ORNL-1771 - Oak Ridge National Laboratory

Studies of the NaF-ZrF,-UF, system were initi-
ated after the solid phase studies in the NaF-ZrF,
system were completed, and to date no ternary com-
pounds have been discovered in the NuF-ZrF,-UF,
system. A tentative equilibrium diagram has been
prepared, The apparatus for vi suul observation of
melting temperatures was used to observe eleven
NaF-UF, mixtures in the composition range 20 to
50 mole % UF,, and a partial phase diagram of the
system was prepared. A new apparatus has been
constructed that will permit some mnnipulations to
be carried out with the fused salts in an inert
atmosphere.
Recent attempts to correlate the anticipated re-
duction of UF, in the preparation of UF3-bearing
melts with wet chemical analysis for UF, and UF,
and results of petrographic examination show some
surprising anomalies. When UF, dissolved in LiF,
in NaF-ZrF, mixtures, or in NaF-LiF mixtures is
treated under flowing hydrogen at 800°C with ex-
cess uranium metal, 90% or more of the UF, is
reduced to UF,. However, when this technique is
applied to UF, in NaF-KF-LiF mixtures, the re-
duction is only 50% complete at 800°C and, perhaps,
75% complete at 600°C. Petrographic examinations
of the specimens reveal no complex compounds of
tetravalent uranium; it is possible that the UF, is
“hidden”in solid solutions or in complex UF,-UF,
compounds in which it is not at present recogniz-
able.
A method for the large-scale Purification of
rubidium fluoride has been developed. All the
rubidium fluoride obtained from commercial sup-
pliers to date has contained considerably more than
the specified quantity of cesium compounds, and
therefore almost all of it has been returned io the
vendors for further processing. The purification
method developed can be used at a reasonable cost
on a large scale if material sufficiently free from
cesium cannot be obtained from commercial sources.
Values for the equi!ibrium constant for the re-
action
Cr” + 2UF, 2UF, t CrF,
in molten NaZrF, have been re-examined by the use
of various ratios of UF3/UF, with chromium metal
in the charge. From the data obtained when this
5. CHEMISTRY OF MOLTEN ~ ~ ~ ~ R ~ ~ L S
W. R, Grimes
Materials Chemistry Division
initial ratio is less than 3, average values of
5 x IO-, at 600°C and 6 x lom4 at 800°C can be
computed, At ratios larger than 3 the values in-
crease regularly; this rise is probably due to the
extreme difficulty in filtration and analysis of
samples containing 1 to 20 ppm of Cr++. The
values at low UF,/UF, ratios agree quite well
with the corresponding values of 4.2 x lo-, at
600°C and 4.1 x low4 at 800’C obtained previously
when UF, and chromium metal were the charge
mater i a1
Fundamental studies were made of the reduction
of NiF, and FeF, by H, in NaF-ZrF, systems as
a means of determining possible improvements in
purification techniques. Also, methods for pre-
paring simple structural metal fluorides were
studied. Additional measurements of decomposition
potentials of KCI and of various chlorides in molten
KCI at 850°C were made.
Preliminury measurements of the solubility of
xenon in KNO,-NaNO, eutectic (66 mole 7; NaNQ,)
show values of 8.5 x low8 and mo6e/cm3 at
280 and 3M)”C, respectively, at 1 atm xenon pres-
sure. The all-glass apparatus used has been re-
placed with CI nickel and glass combination, and
measurements of xenon solubility in molten fluo-
rides are being made.
Large quantities of purified ZrF4-base fluorides
are being prepared for engineering tests at ORNL
and elsewhere, and the demand for purified fluo-
rides of other types for possible reactor fuel appli-
cation is increasing rapidly. Consequently, an
increasing fraction of the effort is devoted to pro-
duction or to research in direct support of produc-
tion functions.
Since the consumption of NaF-ZrF, and NaF-
ZrF,-UF, mixtures is expected to reach 10,000 Ib
during the fiscal year, it is important to decrease
the cost of production of this material. The HF-H,
processing currently used is adequate from all
points of view, but processing times of nearly
I00 hr per batch ore now required with the rela-
tively poor raw materials available. The sub-
stitution of hafnium-Free ZrF, and commercially
available NaFx.ZrF, for the impure ZrF, now
used should afford a considerable saving. The
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