ORNL-1816 - the Molten Salt Energy Technologies Web Site

I
A trap for fluoride vapors was developed that
can be used in any high-temperature molten fluoride
system to prevent plugging of the gas lines leading
to or from the vessel containing the fluoride,
particularly if the salt contains ZrF,. Successful
operation of this device was achieved during the
ARE pump tests at K-25.
4. Critical Experiments
The second critical assembly of the reflector-
moderated reactor was constructed that incorporated
a beryllium island. Criticality was achieved with
4.66 kg of U235 at a density of 0.092 g of U235 per
cubic centimeter of fuel annulus. This loading
was shown, by calibrated control rods, to contain
0.92% excess reactivity, equivalent to about 0.31
kg of U235, and therefore the critical mass of the
unpoisoned assembly was 4.35 kg of U235. The
experimental results thus did not agree well with
the calculated critical fuel loading of 7.16 kg of
U235 or 0.142 g of U235 per cubic centimeter of
fuel annulus. A series of measurements of neutron
and fission-rate distributions and of reactivity
coefficients will be made prior to the incorporation,
in the structure, of additional materials to simulate
reactor components.
PART It. MATERIALS RESEARCH
5. Chemistry of Molten Materials
Additional data obtained in solid phase studies
of the NaF-ZrF,-UF, system have essentially
confirmed the previous findings. There was some
indication from thermal analysis of mixtures along
the Na,U,F, ,-Na7Zr6F3, join that these com-
ponents do not form a complete set of solid solu-
tions. A new auenchin atus is beina used
than estimates of its thermodynamic properties
had indicated. It was also fourid in studies of
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PERIOD ENDING DECEMBER 10,7954
UF, mixed with KF and heated in lnconel capsules
that disproportionation of UF, occurred at a lower
temperature than would have been expected in the
absence of KF. For differential thermal analysis
of the uranium-bearing mixtures, improved graphite
containers with provision for the thermocouples to
be immersed directly in the melt are now being
used.
Investigations of the chemical reactions in
molten salts are continuing in an effort to under-
stand the mechanisms involved in the purification
of fluoride mixtures and in the reduction of UF,
to UF, in fluoride melts. Similar studies of the
corrosion products of lnconel in fluoride mixtures
and of the reduction of UF, by structural metals
are under way.
Production of purified zirconium-base fluorides
mixtures has been continued on a large scale in
the 250-lb-capacity facility. It is anticipated that
by full-time operation of this facility by a crew
of one engineer and eight technicians, a sufficient
stockpile of material will be available by December
31, 1954 to allow termination of this operation for
some time. This stock pile (to be -7000 Ib)
should be sufficient to meet the requirements of
Pratt & Whitney Aircraft, other outside requesters,
and those of the Laboratory for research in this
field.
The pilot-scale processing facility continues to
be used for small-scale development of purification
processes for new fuel compositions of interest.
Considerable effort has been expended on attempts
to prepare UF3-bearing mixtures of NaF-LiF-KF.
Careful control of operating conditions has allowed
production of sufficiently consistent UF3-content
material to permit its release for corrosion testing.
fraction of the time required by hydrogen stripping.
It has not been possible to cut the processing
time of UF4-bearing mixtures by using electrolysis,
probably because of the simultaneous reduction of
UF, to UF, at the cathode and oxidation of UF,
at the anode.
The tentative values previously obtained for the
solubility of xenon in fused salts were essentially
confirmed by data obtained with new, improved
apparatus. The new values were 8 x 10-8 and
9.3 x 10-8 mole of xenon per milliliter of melt at
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