Interaction Effects between Dissimilar Metals in High Velocity Sodium at Temperatures up to 760°C I. Mass Transfer of Vanadium onto Type 321 Stainless Steel

Summary

Comparative corrosion studies are being carried out with potential fuel cladding materials for advanced Liquid Metal Fast Breeder Reactors. The materials under test at temperatures as high as 760°C include refractory metal-base, cobalt-base, and iron-base alloys. Two pumped loops, made entirely of stabilized stainless steels, are used to carry out the investigations. The corrosion specimens are exposed to high velocity sodium (22 ft/sec) in a 24"-long rising temperature region (between 710° and 760°C). In the tests, the oxygen content of the sodium has been controlled over the range from <1 to 15 ppm.

Post-test examination has shown dissimilar metal mass transfer. In tests containing V-base alloys, significant amounts of V have been detected on the surfaces of type 321 stainless steel specimens. X-ray fluorescence analysis shows that about 25 times more V is present on the surface of an exposed sample than on an unexposed standard. Microprobe analysis of two type 321 SS specimens that were exposed simultaneously throughout the entire run but at opposite ends of the test section, i.e. 710° vs 760°C, showed that the difference in their corrosion behavior was the depth to which the V penetrates each sample, not the surface concentration of V. In general, increased temperature, exposure time and oxygen concentration in the sodium appeared to increase the extent of dissimilar metal reactions.

This work was performed under the auspices of the U. S. Atomic Energy Commission.