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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Engineering Glass Passivation Layers -Model Results

The immobilization of radioactive waste into glass waste forms is a baseline process of nuclear waste management not only in the United States, but worldwide. The rate of radionuclide release from these glasses is a critical measure of the quality of the waste form. Over long-term tests and using extrapolations of ancient analogues, it has been shown that well designed glasses exhibit a dissolution rate that quickly decreases to a slow residual rate for the lifetime of the glass. The mechanistic cause of this decreased corrosion rate is a subject of debate, with one of the major theories suggesting that the decrease is caused by the formation of corrosion products in such a manner as to present a diffusion barrier on the surface of the glass. Although there is much evidence of this type of mechanism, there has been no attempt to engineer the effect to maximize the passivating qualities of the corrosion products. This study represents the first attempt to engineer the creation of passivating phases on the surface of glasses. Our approach utilizes interactions between the dissolving glass and elements from the disposal environment to create impermeable capping layers. By drawing from other corrosion studies in areas where passivation layers have been successfully engineered to protect the bulk material, we present here a report on mineral phases that are likely have a morphological tendency to encrust the surface of the glass. Our modeling has focused on using the AFCI glass system in a carbonate, sulfate, and phosphate rich environment. We evaluate the minerals predicted to form to determine the likelihood of the formation of a protective layer on the surface of the glass. We have also modeled individual ions in solutions vs. pH and the addition of aluminum and silicon. These results allow us to understand the pH and ion concentration dependence of mineral formation. We have determined that iron minerals are likely to form a complete incrustation layer and we plan to look more closely at Vivianite [Fe3(PO4)2-8(H2O)] and Siderite [FeCO3] in the next stage of the project.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Demonstration of sulfur solubility determinations in high waste loading, low-activity waste glasses

A method recommended by Pacific Northwest National Laboratory (PNNL) for sulfate solubility determinations in simulated low-activity waste glasses was demonstrated using three compositions from a recent Hanford high waste loading glass study. Sodium and sulfate concentrations in the glasses increased after each re-melting step. Visual observations of the glasses during the re-melting process reflected the changes in composition. The measured compositions showed that the glasses met the targeted values. The amount of SO 3 retained in the glasses after washing was relatively high, ranging from 1.6 to 2.6 weight percent (wt %). Measured SnO 2 concentrations were notably low in all of the study glasses. The composition of the wash solutions should be measured in future work to determine whether SnO 2 is present with the excess sulfate washed from the glass. Increases in batch size and the amount of sodium sulfate added did not have a measureable impact on the amount of sulfate retained in the glass, although this was tested for only a single glass composition. A batch size of 250 g and a sodium sulfate addition targeting 7 wt %, as recommended by PNNL, will be used in future experiments.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Composition Measurements of the HLW HAlG Glasses

This report provides the results from the chemical analyses of the glass compositions of the High-Level Waste High-Aluminum Glass study glasses, a series of simulated nuclear waste glasses designed and fabricated at Pacific Northwest National Laboratory. These data will be used in the development, validation, and implementation of enhanced property/composition models for waste glass vitrification at Hanford. Chemical analyses were performed on a representative sample of each of the quenched glasses to allow for comparisons with targeted compositions. The relative differences between the targeted and measured concentrations of Cr 2 O3, P 2 O 5 , and ZrO 2 for several of the glasses were greater than 10%. The relative difference between the targeted and measured concentrations of CaO was greater than 10% for one glass. The relative difference between the targeted and measured concentrations of Li 2 O was greater than 10% for one glass. These results can be used in further characterization of this series of glasses, including the normalization of Product Consistency Test results.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Characterization of the Sulfur-Saturated Melt Versions of the HLW HAlG Glasses

This report provides the results from the chemical analyses of a series of sulfur-saturated melt versions of the High-Level Waste High-Aluminum Glass study glasses, a series of simulated nuclear waste glasses designed and fabricated at Pacific Northwest National Laboratory. These data will be used in the development, validation, and implementation of enhanced property/composition models for waste glass vitrification at Hanford. Chemical analyses were performed on a representative sample of each of the sulfur-saturated melt versions of the glasses to allow for comparisons with targeted compositions as well as the measured compositions of the quenched glasses. The relative differences between the targeted and measured concentrations of B 2 O 3 , Cr 2 O 3 , K 2 O, Li 2 O, Na 2 O, and P 2 O 5 for several of the glasses were greater than ±10%. The relative differences between the targeted and measured concentrations of Al 2 O 3 and ZrO 2 for one of the glasses were greater than ±10%. As expected, the measured concentrations of SO 3 in most of the glasses were higher than targeted due to the use of the sulfur saturation method in fabricating these glasses. The wash solutions contained mainly sodium, sulfur, and sulfate ions.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Composition Measurements of the LAW ML1 Glasses

This report provides the results from the chemical analyses of the glass compositions of the quenched Low Activity Waste Machine Learning study glasses, a series of simulated nuclear waste glasses designed and fabricated at Pacific Northwest National Laboratory. These data will be used in the development, validation, and implementation of enhanced property/composition models for waste glass vitrification at Hanford. Chemical analyses were performed on a representative sample of each of the quenched glasses to allow for comparisons with target compositions. The relative differences between the target and measured concentrations of F - for one glass, P 2 O 5 for two glasses, SO 3 for three glasses, and ZrO 2 for two of the glasses were greater than 10%. These results can be used in further characterization of this series of glasses, including the normalization of Product Consistency Test results.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

The Effect of Heavy Ion Irradiation on the Forward Dissolution Rate of Borosilicate Glasses Studied In Situ and Real Time by Fluid-Cell Raman Spectroscopy

Borosilicate glasses are the favored material for immobilization of high-level nuclear waste (HLW) from the reprocessing of spent fuel used in nuclear power plants. To assess the long-term stability of nuclear waste glasses, it is crucial to understand how self-irradiation affects the structural state of the glass and influences its dissolution behavior. In this study, we focus on the effect of heavy ion irradiation on the forward dissolution rate of a non-radioactive ternary borosilicate glass. To create extended radiation defects, the glass was subjected to heavy ion irradiation using 197 Au ions that penetrated ~50 µm deep into the glass. The structural damage was characterized by Raman spectroscopy, revealing a significant depolymerization of the silicate and borate network in the irradiated glass and a reduction of the average boron coordination number. Real time, in situ fluid-cell Raman spectroscopic corrosion experiments were performed with the irradiated glass in a silica-undersaturated, 0.5 M NaHCO 3 solution at temperatures between 80 and 85 °C (initial pH = 7.1). The time- and space-resolved in situ Raman data revealed a 3.7 ± 0.5 times increased forward dissolution rate for the irradiated glass compared to the non-irradiated glass, demonstrating a significant impact of irradiation-induced structural damage on the dissolution kinetics.

36 MATERIALS SCIENCE↗
DOE OSTI2012

IMPACT OF URANIUM AND THORIUM ON HIGH TIO2 CONCENTRATION NUCLEAR WASTE GLASSES

This study focused on the potential impacts of the addition of Crystalline Silicotitanate (CST) and Monosodium Titanate (MST) from the Small Column Ion Exchange (SCIX) process on the Defense Waste Processing Facility (DWPF) glass waste form and the applicability of the DWPF process control models. MST from the Salt Waste Processing Facility (SWPF) is also considered in the study. The KT08-series of glasses was designed to evaluate any impacts of the inclusion of uranium and thorium in glasses containing the SCIX components. All but one of the study glasses were found to be amorphous by X-ray diffraction (XRD). One of the slowly cooled glasses contained a small amount of trevorite, which is typically found in DWPF-type glasses and had no practical impact on the durability of the glass. The measured Product Consistency Test (PCT) responses for the study glasses and the viscosities of the glasses were well predicted by the current DWPF models. No unexpected issues were encountered when uranium and thorium were added to the glasses with SCIX components.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

ITEAM - An international mechanistic approach to modeling glass behavior over geologic time scales - 15527

Vitrification is a common worldwide solution for radioactive waste immobilization. Although the excellent chemical durability of glass has been demonstrated in ancient man-made and natural analogues, the lack of an international consensus on a glass corrosion rate law limits the application of glass in high-level waste repository performance models. The contributions of physical and chemical processes controlling the long-term glass dissolution rate in geologic disposal remain uncertain resulting in this non-consensus. A thorough mechanistic understanding of waste form durability in geologic environments would improve public and regulator confidence. In addition, this understanding could lead to cost savings if it becomes possible to take credit for the true durability of the waste form itself in system evaluations rather than requiring expensive engineered barrier systems. To this end, five nations (US, UK, France, Japan, and Belgium) have joined together to formulate a joint plan for collaborative research into the mechanisms controlling the long-term corrosion of glass. Over the last five years, the coordinated research performed by these countries has produced a new level of understanding about the glass corrosion mechanisms, specifically as they apply to glasses similar in composition to the French R7T7 glass. Some recent results are presented as they relate to several mechanisms that are thought to control glass alteration at long time periods. It is important to understand the effects of each particular mechanism on the overall radionuclide release and the relative importance of each process model to the performance assessment calculation. In addition, a new series of experiments calls out potential sources of error due to the use of irregular shapes (such as crushed glass powder) in dissolution experiments. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Chemical durability of glasses

The chemical durability of silicate glasses has long been studied for many applications, in particular when glasses are subjected to environmental weathering and aqueous corrosion. Typical applications include optical instruments, glass vessels, radioactive waste confinement, and bone reparation. Glass corrosion involves ion exchange, water diffusion, network dissolution-recondensation, and secondary phase precipitation. These reactions may impact, among other things, the release of contaminants from waste glasses, and the glass mechanical, optical and catalytic properties. The glass corrosion mechanisms and alteration product formation have been well studied as a function of many environmental parameters (temperature, pH, water composition, etc.). The present chapter describes the general phenomena behind glass corrosion and details glass dissolution in aqueous conditions on one hand and glass vapor hydration on the other hand. The latter phenomenon has not received the same level of attention in the literature relative to the corrosion in aqueous solutions. Research and Development needs, in particular in complex systems such as radioactive waste geological repositories, are discussed in the conclusion of the chapter.

Abdelouas, Abdesselam↗
DOE OSTI2023

Microbial interactions with phosphorus containing glasses representative of vitrified radioactive waste

The presence of phosphorous in borosilicate glass (at 0.1 – 1.3 mol % P 2 O 5 ) and in iron-phosphate glass (at 53 mol % P 2 O 5 ) stimulated the growth and metabolic activity of anaerobic bacteria in model systems. Dissolution of these phosphorous containing glasses was either inhibited or accelerated by microbial metabolic activity, depending on the solution chemistry and the glass composition. The breakdown of organic carbon to volatile fatty acids increased glass dissolution. The interaction of microbially reduced Fe(II) with phosphorus-containing glass under anoxic conditions decreased dissolution rates, whereas the interaction of Fe(III) with phosphorous-containing glass under oxic conditions increased glass dissolution. Phosphorous addition to borosilicate glasses did not significantly affect the microbial species present, however, the diversity of the microbial community was enhanced on the surface of the iron phosphate glass. Results demonstrate the potential for microbes to influence the geochemistry of radioactive waste disposal environments with implication for wasteform durability.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Augmented Adam-Gibbs model for glass melt viscosity and configuration entropy as functions of temperature and composition

As the temperature of glass melt increases, its structure approaches the state of a simple liquid while the configuration entropy approaches a maximum value. We describe this gradual change using a power law function of inverse temperature. The Adam-Gibbs model for glass viscosity as a function of temperature and glass composition augmented in this way is greatly simplified when applied to common glass families occupying moderate composition regions, such as float glass or nuclear waste glasses, on which properties can be approximated as linear functions of composition. The parsimonious model thus obtained is preferable for use in optimizing glass formulation and mathematical modeling of glass melting and forming. For multicomponent glasses with N viscosity-affecting components, the augmented Adam-Gibbs model requires 2N + 3 adjustable parameters. The model efficacy is demonstrated by fitting the model to a viscosity-temperature-composition dataset for low-activity nuclear waste glasses.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Micron-sized spinel crystals in high level waste glass compositions: Determination of crystal size and crystal fraction

The compositions utilized for immobilization of nuclear waste are controlled using glass property models to avoid the deleterious effects of crystallization in the high-level waste (HLW) vitrification melters. The type and size of the crystals that precipitate during melter operations (typically at 1150 °C) and idling (~ 1000 °C) are significantly impacted by glass composition and thermal history. This study was conducted to measure the impact of melt composition and heat treatment temperature on crystal size and fraction. A matrix of 31 multi-component glasses canvasing the expected Hanford HLW compositional space was developed and the glasses fabricated and heat treated at 850 = T = 950°C. The crystal filling fraction values, as determined by X-ray diffraction, varied from 0.2 to 41.0 wt%. Spinel filling fraction values ranged from 0.0 to 13.8 wt%. One glass of the matrix did not precipitate spinel and contained 0.2 wt% RuO 2 , which was assumed to be undissolved from the melting process. All compositions contained crystals in the as-quenched glass. All of the spinel based crystals present in the glasses were less than 10 µm in diameter, as determined by scanning electron microscopy. Composition and temperature dependent models were generated using the resulting data and the best model fit was obtained by only considering spinel filling fractions (R 2 = 0.83). Two glasses were unable to be characterized due to an inability to process the glass under the conditions of this study. Those glasses were utilized to give insight into a potential multi-component constraint to aid in future statistical composition designs.

Lonergan, C. E.↗
DOE OSTI2022

The Effects of Mixing Multi-Component HLW Glasses on Spinel Crystal Size

The Hanford Waste Treatment and Immobilization Plant will vitrify radioactive waste into borosilicate glass. The high-level waste (HLW) glass formulations are constrained by processing and property requirements, including restrictions aimed at avoiding detrimental impacts of spinel crystallization in the melter. To understand the impact of glass chemistry on crystallization, two HLW glasses precipitating small (?5 µm) spinel crystals were individually mixed with a glass that precipitated large (?45 µm) spinel crystals in ratios of 25, 50, and 75 wt%. The size of spinel crystals in the mixed glasses varied from 5 to 20 µm. Small crystal size was attributed to: (1) high concentrations of nuclei due to the presence of ruthenium oxide and (2) chromium oxide aiding high rates of nucleation. Results indicate that the spinel crystal size can be controlled using chromium oxide and/or noble metal concentrations in the melt, even in complex mixtures like HLW glasses. Small crystals tend to settle slowly, so they are acceptable in the melter without a risk of failure. Allowing higher concentrations of spinel-forming waste components in the waste glass enables glass compositions with higher waste loading, thus increasing plant operational flexibility. An additional benefit to the presence of chromium oxide in the glass composition is the potential for the oxide to protect melter walls against corrosion.

Lonergan, Charmayne E.↗
DOE OSTI2016

Refractive index and compressibility of LiAlSi{sub 3}O{sub 8} glass in the pressure range up to 6.0 GPa

Highlights: • Refractive index and the compressibility of LiAlSi{sub 3}O{sub 8} glass are obtained. • Among Li(Na,K)AlSi{sub 3}O{sub 8} glasses LiAlSi{sub 3}O{sub 8} glass has the lowest compressibility. • Degree of depolymerization (NBO/T = 0.31) for LiAlSi{sub 3}O{sub 8} glass was calculated. • NBO/T = 0.31 indicates a high content of NBOs atoms and Al in LiAlSi{sub 3}O{sub 8} glass. • Proposed reaction corresponds to the condition of the existence of ∼9% Al. - Abstract: The refractive index and the relative changes in the density for LiAlSi{sub 3}O{sub 8} glass in the pressure range up to 6.0 GPa were obtained using a polarization-interference microscope and an apparatus with diamond anvils. The results were compared with the previous data for the NaAlSi{sub 3}O{sub 8} and KAlSi{sub 3}O{sub 8} glasses. The compressibility of glasses increases in a series of alkali metal cations Li{sup +}, Na{sup +}, K{sup +}. From the previously found dependence of the compressibility (at P = 4.0 GPa) on the degree of depolymerization the value of NBO/T = 0.31 for LiAlSi{sub 3}O{sub 8} glass was calculated. A high degree of depolymerization of the LiAlSi{sub 3}O{sub 8} glass indicates not only a high content of NBOs atoms in the structural network, but also the presence of highly coordinated aluminum (according to the literature data ∼9%). The proposed schematic reaction for the formation of different structural groups corresponds to the condition of the existence of 9% highly coordinated aluminum.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Dissolution kinetics of a sodium borosilicate glass in Tris buffer solutions: impact of Tris concentration and acid (HCl/HNO 3 ) identity

Here, understanding the corrosion behavior of glasses in near-neutral environments is crucial for many technologies including glasses for regenerative medicine and nuclear waste immobilization. To maintain consistent pH values throughout experiments in the pH = 7 to 9 regime, buffer solutions containing tris(hydroxymethyl)aminomethane (“Tris”, or sometimes called THAM) are recommended in ISO standards 10993-14 and 23317 for evaluating biomaterial degradation and utilized throughout glass dissolution behavior literature—a key advantage being the absence of dissolved alkali/alkaline earth cations (i.e. Na + or Ca 2+ ) that can convolute experimental results due to solution feedback effects. Although Tris is effective at maintaining the solution pH, it has presented concerns due to the adverse artificial effects it produces while studying glass corrosion, especially in borosilicate glasses. Therefore, many open questions still remain on the topic of borosilicate glass interaction with Tris-based solutions. We have approached this topic by studying the dissolution behavior of a sodium borosilicate glass in a wide range of Tris-based solutions at 65 °C with varied acid identity (Tris–HCl vs. Tris–HNO 3 ), buffer concentration (0.01 M to 0.5 M), and pH (7–9). The results have been discussed in reference to previous studies on this topic and the following conclusions have been made: (i) acid identity in Tris-based solutions does not exhibit a significant impact on the dissolution behavior of borosilicate glasses, (ii) ~0.1 M Tris-based solutions are ideal for maintaining solution pH in the absence of obvious undesirable solution chemistry effects, and (iii) Tris–boron complexes can form in solution as a result of glass dissolution processes. The complex formation, however, exhibits a distinct temperature-dependence, and requires further study to uncover the precise mechanisms by which Tris-based solutions impact borosilicate glass dissolution behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Thermoluminescence and phototransferred thermoluminescence dosimetry on mobile phone protective touchscreen glass

Thermoluminescence and phototransferred thermoluminescence measurements of protective glass from smartphones are described. Samples of Gorilla Glass were examined from nine different manufacturers and 40 different phone models. Additionally, 12 glasses believed to be original equipment manufacturer replacements, as well as three glass samples from U.S. finishers, were also studied. Altogether, 99 different Gorilla Glass samples were examined. The radiation-induced thermoluminescence signal produced glow curve shapes specific to the Gorilla Glass generations and could be used to distinguish between them. A background thermoluminescence (and phototransferred thermoluminescence) signal was found in all unirradiated samples. Its intensity and shape were found to be dependent on the Gorilla Glass generation, phone manufacturer, and phone model. The background signal was demonstrated to be produced by ultraviolet light exposure; the shape of the background signal was able to be reproduced by the combined exposure to a broad-spectrum solar simulator and a 302 nm ultraviolet light source. The background signal intensity was found to vary with the location from which it was taken on the glass. It was also found to be dependent on the depth within the Gorilla Glass due to absorption of the ultraviolet light as it traversed the medium. Removal of the glasses’ surface layers was found to be an inadequate method for removing the background signal. In some samples, the background signal intensity was large enough to significantly contribute to the total thermoluminescence (and phototransferred thermoluminescence) signal; therefore, a matrix deconvolution method was introduced to separate the background signal and radiation-induced signal. This method was found to enable dose reconstruction using the radiation-induced signal alone.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2023

Micro- and Nanoscale Surface Analysis of Late Iron Age Glass from Broborg, a Vitrified Swedish Hillfort

Abstract Archaeological glasses with prolonged exposure to biogeochemical processes in the environment can be used to understand glass alteration, which is important for the safe disposal of vitrified nuclear waste. Samples of mafic and felsic glasses with different chemistries, formed from melting amphibolitic and granitoid rocks, were obtained from Broborg, a Swedish Iron Age hillfort. Glasses were excavated from the top of the hillfort wall and from the wall interior. A detailed microscopic, spectroscopic, and diffraction study of surficial textures and chemistries were conducted on these glasses. Felsic glass chemistry was uniform, with a smooth surface showing limited chemical alteration (<150 nm), irrespective of the position in the wall. Mafic glass was heterogeneous, with pyroxene, spinel, feldspar, and quartz crystals in the glassy matrix. Mafic glass surfaces in contact with topsoil were rougher than those within the wall and had carbon-rich material consistent with microbial colonization. Limited evidence for chemical or physical alteration of mafic glass was found; the thin melt film that coated all exposed surfaces remained intact, despite exposure to hydraulically unsaturated conditions, topsoil, and associated microbiome for over 1,500 years. This supports the assumption that aluminosilicate nuclear waste glasses will have a high chemical durability in near-surface disposal facilities.

Matthews, Bethany E. (ORCID:0000000171932583)↗
DOE OSTI2017

Understanding the structural origin of crystalline phase transformations in nepheline (NaAlSiO 4 )‐based glass‐ceramics

Abstract Nepheline (Na 6 K 2 Al 8 Si 8 O 32 ) is a rock‐forming tectosilicate mineral which is by far the most abundant of the feldspathoids. The crystallization in nepheline‐based glass‐ceramics proceeds through several polymorphic transformations — mainly orthorhombic, hexagonal, cubic — depending on their thermochemistry. However, the fundamental science governing these transformations is poorly understood. In this article, an attempt has been made to elucidate the structural drivers controlling these polymorphic transformations in nepheline‐based glass‐ceramics. Accordingly, two different sets of glasses (meta‐aluminous and per‐alkaline) have been designed in the system Na 2 O–CaO–Al 2 O 3 –SiO 2 in the crystallization field of nepheline and synthesized by the melt‐quench technique. The detailed structural analysis of glasses has been performed by 29 Si, 27 Al, and 23 Na magic‐angle spinning — nuclear magnetic resonance ( MAS NMR ), and multiple‐quantum MAS NMR spectroscopy, while the crystalline phase transformations in these glasses have been studied under isothermal and non‐isothermal conditions using differential scanning calorimetry ( DSC ), X‐ray diffraction ( XRD ), and MQMAS NMR . Results indicate that the sequence of polymorphic phase transformations in these glass‐ceramics is dictated by the compositional chemistry of the parent glasses and the local environments of different species in the glass structure; for example, the sodium environment in glasses became highly ordered with decreasing Na 2 O/CaO ratio, thus favoring the formation of hexagonal nepheline, while the cubic polymorph was the stable phase in SiO 2 –poor glass‐ceramics with (Na 2 O+CaO)/Al 2 O 3 > 1. The structural origins of these crystalline phase transformations have been discussed in the paper.

Deshkar, Ambar↗