Lanthanide Borosilicate Glass Research Articles

Waste form evaluation for RECl3 and REOx fission products separated from used electrochemical salt

The work presented here is based off the concept that the rare earth chloride (RECl3) fission products within the used electrorefiner (ER) salt can be selectively removed as RECl3 (not yet demonstrated) or precipitated out as a mixture of REOCl and REOx through oxygen sparging (has been demonstrated). This paper presents data showing the feasibility of immobilizing a mixture of RECl3s at 10 mass% into a 78%TeO2-22%PbO glass while also showing that this same mixture of RECl3s can be oxidized to REOCl at 300 °C and then to REOx by 1200 °C, evolving Cl2(g). When the REOx mixture is heated at temperatures >1200 °C, the ratios of REOxs change. The mixture of REOx was then immobilized in a lanthanide borosilicate (LABS) glass at a high loading of 60 mass%. Both the 78%TeO2-22%PbO glass and LABS glass systems show good chemical durability. The advantages and disadvantages of tellurite and LABS glasses are compared.

Plutonium Environment in Lanthanide Borosilicate Glass

AbstractTwo lanthanide borosilicate (LaBS) glasses containing 9.5 and 5.0 wt.% PuO2 prepared at 1500 °C consisted of a vitreous phase and minor crystalline PuO2 (or PuO2-HfO2 solid solution with minor HfO2) and britholite-type phases. X-ray absorption spectra of Pu LIII edge in the as-prepared and stored for various periods LaBS glasses were recorded, analyzed and compared with the spectra of crystalline PuO2. Pu in the as-prepared glass existed in predominantly tetravalent form (Pu4+ ions) but its storage in air results in partial oxidation as was seen from shift of peak energy values. In the structure of the as-prepared glass, Pu4+ ions had a co-ordination number (CN) close to 6 (˜6.3) and were located within the axially squeezed octahedra with five equidistant oxygen ions at a distance of 2.265±0.015 Å and one – at shorter distance (2.130±0.010 Å) from the Pu4+ ion. The Pu—Pu(M) distance (second co-ordination shell) was 3.675±0.015 Å. “Aging” of the LaBS glass with transformation of some fraction of Pu into penta- or/and hexavalent form was accompanied by a structural transformation.

Multivariate calibration of spectra obtained by Laser Induced Breakdown Spectroscopy of plutonium oxide surrogate residues

Laser Induced Breakdown Spectroscopy (LIBS) was used to determine elemental concentration of plutonium oxide surrogate (cerium oxide) residue for monitoring the fabrication of lanthanide borosilicate glass. Quantitative analysis by LIBS is affected by the severe limitation of variation in the induced plasma due to changes in the matrix. Multivariate calibration was applied to LIBS data to predict the concentrations of Ce, Cr, Fe, Mo, and Ni. A total of 18 different samples were prepared to compare calibration from univariate data analysis and from multivariate data analysis. Multivariate calibration was obtained using Principal Component Regression (PCR) and Partial Least Squares (PLS). Univariate calibration was obtained from background-corrected atomic emission lines. Calibration results show improvement in the coefficient of determination from 0.87 to 0.97 for Ce compared to univariate calibration. The root mean square error also reduced from 7.46 to 2.93%. A similar trend was obtained for Cr, Fe, Mo, and Ni also. These results clearly demonstrate the feasibility of using LIBS for online process monitoring in a hazardous waste management environment.

X-ray photoelectron study of lanthanide borosilicate glass

The elemental and ionic quantitative analyses of the synthetic lanthanide borosilicate glass (Al-B-Gd-Hf-La-Nd-Pu-Si-Sr-O) are performed using the characteristics of the X-ray photoelectron spectra of the outer-shell and inner-shell electrons in the binding energy range 0–1000 eV. The oxidation states of the metal ions in this glass are determined and correspond to the Al3+, La3+, Nd3+, Gd3+, Hf4+, Pu4+, Si4+, and Sr2+ ions. Taking into account the binding energies of the O 1s electrons for the glass sample under investigation, the average lengths of metal-oxygen bonds on the surface of the sample are estimated to be 0.191 and 0.176 nm, which correspond to oxygen binding energies of 531.3 and 532,3 eV, respectively.

Analysis of plutonium oxide surrogate residue using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy was used to determine the elemental composition of a CeO 2 composite powder for process control verification during lanthanide borosilicate glass fabrication. Cerium oxide is used as a surrogate for plutonium oxide, which along with other canister contents will be combined with frit to make glass. Laser-induced breakdown spectroscopy data for the composition of the CeO 2 batch containing concentrations of Ce, Cr, Si, Fe, Ta, Ni, Zn, Al Mg, Gd, and W were quantitatively determined from laser-induced breakdown spectroscopy spectra of both pellet and powder samples. The results of both forms were compared and it was determined that the pellet data gave slightly better precision than the powder sample.

Plutonium Feed Impurity Testing in Lanthanide Borosilicate (LaBS) Glass

AbstractA vitrification technology utilizing a lanthanide borosilicate (LaBS) glass is a viable option for dispositioning excess weapons-useable plutonium that is not suitable for processing into mixed oxide (MOX) fuel. A significant effort to develop a glass formulation and vitrification process to immobilize plutonium was completed in the mid-1990s. The LaBS glass formulation was found to be capable of immobilizing in excess of 10 wt % Pu and to be tolerant of a range of impurities. A more detailed study is now needed to quantify the ability of the glass to accommodate the anticipated impurities associated with the Pu feeds now slated for disposition.The database of Pu feeds was reviewed to identify impurity species and concentration ranges for these impurities. Based on this review, a statistically designed test matrix of glass compositions was developed to evaluate the ability of the LaBS glass to accommodate the impurities. Sixty surrogate LaBS glass compositions were prepared in accordance with the statistically designed test matrix. The heterogeneity (e.g. degree of crystallinity) and durability (as measured by the Product Consistency Test – Method A (PCT–A)) of the glasses were used to assess the effects of impurities on glass quality.

Accelerated weathering of high-level and plutonium-bearing lanthanide borosilicate waste glasses under hydraulically unsaturated conditions

The US Department of Energy (DOE) has proposed that a can-in-canister waste package design be used for disposal of excess weapons-grade Pu at the proposed mined geologic repository at Yucca Mountain, Nevada. This configuration consists of a high-level waste (HLW) canister fitted with a rack that holds mini-canisters containing a Pu-bearing lanthanide borosilicate (LaBS) waste glass and/or titanate-based ceramic (∼15% of the total canister volume). The remaining volume of the HLW canister is then filled with HLW glass (∼85% of the total canister volume). A 6-a pressurized unsaturated flow (PUF) test was conducted to investigate waste form–waste form interactions that may occur when water penetrates the canisters and contacts the waste forms. The PUF column volumetric water content was observed to increase steadily during the test because of water accumulation associated with alteration phases formed on the surfaces of the glasses. Periodic excursions in effluent pH, electrical conductivity, and solution chemistry were monitored and correlated with the formation of a clay phase(s) during the test. Geochemical modeling, with the EQ3NR code, of select effluent solution samples suggests the dominant secondary reaction product for the surrogate HLW glass, SRL-202, is a smectite di-octahedral clay phase(s), possibly nontronite [Na 0.33 Fe 2(AlSi) 4O 10(OH) 2 · n(H 2O)] or beidellite [Na 0.33Al 2.33Si 3.67O 10(OH) 2]. This clay phase was identified in scanning electron microscope (SEM) images as discrete spherical particles growing out of a hydrated gel layer on reacted SRL-202 glass. Alpha energy analysis (AEA) of aliquots of select effluent samples that were filtered through a 1.8 nm filter suggest that approximately 80% of the total measurable Pu was in the form of a filterable particulate, in comparison to unfiltered aliquots of the same sample. These results suggest the filterable particles are >1.8 nm but smaller than the 0.2 μm average diameter openings of the Ti porous plate situated at the base of the column. In this advection-dominated system, Pu appeared to be migrating principally as or in association with colloids after being released from the LaBS glass. Analyses of reacted LaBS glass particles with SEM with energy dispersive X-ray spectroscopy suggest that Pu may have segregated into a discrete disk-like phase, possibly PuO 2. Alteration products that contain the neutron absorber Gd have not been positively identified. Separation of the Pu and the neutron absorber Gd during glass dissolution and transport could be a criticality issue for the proposed repository. However, the translation and interpretation of these long-term PUF test results to actual disposed waste packages requires further analysis.

Glass fabrication and product consistency testing of lanthanide borosilicate glass for plutonium disposition

The Department of Energy Office of Environmental Management (DOE/EM) plans to conduct the Plutonium Disposition Project at the Savannah River Site (SRS) in Aiken, SC, to disposition excess weapons-usable plutonium. A plutonium glass waste form is a leading candidate for immobilization of the plutonium for subsequent disposition in a geologic repository. The objectives of this present task were to fabricate plutonium-loaded lanthanide borosilicate (LaBS) Frit B glass and perform testing to provide near-term data that will increase confidence that LaBS glass product is suitable for disposal in the proposed Federal Repository. Specifically, testing was conducted in an effort to provide data to Yucca Mountain Project (YMP) personnel for use in performance assessment calculations. Plutonium-containing LaBS glass with the Frit B composition with a 9.5 wt% PuO 2 loading was prepared for testing. Glass was prepared to support glass durability testing via the ASTM product consistency testing (PCT) at Savannah River National Laboratory (SRNL). The glass was characterized with X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) prior to performance testing. This characterization revealed some crystalline PuO 2 inclusions with disk-like morphology present in the as-fabricated, quench-cooled glass. A series of PCTs was conducted at SRNL with varying exposed surface area and test durations. Filtered leachates from these tests were analyzed to determine the dissolved concentrations of key elements. The leachate solutions were also ultrafiltered to quantify colloid formation. Leached solids from select PCTs were examined in an attempt to evaluate the Pu and neutron absorber release behavior from the glass and to investigate formation of alteration phases on the glass surface. A series of PCTs was conducted at 90 °C in ASTM Type 1 water to compare the Pu LaBS Frit B glass durability to current requirements for high level waste (HLW) glass in a geologic repository. The PCT (7-day static test with powdered glass) results on the Pu-containing LaBS Frit B glass at SA/V of ≈2000 m −1 showed that the glass was very durable with an average normalized elemental release value for boron of 0.013 g/m 2. This boron release value is ≈640× lower than normalized boron release from current environmental assessment (EA) glass used for repository acceptance. The PCT-B (7-, 14-, 28- and 56-day, static test with powdered glass) normalized elemental releases were similar to the normalized elemental release values from PCT-A testing, indicating that the LaBS Frit B glass is very durable as measured by the PCT. Normalized plutonium releases were essentially the same within the analytical uncertainty of the ICP-MS methods used to quantify plutonium in the 0.45 μm-filtered leachates and ultra-filtered leachates, indicating that colloidal plutonium species do not form under the PCT conditions used in this study.

Demonstration of the Feasibility of Recovering Americium and Curium Isotopes from a Lanthanide Borosilicate Glass

ABSTRACTA solution containing kilogram quantities of highly radioactive isotopes of americium and curium (Am/Cm) is currently stored in a process tank at the Department of Energy's Savannah River Site. This tank and its vital support systems are old, subject to deterioration, and prone to possible leakage. To address the stabilization of this material, vitrification of the isotopes has been considered. Potentially, the glass could be shipped to the isotope production and distribution programs at the Oak Ridge National Laboratory for californium-252 production and use by the transplutonium research community. However, before the Am/Cm could be used in these programs, it must be recovered from the glass.To demonstrate the feasibility of recovering the Am/Cm isotopes from a glass, a series of small-scale experiments was performed as part of a compositional variability study. Glasses fabricated during the study utilized lanthanide elements as surrogates for Am/Cm due to the high specific activity of these materials. In the dissolution tests, glass formulations representative of potential uncertainties in the composition of the Am/Cm solution were fabricated, ground to a -35 to +60 mesh particle size, and dissolved in 8M nitric acid at 110°C. Under these conditions, at least 98% of the lanthanide oxides in the glass dissolved in less than 2 h meeting a recoverability criterion established for the vitrification process and imposing no limitations on the acceptable glass composition region.Dissolution of the lanthanide borosilicate glasses was described by a spherical particle model based on the observation that the rate of change of the mass to surface area ratio remains constant. Calculation of dissolution rates using the model showed that the rate was proportional to the lanthanide oxide concentration in the glass. When silicon oxide (SiO2) was replaced with a lanthanide element at higher (simulated Am/Cm) loadings, the glass became more easily dissolved in nitric acid due to the solubility of the lanthanide oxides compared to SiO2.

Plutonium Alteration Phases from Vapor Hydration of Lanthanide Borosilicate Glass for Weapons Material Disposition: a TEM Study

A lanthanide borosilicate glass, also known as LaBS glass, is being considered for the disposition of surplus weapons plutonium and plutonium residues. The LaBS glass, based upon Löffler-type glasses, is chemically durable and can dissolve substantial amounts of plutonium as well as the neutron absorbers gadolinium and hafnium [1]. Samples of a prototype LaBS glass composition containing 10 wt. % plutonium were subjected to water vapor at 200 °C for periods of 14 to 56 days. The Argonne Vapor Hydration Test Procedure was followed [2]. This test, while not designed to replicate specific conditions that may be found in a potential geologic repository (e.g., Yucca Mountain), has been shown to accelerate alteration phase formation that is usually observed in low-temperature tests over extended time periods [2]. The surfaces of the glass samples, along with alteration phases, were examined with a transmission electron microscope (TEM) to determine the characteristic alteration products.

Optimization of Lanthanide Borosilicate Frit Compositions for the Immobilization of Actinides Using a Plackett-Burman/Simplex Algorithm Design

ABSTRACTImmobilization by vitrification is one potential disposition option for a portion of the United States' excess plutonium inventory. Research has been performed at the Savannah River Site (SRS) to determine the optimum composition of a lanthanide borosilicate frit for the vitrification of plutonium using a Plackett-Burman design and simplex algorithm as a statistical tool. This technique uses various response variables to rank and optimize a composition. The variables used in this study correspond to homogeneity, durability, actinide solubility and devitrification after heat-treatment.The optimized frit composition was determined using a constant ThO2 loading of 20 wt%. No noticeable trends were followed with respect to the individual components which may indicate a relatively robust system able to accommodate variations in the feed.Batches containing various loadings of ThO2 were melted to determine if actinide solubility was improved in the optimized composition compared to that of a similar lanthanide borosilicate glass. No noticeable improvement in ThO2 solubility was realized as a result of using this optimization technique.