The Results of Testing to Evaluate Crystal Formation and Settling in the Cold Crucible Induction Melter

The Cold Crucible Induction Melter (CCIM) technology offers the potential to increase waste loading for High Level Waste (HLW) glasses leading to significant improvements in waste throughput rates compared to the reference Joule Heated Melter (JHM). Prior to implementation of a CCIM in a production facility it is necessary to better understand processing constraints associated with the CCIM. The glass liquidus temperature requirement and tolerance to crystal formation for processing in the CCIM is an open issue. Testing was conducted to evaluate crystal formation and crystal settling during processing in the CCIM to gain insight into the effects on processing. A high aluminum/high iron content glass composition with known crystal formation tendencies was selected for testing. A continuous melter test was conducted for approximately 51 hours. To evaluate crystal formation, glass samples were obtained from pours and from glass receipt canisters where the glass melt had varying residence time in the melter. Additionally, upon conclusion of the testing, glass samples from the bottom of the melter were obtained to assess the degree of crystal settling. Glass samples were characterized in an attempt to determine quantitative fractions of crystals in the glass matrix. Crystal identity and relative composition were determined using a combination of x-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS). Select samples were also analyzed by digesting the glass and determining the composition using inductively coupled atomic emission spectroscopy (ICP-AES). There was evidence of crystal formation (primarily spinels) in the melt and during cooling of the collected glass. There was evidence of crystal settling in the melt over the duration of the melter campaign.