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Metal waste generated from domestic nuclear operations for defense and commercial applications has led to a growing stockpile of radioactively contaminated scrap metal, much of which is stainless steel. This steel contains large quantities of strategic elements such as nickel and chromium and constitutes a valuable domestic resource [1]. A significant fraction of this material cannot be efficiently surface decontaminated, and burial of this material would be wasteful and expensive, since long term monitoring would be necessary in order to minimize environmental risk. Melt decontamination of this material would maintain the chemical pedigree of the stainless steel, allowing its controlled reuse within the nuclear community. This research addresses the melt decontamination of radioactively contaminated stainless steel by electroslag remelting (ESR). ESR is industrially used for the production of specialty steels and superalloys to remove a variety of contaminates and to improve metal chemistry. Correctly applied, it could maintain the specified chemistry and mechanical properties of the original material while capturing the radioactive transuranic elements in a stable slag phase. The ESR process also produces a high quality metal ingot free of porosity that can be directly forged or rolled into final shapes. The goal of this project was to optimize a melt decontamination process through a basic understanding of the factors which govern the partitioning of various radionuclides between the metal, slag, and gas phases. Radionuclides which are captured by a slag phase may be stabilized by promoting the formation of synthetic minerals within a leach resistant matrix. This research program included three segments. At Boston University, Prof. Uday Pal and his group conducted research to develop a fundamental understanding of thermochemical and electrochemical behaviors of slag/metal/radionuclide surrogate systems. This work combined experimental characterization and thermochemical modeling of these high temperature systems. The second segment utilized Sandia expertise and ongoing work in fundamental separation science and liquid metal processing technology to investigate and optimize ESR decontamination using representative surrogate compounds to represent contaminate radionuclides. This work evaluated partitioning of the surrogates between the slag and metal ingot in ESR experiments. Furnace operating parameters were systematically varied to determine the optimum slag processing conditions. The third effort in Russia conducted ESR melting experiments using contaminated stainless steel pipe electrodes doped with plutonium. This work provided separation data for the radioactive compounds

osti oai (u.s. department of energy office of scientific and technical information)

Optimization of Thermochemical, Kinetic, and Electrochemical Factors Governing Partitioning of Radionuclides during Melt Decontamination of Radioactively Contaminated Stainless Steel