Simulated High-level 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.

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

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

REDOX state analysis of platinoid elements in simulated high-level radioactive waste glass by synchrotron radiation based EXAFS

Extended X-ray Absorption Fine Structure (EXAFS) analyses were performed to evaluate REDOX (REDuction and OXidation) state of platinoid elements in simulated high-level nuclear waste glass samples prepared under different conditions of temperature and atmosphere. At first, EXAFS functions were compared with those of standard materials such as RuO2. Then structural parameters were obtained from a curve fitting analysis. In addition, a fitting analysis used a linear combination of the two standard EXAFS functions of a given elements metal and oxide was applied to determine ratio of metal/oxide in the simulated glass. The redox state of Ru was successfully evaluated from the linear combination fitting results of EXAFS functions. The ratio of metal increased at more reducing atmosphere and at higher temperatures. Chemical form of rhodium oxide in the simulated glass samples was RhO2 unlike expected Rh2O3. It can be estimated rhodium behaves according with ruthenium when the chemical form is oxide.

白金族元素の結晶相の化学組成に基づく模擬高レベルガラス固化体の酸化還元状態の推定

白金族元素の結晶相の化学組成に基づく模擬高レベルガラス固化体の酸化還元状態の推定

Phase equilibrium experiments on the simulated high-level waste glass containing platinum group elements

Phase equilibrium experiments for the simulated high-level waste (HLW) glass containing palladium, rhodium and ruthenium discharged from a full scale mock up melter have been carried out between 1073 and 1473 K under air and CO2 atmosphere. The chemical compositions of Pd–Rh–Ru–Te (Pd metal phase) and (Ru, Rh)O2 (Ru oxide phase) solid solutions and glass matrix were measured by electron probe micro analysis. Palladium content in the Pd metal phase decreased and ruthenium content in the Ru oxide phase increased with increasing temperature and decreasing oxygen fugacity due to progressive reduction of rhodium. The chemical compositions of these crystalline phases are independent of that of borosilicate glass matrix. Partition coefficient of rhodium between Pd metal phase and Ru oxide phase (KRh) can be expressed bywhere T and represent absolute temperature and oxygen fugacity. Based on the comparison of crystal compositions in the HLW glass with experimental results, it can be expected that the HLW glass examined in this study had been equilibrated in the temperature range from 1273 to 1373 K and oxygen fugacity close to that of air just before discharging from the melter.

Effect of Callovo-Oxfordian clay rock on the dissolution rate of the SON68 simulated nuclear waste glass

Long-term storage of high-level nuclear waste glass in France is expected to occur in an engineered barrier system (EBS) located in a subsurface Callovo-Oxfordian (COx) clay rock formation in the Paris Basin in northeastern France. Understanding the behavior of glass dissolution in the complex system is critical to be able to reliably model the performance of the glass in this complex environment. To simulate this multi-barrier repository scenario in the laboratory, several tests have been performed to measure glass dissolution rates of the simulated high-level nuclear waste glass, SON68, in the presence of COx claystone at 90°C. Experiments utilized a High-Performance Liquid Chromatography (HPLC) pump to pass simulated Bure site COx pore water through a reaction cell containing SON68 placed between two COx claystone cores for durations up to 200days. Silicon concentrations at the outlet were similar in all experiments, even the blank experiment with only the COx claystone (∼4mg/L at 25°C and ∼15mg/L at 90°C). The steady-state pH of the effluent, measured at room temperature, was roughly 7.1 for the blank and 7.3–7.6 for the glass-containing experiments demonstrating the pH buffering capacity of the COx claystone. Dissolution rates for SON68 in the presence of the claystone were elevated compared to those obtained from flow-through experiments conducted with SON68 without claystone in silica-saturated solutions at the same temperature and similar pH values. Additionally, through surface examination of the monoliths, the side of the monolith in direct contact with the claystone was seen to have a corrosion thickness 2.5× greater than the side in contact with the bulk glass powder. Results from one experiment containing 32Si-doped SON68 also suggest that the movement of Si through the claystone is controlled by a chemically coupled transport with a Si retention factor, Kd, of 900mL/g.

High-temperature heat capacity and density of simulated high-level waste glass

The heat capacities of two simulated high-level waste borosilicate glasses and glass melts have been determined from differential scanning calorimetry and drop-calorimetry measurements between 345K and 1673K. The densities of the glass melts have been measured by double-bob Archimedean method between 1273K and 1573K. The volume expansivity between glass transition temperature and 1573K has been determined by combining the measured densities and density of supercooled melts below 1273K reported previously. Both of the heat capacity and the volume expansivity of the simulated high-level waste glass melts are characterized by a large increase at the glass transition temperature and the rapid decrease with increasing temperature. The configurational contributions to the heat capacity and the volume expansivity at the glass transition temperature are 35% and 88%, respectively. The significant change of the heat capacity is probably attributed to temperature dependence of chemical mixing of boron, aluminum and silicon in the tetrahedral sites, while the change of the volume expansivity is caused by temperature-induced coordination change of boron.

Viscoplasticity of simulated high-level radioactive waste glass containing platinum group metal particles

The shear rate dependency of the viscosity of three simulated high-level radioactive waste glasses containing 0, 1.2 and 4.5wt% platinum group metals (PGMs) was examined at a temperature range of 1173–1473K by a rotating viscometer. Shear stress when the shear rate equals zero, i.e. yield stress, was also measured by capillary method. The viscosity of the glass containing no PGM was shear rate-independent Newtonian fluid. On the other hand, the apparent viscosity of the glasses containing PGMs increased with decreasing shear rate, and nonzero amount of yield stresses were detected from both glasses. The viscosity and yield stress of the glass containing 4.5wt% PGMs was roughly one to two orders of magnitude greater than the glass containing 1.2wt% PGMs. These viscoplastic properties were numerically expressed by Casson equation.

カルシウムイオンや金属鉄がガラス固化体の溶解／変質挙動に及ぼす影響

カルシウムイオンや金属鉄がガラス固化体の溶解／変質挙動に及ぼす影響

High-temperature X-ray Imaging Study of Simulated High-level Waste Glass Melt

High-temperature X-ray Imaging Study of Simulated High-level Waste Glass Melt

Initial dissolution rate of a Japanese simulated high-level waste glass P0798 as a function of pH and temperature measured by using micro-channel flow-through test method

Aqueous dissolution tests were performed for a Japanese type of simulated high-level waste (HLW) glass P0798 by using a newly developed test method of micro-channel flow-through (MCFT) method, and the initial dissolution rate of glass matrix, r 0, was measured as a function of solution pH (3–11) and temperature (25–90°C) precisely and consistently for systematic evaluation of the dissolution kinetics. The MCFT method using a micro-channel reactor with a coupon shaped glass specimen has the following features to provide precise and consistent data on the glass dissolution rate: (1) any controlled constant solution condition can be provided over the test duration; (2) the glass surface area actually reacting with solution can be determined accurately; and (3) direct and totally quantitative analyses of the reacted glass surface can be performed for confirming consistency of the test results. The present test results indicated that the r 0 shows a “V-shaped” pH dependence with a minimum at around pH 6 at 25°C, but it changes to a “U-shaped” one with a flat bottom at neutral pH at elevated temperatures of up to 90°C. The present results also indicated that the r 0 increases with temperature according to an Arrhenius law at any pH, and the apparent activation energy evaluated from Arrhenius relation increases with pH from 54 kJ/mol at pH 3 to 76 kJ/mol at pH 10, which suggests that the dissolution mechanism changes depending on pH.

Synchrotron Radiation-Based X-ray Imaging Study of Ruthenium in Simulated High-Level Waste Glass

Synchrotron Radiation-Based X-ray Imaging Study of Ruthenium in Simulated High-Level Waste Glass

Structural analysis of some sodium and alumina rich high-level nuclear waste glasses

Sodium- and aluminum-rich high-level nuclear waste glasses are prone to nepheline (NaAlSiO4) crystallization. Since nepheline removes three moles of glass-forming oxides (Al2O3 and SiO2) per mole of Na2O, the formation of this phase can result in severe deterioration of the chemical durability in a given glass. The present study aims to investigate the relationships between the molecular-level structure and the crystallization behavior of sodium alumino-borosilicate-based simulated high-level nuclear waste glasses with infrared spectroscopy (FTIR) and X-ray diffraction, respectively. The molecular structure of most of the investigated glasses comprise a mixture of Q2 and Q3 (Si) units while aluminum and boron are predominantly present in tetrahedral and trigonal coordination, respectively. The increasing boron content has been shown to suppress the nepheline formation in the glasses. The structural influence of various glass components on nepheline crystallization is discussed.

Long-term product consistency test of simulated 90-19/Nd HLW glass

Abstract Chemical durability of 90-19/Nd glass, a simulated high-level waste (HLW) glass in contact with the groundwater was investigated with a long-term product consistency test (PCT). Generally, it is difficult to observe the long term property of HLW glass due to the slow corrosion rate in a mild condition. In order to overcome this problem, increased contacting surface ( S / V = 6000 m −1 ) and elevated temperature (150 °C) were employed to accelerate the glass corrosion evolution. The micro-morphological characteristics of the glass surface and the secondary minerals formed after the glass alteration were analyzed by SEM-EDS and XRD, and concentrations of elements in the leaching solution were determined by ICP-AES. In our experiments, two types of minerals, which have great impact on glass dissolution, were found to form on 90-19/Nd HLW glass surface when it was subjected to a long-term leaching in the groundwater. One is Mg–Fe-rich phyllosilicates with honeycomb structure; the other is aluminosilicates (zeolites). Mg and Fe in the leaching solution participated in the formation of phyllosilicates. The main components of phyllosilicates in alteration products of 90-19/Nd HLW glass are nontronite (Na 0.3 Fe 2 Si 4 O 10 (OH) 2 ·4H 2 O) and montmorillonite (Ca 0.2 (Al,Mg) 2 Si 4 O 10 (OH) 2 ·4H 2 O), and those of aluminosilicates are mordenite ((Na 2 ,K 2 ,Ca)Al 2 Si 10 O 24 ·7H 2 O)) and clinoptilolite ((Na,K,Ca) 5 Al 6 Si 30 O 72 ·18H 2 O). Minerals like Ca(Mg)SO 4 and CaCO 3 with low solubility limits are prone to form precipitant on the glass surface. Appearance of the phyllosilicates and aluminosilicates result in the dissolution rate of 90-19/Nd HLW glass resumed, which is increased by several times over the stable rate. As further dissolution of the glass, both B and Na in the glass were found to leach out in borax form.

High level nuclear waste glass corrosion in synthetic clay pore solution and retention of actinides in secondary phases

The corrosion of the simulated high level waste glass GP WAK1 in synthetic clay pore solution was studied in batch-type experiments at 323 and 363K with special focus on the effect of high carbonate concentration in solution. The corrosion rate after 130 days was <10−4gm−2d−1 – no significant effect of the carbonate was identified. During glass corrosion, crystalline secondary phases (powellite, barite, calcite, anhydrite and clay-like Mg(Ca,Fe)-silicates) were formed. To obtain a molecular level picture of radionuclide speciation within the alteration layer, spectroscopic methods have been applied including grazing incidence X-ray absorption spectroscopy (XAS) to study the structural changes in the coordination of uranyl upon alteration layer formation. The number of equatorial oxygen atoms increases from 4 in the bulk glass to 5 in the alteration layer. Furthermore, reduced coordination symmetry was found. Hectorite, a frequently observed secondary clay mineral within the glass alteration layer, was synthesized in the presence of trivalent f-elements (e.g. Eu) and structurally characterized using time-resolved laser fluorescence spectroscopy. Structural incorporation into the octahedral layer is indicated.

Recovery of Metals from Simulated High-Level Radioactive Waste Glass through Phase Separation

The recovery of metals from simulated high-level radioactive waste (HLW) in a glass form using the phase separation of borosilicate glass was studied in order to satisfy possible future demands such as the adoption of some new treatments for the waste in the glass or use of the vitrified elements as resources. The simulated HLW glass was separated into SiO2-rich and B2O3-rich phases at 973 and 873K when the ternary mass ratio of SiO2:B2O3:Na2O was adjusted to 68:27:5 by the addition of SiO2 and B2O3 to the simulated HLW glass. Annealing at the lower temperature of 878K promoted the distribution of the elements in the B2O3-rich phase. Approximately 90% of the Ni, Zn, Fe, Nd, Te, Zr, and Mo were distributed in the B2O3-rich phase, and these elements, except Zr, were almost completely leached into 1 mol dm−3 nitric acid at 363 K. The leaching of Zr was also achieved using 1.5 mol dm−3 sulfuric acid after the nitric acid leaching. The leached fractions of the glass-network components, such as B and Al, were lower than the other elements at approximately 70–80% due to the existence in the SiO2-rich phase. An increase in the concentration of CaO in the glass in the range of 2–5 wt% inhibited the distribution of elements into the B2O3-rich phase. The increase in the concentration of CaO also changed the structure of the B2O3-rich phase from the continuous unit shape to the discontinuous spherical shape. Consequently, the leaching fraction of every element dramatically decreased. The structure of the B2O3-rich phase returned to continuous when the concentration of CaO was more than 10 wt%. From this glass, the leaching of 69% Zr was possible using only nitric acid without any sulfuric acid.

Recovery of Metals from Simulated High-Level Radioactive Waste Glass through Phase Separation

The recovery of metals from simulated high-level radioactive waste (HLW) in a glass form using the phase separation of borosilicate glass was studied in order to satisfy possible future demands such as the adoption of some new treatments for the waste in the glass or use of the vitrified elements as resources. The simulated HLW glass was separated into SiO2-rich and B2O3-rich phases at 973 and 873K when the ternary mass ratio of SiO2:B2O3:Na2O was adjusted to 68:27:5 by the addition of SiO2 and B2O3 to the simulated HLW glass. Annealing at the lower temperature of 878K promoted the distribution of the elements in the B2O3-rich phase. Approximately 90% of the Ni, Zn, Fe, Nd, Te, Zr, and Mo were distributed in the B2O3-rich phase, and these elements, except Zr, were almost completely leached into 1 mol dm−3 nitric acid at 363 K. The leaching of Zr was also achieved using 1.5 mol dm−3 sulfuric acid after the nitric acid leaching. The leached fractions of the glass-network components, such as B and Al, were lower than the other elements at approximately 70–80% due to the existence in the SiO2-rich phase. An increase in the concentration of CaO in the glass in the range of 2–5 wt% inhibited the distribution of elements into the B2O3-rich phase. The increase in the concentration of CaO also changed the structure of the B2O3-rich phase from the continuous unit shape to the discontinuous spherical shape. Consequently, the leaching fraction of every element dramatically decreased. The structure of the B2O3-rich phase returned to continuous when the concentration of CaO was more than 10 wt%. From this glass, the leaching of 69% Zr was possible using only nitric acid without any sulfuric acid.