HIPed Tailored Pyrochlore-Rich Glass-Ceramic Waste Forms for the Immobilization of Nuclear Waste
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1124-Q04-01
HIPed Tailored Pyrochlore-Rich Glass-Ceramic Waste Forms for the Immobilization of Nuclear Waste Melody L. Carter, Huijun Li, Yingjie Zhang, Andrew L. Gillen and Eric. R. Vance Ansto, New Illawarra Rd, Lucas Heights, NSW 2234, Australia.
ABSTRACT Hot isostatically pressed (HIPed) glass-ceramics for the immobilization of uranium-rich intermediate-level wastes and Hanford K-basin sludges were designed. These were based on pyrochlore-structured Ca(1-x)U(1+y)Ti2O7 in glass, together with minor crystalline phases. Detailed microstructural, diffraction and spectroscopic characterization of selected glass-ceramic samples has been performed, and chemical durability is adequate, as measured by both MCC-1 and PCT-B leach tests. INTRODUCTION The use of glass-ceramics to combine the process and chemical flexibility of glasses with the excellent chemical durability of ceramics is a well-known method to immobilize nuclear waste. This can be achieved by exploiting the glass forming components present in the waste, along with appropriate additives to modify the glass and produce the desired crystalline phases. Hotisostatic pressing (HIPing) technology offers zero off-gas emissions during the high-temperature consolidation, which mitigates volatility concerns, which in turn reduce the footprint of the system. Secondly the process places minimal constraints on the waste form chemistry insofar as the redox conditions can be adjusted from near-neutral to quite reducing by the addition of metal powders to the waste form precursors. Also the HIP can material can be selected to be reasonably compatible with the waste form and these factors permit significantly higher waste loadings to be employed. In addition, the HIP process readily produces a dense monolithic waste form, which both minimizes disposal volume and reduces surface area available for aqueous attack once emplaced in a repository. The development of glass-ceramics for nuclear waste has been studied by many workers [17]. Many of the glass-ceramics developed were targeted at zirconolite-glass ceramics and the resultant waste form were very durable, with aqueous leach rates 10-100 times better than glass [7]. Earlier work [8-9] on pyrochlore-glass ceramics was effected by mixing glass with crystalline pyrochlore and making a composite by sintering at
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