
U + 3UF4+4UF,
did not go to completion, the presence of uranium
metal in the reactor vessel after completion of a
processed batch was expected and was verified
by examination of the heels left in the vessel.
A rigid program of equipment preparation was also
initiated. All reactor vessels and receiver vessels
are flange-topped to allow access for cleaning, and
the reactor vessels are equipped with nickel liners
to allow easy removal and cleansing. Receiver
vessels are presently equipped with lnconel liners
because attack by HF gas is no longer a problem
since HF was eliminated from the process. Each
unit is completely disassembled after each run,
and all parts are cleaned or replaced when neces-
sary. c
Purification of KF and RbF
C. M. Blood
Mater io Is Chemistry D i vi s ion
Several batches of KF and RbF have been proc-
essed to meet requirements for these materials in
purified form. The RbF, when received, contained
0
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