ORNL-1771 - Oak Ridge National Laboratory

ANP QUARTERLY PROGRESS REPORT
apparatus, both from visual observation of crystal-
lization and from thermal effects recorded during the
course of the vi sua1 observations, were generally
a little higher than those indicated by the published
diagram for this system.' The data are shown on
the partial phase diagram for the NaF-UF, system
in Fig. 5.2. A solid circle indicates the tempera-
ture at which the composition appeared to be com-
pletely solidified. This point could not be de-
termined with any degree of certainty with some
compositions, uncl the disoppeorunce of the liquid
phase wus not always accompanied by B noticeable
thermal effect. The liquidus temperatures shown in
Fiy. 5.2 seem to indicate that Na,UF, melts con-
gruently at 629OC, that is, at a temperature only u
few degrees higher than the eutectic temperatures
on both sides of the compound. The data also
support the results of petrographic studies which
indicate that the compound in the 50 mole % UF,
region has the approximate composition Na,U,F,
rather than NaUF,.
A new appnratus has been constructed that will
permit some manipulations to be carried out with
the fused salts in an inert utnwsphere. It consists
essentially of a small dry box, with i-in.-thick
750
700 ~
600
550 ~
15 20 25 30 35 40
UF4 hole %)
ORNL 922
Fig. 5.2. Por4ial Wase Diagram of the NaF-UF,
SyeBcm.
54
Lucite side walls and top, attached to a stainless
steel bottom plate which has a &in. length of
2-in.-dia stainless steel pipe welded onto it to
serve CIS a furnace core. The pipe is surrounded
by resistance coils and insulating tape. The box is
equipped with face plates for covering the glove
holes so that the box can be partly evacuated
before it is filled with inert gas,
PHASE REhATlONSHlPS IN UF3-5EARING
SYSTEMS
C. J. Barton
R. J. SheiI
L. M. Brntcher
A. B. Wilkerson
Materials Chemistry Division
G. D. White, Metallurgy Division
T. N. McVay, Consultant
It was assuined in the previous studies* of solu-
bility relationships for IJF, in various fluoride
mixtures that in the presence of excess metallic
uranium or zirconium the uranium present in the
fused salt solution WQS trivalent, This assumption
seemed justified, since, for the reaction
Brewer's tabulation' of standard free energies of
formation yields
AF" = -16 kcal .
In addition, petrographic examination of the melts
obtained revealed the presence of red materials
tentatively identified as complex compounds of
UF,, with green compounds of UF, showing only
in traces, if at all. Since these observations were
those anticipated and since the petrographic ex-
ominations had previously been shown to be very
sensitive in detecting compounds of trivalent ura-
nium in systems which had been slightly reduced,
there seemed to be little reason to believe that the
results of such examination might be unreliable.
During the past quarter, however, considerable evi-
dence ha:, been accumulated by the most accurate
wet-chemicol methods yet devised for determining
U3+ and U4' in fluoride mixtures which shows
that the reduction of UF, by excess uranium metal
is not complete at 800°C. While the reduction in
*G. M. Watson and C. Ah. Blood, ANP @UT. Prog. Rep.
lune IO, 1954, QHNL-1729, p 51.
'L, Brewer et ul., Thenodynarfiic Properties and Eyui-
libria at High Temperalures of Uranium Halides, Oxides,
Nitrides, urd Carbides, MDDC-1543 (Sept. 20, 1945, rev.
Apr. 1, 11947).