ORNL-1771 - Oak Ridge National Laboratory

ANP QUARTERLY PROGRESS REPORT
uranium concentrations an olive-drab cubic phase
(refractive index, 1.46) and a blue biaxial phase
(refractive index, 1.544) also appear. There is
evidence that the blue material is a solid solution
of Na,lJ,F~,-K,U,F,; whether it dissolves UF, is
not known,
UF, in NoF-RbF-LiF Mixtures
The previously reported '' data on the solubility
of UF, in the NaF-RbF-LiF eutectic composition
were based an the assumption that all the uranium
in the filtered specimens was UF,. For more.recent
studies, the solubilities were determined by using
200-9 samples of melt, mechanical agitation during
the equi I i bration period, and 20% excess uranium
for the reduction step. Samples of the equilibrium
mixture were withdrawn with a filter stick contain-
ing sintered nickel as the filter medium. The
samples were then analyzed for trivalent uranium
and for total uranium. The results of the analyses
are presented in Table 5.3.
"R. J. Sheil and C. J. Barton, ANP QUUY. Prog. Rep.
lune 10, 1954, ORNL-1729, p 53.
58
The significance of the analyses for UF, is not
entirely clear, Petrographic examination of the
solidified filtrates indicated a reddish-brown ma-
terial, presumed to be Rb,UF,, as the only colored
phase, While it is possible that this material could
acconirnodate UF, in solid solution, it does not
appear likely that as much as 75% of the total
uranium present could be hidden in this fashion.
The good agreement, for some of the mixtures
studied, between the theoretical uranium content
and the measured total uranium content indicates
that the reaction of UF, with uranium metal pro-
ceeded nearly to completion. Additional data on
this system will be needed before an interpretation
of the results can be presented.
UF in the Individual Alkali-Metal Fluorides
Filtered specimens from preparations in which
UF, dissolved in LiF was treated at 825 to 850°C
with excess uranium iiietal have shown that more
than 90% of the dissolved uranium is trivalent and
that it crystallizes as UF,. Accordingly, it is
believed that the behavior observed by thermal
analysis of this system is that of LiF with pure,
TABLE 5.3- SOLUBlLlTY OF UF3 iN NaF-RbF-LiF MlXTURES AT VARIOUS TEMPERATURES
Theoretical Composition Theoretical F i I tiati on
Filtrate Composition
(mole W) u3+ Content Temperature (wt %I
........
__
NaF RbF LiF (wt W)
(OC)
u3+ Total 1
.......... uF3
......... .
14.1 37,6 42.3 6.0 19.3 793 2,92 15.2
7 00 1.41 16.9
6 45 4.54 16.7
600 1.17 14.7
550 10.7
495 5.26
9.4 47.0 37.6 6.0 17.7 750 5.51 17.0
675 9.18 16.9
6 50 3,22 18.0
6 25 9.95 16.4
6 00 No sample*
5.6 48.9 39"5 6.0 17.3 8 00 5.07 16.8
750 4.02 17.0
700 4.07 17.3
6 50 4.76 16.4
6 25 4.86 13.1
600 6.35
~ ............... ._____
___
*Filtration wc?s attempted, but the filter apparently clogged at this temperature and the sample could not be 05tained.