Modeling of Spinel Settling in Waste Glass Melter

Each 1% increase of waste loading (W), defined as the high-level waste (HLW) mass fraction in glass, can save the U.S. Department of Energy (DOE) over a half billion U.S. dollars for vitrification and disposal. For a majority of Hanford and Savannah River waste streams, W is limited by spinel precipitation and settling in waste glass melters. Therefore, a fundamental understanding of spinel behavior is crucial for economy and the low-risk operation of HLW vitrification. The goal of this research is to develop a basic understanding of the dynamics of spinel formation and motion in velocity, temperature, and redox fields that are characteristic for the glass-melting process. This goal is being achieved by directly studying spinel formation and settling in molten glass and by developing a mathematical tool for predicting the spinel behavior and accumulation rate in the melter. The main potential benefit of this study is achieving a lower waste-glass volume, which translates into a shorter cleanup time, a smaller processing facility, a smaller repository space, and, hence, a reduced investment of time and money to reach acceptable technical risks. Additional benefits include (1) more accurately assessing sensible limits for problem constituents (such as chromium) in the melter feed, (2) reducing the blending requirements, and (3) comparing cost and risk with other options (pretreatment, blending or diluting the waste) to determine the best path forward. The results of this study will allow alternate melter designs and operating conditions to be evaluated. The study will also address the option of removing the settled sludge from the melter

INDUSTRIAL OPPORTUNITIES OF CONTROLLED MELT FLOW DURING GLASS MELTING PART 2: POTENTIAL APPLICATIONS

A review of the recent results and applications of controlled melt flow in the glass melting spaces [1] leads to the idea of helical flow as the most efficient way of melt flow through the continuous glass melting space. The results of mathematical modelling provide conditions under which the character of the melt flow can be set up and quantity space utilization is used for the quantitative evaluation. We designed a melting device (module) without a batch blanket and with a controlled melt flow that performs both homogenization processes in parallel, substantially increases the melting performance and reduces the total energy consumption. We also delivered an overview of non-traditional melting techniques and discussed possibilities for implementing the module in real technology. The concept of the implementation of the controlled melt flow into spaces with a batch blanket and the preliminary results of the mathematical modelling are presented as well

Modeling of Spinel Settling in Waste Glass Melter

Our objective is to determine the fraction and size of spinel crystals in molten HLW glass that are compatible with low-risk melter operation. To this end, we are investigating spinel behavior in HLW glass and obtaining data to be used in a mathematical model for spinel settling in a HLW glass melter. We will modify the current glass-furnace model to incorporate spinel concentration distribution and to predict the rate of spinel settling. Also, we will determine the nucleation agents that control the number density and size of spinel crystals in HLW glass

ROLE OF GLASS MELT FLOW IN CONTAINER FURNACE EXAMINED BY MATHEMATICAL MODELLING

The character of the glass melt flow in a regenerative container furnace was simulated by mathematical modeling under conditions of various energy distributions in the melting space with the application of electric boosting. The aim was the achievement of high melting performance and the decrease of heat losses. The results of the modeling have confirmed that the melting performance generally increased and heat losses decreased with the growth of the total amount of energy added to the batch region of the furnace. The amount of energy delivered to the furnace batch region moved between 30-60% of the total supplied energy; the melting performance then corresponded with 230-460 tons/day, and the specific heat losses were between 1450-2100 kJ/kg of glass. The energetic model of melt flows is presented providing the diagram of various flow characters

SETTLING OF SPINEL IN A HIGH-LEVEL WASTE GLASS MELTER

High-level nuclear waste is being vitrified, i.e., converted to a durable glass that can be stored in a safe repository for hundreds of thousands of years. Waste vitrification is accomplished in reactors called melters to which the waste is charged together with glass-forming additives. The mixture is electrically heated to a temperature as high as 1150 decrees C to create a melt that becomes glass on cooling

Settling of Spinel in A High-Level Waste Glass Melter

High-level nuclear waste is being vitrified, i.e., converted to a durable glass that can be stored in a safe repository for hundreds of thousands of years. Waste vitrification is accomplished in reactors call melters to which the waste is charged together with glass-forming additives. The mixture is electrically heated to a temperature as high as 1150 degree C (or even higher in advanced melters) to create a melt that becomes glass on cooling. This process is slow and expensive. Moreover, the melters that are currently in use or are going to be used in the U.S. are sensitive to clogging and thus cannot process melt in which solid particles are suspended. These particles settle and gradually accumulate on the melter bottom. Such particles, most often small crystals of spinel ( a mineral containing iron, nickel, chromium, and other minor oxides), inevitably occurred in the melt when the content of the waste in the glass (called waste loading) increases above a certain limit. To avoid the presence of solid particles in the melter, the waste loading is kept rather low, in average 15% lower than in glass formulated for more robust melters

Laser Desorption Ionization Time-of-Flight Mass Spectrometry of Glasses and Amorphous Films from Ge-As-Se System

International audienceLaser Desorption Ionization Time-of-Flight Mass Spectrometry was exploited for the characterization of Ge-As-Se chalcogenide glasses and corresponding thin films fabricated using pulsed laser deposition. Main achievement of the paper is the determination of laser generated clusters' stoichiometry. The clusters observed were As-b(+) (b = 1-3), Se-2(-), binary AsbSe+ (b = 1-3), AsbSec- (b = 1-3, c = 1-4), Ge2Sec- (c = 2-3), As3Se2+, Ge2Asb- (b = 2-3), Ge3Asb- (b = 1-2), Ge3Se4-, As5Sec- (c = 4-5), GeAsSe4-, GeaAsSe5- (a = 1-4), GeAs2Se3-, GeAs3Se2-, Ge2As2Se2-, Ge2AsSec- (c = 6-7), and GeAs3Sec- (c = 5-6) (in positive as well as in negative ion mode). The stoichiometries of identified species are compared with the structural units of the glasses/thin films revealed via Raman scattering spectra analysis. Some species are suggested to be fragments of bulk glass as well as thin films. Described method is useful also for the evaluation of the contamination of chalcogenide glasses or their thin films

Laser Desorption Ionisation Time-​of-​Flight Mass Spectrometry of Chalcogenide Glasses from (GeSe2)​100-​x(Sb2Se3)​x System

International audienceLaser Desorption Ionization Time-​of-​Flight Mass Spectrometry (LDI TOFMS) was used to characterize chalcogenide glasses from pseudobinary (GeSe2)​100-​x(Sb2Se3)​x system, where x = 5-​60, aiming description of their partial structure through the anal. of the plasma formed due to interaction of pulsed laser beam with studied glasses. The plasma contains pos. or neg. charged clusters; their stoichiometry was detd. as Sec-​ (c = 2-​3)​, Sb+, Se2+, and Sb3+; binary GeSec+, SbSec+​/-​ (c = 1-​2)​, SbbSec+ (b = 2-​3, c = 1-​4)​, GeaSb3+ (a = 1-​4)​, Sb2Sec-​ (c = 3-​4)​, SbSe3-​, and Sb3Se5+; ternary GeSbSe2+, GeSbSec-​ (c = 3-​5)​, GeSbbSe+ (b = 4-​5)​, and Ge9Sb2Sec+ (c = 5-​7) ones. Described method is generally useful not only for partial structural characterization of chalcogenide glasses and corresponding thin films but also for evaluation of their contamination with oxygen and​/or hydrogen

Arsenic-Doped SnSe Thin Films Prepared by Pulsed Laser Deposition

International audiencePulsed UV laser deposition was exploited for the preparation of thin Sn As Se ( = 0, 0.05, 0.5, and 2.5) films with the aim of investigating the influence of low arsenic concentration on the properties of the deposited layers. It was found that the selected deposition method results in growth of a highly (00) oriented orthorhombic SnSe phase. The thin films were characterized by different techniques such as X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, atomic force microscopy, Raman scattering spectroscopy, and spectroscopic ellipsometry. From the results, it can be concluded that thin films containing 0.5 atom % of As exhibited extreme values regarding crystallite size, unit cell volume, or refractive index that significantly differ from those of other samples. Laser ablation with quadrupole ion trap time-of-flight mass spectrometry was used to identify and compare species present in the plasma originating from the interaction of a laser pulse with solid-state Sn As Se materials in both forms, i.e. parent powders as well as deposited thin films. The mass spectra of both materials were similar; particularly, signals of Sn Se clusters with low and values were observed

Mass spectrometric investigation of amorphous Ga-Sb-Se thin films

International audienceAmorphous chalcogenide thin films are widely studied due to their enhanced properties and extensive applications. Here, we have studied amorphous Ga-Sb-Se chalcogenide thin films prepared by magnetron co-sputtering, via laser ablation quadrupole ion trap time-of-flight mass spectrometry. Furthermore, the stoichiometry of the generated clusters was determined which gives information about individual species present in the plasma plume originating from the interaction of amorphous chalcogenides with high energy laser pulses. Seven different compositions of thin films (Ga content 7.6–31.7 at. %, Sb content 5.2–31.2 at. %, Se content 61.2–63.3 at. %) were studied and in each case about ~50 different clusters were identified in positive and ~20–30 clusters in negative ion mode. Assuming that polymers can influence the laser desorption (laser ablation) process, we have used parafilm as a material to reduce the destruction of the amorphous network structure and/or promote the laser ablation synthesis of heavier species from those of lower mass. In this case, many new and higher mass clusters were identified. The maximum number of (40) new clusters was detected for the Ga-Sb-Se thin film containing the highest amount of antimony (31.2 at. %). This approach opens new possibilities for laser desorption ionization/laser ablation study of other materials. Finally, for selected binary and ternary clusters, their structure was calculated by using density functional theory optimization procedure