Simulated Waste Glass Research Articles

Statistical glass structure gene modeling on liquidus temperature of high level waste glasses

Statistical glass structure gene modeling (GSgM) on liquidus temperature (TL) of simulated high level waste (HLW) glass is detailed in this article. TL values of a set of HLW borosilicate glasses were experimentally determined by x-ray diffraction (XRD) method with 24 h heat-treated glass in gradient temperature furnace, and the primary crystalline phase was CaMoO4. Integral peak areas obtained from the FTIR peak fitting were used as the structural data, and the statistical TL-structure model was first established. The S-P (TL) model was shown to have a high accuracy, i.e., R2 0.978, P value 0.0009 and RMSE 7.6 °C. Model validation showed the predicted and measured TL values were 960.4 °C and 965 °C, respectively. Model iteration further reduced P value to 0.0001 and RMSE to 7 °C. Relationship between composition (C) and the glass network structure (S) was then simulated, and composition-FTIR structure-TL analysis indicated that SiO2, ZnO, rB3+, MoO3, ZrO2, B2O3 and rare earth affect TL by influence the structural units Si–O–Si rocking vibrations, νs (Si–O–Si) in [SiO4] and νs ([BO3] or BO2O−). Results showed that GSgM offers an alternative approach to simulate TL of complex glass with limited experimental data, providing a plausible linkage between composition, structure and property.

Volatilization of sodium and boron from nuclear waste glass and associated effects on glass structure and thermal stability

During nuclear waste vitrification, loss of sodium (Na) and boron (B) occurs, as these elements are highly volatile at high temperatures, which affects the properties of the glass products. Moreover, the evaporation of volatile nuclides (Cs and Tc) occurs together with that of Na and B, which may cause environmental hazards. Thus far, only a few studies have focused on the volatilization of Na and B from nuclear waste glass and loss-related effects on glass properties. In this study, we investigated the volatilization behaviors of Na and B from a simulated high-level waste glass as functions of heating temperature and dwelling duration, and evaluated the effects of Na and B loss on the glass structure and thermal stability. The results showed that volatilization of Na occurs predominantly through the diffusion-controlled process at a temperature range of 950 °C to 1100 °C, and owing to its higher frequency factor, Na diffuses and volatilizes at a faster rate than that of B. Volatilization of B occurs by both a diffusion-controlled process from bulk to the surface and a chemical reaction process on the surface. Based on the data obtained regarding the composition of Na and B and structure of the glass, a hypothetical model was proposed to explain the volatilization behaviors of Na and B from a structural viewpoint. As the loss of Na and B increases, the amount of BO4− reduces, whereas the amount of BO3 increases; finally, the Si-O network becomes more polymerized and has less thermal stability, resulting in the crystallization of the glass at elevated temperatures. These results would serve as the basis to estimate the amount of Na and B loss and the properties of the glass melt during nuclear waste vitrification, especially in melter idling.

Solubility and Valence Variation of Ce in Low-Alkali Borosilicate Glass and Glass Network Structure Analysis.

Low-alkali borosilicate glass was used as the immobilization substrate, and Ce was used to replicate the trivalent and tetravalent actinides, in order to create simulated waste glass through melt heat treatment. The valence of Ce and solubility of CeO2 in waste glass were studied as well as its network structure and thermal and chemical stability. The solubility of Ce in waste glass was examined by XRD and SEM. The network structure was examined by Raman spectroscopy. The valence of Ce was determined by X-ray photoelectron spectroscopy. Thermal analysis and product consistency (PCT) were employed to determine the thermal and chemical stability of waste glasses. The results show that the solubility of cerium in low-alkali borosilicate glasses is at least 25.wt.% and precipitates a spherical CeO2 crystalline phase when it exceeds the solid solution limit; Ce is immobilized in the glass by entering the interstices of the glass network. Depolymerization and the transition from [BO3] to [BO4] occurs when CeO2 doping levels rise. About 60 percent of Ce4+ is converted to Ce3+, and the thermal stability of glass rises then falls with the increase of CeO2. All samples exhibit strong leaching resistance, with the average mass loss of Ce at 28 days being less than 10-4 gm-2d-1.

Crystallization of molybdenum oxide phase from simulated high-level waste glass under slow cooling

Crystallization of molybdenum oxide phase from simulated high-level waste glass under slow cooling

The S solubility of Cr and Al containing simulated low-activity waste glass

The presence of sulfur-containing molten salt phases during vitrification is a particular problem which can be detrimental to the melter. Borosilicate compositions were designed to explore both the effects of a fixed amount of Cr, as Cr2O3 or Na2CrO4, and the impact of Al2O3, on sulfur solubility as determined by progressively adding elemental S. The NABS series (with Al2O3) has a higher SO3 solubility of ∼3.5 mol% while the NBS series (without Al2O3) has a SO3 solubility of ∼2 mol%. Crystalline Cr2O3 formed in the NABS series upon the addition of S but is not present in the NBS series. At the highest S addition, a separate salt phase always forms, and was identified as Na2(S,Cr)O4 via electron dispersive spectroscopy, ultraviolet-visible spectroscopy, x-ray diffraction, and thermal analysis. Magic angle spinning nuclear magnetic resonance identified no change in the B coordination in either series as S is added, suggesting that the Na is scavenged from other locations, such as the Si sites, to charge compensate sulfate, whether in the glass or in the salt. The Cr precursor identity did not affect the observed overall behavior regarding sulfur, but did impact Cr redox as identified with Raman spectroscopy.

In-situ X-ray and visual observation of foam morphology and behavior at the batch-melt interface during melting of simulated waste glass

To attain a basic understanding of the primary foam structure and behavior, which affects the heat and mass transfer and the efficiency of the glass melting process, we investigated the primary foam layer under the glass batch floating on molten glass. The primary foam affects mass transfer during batch melting, in turn affecting the melting process. The recently performed direct in-situ three-dimensional X-ray computed tomography of the batch melting in a laboratory-scale melter vessel allowed us to visualize the features of the reacting batch layer and the foam that develops at its bottom, though with an insufficient resolution of images. In this study, we obtained better temporal and spatial resolution using the two-dimensional X-ray radiography and visual observation of the structure and behavior of transient primary foam as it formed and decayed. As soon as the batch was charged onto the melt surface, foam bubbles began to evolve, grow, and coalesce, forming a primary foam layer, 5–10 mm thick, within tens of seconds. This foam layer was sustained by ongoing gas evolving reactions counterbalanced by bubble coalescence into cavities that moved sideways and escaped to the atmosphere. Eventually, the entire remaining batch turned into foam that gradually decayed at the melt surface. The decay rate agreed with literature observations of surface foam produced by secondary foaming.

Probing electronic environment in gamma irradiated sodium borosilicate glass and simulated waste glass: a perturbed angular correlation spectroscopy study

Time Differential Perturbed Angular Correlation (TDPAC) has been used to investigate the local structural changes (if any) in Sodium borosilicate (NBS) Glass and Simulated Waste Oxide loaded sodium borosilicate glass (SNBS) used for immobilization of high-level liquid waste at Trombay, Mumbai. The glasses were doped with 181Hf tracer as TDPAC probe and irradiated with varying dose (1–50 MGy) of gamma radiation using 60Co (average γ energy 1.25 MeV) source. Hyperfine interaction parameters (quadrupole interaction frequency, its distribution and asymmetry of electric field gradient) were obtained for irradiated NBS and SNBS glasses from fitting of TDPAC data using DPAC software. The data was compared with the corresponding unirradiated glasses. Results do not show any micro-crystallinity upon irradiation in both the NBS and SNBS glass even at the highest gamma dose of 50 MGy even though small changes were observed in quadrupole interaction frequency at doses beyond 30 MGy. This suggests that the sodium borosilicate glass used for immobilization of high-level waste at Trombay is stable towards gamma radiation at least up to a gamma dose of 50 MGy.

Through a glass darkly: In-situ x-ray computed tomography imaging of feed melting in continuously fed laboratory-scale glass melter

This study describes the first direct in-situ 3-D observation of a steady-state melting process by imaging a laboratory-scale slurry-fed glass melter in operation by x-ray computed tomography. Features of the reacting glass-feed, the foam layer underneath, and cavities in the glass melt pool are reconstructed in three-dimensional images. A slurry pool formed in a deep central caldera of dense dried feed, which penetrated into the glass melt. Slurry overflow from the caldera led to fast-dried and highly porous feed structure. A thin layer of foam separated the caldera from the melt. Bubbles ~5–15 mm in diameter were seen to grow beneath the reacting feed and move through the melt to escape at the edge. Pore morphology is benchmarked against computed tomography scans of a pellet of reacting simulated waste glass feed, and evolved gas analysis describes the gases generated as a function of temperature. Cooling artifacts are imaged and compared to previous studies of quenched cold caps. Detailed understanding of processes occurring during the conversion process in and below the reacting feed layer is necessary for the development of representative models of the melting process.

XAFS analysis of ruthenium in simulated iron phosphate radioactive waste glass

The chemical state of ruthenium in simulated iron phosphate radioactive waste glass was investigated by conventional X-ray absorption fine structure (XAFS) and imaging XAFS analyses. The EXAFS analysis suggested that ruthenium was contained as glass phase when content of the waste components was less than 10 wt.% in 30 mol%Fe2O3-P2O5 base glass. In other samples, crystalline RuO2 was observed and became prominent with the increase of waste content. According to the imaging XAFS analysis, RuO2 particles in all samples had length smaller than 50 μm. Large size aggregations of RuO2, which are found frequently in nuclear waste borosilicate glass, were not seen in any of the iron phosphate glass samples.

In situ characterization of foam morphology during melting of simulated waste glass using x-ray computed tomography

During batch-to-glass conversion, a glass-forming melt connects, creating a foam layer between the batch and the glass melt. Due to its transience and opacity, investigation of this foam layer presents a formidable challenge. In this work, we use in situ x-ray computed tomography to characterize the foam morphology that evolves during batch-to-glass conversion of a simulated nuclear waste glass. Rapid 1-min scans with 38 μm voxels were performed to capture the foam structure during heating. Geometric volume, total porosity, and bubble size distribution are reported. Using evolved gas analysis and combining the temperature-dependent melt viscosity with x-ray data, we describe the evolution of foam structure during the foam growth and subsequent collapse.

Preparation and Study of Corrosion Behavior of Some Simulated Radioactive Waste Glasses

To safe environment from radioactive waste it is important to fix them as radioactive waste glasses. The corrosion behavior of radioactive waste glasses in water is significantly important. Radionuclides return to the biosphere by means of leaching from waste form into ground water. Finally the ground water containing the radionuclide are transported to the surface. In this study, the preparation, characterization and leaching behavior of some borosilicate (BS) and lead iron phosphate (LIP) of different chemical composition doped with simulated nuclear waste oxide were investigated. We measured the pH found to be in the range from 6.78 up to 7.79 of the leachate solution at normal temperature and at varying time intervals. Leaching study of these glasses were conducted with the help of Soxhlet distillation apparatus with distilled water upto 24 hours and for BS9 - BS12 upto 100 hours duration. Weight losses were are measured with respect to time of leaching. Leach rate of some borosilicate glass samples loaded with uranium are calculated from surface area measurements. The results are reported in the range 1.34x10-4 g.m-2.hr-1 and 6.26 x 10-4 g.m-2.hr-1 respectively at 90°C.

Recycling of waste glass generated from end-of-life LCD devices: A feasibility study using simulated waste glass

The liquid crystal display (LCD) industry has undergone drastic growth over the past decade. Considering that the lifetime of an LCD device is approximately ten years, a huge end LCD waste glass (ELWG) is being produced from end-of-life LCD devices. The recycling of ELWG derived from LCD device produced before 2011 is limited by the presence of toxic components such as As, Sb and Ba. In this work, the potential of recycling ELWG was examined to be used in the glass wool industry. 17 glass batches using four different simulated ELWGs (mixtures corresponding to LCD glasses produced in 2006, 2008, 2009, and 2010) were prepared and melted. ELWG was introduced up to 20% of the total glass. Two fixed viscosity points (Tm, Tw) corresponding to 102 and 103 dPas, and the liquidus temperature (TL) were determined in the melt state, and leaching tests of the glass powder in an acidic solution based on the toxicity characteristic leaching procedure (TCLP) were also carried out. As the ELWG content was increased, the Tm, Tw, and TL values did not show a linear relationship with the ELWG content, but some fluctuation in the values was observed. The Tm value showed a larger deviation of 28–36 °C from that of the original glass than the Tw (6–14 °C) and TL (2–16 °C) values. As and Sb were not detected in the leaching tests, and the Ba concentration (1.232–2.279 mg/L) was much lower than the TCLP regulatory level (100 mg/L). The observed TW-TL values suggested that the replacement of 20% or more of the total glass by ELWG is possible. Additionally, the economic and environmental effects of the recycling process were discussed.

Nepheline crystallization behavior in simulated high-level waste glasses

The U.S. Department of Energy immobilizes legacy nuclear high-level waste (HLW) in borosilicate glass. HLW glass with elevated Na2O and Al2O3 concentrations have a demonstrated propensity for precipitating nepheline (NaAlSiO4) during cooling, which adversely affects the waste form performance. Currently, nepheline is suppressed by controlling the HLW glass composition, but this can limit the waste loading and result in longer mission life and cost. Correlation between composition and thermal history experienced during processing with time-temperature relationships that enable nepheline crystal growth would facilitate a more realistic prediction of nepheline crystallization in HLW glass and allow for a wider range of compositions to be accessed. In this work, crystallization behavior in simulated HLW glass was investigated to identify key attributes that lead to nepheline formation, with results indicating that the rate of diffusion for crystal growth may be controlled by glass structure connectivity.

Charge Neutralization in Nickel Coated Simulated High Level Waste Glass Analyzed by Secondary Ion Mass Spectrometry

Charge Neutralization in Nickel Coated Simulated High Level Waste Glass Analyzed by Secondary Ion Mass Spectrometry

Effect of Technetium-99 sources on its retention in low activity waste glass

Small-scale crucible melting tests on simulated waste glass were performed with technetium-99 (Tc-99) introduced as different species in a representative low activity waste simulant. The glass saw an increase in Tc-99 retention when TcO2∙2H2O and various Tc-minerals containing reduced tetravalent Tc were used compared to tests in which pertechnetate with heptavalent Tc was used. We postulate that the increase of Tc retention is likely caused by different reaction paths for Tc incorporation into glass during early stages of melting, rather than the low volatility of reduced tetravalent Tc compounds, which has been a generally accepted idea. Additional studies are needed to clarify the exact mechanisms relevant to the effect of reduced Tc compounds on Tc incorporation into or volatilization from the glass melt.

Comparison of univariate and multivariate data analysis models for uranium quantification in Trombay historical nuclear waste glass

Abstract Laser induced breakdown spectroscopy recently has been investigated for analysis of nuclear waste glass for uranium quantification. The initial obtained accuracy and precision was ~15%. In this paper, we have compared the analytical merit of the univariative and multivariative PLSR regression models for the determination of U in barium borosilicate simulated waste glass containing significant amount of U. The analytical merit of a Czerny-Turner spectrograph with high spectral resolution and Echelle spectrograph with broadband spectrum recording capacity were compared using spectra simultaneously record from the same plasma. For univariative calibration the superiority of Czerny-Turner spectrograph over the Echelle has been demonstrated here. Multivariative chemometric PLSR model was found to drastically improve the results. It was also observed that selection of spectral window for analysis significantly affects the analytical merit of multivariative analysis. Echelle though shows relatively inferior analytical merit, but by applying Analytical spectral dependant PLSR in Echelle spectra, a much higher degree of improvement was observed. Using ASD-PLSR and Czerny-Turner spectrograph generated spectra an accuracy and precision of 2–2.5% was achieved in this study.

Evaluation of sodium borate glasses for radioactive waste immobilization applications

Properties of sodium borate glasses, including chemical durability, leaching rate, glass transformation temperature, and melting temperature were analyzed for waste immobilization applications. The lowest dissolution rate (1.6 × 10−8 g cm−2 min−1) among candidate sodium borate host glasses was achieved in 45Na2O·5P2O5·5PbO·45B2O3. Similarly, the lowest dissolution rate (5.5 × 10−8 g cm−2 min−1) for simulated waste glass compositions was achieved in 20SrO·80(30Na2O·60PbO·10B2O3). Clear vitrified waste products containing up to 35 mol% SrO and 25 mol% Cs2O were obtained. Low melting temperatures ranging from 222 to 440 °C were achieved in simulated waste glasses.

Investigation of the maximum dissolution rates and temperature dependence of a simulated UK nuclear waste glass in circum-neutral media at 40 and 90°C in a dynamic system

This study investigates the influence of temperature on the dissolution of MW25, a non-radioactive simulant of UK Magnox glass. A single-pass flow-through (SPFT) system was used to measure the forward dissolution rate of MW25 at 40 and 90 °C and circum-neutral pH. The forward dissolution rate was found to be approximately one order of magnitude higher at 90 °C than at 40 °C. A similar release was observed for Si, Mg and Al at 40 °C and 90 °C, whereas the B, Cs, Na, Li and Mo showed an order of magnitude increase when the temperature was increased from 40 to 90 °C for low q/S values. The temperature dependence of the dissolution rates was determined using the Arrhenius rate law and the resultant activation energy (Ea) shows that the dissolution process is a surface phenomenon. At 90 °C, the net effect of the processes governing MW25 dissolution led to preferential release of boron and alkali metals relative to the release of Si during the transient dissolution stage, accompanied by an increase in the concentration of silicic acid. This suggests that the solution activity of silicic acid at higher temperature has a weak influence on the release of the mobile elements. This study features a new method for estimating the surface area of reacted glass powder more accurately than the geometric surface area estimate, which is the preferred standard method among researchers.

X‐ray tomography of feed‐to‐glass transition of simulated borosilicate waste glasses

AbstractHigh‐level waste feed composition affects the overall melting rate by influencing the chemical, thermophysical, and morphological properties of a cold cap layer that floats on the molten glass where most feed‐to‐glass reactions occur. Data from X‐ray computed tomography imaging of melting pellets comprised of a simulated high‐aluminum feed reveal the morphology of bubbles, known as the primary foam, for various feed compositions at temperatures between 600°C and 1040°C. These feeds were formulated to make glasses with viscosities ranging from 0.5 to 9.5 Pa s at 1150°C, which was accomplished by changing the SiO2/(B2O3+Na2O+Li2O) ratio in the final glass. Pellet dimensions and profile area, average and maximum bubble areas, bubble diameter, and void fraction were evaluated. The feed viscosity strongly affects the onset of the primary foaming and the foam collapse temperature. Despite the decreasing amount of gas‐evolving components (Li2CO3, H3BO3, and Na2CO3), as the feed viscosity increases, the measured foam expansion rate does not decrease. This suggests that the primary foaming is not only affected by changes in the primary melt viscosity but also by the compositional reaction kinetic effects. The temperature‐dependent foam morphological data will be used to inform cold cap model development for a high‐level radioactive waste glass melter.

放射光XAFSおよびイメージングXAFS法による模擬ガラス試料中のロジウム元素の化学状態分析

放射光XAFSおよびイメージングXAFS法による模擬ガラス試料中のロジウム元素の化学状態分析