Experimental Investigation and Mathematical Modeling of Cold Cap Behavior in High‐Level‐Waste Glass Melter

Abstract

The cold cap is a layer of reacting melter feed floating on the surface of molten glass in a glass-melting furnace. The cold cap consists of two distinct portions, the upper portion which allows the reaction gases to escape through open pores, and the lower portion which traps the gases within the continuous glass-forming melt, creating foam. The temperature span over the cold cap is ~1000 K. Data needed to simulate the cold cap mathematically include the kinetics of multiple reactions, reaction enthalpies, heat capacity, density, porosity, and heat conductivity as functions of both the temperature and the rate of heating. These data were produced via crucible experiments. The mathematical model has been completed. It relates the cold cap thickness, the rate of melting, the temperature field, and cold cap structure (foaming, dissolution of quartz particles, and formation and subsequent dissolution of crystalline phases, such as spinel) to the cold cap bottom temperature, the fraction of heat flow to the upper cold cap surface, the melt foaminess, and the chemical and physical nature of melter feed materials. To verify the model, cold caps were produced in a laboratory-scale melter and their structure is currently investigated.

Glass-contact refractory of the nuclear waste vitrification melters in the United States: a review of corrosion data and melter life

“…Convection can be also forced through the glass pool through differential control of the upper and lower electrodes. The cold cap region controls the feed-to-glass conversion reactions and is critical to managing volatile species during glass production [46][47][48][49][50][51][52][53]. Glass is drawn from near the bottom of the melter and discharged be an overflow weir.…”