The Underground Corrosion of Selected Type 300 Stainless Steels After 34 Years

Because of the ongoing need to dispose of nuclear waste and because the Nuclear Waste Policy Act of 1982 requires disposal of high-level nuclear waste in an underground repository, interest in long-term underground corrosion has increased. Current contaminant release and transport models use limited available short-term corrosion rates when considering container and waste form degradation; and as such, the models oversimplify the complex mechanisms of underground metal corrosion. The complexity of stainless steel corrosion mechanisms and the processes by which corrosion products migrate from their source are not well represented by a corrosion rate. The research presented here is the analysis of austenitic stainless steels after 34 years of underground exposure. In this research, the corrosion specimens are analyzed using acceptable ASTM standards as well as microscopic and X-ray examination to theorize the mechanisms of stainless steel corrosion. As presented, the differences in the corrosion mechanisms vary with the type and the treatment of the samples. The uniqueness of the long sampling time allows for further understanding of the actual stainless steel corrosion mechanisms, and when applied back into predictive models, will assist in reduction of the uncertainty in parameters for predicting long-term fate and transport.