STRUCTURE OF OXIDE LAYERS FORMED ON CANDIDATE STEEL ALLOYS EXPOSED TO FLOWING LEAD-BISMUTH EUTECTIC FOR GENERATION IV REACTOR APPLICATIONS
Open Access
- Author:
- Kunkle, Jamie McKinney
- Graduate Program:
- Nuclear Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Arthur Thompson Motta, Thesis Advisor/Co-Advisor
Arthur Thompson Motta, Thesis Advisor/Co-Advisor - Keywords:
- lead-bismuth eutectic
corrosion
Generation IV Nuclear Reactors
lead cooled fast reactor - Abstract:
- Ferritic-martensitic steels of interest for use in Generation IV lead cooled fast reactors were corroded in a flowing lead-bismuth eutectic environment and the microstructures of the oxide layers they formed were characterized using microbeam synchrotron radiation. Five samples were studied, four of which (HT-9, HT-9 Annealed, T91, and a model alloy) were corroded at 500°C for 666 hours and one of which (HT-9) was corroded at 550°C for 3000 hours in flowing lead bismuth eutectic environments. Studies performed on oxide layers using microbeam synchrotron radiation yielded a detailed view of fluorescence and diffraction data from each of the oxide layers and sublayers formed. Each alloy exhibited a duplex oxide structure consisting of an inner and outer oxide layer. The interface of these two layers corresponded to the original pre-corrosion metal surface. In general, the oxide layers appeared to have been formed in a manner similar to those formed in other gaseous and liquid environments i.e. via the simultaneous ingress of oxygen (O2-) and egress of iron (Fe2+) across the inner oxide – outer oxide interface. The outer oxide layers observed were formed entirely of Fe3O4 magnetite, contained contaminates (Pb, Bi) from the coolant, and showed evidence of liquid metal dissolution. Inner oxide layers were formed primarily from Fe3O4, but also contained retained ferrite from the bulk metal, carbides, and chromium oxides. Chromium oxides, specifically Cr2O3, are known to act as barriers against the diffusion of oxygen and iron in these materials, slowing oxidation in these materials. The retained bcc iron, or ferrite, in the inner oxide combined with preferential oxidation along lath boundaries suggest that the oxide front advancement proceeded into the metal via preferential oxidation along lath boundaries, followed by selective oxidation of the laths.