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constituent was found in this loop.
A considerable change had taken place
in the fluorides in both loops, as
evidenced by the unidentified brownish
material found, along with the green
phase, in all sections. No free UF,
was produced, a1 though intermediate
reduction products similar to those
present in NaK loops were found.
The static corrosion tests had
indicated optimistic results when
base metals were used as inhibitors.
Previously reported work had also
shown a reduction in attack when
nonuranium-hearing fluorides viere
circulated. Small amounts (about 10
cm3) of NaK were therefore added to
two Inconel loops, one of which
contained NaI;'-ZrF4 -UF, and the other
NaF-KF-LiF-UF4. In these loops, both
the amount and maximum depth of attack
were lower than those in comparable
loops without, the NaK. Although the
improvements were not large and could
have resulted from the normal spread
in results, the fact that the metallic
impurities in the fluorides were so
low would indicate that the i m -
provements were real. The NaF-ZrF4-UF4
(44-50-4 mole %) was changed in
appearance and included yellow material
that was present both as clumps and
as a grain-boundary constituent.
This loop also gave considerable
difficulty during startup, and it was
necessary to strike the legs frequently
with a hammer to maintain circulation.
Free UF,, as well as intermediates,
was produced in the fluoride.
Since chromium is the material
being leached from the hot leg, the
addition of chromium to the fuel could
possibly slow down the reaction. It
would be necessary to keep the chromium
concentration low enough to prevent
saturation and deposition in the cold
leg, but high enough to reduce the rate
of solution in the hot leg. The solu-
bility of chromium in the fluorides
has not yet been determined. Two
loops were operated with a chromium
138
addition, but the results are inconclusive
since the chroinium did not
mix with the fluorides. The analysis
of the fluorides in both loops showed
a chromium concentration in the various
loop sections that was even lower than
normal, whereas a chromiuin concentration
of over 5% was observed in the
fluorides in the expansion pot of one
1 oop.
Inserted Corrosion samples. Two
Inconel loops were operatedwith small,
flat, Inconel samples inserted in the
top of the hot leg. In a loop operated
with NaF-ZrF4-UF, (46-50-4 rirole %>,
the wall attack in the hot leg con-
sisted of moderate integranular
and general attack from 9 to 17 m i l s
deep, which is deeper than normal.
The sample in this loop, however, was
attacked to adepth of only 1 mil. The
second loop, which contained NaF-KF-
LiF-UF, (10.9-43.5-44.5-1.1 mole %),
showed moderat,e wall attack from 5 to
11 m i l s deep, which is average attack
for NaF-KF-I,iF-UF4. The sample was
attacked lightly to only 3 m i l s in
depth. Two more loops are now circu-
lating with small thin-walled tubes
inserted in the hot leg. Thermocouples
inserted in these tubes show that a
large temperature drop is not responsi-
ble for the lack of attack on the
sainples.
Crevice Corrosion. As an additional
check on the crevice corrosion found
at the top weld in the thermal loops
and in one of the pump loops, a loop
was operated with two crevices fabri-
cated into the hot leg. NaF-KF-LiF-UF4
(10.9-43.5-44.5-1.1 mole %) was circu-
lated in this loop at 1500°F. In
the upper section of the hot leg,
the w a l l attack varied from 4 to 7
mils, whereas in an adjoining crevice,
the attack was from 6 to 8 mils and
twice as concentrated. At the lower
crevice, the pipe showed only scattered
pits, up to 5 m i l s deep, whereas
normal attack, up to 6 mils, was found
in the crevice. This loop showed only
a slight increase in depth of attack