ORNL-1771 - Oak Ridge National Laboratory

A N P Q UA R I-EKIY PRO G R ESS R E P ORT
The paition of a hot leg shown in Fig. 6-14 was
taken from an Inconel thermal-convection loop which
had circulated UF, (2,l wt !% UF, in 2.4 wt %
total U) in NaF-ZrF, (53-47 innlc %) for 508 hr at
a hot-leg temperature of 1500°F. The fluoride mix-
ture was drained from the loop at the operating
temperature to ascertain whether the layers pre-
viously noted had formed during cooling of the loopa
Since the layer was again present, it is now ton-
sidered to have formed during operation. This
conclusion was further strengthened when the
metal lographic examination revealed e diffusion
zone between the layer and the base metal. An
examination of the layer by ii microspark spectro-
graphic: technique3 showed it to be predominantly
zirconium. Since this technique is not sensitive
to uraniuii~, the layer could also contoin uranium.
Thwe is some indication that some of the LJF,
dissociates to produce uranium metal, which re-
duces some of the ZrF, to produce zirconium metal.
The accuracy of the analytical determination for
zirconium is not sufficient to reveal ;he reaction
products postulated, since some zirconium is also
lost by sublimation.
graphic exarninatian. The voids did not appear to
be the same QS those normally found, and it is
thought that they were formed when brittle inter-
metallic compounds were pulled out of the base
metal during polishing. No hot-leg attack could be
found, as shown in Fig. 6.15, but there was a layer
0.5 mil thick on the hot-leg surface. This layer
was also reported to be predominantly zirconium.
It has been definitely established that the use of
UF, rather than UF, in ZrF4-base mixtures will
lower the corrosive attack and mass transfer in
lnconel systems. s-lO\Mevei, it has been found to be
impossible to dissolve sufficient UF, in ZrF4-base
mixtures to obtain fuels of interest for high-temper-
ature ienctms, To obtain a fuel with sufficient
uranium, it would be necessary to use a mixture
of UF, and UF,. Data obtained from loops oper-
ated with such mixtures and with standard UF,-
bearing mixtures are presented in Table 6.7. The
data show clearly that a mixture of UF, and UF,
produces less attack than UF, alone, but the mixture
does not eliminate the attack, as is the case
with UF, alone.
In another lncowel loop in which UF, in NaF-
Effect of
ZrF, wos circulated for 2000 hs at 1500°F,
UF, in AJkali-Metal Base Fuels
some
7
voids were found to a Cllcpth of 4 mils upon metallo- It has been found that more UF, can be dissolved
'Examination made by C. Feidmon, Chemistry Division. in the alkal i-metal-base fluoride mixtures than in
the ZrF4-base mixtures, and therefore additional
tests were made with NuF-KF-LiF (1 1.5-42.0-46.5
36
d
mole %) containing UF, UF,, and mixtures of the
two.
.
. 8
0
.
4p
.
.
PI.
a
Fig. 8.15. Hot-Reg Surface ab Inconel Loop
After Circulating UF, in HaF-ZrF4 for 2000 ha
OF. Unetched. 250X. Reduced 36%.
a
5
.