Effects of heating rate, quartz particle size, viscosity, and form of glass additives on high‐level waste melter feed volume expansion

Abstract

Nuclear waste can be vitrified by mixing it with glass‐forming and ‐modifying additives. The resulting feed is charged into an electric glass melter. To comprehend melting behavior of a high‐alumina melter feed, we monitored the volume expansion of pellets in response to heating at different heating rates. The feeds were prepared with different particle sizes of quartz (the major additive component) and with varied silica‐to‐fluxes ratio to investigate the glass melt viscosity effects. Also, we used additional melter feeds with additives premelted into glass frit. The volume of pellets was nearly constant at temperatures <600°C. After a short period of volume shrinkage at ~600°C‐700°C, foam generation produced massive volume expansion. The low heat conductivity of foam hinders the transfer of heat from molten glass to the reacting feed. The extent of foaming increased with faster heating and higher melt viscosity, and decreased with increasing size of quartz particles and fritting of the additives. Volume expansion data are needed for the mathematical modeling of the cold cap.

Foaming during nuclear waste melter feeds conversion to glass: Application of evolved gas analysis

“…To investigate the effect of melt viscosity on foaming, Figure displays the EGA data obtained for six feeds of the viscosity test series in the primary foaming region (650‐1150°C). Figure shows the feed porosity as a function of temperature evaluated from FET data . The dashed lines represent a cubic fit to data using the least squares analysis:…”

“…Porosity of feeds in viscosity test series as a function of temperature . Dashed lines illustrate empirical fit using cubic parabola, with coefficients being linear functions of viscosity…”

“…Both the foam‐onset and foam‐collapse temperatures ( T FO and T FM ) increased as the feed viscosity increased. The shift of T FO and T FM is caused by the later formation of primary borosilicate melt, resulting from the decreasing amount of fluxes (sodium and lithium borates from Li 2 CO 3 , Na 2 CO 3 , and H 3 BO 3 ). In the A19‐7 and A19‐9 feeds, which had higher SiO 2 content, maximum porosity increased noticeably (see Figure and Table ).…”

Glass production rate in electric furnaces for radioactive waste vitrification

“…The feed expansion test (FET), performed by observing a 1.5‐g feed pellet during heating to 1100°C at 10 K min −1 , measures feed volume as a function of temperature . As described in‚ the foam onset temperature, T FO , and maximum foam‐volume temperature, T FM , which marks the beginning of foam collapse, were obtained by fitting a cubic parabola to the expansion segment of the foaming interval.…”

Heat transfer from glass melt to cold cap: Gas evolution and foaming

“…The pellets, weighing ~1.5 g, were heated in a furnace at 10 K min −1 and photographically monitored with camera to record their changing profiles. The normalized volume of pellets was computed using a MATLAB program …”