ORNL-1771 - Oak Ridge National Laboratory

alloys, special Stellite heats, Hastelloy R, In-
conel, graphite, and various ceramics in sodium,
fluoride fuel mixtures, and other mediums (Sec. 6).
The brazing alloy 67% Ni-13% Ge-11% Cr-6%
Si-2% Fe-1% Mn was found to have good corrosion
resistance in fluoride fuels and fair corrosion
resistance in sodium and therefore will be useful
for the fabrication of many reactor components.
In the thermal-convection loop studies, UF,-
bearing fuels were tested in Inconel. Hot-leg
attack is not found in lnconel loops in which ZrF,-
base fluoride mixtures with the uranium as UF,
are circulated. A deposit is, however, found on
the hot-leg surface. Only preliminary information
is available, but it appears that neither attack
nor a hot-leg layer is found with alkali-metal-base
fluoride mixtures containing UF,. Mixtures of
UF, and UF, result in a reduction in attack from
that found with only UF, but some attack is
present, and in high-uranium-content systems the
attack may be significant.
Several Hastelloy 8 loops have now been suc-
cessfully operated in both the as-received and the
over-aged conditions. In both cases a consider-
able increase in hardness occurs during operation.
With ZrF,-base mixtures containing UF, very
little attack is found, even after 1000 hr.
Thermal-convection loop tests of molten lithium
in type 316 stainless steel were operated for 1000
hr. There were no signs of plug formation, and
only a small amount of mass transferred material
was found in one loop. Alloys of 45% Cr-55% CO,
Ni-Mo alloys, and the Fe-Cr-base stainless steels
have been shown to be more resistant to corrosion
and mass transfer in liquid lead than are the pure
metals. Their resistance to mass transfer can
probably be related to the formation of interme-
tallic compounds.
Metallurgy
Creep and stress-rupture testing by the tube-
burst method has been studied intensively (Sec. 7).
In the tube-burst tests, a tube that is closed at
one end is stressed with an internal gas pressure.
The stress pattern introduced into the specimen
in this test approaches the stress pattern that will
be found in ANP-type reactors. Apparatus for the
tests has been constructed, and a theoretical
analysis has been made with which a check on the
experimental results con be obtained.
In the investigation of high thermal-conductivity
PERIOD ENDING SEPTEMBER 70, 7954
fins for sodium-to-air radiators, stress-rupture and
creep tests were made on copper fins with various
types of cladding at stress levels between 500 and
2000 psi at 15OOOF. The tests show that for a
1000-hr exposure in air, stresses greater than 500
psi and less than 1000 psi are tolerable; that is,
in this stress range there is no indication of
brittleness in the core or oxidation of the core
due to cladding failure of type-310 stainless-steel-
clad copper fins. From the over-all considerations
of melting point, oxidation resistance, dilution of
fin and tube wall, formation of low-melting eu-
tectics, and flowability, it was found that Coast
Metals alloy 52 was the best brazing alloy for
use in the construction of radiators with high-
conductivity fins. A sodium-to-air radiator with
6 in. of type-430 stainless-steel-clad copper high-
conductivity fins was fabricated by use of u combi-
nation heliarc welding and brazing procedure.
Packed-rod nozzle assemblies were fabricated
for the 100-kw gas-fired I iquid-metal-heater system,
and work was started on the formation of duplex
tubing. An attempt is being made to prepare tubing
that will have good corrosion resistance on the
inner surface and oxidation resistance on the outer
surface.
Attempts are being made to find new alloys in
the nickel-molybdenum system that will have better
high-temperature strength and fluoride corrosion
resistance than lnconel has. Hastelloy 6 satisfies
these requirements, but it has poor fabrication
properties and oxidation resistance; it also loses
its ductility in the temperature range of interest
for application in high-temperature circulating-fuel
reuctors. Investigations are under way to find a
suitable melting practice and heating treatment
that will increase the ductility of Hastelloy B in
the temperature range of interest.
Heat Transfer and Physical Properties
The enthalpies and heat capacities of NaF-ZrF,-
UF, (65-15-20 mole %) and of LiF-NaF-UF, (57.6-
38.4-4.0 mole %) were determined (Sec. 8). The
thermal conductivity of NaF -K F-U F , (46.5-26.0-
27.5 mole %) was found to be 0.7 Btu/hr-ft2("F/ft),
that for KF-LiF-NaF-UF, (43.5-44.5-10.9-1.1 mole
%) was 2.0, and that for LiF-KF-UF, (48.0-48.0-
4.0 mole 76) was 1.4. A new electrical conduc-
tivity device has been constructed and has been
successfully checked with molten salts of known
conductivity.
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