Chemical Durability Studies of Waste-Simulant Doped Borosilicate Glasses
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&KHPLFDO'XUDELOLW\6WXGLHVRI:DVWH6LPXODQW'RSHG%RURVLOLFDWH*ODVVHV Adam Duddridge1, Moinul Islam1, Diane Holland1 and Charlie R. Scales2 1 Centre for Advanced Materials, Department of Physics, University of Warwick, Coventry, CV4 7AL, U.K. 2 British Nuclear Fuels, Ltd., Sellafield, Seascale, Cumbria, CA20 8PG. U.K. $%675$&7 A mixed-alkali modified borosilicate base glass used in the vitrification of high-level nuclear waste (HLW) has been doped with a number of waste simulants to between 2 and 12 mol%. The simulants have been chosen to give two distinct series of glasses: one consisting of trivalent ions having the form M2O3 (where M is La, Bi, Al or Fe) and the other consisting of divalent simulants of the form MO (where M is Pb, Zn or Ba). An international standard Soxhlet leach test procedure was performed on each glass to study the effect of prolonged, moderatetemperature, dynamic water corrosion. Results of these studies show that, except for BaO, as the amount of simulant is increased, the amount of Na and Li leached decreases showing them to become more chemically resistant. These corrosion tests have been correlated to ionic (D.C.) conductivity measurements, which show a decrease in the conductivity of the glass as the amount of waste simulant is increased, and 11B magic-angle spinning nuclear magnetic resonance (MAS-NMR) studies, which have shown that, as more waste-simulant is loaded into the glasses the rate of conversion of [BO4] to [BO3] units increases. All of the data from these studies reflect the different network forming abilities of the divalent and trivalent cations. ,1752'8&7,21 The most widely accepted HLW immobilisation route involves immobilisation into a solid waste form followed by long term storage or disposal. Borosilicate glass is, at present, the waste form of choice for most nuclear waste compositions and for most countries. This selection is based on the acceptable performance of the product, the fact that the glass will easily accommodate variations in waste stream composition that are extremely complex (20 to 30 component systems) and also the fabrication process has been demonstrated on a large scale [1,2]. The ability for these glasses to withstand prolonged, moderate-temperature, dynamic water corrosion is of major concern, as the final storage environment may present these factors. A number of glasses based on the mixed alkali modified borosilicate base glass that is commonly used for the immobilisation of commercial HLW, denoted as MW in Table I, have been studied using Soxhlet tests to see how the addition of waste simulants affects the chemical durability of the glasses. Previous Soxhlet studies [3] have optimised the composition of MW, but the effect of waste loading on the performance of the glass have not been investigated. 11B MAS-NMR has been used to measure the fraction of the boron atoms that are present as either [BO4] or [BO3] units and ionic (D.C.) conductivity studies have been used to measure the mobility of Na+ and Li+ ions, all of which affect the corro
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