Effect of Alumina Source on the Rate of Melting Demonstrated with Nuclear Waste Glass Batch

Abstract

The selection of raw materials affects the rate of batch‐to‐glass conversion. In all‐electric melters, foam under the batch blanket limits the heat flux from the molten glass, thus slowing the rate of melting. Our study, in which we compare the melting behaviors of three batches formulated to vitrify high‐alumina high‐level waste, shows that a slowly dissolving refractory component can cause excessive foaming. Faster melting batches with gibbsite [Al(OH)3] or boehmite [AlO(OH)] as an alumina source produced substantially less foaming than a batch with corundum (Al2O3). Although gibbsite and boehmite dissolved below 500°C, corundum was still present in the batch up to 900°C; hence, the glass‐forming melt lacked alumina in the batch with corundum. The low viscosity of that batch caused the open pores to close prematurely at 660°C, trapping gases and expanding to foam. This would explain the literature‐reported slow melting rate of a batch with corundum, as compared to batches with gibbsite and boehmite.

Kinetic model for quartz and spinel dissolution during melting of high-level-waste glass batch

“…The properties of this batch have been well, although not completely, characterized [11,31,32,33,34] and were used for the initial mathematical modeling of the cold cap [22].…”

Rhenium volatilization in waste glasses

“…Changes in feed volume were monitored using heated feed pellets [25,32,33]. Pellets $13 mm in diameter and $6.5 mm high were prepared from 1.5 g dry feed and pressed at $7 MPa.…”

“…Pellet profile areas were evaluated using Adobe Photoshop CS3 Extended. The platinum wire (10-mm in length) next to the pellet was used as a scale gauge, which allowed the program to calculate the cross-section areas of the pellets [32].…”

Conversion of Nuclear Waste into Nuclear Waste Glass: Experimental Investigation and Mathematical Modeling

“…As temperature increased above T P , the melt expanded to foam that peaked at the cavity collapsing temperature, T C , above which foam rapidly collapsed to a bubble-free melt. The degrees of conversion related to mass change, b (T) and M , were determined by the thermogravimetric analysis Pierce et al, 2012a and2012b). The differential scanning calorimetry was employed (Chun et al, 2013) to determine the effective heat capacity of the condensed phase, c p Eff = c p + Hd H /dT, where c p is the true heat capacity, ΔH is the total reaction heat (J kg -1 ), and H is the degree of conversion related to reaction heat.…”