Effects of alumina sources (gibbsite, boehmite, and corundum) on melting behavior of high-level radioactive waste melter
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Effects of alumina sources (gibbsite, boehmite, and corundum) on melting behavior of high-level radioactive waste melter feed SeungMin Lee1, Pavel Hrma1, Richard Pokorny2, Jaroslav Klouzek2, Bradley J. VanderVeer1, Carmen P. Rodriguez1, Jaehun Chun1, Michael J. Schweiger1, and Albert A. Kruger3 1
Radiological Material & Detection Group, Pacific Northwest National Laboratory, Richland,
WA 99352, U.S.A. 2
Laboratory of Inorganic Materials, joint workplace of the University of Chemistry and
Technology and the Institute of Rock Structure and Mechanics of the ASCR, V Holešovičkách 41, 182 09 Prague 8, Czech Republic 3
U.S. Department of Energy, Office of River Protection, Richland, WA 99352, U.S.A.
ABSTRACT Types of melter feed materials affect glass production rates. This study focuses on the effects of alumina sources on melting behavior of high-alumina high-level-waste melter feeds containing different alumina sources, namely, gibbsite, boehmite, and corundum. The heat flow from the glass melt to the cold cap, a floating layer of the reacting feed, is partially hindered by a foam layer at the bottom of the cold cap. Volume expansion tests and thermoanalytical methods revealed that a slow-melting feed with corundum foamed extensively, whereas a fast-melting feed with boehmite had a low reaction heat and produced less stable foam. The foam thickness, a critical factor for the rate of melting, estimated using the relationship between the heat conductivity and foam porosity was in reasonable agreement with experimental observation. INTRODUCTION The Hanford Tank Waste Treatment and Immobilization Plant, currently under construction, will immobilize over 0.2 million m3 of radioactive waste stored in underground tanks at the Hanford Site in Washington State. The waste will be vitrified by mixing it with glass-forming and glass-modifying additives to produce slurry feed, which will be charged into an electric melter [1-3]. In the melter, the feed is converted into glass [2-6]. The conversion occurs in the cold cap that floats on the molten glass. In a steady state, the heat flows up from the molten glass into the cold cap, and feed materials move down while converting to glass. Most of the heat is consumed in the reaction layer [4-6]. Thus, the heat flux, Q, and the melting rate, j, are related as ܳ ൌ ൫ȟ ܪ ܿ ȟܶ൯݆
(1)
where ΔH is the conversion heat, cp is the heat capacity, and ΔT is the cold cap temperature difference. The response of the melter feed to heating is affected by the choice of feed materials, including the particle size of chemicals and minerals [2, 3, 6]. About 46% of the Hanford high-
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level waste (HLW) contains high fractions of alumina [2]. High-alumina feeds were extensively tested at the Vitreous State Laboratory (VSL) [7]. Melter feeds for identical
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