Radioactive Waste Glass Research Articles

Neutron transmission measurements for silica glass at the KURNS-LINAC

Silica glass has been used as a base and host material in vitrified radioactive waste and lithium glass scintillators for neutron detection because of its superb transparency, high heat resistance, and excellent chemical inertness. Therefore, an accurate total cross section of the silica glass is crucial to evaluate the criticality safety of vitrified wastes and understand the neutron response for lithium glass scintillators. This study performed neutron transmission measurements for silica glass using a pulsed neutron beam with the time-of-flight method at the Kyoto University Institute for Integrated Radiation and Nuclear Science − Linear Accelerator to provide an accurate total cross section in the thermal and epithermal energy range. We obtained the neutron total cross section of the silica glass in the energy region from 0.002–25 eV. The results were compared and discussed with previous results and evaluated data.

Studying microbially induced corrosion on glass using ToF-SIMS.

Microbially induced corrosion (MIC) is an emerging topic that has huge environmental impacts, such as long-term evaluation of microbial interactions with radioactive waste glass, environmental cleanup and disposal of radioactive material, and weathering effects of microbes. Time-of-flight secondary ion mass spectrometry (ToF-SIMS), a powerful mass spectral imaging technique with high surface sensitivity, mass resolution, and mass accuracy, can be used to study biofilm effects on different substrates. Understanding how to prepare biofilms on MIC susceptible substrates is critical for proper analysis via ToF-SIMS. We present here a step-by-step protocol for preparing bacterial biofilms for ToF-SIMS analysis, comparing three biofilm preparation techniques: no desalination, centrifugal spinning (CS), and water submersion (WS). Comparisons of two desalinating methods, CS and WS, show a decrease in the media peaks up to 99% using CS and 55% using WS, respectively. Proper desalination methods also can increase biological signals by over four times for fatty acids using WS, for example. ToF-SIMS spectral results show chemical compositional changes of the glass exposed in a Paenibacillus polymyxa SCE2 biofilm, indicating its capability to probe microbiologically induced corrosion of solid surfaces. This represents the proper desalination technique to use without significantly altering biofilm structure and substrate for ToF-SIMS analysis. ToF-SIMS spectral results showed chemical compositional changes of the glass exposed by a Paenibacillus bacterial biofilm over 3-month inoculation. Possible MIC products include various phosphate phase molecules not observed in any control samples with the highest percent increases when experimental samples were compared with biofilm control samples.

Evidence of nuclide migration from high-level radioactive waste glass via geogas

Characteristics of high-level radioactive waste transport in glass as gases were studied. A transmission electron microscope was used to observe the morphology of the substance after penetrating the high-level radioactive waste glass and the bentonite soil column, and the composition of the substance was analyzed using electron probe energy spectroscopy. The results show that the radionuclides in the high-level radioactive waste glass were transported out of the glass, the bentonite was penetrated by the geogas, and the transported substance occurred as nanometer-size particles and particle aggregates.

Potential methods to reduce the thermal impact of vitrified waste from spent mixed oxide fuel on geological repositories

Compared to the vitrified, high-level radioactive waste (HLW) from spent UO2 fuel (UO2-HLW glass), that of mixed oxide (MOX) fuel (MOX-HLW glass) exhibits high heat generation over a long period of time. Thus, to reduce the associated waste volume and repository footprint, it is essential to prevent bentonite buffer alteration by mitigating heat generation. In this study, we evaluated five potential methods of decreasing the bentonite buffer temperature in a geological repository for MOX-HLW glass. Of these five methods, the separation of minor actinides (MA) from high-level liquid waste (HLLW) was the most effective. This is because the main nuclide involved in heat generation in MOX-HLW glass is Am-241. An MA separation rate of 81% was required to maintain the bentonite buffer temperature below the Japanese upper disposal limit of 100 °C. Thus, it is important to measure the amount of Am-241 when disposing of MOX-HLW glass. Assuming that only Am-241 was disposed of, the maximum Am-241 waste loading under a bentonite buffer temperature of 100 °C was 0.33 wt%, equating to the disposal of only 1.32 kg of Am-241 per 400 kg of MOX-HLW glass. Thus, there is a need for new methods of treating and disposing of Am-241.Graphical abstractRelationship between bentonite buffer temperature and (a) minor actinide (MA) separation ratio from high-level liquid waste (HLLW), (b) mixed oxide (MOX) high-level radioactive waste (HLW) glass and UO2 HLLW mixing ratio, (c) waste loading in MOX-HLW glass, (d) MOX-HLW glass storage time, and (e) canister footprint, representing five methods of mitigating heat generation from disposed MOX-HLW glass.

Surface interfacial analysis of simulant high level nuclear waste glass dissolved in synthetic cement solutions

The corrosion mechanisms and kinetics of a Mg-rich alkali aluminoborosilicate glass simulating UK high-level waste (CaZn28) were investigated upon dissolution in synthetic cement solutions. Dissolution varied as a function the different pH and alkali/alkaline earth content of each cement solution. High resolution microscopy and spectroscopy techniques ascertained the nature of the interface between the glass and the cement solutions. TEM-EDS revealed alkali- and alkaline earth-rich silica gels, into which K, Ca and Mg were incorporated. TEM-SAED, combined with synchrotron micro-focus XRD, identified the ubiquitous precipitation of the Mg-aluminate layered double hydroxide phase, meixnerite (Mg6Al2(OH)18·4H2O), in addition to goethite (FeOOH) and crystalline silica. The C-S-H phase, tobermorite (Ca5Si6O16(OH)2·4H2O), was identified in the most Ca-rich solution only. These data give insight to the role of alkali/alkaline earth-rich solutions in the dissolution or radioactive waste glasses, of importance to the final disposition in a geological disposal facility.

Recovery of Se, Zr, Pd, and Cs from simulated high‐level radioactive waste glass through phase separation

AbstractIn this study, elemental recovery was performed using phase separation from simulated high‐level radioactive waste (HLW) glass. To cause phase separation, SiO2 and B2O3 were added to the simulated HLW glass and adjusted the ratio of SiO2: B2O3: other oxides to 40:50:10. The phase separated glass was immersed in aqueous solutions of 0–3 mol/L of HNO3, H2SO4, and a 1:1 mixture of HCl–HNO3 at 363 K for 20 h, and the dissolution behavior of 17 elements was examined. The relationship between the dissolved mass fraction of each element and the acid concentration in the immersion liquid could be approximated by the modified sigmoid function. The recovery of stable nuclei Se, Zr, Pd, and Cs instead of long‐lived radioactive nuclei was tested using a four‐stage leaching process in which the sample was immersed sequentially in four aqueous solutions at 363 K of distilled water, HNO3, H2SO4, and a 1:1 mixture of HCl–HNO3 for 20 h. It was confirmed that Se, Zr, Pd, and Cs could be recovered selectively. Furthermore, the recovery result could be predicted based on the individual dissolution results described above.

Optimization of waste management for mixed oxide fuel in light-water reactors: Evaluation of the effectiveness of blending spent uo2 and mixed oxide fuels in reprocessing

This study evaluated the impact of using mixed oxide fuel in light- water reactors (MOX-LWRs) from the viewpoint of waste management. As one of the challenges of MOX-LWR fuel is the high decay heat, one reasonable option for waste management may be to reduce the heat generation of high-level radioactive waste (HLW) glass by blending spent MOX and UO2 fuels. Both the thermal properties of the HLW glass and the thermal impact on the repository are examined. The results indicate that introducing blended UO2–MOX HLW glass (blended HLW) as a technical option can control the heat generation of the HLW glass and the thermal impact on the repository, which then lead to a reduction of 5–30% in the emplacement area. The obtained results demonstrate the viability of a future alternative approach for the management of MOX-LWR.

Thermal treatment of nuclear fuel-containing Magnox sludge radioactive waste

Magnesium aluminosilicate and magnesium borosilicate glass formulations were developed and evaluated for the immobilisation of the radioactive waste known as Magnox sludge. Glass compositions were synthesised using two simplified bounding waste simulants, including corroded and metallic uranium and magnesium at waste loadings of up to 50 wt.%. The glasses immobilising corroded simulant waste formed generally homogenous and fully amorphous glasses, while those immobilising metallic wastes contained crystallites of UO 2 and U 3 O 8 . Uranium speciation within the glass was investigated by micro-focus X-ray absorption near edge spectroscopy and it was shown that the borosilicate glass compositions were characterised by a slightly lower mean uranium oxidation state than the aluminosilicate counterparts. This had an impact upon the durability, and uranium within glasses of higher mean oxidation states was dissolved more readily. All material showed dissolution rates that were comparable with simulant high level radioactive waste glasses, while the borosilicate-based formulations melted at a temperature suitable for modern vitrification technologies used in radioactive waste applications. These data highlight the potential for vitrification of hazardous radioactive Magnox sludge waste in borosilicate or aluminosilicate glass formulations, with the potential to achieve >95 % reduction in conditioned waste volume over the current baseline plan. • Magnesium aluminosilicate and magnesium borosilicate glass systems were synthesised to incorporate metallic uranium and magnesium, U 3 O 8 and Mg(OH) 2 • Uranium speciation within the glass was investigated by micro-focus X-ray absorption near edge spectroscopy • Borosilicate glasses possessed greater chemically durable than their aluminosilicate counterparts • All glass compositions demonstrated durability that is comparable to UK and French high level waste glass

Assessing the effect of radioactive waste glass dissolution on early-stage radionuclide migration using simplified geological repository Monte Carlo transport models

The vitrification of radioactive waste within glass and subsequent disposal within a geological disposal facility (GDF) requires a comprehensive understanding of the effect of glass dissolution on GDF performance. This paper aims to analyse the effect of both high-level and intermediate-level waste (HLW and ILW) glass dissolution source terms on radionuclide release into the geosphere just above the disposal vault (the ‘crown’). Radionuclide migration was simulated in GoldSim for HLW in either granite or clay host rocks with a bentonite buffer using carbon steel or copper canisters, whereas ILW simulations considered either granite or clay host rocks, in either bentonite buffer or cement backfill, using concrete or cast-iron canisters. Glass dissolution source terms were varied by coupling GoldSim and MATLAB to modify the initial, residual, and resumption dissolution rates of the glass or by applying the analytical GRAAL model to glass dissolution. HLW glass results indicate no preference of granite over clay host rocks for a given canister type but that a copper canister is preferable to steel. ILW results suggest that a granite–bentonite–cast-iron environment yields lowest crown activities with cast-iron preferable to concrete as the canister, bentonite preferable to cement as the buffer/backfill, and granite preferable to clay as the host rock. Varying glass dissolution source terms (initial, residual, and resumption dissolution rates) had an understood effect on radionuclide migration, although changes were arguably insignificant considering peak crown activity for both HLW and ILW.

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.

Niche Partitioning of Microbial Communities at an Ancient Vitrified Hillfort: Implications for Vitrified Radioactive Waste Disposal

Because microbes cannot be eliminated from radioactive waste disposal facilities, the consequences of bio-colonization must be understood. At a pre-Viking era vitrified hillfort, Broborg, Sweden, anthropogenic glass has been subjected to bio-colonization for over 1,500 years. Broborg is used as a habitat analogue for disposed radioactive waste glass to inform how microbial processes might influence long-term glass durability. Electron microscopy and DNA sequencing of surficial material from the Broborg vitrified wall, adjacent soil, and general topsoil show that the ancient glass supports a niche microbial community of bacteria, fungi, and protists potentially involved in glass alteration. Communities associated with the vitrified wall are distinct and less diverse than soil communities. The vitrified niche of the wall and adjacent soil are dominated by lichens, lichen-associated microbes, and other epilithic, endolithic, and epigeic organisms. These organisms exhibit potential bio-corrosive properties, including silicate dissolution, extraction of essential elements, and secretion of geochemically reactive organic acids, that could be detrimental to glass durability. However, long-term biofilms can also possess a homeostatic function that could limit glass alteration. This study documents potential impacts that microbial colonization and niche partitioning can have on glass alteration, and subsequent release of radionuclides from a disposal facility for vitrified radioactive waste.

Predicting radioactive waste glass dissolution with machine learning

The vitrification of high-level nuclear waste within borosilicate glass and its disposition within a multi-barrier repository deep underground is accepted as the best form of disposal. Here, the ability of machine learning to predict both static and dynamic glass leaching behavior is analysed using large-scale unstructured multi-source data, covering a diverse range of experimental conditions and glass compositions. Machine learning can accurately predict leaching behavior, predict missing data, and time forecast. Accuracy depends upon the type of learning algorithm, model input variables, and diversity or size of the underlying dataset. For static leaching, the bagged random forest method predicts well, even when either pH or glass composition are neglected as input variables, additionally showing potential in predicting independent glass dissolution data. For dynamic leaching, accuracy improves if replacing final pH with a species dissolution rate as an input variable, although results show no preferred output species (Si, Na, or Al).

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.

Corrosion of glass used for radioactive waste disposal influenced by iron corrosion products

Iron corrosion products of the steel canister in the nuclear waste container are highly silica sorptive materials and very much expected to delay formation of the protective layer (gel) on the nuclear glass interface. This study is focusing on the role of the iron carbonates (ankerite), which is probably one of iron corrosion products and already exists in the clay structure of the disposal depth. Simulating nuclear borosilicate glass samples (alternative to the R7T7-type) samples are planned to leach in different series of experimental models with dissimilar quantities of ankerite. Batch experiments all will be cultivated in synthetic groundwater; where different pH (4-9) values and temperatures (35, 50, 90 °C) are considered. In this paper the state of the art of the radioactive waste glass corrosion in the circumstances of deep geological disposal will focus on the role of ankerite as one of the iron corrosion products and clarify how it is expected to show delay in achieving the Si saturation status and accelerate glass alterations.

Relating Magnox and international waste glasses

Magnox and international radioactive waste glasses observe significantly different aqueous dissolution behaviours. Previously, the effects of Li on the kinetics of dissolution and B network of analogues of a complex Magnox waste glass were investigated (Li-Mg-EM). Here, an “International Simple Glass” with Li substituted for Na at two ratios (Li-ISG) was fabricated to compare the aqueous durability of Magnox and international glasses. 11B MAS-NMR, 23Na MAS-NMR, 6Li1H CP-NMR and SEM studies are presented. The IIIB/IVB ratio and the role of Na in the pristine glasses varied insignificantly with the Li:Na ratio. Further, the B network of Li-ISG was shown to leach congruently. Li, Na and Mg-containing secondary phases were present for Li-Mg-EM, whilst no precipitates were observed for Li-ISG. Li in ISG was shown to be detrimental but further substitution of Li improved long-term aqueous durability, which was attributed to a LiNa mixed alkali effect for Li-ISG but not Li-Mg-EM.

Corrosion of glass used for radioactive waste disposal – state of the art

Iron corrosion products of the steel canister in the nuclear waste container are highly silica sorptive materials and very much expected to delay formation of the protective layer (gel) on the nuclear glass interface. This study is focusing on the role of the iron carbonates (ankerite), which is probably one of iron corrosion products and already exists in the clay structure of the disposal depth. French SON68 inactive reference glass (alternative to the R7T7- type) samples are planned to leach in different series of experimental models with dissimilar quantities of natural ankerite. All batch experiments will be cultivated in synthetic Callovo-Oxfordian groundwater; where different pH (4-9) values and temperatures (35, 50, 90 °C) are considered. In this paper the state of the art of the radioactive waste glass corrosion in the circumstances of deep geological disposal were extensively studied.

Thermodynamic assessment of the Na2O-Al2O3-SiO2-B2O3 pseudo-binary and -ternary systems

Thermodynamic assessments of the pseudo-binary and -ternary systems formed by B2O3 with Na2O, Al2O3, and SiO2 were conducted according to the CALPHAD methodology. The compound energy formalism and two-sublattice partially ionic liquid models were used to thermodynamically represent the solid solutions malinkoite and mullite and the liquid phase of each system, respectively. A comprehensive literature review of available phase equilibria and thermodynamic experimental data as well as a detailed discussion of the modeling approaches implemented to optimize each system is provided. Assessment results are then presented and discussed, and the future path forward is outlined. The addition of B2O3 to the Na2O-Al2O3-SiO2 system contributes to the development of a thermodynamic database that will ultimately predict the equilibrium behavior of nepheline formation in high-level radioactive waste glass.

The effect of magnesium on the local structure and initial dissolution rate of simplified UK Magnox waste glasses

A series of simplified glasses were prepared to mimic the United Kingdom's Magnox radioactive waste glasses and determine the separate effect of the presence of Mg on the glass structure and the initial dissolution rate. These glasses had an alkaline earth (Ca/Mg) content of 6.5 mol% and relative ratios of Si, B and Na similar to 25 wt% waste loaded Magnox waste glass simulant. Each simplified glass had similar macroscopic properties, differing only in Ca/Mg ratio. 25Mg magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of the simplified Mg endmember (MgEM) glass (with no Ca) and the full-component simulant glass were similar, consistent with the similar Mg local environments in both glasses. 11B MAS NMR spectra of the series of simplified glasses showed a systematic increase in the amount of three-coordinated boron ([3]B) with increasing amounts of Mg. A clear change in the charge balancing of four-coordinated boron ([4]B) by Mg compared with Ca is observed. However, 11B NMR measurements of the leached material showed that the additional [3]B was not preferentially leached from the Mg containing samples. Despite the structural changes in the glass induced by Ca/Mg substitution, initial dissolution rates (r0) remained invariant, within error, with Ca/Mg ratio. This indicates that the poorer aqueous durability of Mg-containing Magnox waste glass measured experimentally in long-term leaching experiments, compared with SON68 glass containing Ca, is not caused by a primary structural effect in the glass.

Effect of clayey groundwater on the dissolution rate of SON68 simulated nuclear waste glass at 70 °C

To predict the long-term behavior of high-level radioactive waste glass, it is necessary to study aqueous dissolution of the glass matrix under geological repository conditions. The present article focuses on SON68 (an inactive surrogate of the R7T7 glass) glass alteration in synthetic clayey groundwater at 70 °C. Experiments in deionized water as reference were also performed in the same conditions. Results are in agreement with those of previous studies showing that magnesium present in the solution is responsible for higher glass alteration. This effect is transient and pH-dependent: Once all the magnesium is consumed, the glass alteration rate diminishes. Precipitation of magnesium silicate of the smectite group seems to be the main factor for the increased glass alteration. A pH threshold of 7.5–7.8 was found, above which precipitation of these magnesium silicates at 70 °C is possible. TEM observations reveal that magnesium silicates grow at the expense of the passivating gel, which partly dissolves, forming large pores which increase mass transfer between the reacting glass surface and the bulk solution.

X-ray Absorption Fine Structure (XAFS) Studies of Oxide Glasses-A 45-Year Overview.

X-ray Absorption Fine Structure (XAFS) spectroscopy has been widely used to characterize the short-range order of glassy materials since the theoretical basis was established 45 years ago. Soon after the technique became accessible, mainly due to the existence of Synchrotron laboratories, a wide range of glassy materials was characterized. Silicate glasses have been the most studied because they are easy to prepare, they have commercial value and are similar to natural glasses, but borate, germanate, phosphate, tellurite and other less frequent oxide glasses have also been studied. In this manuscript, we review reported advances in the structural characterization of oxide-based glasses using this technique. A focus is on structural characterization of transition metal ions, especially Ti, Fe, and Ni, and their role in different properties of synthetic oxide-based glasses, as well as their important function in the formation of natural glasses and magmas, and in nucleation and crystallization. We also give some examples of XAFS applications for structural characterization of glasses submitted to high pressure, glasses used to store radioactive waste and medieval glasses. This updated, comprehensive review will likely serve as a useful guide to clarify the details of the short-range structure of oxide glasses.