| Summary: | Stainless steel - zirconium alloys were developed by the US Department of
Energy Laboratories as metallic waste forms for noble metal fission products. This
thesis evaluates iron-zirconium-rhenium alloys to establish a technical basis for using
metal waste form alloys for technetium-99 immobilization. Rhenium is used as a
surrogate for Tc-99 since Tc is not naturally available and Re is metallurgically similar
to Tc.
The iron-zirconium system has two eutectic compositions, Fe-15 wt % Zr and Zr-
16 wt% Fe. Ten test samples were successfully cast in yttrium oxide crucibles at
1600°C, half near each eutectic composition, with Re amounts varying from 2.5 to 12.5
weight percent.
A scanning electron microscope (SEM) with energy dispersive X-ray
spectroscopy (EDS) capability was employed to determine the phase structure and phase
composition of each sample. Iron rich samples were found to form up to three phases,
with the rhenium content favoring the intermetallic phases: 1) an Fe solid solution phase,
2) an FeZr2-type intermetallic with 11 wt % or less Re, and 3) a second intermetallic with about 18 wt % Re. Zirconium rich samples formed as many as five distinct phases:
1) a Zr solid solution phase, 2) a Zr3Fe-type intermetallic with as much as 13 wt% Re, 3)
a rhenium-zirconium intermetallic, 4) another Fe-Zr intermetallic with very little Re, and
5) a Fe-Re intermetallic.
Potentiostatic and potentiodynamic electrochemical tests were performed using
sulfuric acid to evaluate the corrosion resistance of each sample. These tests found that
the zirconium rich samples were very corrosion resistant but became increasingly
susceptible at higher rhenium concentrations. The iron rich samples were not very
resistant to corrosion under the test conditions; there was no notable trend in corrosion
behavior related to the introduction of rhenium.
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