ORNL-4191 - the Molten Salt Energy Technologies Web Site

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ORNL -DWG 67-7941
Fig. 16.6. Comparutive Rupture Strains for Various Heats of Hastelloy N Irradiated and Tested at 1200'F.
We removed a second set of Hastelloy N speci-
mens in June 1967. The specimens removed from
the core had been at temperature for 5500 ht and had
accumulaied a peak thermal dose of approximately
4 i lo2') neutroms/ctn'. The core specimens were
modified alloys containing approximately 0.5% Ti
(heat 31545) and 0.5% Zr (heat 21554). A stringer
of vessel specimens was also removed. These
specimens had been exposed to the MSRE cell
environment for about 11,000 hr and had accumulated
a peak thermal dose of about 3 x 10'' neutrons/cm2.
The vessel specimens were made of the same heats
used in constructing the MSRE.
We have not completed the mechanical testing of
these m a t eria Is, but preliminary metallo graphic
studies have been completed The primary concern
with the vessel specimen was whether they were
being nitrided by the cell environment. Figure 16.7
shows the surface of heat 5085. There is no evi-
dence of^ nitriding, and the maximum depth of oxida-
tion is about 0.003 in. The specimen taken from
1 o3
heat 5065 happened to be a weld made in construct-
ing the stringer. This specimen is shown in Fig.
16.8. The amount of surface oxidation is greater,
but the depth of oxidation is still. small, and there
is no evidence of nitriding.
Heat 21545 contained 0.5% Ti, arid our main con-
cern was whether the alloy would corrode in the
fused salt environment. Figure 16.9 shows that
there is some slight surface reaction but no ex-
tensive corrosion. Heat 21554 contained 0.5% Zr,
and we were again concerned with the corrosion re-
sistance. Figure 16.10 shows the surfaces of the
surveillance specimens of this heat and indicates
the lack of significant corrosion.
Thus we are encouraged by the observations that
(1) the MSRE grades of Hastelloy N are not being
oxidized at a high rate, and there is no evidence of
nitriding in the cell environmeni; and (2) the small
zirconium and titanium additions that we are making
to Hastelloy N do not appear detrimental.
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