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ANP PROJECT PROGRESS REPORT
equivalent chromium contents, approximately
400 ppm. Thus the increase in the cold-zone
surface area produced 00 apparent effect on
corrosion under the conditions of these tests.
Some increase in the ovount of mass transfer,
as evidenced by increased hot-leg attack, was
expected with increased cold-leg surface area on
the basis of thermodynamic studies of the reactions
of fluoride.salts with pure chromium and with the
chromium in lnconel (see Chap. 2.2, "Chemical
Reactions in Molten Salts"). These studies
predict that mass transfer of lnconel in ZrF4-
bearing fluoride mixtures should be rate-controlled,
in port, by the amount of chromium which can
diffuse from the circulated fluid into the cold leg.
Such a process would be related directly to the
cold-zone surface area,
Examination was completed of loop 7425-43,
which was operated as a part of a series of tests
to study the effect of the bulk fluoride temperature
on the corrosion of Inconel. The loop circulated
the fuel mixture (No. 30) NaF-ZrF,-UF, (50-46-4
mole %), and it operated with a maximum wall
temperature of 1700°F, a maximum fluid temperature
of 1500°F, and a fluid temperature drop of 20OOF.
The results of operation of this loop are to be
compared with those for -loop 7425-41, which, as
reported previously,2 was operated with a similar
maximum wal I temperature and temperature drop,
but with a maximum fluid temperature of 165OOF.
Other conditions of operation for these two loops
are compared in Table 3.1.1.
The maximum attack was found in the region of
maximum wall temperature in both loops. As
shown in Figs. 3.1.1 and 3.1.2 the types of attack
were quite similar, as were the depths of attack,
being 9 mils in loop 7425-43 in which the maximum
fluid temperature was 1500°F and 10 mils in
loop 7425-41 in which the maximum fluid temper-
ature was 1650OF. The amounts of chromium in
solution in the fluoride mixtures in both loops,
as shown in Table 3.1.2, were also comparable,
with the amount in the fluid circulated at 1500°F
actually being greater. If variations in Reynolds
number are neglected, as argued previously,2
the insignificance of the effect of the differences
in bulk fluoride mixture temperature in these two
tests is apparently the result of the similarity in
maximum wall temperatures (170OOF in both loops).
2J. H. DeVan, ANP Qum. Ptog. Rep. Dec. 10. 1955.
ORNL-2012, P 105.
The importance of the wall temperature to .cor- U
rosion in Inconel-fluoride fuel systems was ?
discussed previously.
Fig. 3.1.1. Region of Maximum Attack in lnconel
Forced-Circulation Loop 7425-43 Which Circulated
the Fuel Mixture (No. 30) NaF-ZrF,-UF, (50-46-4
mole %) for 1000 hr with a Maximum Wall Tempera-
ture of 1700°F and a Maximum Fluid Temperature
of 1500OF. Etched with modified aqua regia.
250X. Reduced 32.5%.
Fig. 3.1.2. Region of Maximum Attack in lnconel
Forced-Circulation Loop 7425-41 Which Circulated
the Fuel Mixture (No. 30) NaF-ZrF,-UF, (50-46-4
mole %) for 1000 hr with a Maximum Wall Tempera-
ture of 170PF and a Maximum Fluid Temperature
of 165OOF. Etched with modified aqua regia.
250X. Reduced 32.5%.
F