ORNL-1771 - Oak Ridge National Laboratory

ANP QUARTERLY PROGRESS REPORT
and UF, to the corresponding chloride^,^ it was
noted that UF, was dissolved much more readily
than UF, by fused NaAICI,. Measurements of the
solubilities were carried out by equilibrating sain-
ples of the uranium fluorides with molten NaAICI,
for periods up to 5 hr, under an inert atmosphere,
followed by the separation of the undissolved
solids by filtration and calculation of the solubility
from the concentration of uranium in the filtrate.
Solubilities of 18 and 16 mg of UF, per gram of
NaAICI, were found at 200 and 175OC, respectively.
However, the solubility of UF, decreased from
5 iiig/g of NaAICI, at 225OC to less than 1 mg/g at
2OOOC. Since UCI, was also found to be sparingly
soluble at the lower temperatures, the above values
are indicative of the true solubility of trivalent ura-
nium in this medium rather than of incomplete con-
version of the fluoride to chloride. At temperatures
lower than 200'6, molten NaAICI, is expected to
dissolve tetravalent uranium selectively from UF,
which hos been complexed by potassium fluoride in
the fuel.
Since all available UF, samples are contaminated
with tetravalent uranium, it has not been possible
to carry out accurate solubility measurements at
the lower temperatures by relying on the determina-
tion of total dissolved uranium. An apparatus has
been constructed for the determination of microgram
quantities of trivalent uranium in the filtrates by
hydrogen evolution. This apparatus, which is based
on the measurement of evolved gases at reduced
pressures, is now being calibrated against cou-
lonietrically generated hydrogen. In order to carry
out dissolutions at lower temperatures, LiCl-AICI
fluxes which melt at approximately 120OC have
been prepared.
Oxidation of UF, with Oxygen
A. S. Meyer, Jr. W. J. Ross
Analytical Chemistry Division
Preliminary investigations have been initiated to
determine the extent of the oxidation of UF, by
oxygen at elevated temperatures. The reaction is
assumed to be
4UF, + O,+ 3UF, + UO, .
its uranium content, which is assumed to be UF,.
In these tests the reaction time was held constant
at 2 hr and the temperature was varied from 200 to
600oC, with the results shown in the following:
Ternperoture Reactivity
(OC) (%I
200
3 00
500
600
30
100
91
25
At 300°@ the reaction proceeds quantitatively as
written. At higher temperatures, however, the con-
centration of soluble uraniuiii (UF, in ammonium
oxalate) decreased rapidly from the theoretical
content with increasing temperature, probably as u
consequence of a further reaction of oxygen with
UF,.
The experiment was then repeated with UF, and
oxygen. At 2OOOC the entire sample was soluble
in ammonium oxalate, as expected, which indicated
no oxide formation. At higher temperatures, a black
insoluble residue was formed upon dissolution of
the sample in oxalate solution. The amount of
residue increased at higher temperatures from 11%
at 3OOOC to 27% at 600OC. The major portion of
the sample dissolved rapidly, and a yellow filtrate
was formed. It is to be noted that Kraus6 reported
that the following reaction occurs at 8OOT:
UF, + O,+ UF, + UO,F, .
The yellow color of the filtrate substantiates this
reaction in part, but there is no way of accounting
for the black residue, obviously an oxide of ura-
nium. it is known,7 however, that UF, is converted
quantitatively to U,Q, when ignited at 900°C in
air. Petrographic and x-ray studies of the material
will be made. Further tests are planned at various
reaction times and temperatures.
Determination of Lithium, Potassium, Rubidium,
and Fluoride !Qn in NoF-KF(RbF)-LiF-Base Fuels
J. C. White G. Goldberg
B, L. McDowell
Analytical Chemistry Division
A critical review of the onalvtical methods for
solution, and the soluble portion is analyzed for
- -
6c. A. Kraus, Technical Report 107 the Months 01 Apnl,
1943: Chemical Reseurch - General,
!?17?$ 1r39, 1944.
'W. J. Rodd and J. L, Mattern, ANP Quur. Prog. Rep.
Mar. 10, 1954, ORNL-1695 p 111.
'J. J. Katz and E. Rabinowitch, The Chemistry of
Urmium, p 374, MeGraw-Hill, New York, 1951.
152