DEVELOPMENT OF GLASSES FOR THE VITRIFICATION OF HIGH-LEVEL LIQUID WASTE (HLLW) IN A JOULE HEATED CERAMIC MELTER

A vitrification process was developed at Forschungszentrum Karlsruhe, Institut fur Nukleare Entsorgungstechnik (INE), for solidifying in bor osilicate glasses High Level Waste (HLW) solutions from the nuclear fu el cycle. To optimise melter operation the glass melt should have a fl at viscosity curve and a relatively high specific electrical resistanc e of less than or equal to 6.5 Omega.cm at 1150 degrees C. Further req uirements are: no liquid-liquid immiscibility and no crystallization o f the glass, waste loading greater than or equal to 15 wt% and, in vie w of repository storage of the HLW glass, a chemical durability compar able to that of other HLW glasses. The main emphasis of experimental w ork was put on finding out how the viscosity, the slope of the viscosi ty curve, the specific electric resistance and the chemical durability depend on the chemical composition of the glasses. Especially , the e ffect of the mixed alkalis Li and Na on the glass properties was studi ed. It was found that by increasing from 0 to 1 the Li2O/(Na2O + Li2O) molar ratio of the glass FRIT WAW, the viscosity of the melt decrease s roughly linearly and the slope of the viscosity curve decreases as w ell. The specific electric resistance passes through a maximum and the Soxhlet leach rate through a minimum at an alkali ratio of about 0.5. As a final result, a range of optimum glass compositions was determin ed which meet the required properties. (C) 1997 Elsevier Science Ltd.