Influence of Near-Field Materials on the Durability of Nuclear Waste Glass
Neill, Lindsey M.
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A reliable and effective method of nuclear waste disposal is necessary for the continuing use of nuclear energy. Borosilicate glasses are the currently accepted method of the disposal of these wastes, though a thorough understanding of their behavior in a geological repository is necessary to ensure their safety for hundreds of thousands of years. This work focuses on the alteration behavior of simulated nuclear waste glasses of varying compositions in the presence of near-field materials and conditions expected in a repository. These near-field materials and conditions include changes in leaching solution composition, surface conditions of the glass, and the introduction of iron containing minerals (hematite, magnetite, and siderite). These minerals are representative of corrosion products produced by the stainless steel barrier drum that will contain the waste glass in a geological repository. An in-depth study of the changes in glass surface properties when in the presence of one of these iron bearing minerals was performed. This work highlights the unique chemistry within surface cracks on the glass surface that is enhanced by the introduction of the iron-bearing mineral magnetite. Additional studies were performed with two other iron-bearing minerals, hematite and siderite, to further understand the mechanisms responsible for the changes in glass behavior when in the presence of these minerals. A novel statistical approach was also performed to understand the major effects and the synergistic effects between multiple experimental conditions representative of geological repository near-field materials. This work comprised of a large experimental matrix combining four glass types, three iron minerals, two solution conditions, two glass surface conditions, and two different configurations of iron mineral contact. Fractional factorial design was used to combine these variables into sample sets, and the resulting responses were analyzed with JMP statistical software. This new statistical approach allowed for a better understanding of the mechanisms responsible for glass dissolution behavior under simplified geological repository conditions.