Development and Characterization of Glassy Materials for HLW Immobilization with Datolite and Bentonite as Glass Forming
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Development and Characterization of Glassy Materials for HLW Immobilization with Datolite and Bentonite as Glass Forming Additives Sergey V. Stefanovsky,1 Michael V. Skvortsov,2 Olga I. Stefanovsky,1 Boris S. Nikonov,3 Stepan Kalmykov,4 Igor A. Presniakov,4 Iana S. Glazkova4 1
Frumkin Institute of Physical Chemistry and Electrochemistry (IPCE), Russian Academy of Sciences, Federal Agency of Science Organizations, 31-4 Leninskii av, Moscow 119071 Russia 2 D. Mendeleev University of Chemical Technology, Miusskaya sq. 9, 125047 Moscow, Russia 3 Institute of Geology of Ore Deposits, Mineralogy, Petrography, and Geochemistry, Russian Academy of Sciences, Federal Agency of Science Organizations, Staromonetnii lane 35, Moscow 11017 Russia 4 Lomonosov Moscow State University, Radiochemistry division, Vorobyovy Gory, 1, Building 10, Moscow 119991 Russia ABSTRACT Glassy materials for HLW immobilization were produced from HLW surrogate, quartz sand, datolite (CaBSiO4OH), and bentonite clay at a temperature of up to 1200 qC. Waste loading (WL) ranged between 20 and 40 wt.%. The glasses were characterized by X-ray diffraction, scanning electron microscopy and Fourier-Transform infrared spectroscopy. Glasses with waste loading of up to 35 wt.% obtained by melt pouring onto a metal plate were found to be rather homogeneous but contained minor noble metal oxides and britholite (at high waste loadings) while those annealed in turned-off furnace were partly devitrified. Average chemical composition of britholite corresponded to formula Na1.00Ca4.02Y0.33Ce0.05Nd3.64Gd0.17Si6.79O24.39. The glass network is built from SiO4 units with one or two bridging oxygens and complex borate groups with primarily ternary coordinated boron. Increase of waste loading resulted in shift of band’s maxima to lower wavenumbers exhibiting increasing the fraction of SiO4 unit with lower number of bridging oxygen ions and thus reduction of glass network connectedness. Glasses with up to 30 wt.% waste loading kept their high hydrolytic durability making them suitable for HLW immobilization. INTRODUCTION Currently borosilicate glasses are the only waste form for immobilization of high level waste (HLW) from spent nuclear fuel (SNF) reprocessing approved in France, USA, UK, Germany, Japan, Korea, and PRC while aluminophosphate glass is used in Russia only. Nevertheless in Russia possible application of borosilicate glasses for HLW vitrification is also discussed [1]. In Russia borosilicate glass is also used but for liquid intermediate-level waste (ILW) immobilization. The full scale cold crucible based plant is under exploitation at FSUE “RADON” since 1997 [1]. The technology includes liquid ILW concentrating in a rotary film evaporator to formation of ~1000 kg/m3 concentrate, which is intermixed with natural raw materials – datolite concentrate and bentonite clay producing flowable thin paste which is fed into a cold crucible melter using a peristaltic pump [1]. Datolite, nominal formula CaBSiO4(OH),
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