Simulated Nuclear Waste Research Articles

Site differentiation strategy for selective strontium uptake and elution within an all-inorganic polyoxoniobate framework

Selective uptake and elution of trace amounts of hazardous radioactive 90Sr from large-scale high-level liquid waste (HLW) is crucial for sustainable development. Here, we propose a site differentiation strategy, based on the presence of distinct selective metal capture sites (concavity site and tweezer site) within the giant polyoxoniobate (PONb) nanoclusters of an all-inorganic PONb framework (FZU-1). Through this strategy, FZU-1 can not only effectively remove 98.9% of Sr²⁺ from simulated nuclear liquid waste, performing best among the reported Sr adsorbents, but also achieve desorption of adsorbed Sr²⁺ ions by selectively loading Na⁺ ions, thus enabling the recycling of FZU-1. Based on the well-defined single-crystal structures and theoretical studies, it can be revealed that the rapid and selective uptake of Sr²⁺ is attributed to the strong binding energy between the Sr²⁺ ions and the concavity sites. The effective elution of Sr²⁺, on the other hand, stems from the preferential binding of Na⁺ ions at the tweezer sites, elevating the cluster’s electrostatic potential and indirectly facilitating the elution of Sr²⁺ ions. The exceptional stability of FZU-1, along with its rapid and selective Sr²⁺ capture and elution capabilities, positions it as a promising candidate for large-scale nuclear waste treatment and groundwater remediation applications.

High temperature environmental scanning electron microscopy characterization of transient phase formation during conversion of simulated nuclear waste feed to glass

In-situ High-Temperature Environmental Scanning Electron Microscopy (HT-ESEM) is used to characterize the transient phases formed during the melting of complex glass batch mixtures representing simulated nuclear waste feeds. The first phenomenon that occurs is the formation of oxyanionic salt melt, followed by the reaction of oxyanionic salts with refractory grains containing Si, Al, or Mg through surface reactions to form a molten alkali-alumino-boro-silicate phase. The onset temperatures of gas bubble formation and primary foaming are directly determined from the HT-ESEM measurements. The formation of sulfate lakes as well as the formation of high-temperature transient phases floating at the sample surface are also directly observed and identified. Convection currents are observed and their consequences on glass homogenization are discussed.

Ultra-fast, selective and pseudo-quantitative analysis of 99Tc in nuclear waste for screening purposes

Controlling radioactivity is essential in various fields, such as the decommissioning of nuclear power plants and nuclear medicine. In some cases, a full characterization of samples is not required; instead, a screening analysis that provides an overall indication of the activity present can be sufficient to determine if a sample is radioactive. This article introduces a new system called PSkits designed specifically for ultra-fast and selective screening detection of 99Tc. PSkits consist of a plastic scintillation layer attached to the bottom of a scintillation vial, coated with aliquat·336® as a selective extractant. In this study, the preparation of PSkits was optimized by adjusting the proportions of crosslinker, porogen, and the type of vial used. The analysis method was developed, and the selectivity against common interferences was tested by optimizing the rinsing media. Finally, PSkits were validated by analysing simulated nuclear waste samples and urine spiked samples, achieving satisfactory results with quantification errors below 50 %, demonstrating their effectiveness for the intended purpose

Iterative Regression of Corrective Baselines (IRCB): A New Model for Quantitative Spectroscopy.

In this work, a new model with broad utility for quantitative spectroscopy development is reported. A primary objective of this work is to create a novel modeling procedure that may allow for higher automation of the model development process. The fundamental concept is simple yet powerful even for complex spectra and is employed with no additional preprocessing. This approach is applicable for several types of spectroscopic data to develop regression models that have similar or greater quality than the current methods. The key modeling steps are a matrix transformation and subsequent feature selection process that are collectively referred to as iterative regression of corrective baselines (IRCB). The transformed matrix (Xtransform) is a linearized form of the original X data set. Features from Xtransform that are predictive of Y can be ranked and selected by ordinary least-squares regression. The best features (rows of Xtransform) are linear depictions of Y that can be utilized to develop regression models with several machine learning models. The IRCB workflow is first detailed by using a case study of Fourier transform infrared (FTIR) spectroscopy for prepared solutions of a three-component mixture. Next, IRCB is applied and compared to benchmark results for the 2006 "Chimiométrie" near-infrared spectroscopy (NIR) soil composition challenge and Raman measurements of a simulated nuclear waste slurry.

Laboratory-based correlated X-ray imaging and scattering of inhomogeneous glass-ceramics

Nuclear waste glasses often contain complex microstructures, and understanding these are key to predicting and engineering glass durability, since heterogeneity may exist over multiple length scales. Here we use laboratory-based, spatially-resolved X-ray characterization methods that span length scales (10-10-10-2 m): Wide angle X-ray Scattering (WAXS) provides atomic-scale crystallography; Small Angle X-ray Scattering (SAXS) provides nanoscale phase data; X-ray Computed Tomography and projection X-ray radiography map the materials structure over the micrometer and millimeter scales. The pairing of X-ray radiography with SAXS/WAXS in the same instrument enables specific regions on the sample to be characterized with precise spatial resolution. Two molybdenum- and lanthanum-containing simulated nuclear waste glasses were examined, enabling exploration of hierarchal glassy phase separation and spatial partitioning of crystals of powellite and zircon of different morphologies and sizes 10 nm to 1 mm. The tools described in this study offer means of broadly understanding multi-scale structural attributes of multi-phase materials.

Corrosion property investigation of laser-cladding copper coating in the simulated nuclear waste disposal solution

To explore the efficient corrosion protection for the nuclear waste storage containers, pure copper coatings were successfully prepared on the 20# steel pipe surface using an infrared laser system under different laser powers. The study was conducted on the copper coatings, encompassing the surface quality, defects, microstructure, elemental distribution, phase composition, and corrosion products. The electrochemical and immersion corrosion behavior of the copper coatings in simulated nuclear waste disposal solutions was analyzed. The pure copper coating prepared by 2800 W laser power has fewer amounts and smaller sizes of defects inside the coating with only a slight fusion of Cu and Fe elements at the interface, which exhibits the highest corrosion potential and the smallest self-corrosion current density. During the immersion corrosion process, pores and unfused defects inside the coating, as well as the pits formed by galvanic coupling corrosion, lead to enhanced acidity inside these defects, resulting in a higher corrosion rate. As the immersion time proceeds, the corrosion rate slows down gradually and the content of Cu2+ corrosion product increases significantly.

Model validation and interpretation of the interaction between glass and cement in an integrated glass dissolution experiment

This article presents the modeling results from the interaction between simulated nuclear waste glasses and ordinary Portland cement (OPC). In general, the modeling results are in good agreement with the experimental results. A diffusion-based glass dissolution model well describes the release of B and Li from the glass, and a reactive transport model well describes the profiles of dissolved glass elements in the cement. It is found that the effective diffusion coefficient of Li in the cement is much larger than that of B. Sorption of both Li and B onto the cement is required to better fit their measured diffusion profiles. For B profiles in the cement, one spatially uniform distribution coefficient is needed, while for Li, sorption needs to be linked to the gel-like secondary phase at the surface of the cement. The effective diffusion coefficients for both Li and B are relatively low and can be linked to the pore-filling effects of the gel-like secondary phase. Even though it is generally believed that nuclear waste glass will dissolve faster in cementitious environments, the results show that the gel-like secondary phase can both seal the cement and act as a strong sorbent for dissolved glass species, thus inhibiting the migration of dissolved glass species.

Selective removal of ReO4−/TcO4− by an imidazolyl-based polymer from 3 M HNO3 solution

The effective removal of 99TcO4− in the radioactive waste is very important and ReO4− was often used as the substitute of TcO4− for research. In this paper, an imidazolyl-based polymer TIB-TBPB was successfully synthesized and exhibited excellent adsorption performance for ReO4−. The results showed that the framework of TIB-TBPB is benzene-rich structure, which enhances its hydrophobicity and allows it to exhibit excellent thermal stability and acid-base stability. It could maintain the excellent recyclability even in 3 M HNO3. TIB-TBPB possessed the high capacity of 882 mg g−1 and the superb removal depth for ReO4− and TcO4− with Kd of 2.34 × 106 mL g−1 and 1.35 × 106 mL g−1, respectively. Furthermore, TIB-TBPB has the advantages of excellent selectivity, recyclability and could remove 65.7 % and 86.4 % of ReO4− from 3 M HNO3 and the Hanford LAW simulated nuclear waste, respectively. DFT calculation explained the selectivity of TIB-TBPB for ReO4− over NO3− and verified the experimental results. In a word, the excellent performance suggested TIB-TBPB would be a promising material for TcO4− /ReO4− removal.

A nanotrap infused ultrathin hybrid composite material for rapid and highly selective entrapment of 99TcO4.

99Tc is one of the potentially toxic radioactive substances owing to its long half-life and a high degree of environmental mobility. Hence, the sequestration of 99Tc from radioactive waste has become enormously important and a contemporary research priority. However, selective extraction of this species in its stable oxoanionic form (99TcO4 -) is very challenging on account of bottlenecks such as low charge density, less hydrophilic nature, etc. Herein, an ultrathin hybrid composite material has been strategically designed and fabricated by covalent anchoring of a chemically stable amino functionalized nanosized cationic metal-organic polyhedron with a positively charged robust ionic covalent organic framework. The resulting thin-layer-based hybrid composite presented multiple exfoliated exposed interactive sites, including a Zr(iv)-secondary building unit, amine and triaminoguanidine functional groups, which can selectively interact with TcO4 - oxoanions through a synergistic combination of electrostatic, H-bonding and various other supramolecular interactions. Thus synthesized function-tailored composite, by virtue of its multiple unique characteristics, manifested an ultrafast and very selective, high distribution coefficient (∼106 mL g-1), as well as recyclable entrapment of TcO4 - oxoanions from the complex mixture of superfluous (∼5000-fold) other interfering anions in both high and ultra-trace concentrations along with simulated nuclear waste and from different water systems. Dynamic flow-through experiments were conducted with the membrane of the hybrid material in simulated wastewater, which reduced the concentration of ReO4 - (surrogate of radioactive TcO4 -) to below the WHO permissible level with rapid sequestration kinetics and excellent selectivity over excessive competing anions.

Dissolution of simulated nuclear waste glass at high surface area to solution volume, high pH and 70 °C: comparison of international simple glass and SON68 glass.

Long-term static dissolution experiments, lasting up to ∼1500 days, were conducted on International Simple Glass (ISG) and SON68 glass under hyperalkaline pH, at 70 °C, and at a very high glass surface area to solution volume ratio. The study compared (1) glass dissolution kinetics, (2) secondary phase formation, and (3) the microstructure of the altered glass and secondary phase interface. Boron release indicated rapid initial dissolution followed by a slowdown mainly due to a significant pH drop. ISG reached a residual rate regime, while SON68 approached this regime near the experiment's end, with both glasses having similar final dissolution rates. Electron microscopy (SEM, TEM, EDS) of the reacted glass surfaces and the alteration products revealed nontronite formation on SON68, while C(A)SH phases and later rhodesite appeared on ISG, in addition to phillipsite-type zeolite formation observed in both experimental series. TEM observations revealed a porous, foam-like surface altered layer (SAL) near the pristine glass. SON68's SAL nanostructure, more complex than ISG's, had two porous zones, hindering water transfer and glass constituent release, in addition to a pH drop reducing silica network hydrolysis. TEM-EDS showed cation exchange and iron depletion in SON68's SAL, leading to nontronite formation. Secondary phases at the SAL-solution interface did not destabilize the SAL, and no alteration resumption was observed due to the pH drop below the threshold necessary for an alteration resumption due to zeolite formation. In conclusion, the combination of alkaline conditions and very high reaction progress does not lead to the dissolution of the glass by a dissolution-reprecipitation mechanism, as typically observed at much lower SA/V ratios. At the relatively mildly alkaline pH reached within the first year of the experiments, the diffusion of cations through the SAL becomes rate-controlling.

Real-time infrared spectroscopy coupled with blind source separation for nuclear waste process monitoring

On-line infrared absorbance spectroscopy enables rapid measurement of solution-phase molecular species. Many spectra-to-concentration models exist for spectral data, with some models able to handle overlapping spectral bands and nonlinearities. However, model accuracy is limited by the quality of training data used in model fitting. The process spectra of nuclear waste simulants at the Savannah River Site display incongruity between training and process spectra; the glycolate spectral signature in the training data does not match the glycolate signature in Savannah River National Laboratory process data. A novel blind source separation algorithm is proposed that preprocesses spectral data so that process spectra more closely resemble training spectra, thereby improving model quantification accuracy when unexpected sources of variation appear in process spectra. The novel blind source separation preprocessing algorithm is shown to improve nitrate quantification from an R2 of 0.934 to 0.988 and from 0.267 to 0.978 in two instances analyzing nuclear waste simulants from the Slurry Receipt Adjustment Tank and Slurry Mix Evaporator cycle at the Savannah River Site.

Converting natural metamorphic granite and simulated actinide oxide to aluminosilicate glass for nuclear waste immobilization

To explore the possibility of immobilizing nuclear waste by natural metamorphic granite, the phase, microscopic morphology, elemental distribution and the structural evolution of the final waste form were studied. The maximum loading capacity of natural metamorphic granite to simulated nuclear waste (CeO2) can reach 23 wt%, with half of Ce4+ is reduced to Ce3+ at high temperatures. The mechanical stability of the glass is well kept after waste doping, and the normalized leaching rate of Ce of waste forms is ∼10−6 g/(m2·d) after 42 d. The results indicate that natural metamorphic granite is a stable host matrix for nuclear waste immobilization, which contributes to environmental protection.

In Situ Optical Microspectroscopy Study of Isothermal Bleaching of γ-Irradiated International Simple Glass.

The isothermal bleaching of γ-irradiated glass was studied at elevated temperatures (280-340 °C) by real-time in situ optical microspectroscopy for the first time. The study was performed on γ-irradiated (0.83 and 1.99 MGy) International Simple Glass (ISG) borosilicate nuclear waste simulant made by Mo-SCI Corporation (Rolla, MO, USA). The current investigation proposes real-time optical transmission methodology for the activation energy assessment of isothermal bleaching of γ-irradiated glass. The method is based on robust quantification of the Urbach energy decay rates and yields similar activation energies for both doses within ∼0.24-0.26 eV.

Highly efficient and selective adsorption of palladium(II) from simulated nuclear waste solution using Amberlite XAD-7 resin impregnated with a phenanthroline-derived diamide

The increasing demand and limited natural resources for rare precious metal palladium render its separation and recovery from secondary sources such as acidic nuclear liquid waste greatly interesting. Herein, a novel Et-Tol-DAPhen extraction resin was prepared by impregnating Amberlite XAD-7 resin with a phenanthroline-derived diamide extractant N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), and the adsorption behavior of this new extraction resin towards Pd2+ in HNO3 solution was investigated through the batch and column experiments. The Et-Tol-DAPhen extraction resin exhibited strong adsorbability, high adsorption capacity, excellent selectivity and good reusability for Pd2+ in highly acidic HNO3 solution. In addition, the pseudo-second-order and Langmuir models were applied to understand the adsorption process of Pd2+ on Et-Tol-DAPhen extraction resin, respectively. It demonstrated the characteristics of a uniform single-layer chemisorption. The maximum uptake capacity could reach as high as 74.6 mg g−1 for Pd2+ in 3.0 mol/L HNO3 solution which is much higher than most adsorbent materials of palladium reported before. Furthermore, Et-Tol-DAPhen extraction resin could selectively uptake Pd2+ from a simulated acidic nuclear waste solution containing 20 different kinds of ions with the separation factor SFPd/M values as high as 100 to 10,000. Moreover, although the adsorption efficiency had a slight decrease after 5 times of adsorption-desorption process, it still remained at a high level. This new extraction resin displayed a potential application prospect in the field of separation and recovery of Pd2+ from acidic nuclear liquid waste.

The influence of hydrogen permeation on the protection performance of the Cu coating of nuclear waste containers

Hydrogen permeation and corrosion behaviour of Cu-coated carbon steel under simulated nuclear waste disposal conditions of the Beishan area have been investigated. The permeation current (with −500 μA·cm−2 charging current) decreased from 3778 to 141 and 47 nA.cm−2 respectively when 5 and 10 µm thick Cu coatings were electrodeposited on the steel. The XRD analysis suggests the formation of CuH during the hydrogen charging treatment, and its subsequent decomposition formed a protective CuOH/Cu2O layer on the charging surface when exposed to simulated groundwater for 44 h. No damage to the Cu coating-steel interface was observed in the cross-section analysis.

Physico-chemical properties of γ-irradiated International Simple Glass (ISG) nuclear waste simulants with low levels of iron impurities

The effect of γ-irradiation on physico-chemical properties of International Simple Glass (ISG) nuclear waste glass simulants with low iron impurities was investigated. The study was performed on glasses produced by Corning Inc. (named ISG-1, ISG-2) following a 0.95 MGy dose. Fourier-transform infrared and Raman spectroscopy, chemical durability tests, dilatometry, differential scanning calorimetry, electron paramagnetic resonance (EPR), optical absorption, and photoluminescence (PL) spectroscopy appraisals were done in comparison with pristine glasses. The data indicated that structural, chemical, and thermal properties were not significantly altered following γ-ray exposure. EPR spectroscopy showed radiogenic signatures from spin defects for the γ-irradiated glasses which were absent in the pristine. Optical absorption also changed significantly for the γ-irradiated glasses which exhibited defects-related features around 3.45 and 2.25 eV. The optical band gap and Urbach energies were then determined and compared with those obtained for the γ-irradiated original ISG produced by Mo-SCI Corporation. PL spectroscopy revealed distinct changes after irradiation showing enhanced high-energy emission, contrasting with the γ-irradiated original ISG. The effects of thermal treatment on optical properties of γ-irradiated glasses were finally evaluated. Potential causes at the origin of the contrasting results are discussed based on the effects of different impurities.

Immobilize Nd2O3 as simulated nuclear waste in silicate-apatite glass-ceramics

The solidification of nuclear waste has far-reaching developmental implications. Nuclear waste management is not only essential for the earth’s ecological balance but also can address the increasing depletion of human exploitable resources in the future. Scientists are dedicated to finding a better solidification matrix and ensuring the sustainable development of the nuclear industry in search of alternative energy sources. The present work has fabricated a simulated nuclear waste form using a sintering process of diopside. The results have shown that the Fe element in diopside granite porphyry shows an impact on the amorphization process and mechanical properties of the final waste form. Moreover, the study finds a natural analog in the glassy bulk, i.e. (Ca2Nd8(SiO4)6O2 or (K, Na)Nd9(SiO4)6O2), which can solidify the simulated trivalent actinide of Nd3+. The FT-IR results suggested that the polymerization degree of glass components in waste form decreased initially and then increased with Nd2O3 doping. Q3 unit is considered to be a key component in the waste forms. Finally, the loading capacity of Nd2O3 in waste form reached 19 wt.%. The waste form has the characteristics of glass-ceramics containing a silicate-apatite structure that is evenly distributed and has a quite considerable prospect for mechanical properties.

Unraveling mechanistic insights into covalent organic frameworks for highly efficient sequestration of organic iodides from simulated nuclear waste

A systematic study was conducted to understand the role of framework-integrated functionalities, along with the textural properties, towards organic iodide sequestration by varying the number of N-heteroatomic sites in a series of COFs.

Enhancing the stability of poly(ionic liquids)@MOFs@COFs via core–shell protection strategy for 99TcO4− sequestration

The core–shell polyILs@MOF@COF shows stability in both alkaline and acid solutions and superior ReO4−/TcO4− sequestration from the simulated nuclear waste.

Examining phase separation and crystallization in glasses with X-ray nano-computed tomography

X-ray nano-computed tomography (nano-CT) is a powerful technique to characterize and visualize 3 dimensional (3D) phenomena in complex glasses at the nanoscale. This technique can offer a unique opportunity to explore the intricate morphology of multicomponent glass and glass-ceramic samples, due to its low X-ray energy and high spatial resolution (down to 50 nm). In the current demonstration paper, nano-CT provided insight into crystallization and phase separation, as well as a variety of other phenomena, including corrosion, fracture, and porosity. At scales ranging from 100 to 20 μm, the microstructures of phase separation in borosilicate, complex silicate, and chalcogenide glass compositions were examined. In addition, crystallites present in simulant nuclear waste glasses, volcanic glasses, and other related samples were explored. Nano-CT analysis can add to the understanding of (1) the formation processes, (2) distributions, interactions, and compositions of phases, and (3) the mechanisms, structures, and growth of crystallization and phase separation. Nano-CT offers wide potential in the field of glass science, especially when (1) common characterization methods are insufficient, (2) simple sample preparation is required, (3) 3D rendering is needed, or (4) compelling images of small, complex features are desired.