Search

Monazite, with its unique chemical composition and stable crystal structure, shows significant potential for immobilizing high-level radioactive waste. In this study, a series of monazite ceramics were synthesized to study the effect of entropy change on their structure and aqueous durability. The synthesized ceramics exhibit a monoclinic structure (P2 1 /n), with an average grain size below 80 nm. MCC-1 leaching tests reveal that the normalized leaching rate decreases over time but increases with higher entropy. The five-element high-entropy ceramics have an average leaching rate of 4.2 × 10⁻³ g·m⁻2 d⁻1. Notably, the higher leaching rate in high-entropy nanocrystalline monazites is likely attributed to the reduced grain size. The presence of numerous grain boundaries tends to mitigate the precipitation inhibition effect typically associated with high-entropy ceramics. These findings offer insights into the role of entropy and grain size in ceramic materials for radioactive waste immobilization. [ABSTRACT FROM AUTHOR]

Ensuring environmental safety and regulatory compliance at Department of Energy (DOE) sites demands an efficient and reliable detection system for low-level nuclear waste (LLW). Unlike existing methods that rely on human effort, this paper explores the integration of computer vision algorithms to automate the identification of such waste across DOE facilities. We evaluate the effectiveness of multiple algorithms in classifying nuclear waste materials and their adaptability to newly emerging LLW. Our research introduces and implements five state-of-the-art computer vision models, each representing a different approach to the problem. Through rigorous experimentation and validation, we evaluate these algorithms based on performance, speed, and adaptability. The results reveal a noteworthy trade-off between detection performance and adaptability. YOLOv7 shows the best performance and requires the highest effort to detect new LLW. Conversely, OWL-ViT has lower performance than YOLOv7 and requires minimal effort to detect new LLW. The inference speed does not strongly correlate with performance or adaptability. These findings offer valuable insights into the strengths and limitations of current computer vision algorithms for LLW detection. Each developed model provides a specialized solution with distinct advantages and disadvantages, empowering DOE stakeholders to select the algorithm that aligns best with their specific needs. [ABSTRACT FROM AUTHOR]

Volatility of technetium poses a challenge during the vitrification of low-activity waste (LAW) feed to glass. Although this is typically resolved through recycle loops, this can lead to other problems, such as sulfate phase formation. Thus, ensuring high single-pass retention of Tc (or Re, its non-radioactive surrogate) is required for enabling high waste-loading formulations. In our previous study, we observed significantly higher Re retention in final waste glass produced from a LAW melter feed containing gibbsite as the alumina source compared to a compositionally similar feed containing kyanite. To investigate this effect, we prepared representative LAW melter feeds with kyanite and gibbsite as alumina sources and measured the Re retention in the produced glasses. We found that the Re retention is consistently higher in glasses produced with gibbsite, by up to 20 %. We attribute this result to the formation of nanocrystalline alumina in melter feeds containing gibbsite. Possessing a high surface area, nanocrystalline alumina can adsorb the perrhenate-containing molten salt, increasing the rate at which Re is incorporated into the alkali-alumino-boro-silicate glass-forming melt. In addition, we demonstrate that replacing kyanite with gibbsite in LAW melter feeds has no adverse effects on their processing during vitrification. [ABSTRACT FROM AUTHOR]

This paper reports the average pore water density (ρwp) measured on a Japanese bentonite, which was compacted to a dry density (ρd) range from 0·3 to 1·8 Mg/m3 and saturated under a water pressure of 2·7 MPa. It was found that ρwp monotonically increased from ∼1·0 Mg/m3 at ρd of 0·3 Mg/m3 to ∼1·23 Mg/m3 at ρd of 1·8 Mg/m3. A review of the available literature revealed that the methodology of accurately measuring ρwp in a full range of water content (w) is not available. An upper boundary of ρwp for montmorillonite was drawn, and proportions of water at different swelling states were estimated. [ABSTRACT FROM AUTHOR]

Crystalline rocks in the subsurface are of interest for geothermal energy extraction, nuclear waste storage, and, when weathered or fractured, as aquifers. Compliant discontinuities such as microcracks, cracks and fractures may nucleate and propagate due to changes in pore pressure, stress and temperature. These discontinuities may provide flow pathways for fluids and, if fracturing extends to surrounding rocks, may allow escape of fluids to neighbouring formations. Monitoring such rocks using sonic logs, passive seismic, borehole seismic and surface seismic requires understanding of the propagation of elastic waves in the presence of such discontinuities. These may have an anisotropic orientation distribution as in situ stress may be anisotropic. As crystalline rock may display intrinsic anisotropy due to foliation and the preferential orientation of anisotropic minerals, quantification of the relative importance of intrinsic and microcrack‐induced anisotropy is important. This may be achieved based on the stress sensitivity of elastic wave velocities. A method that allows both the orientation distribution of microcracks and the stress dependence of their normal and shear compliance to be estimated independently of the elastic anisotropy of the background rock is presented. Results are given for anisotropic samples of gneiss from Bukov in the Czech Republic and granite from Grimsel in Switzerland based on the ultrasonic velocity measurements of Aminzadeh et al. The microcrack orientation distribution is approximately transversely isotropic for both samples with a preferred orientation of microcrack normals perpendicular to foliation. This preferred alignment is stronger in the sample of gneiss than in the granite sample, and the normal and shear compliance of the microcracks decreases with increasing compressive stress. This occurs because the contact between opposing faces of the discontinuities grows with increasing compressive stress, and this results in a decrease in elastic anisotropy with increasing compressive stress. At low stress, the ratio of microcrack normal compliance to shear compliance is approximately 0.25 for the granite sample and 0.7 for the sample of gneiss. The normal compliance ZN for both samples decreases faster with increasing compressive stress than the shear compliance ZT, resulting in a decrease in ZN/ZT with increasing compressive stress. [ABSTRACT FROM AUTHOR]

Ceramic materials with excellent radiation resistance stability play an indispensable role in the treatment of nuclear waste. This article uses spark plasma sintering (SPS) to synthesize high-entropy (HE) Y 0.6 Gd 0.6 Sm 0.6 Eu 0.6 Dy 0. 6 Fe 5 O 12 (HEG) and traditional garnet Y 1.2 Nd 1.8 Fe 5 O 12 (YIG). Studied the effects of 2 MeV He2+ irradiation (1 × 1014 ions/cm2 - 1 × 1017 ions/cm2) on the crystal structure, mechanical properties, and chemical stability of ceramics. Research shows that the surface of YIG becomes completely amorphous under ∼30dpa irradiation. Under irradiation at∼30dpa, HEG underwent a small amount of amorphization (with an amorphization rate of 38 %), maintaining the structure of garnet, and the lattice expansion rate of HEG caused by irradiation was lower than that of YIG. After irradiation, the mechanical properties of HEG were improved, while YIG's hardness decreased due to its amorphous state. Radiation has almost no effect on the chemical stability of HEG, and its long-term release mechanism is dominated by diffusion. This study identified HEG as an ideal candidate substrate for immobilizing high-radioactive waste (HLW) the perspective of radiation resistance. [ABSTRACT FROM AUTHOR]

Radioactive iodine from nuclear waste poses a major threat to public safety due to its toxicity and long half-life. The capture and storage of radioactive iodine remains a major challenge. The incorporation of electron-rich heterocycles into the adsorbents could increase the adsorption capacity for iodine due to their strong interaction. In this study, three novel spiro-thioketal-based porous organic polymers, POPSP-1–3, were synthesized in excellent yields by a thiol-aldehyde polycondensation reaction. The polymers of POPSPs were thoroughly characterized using FT-IR, 13C-NMR, BET, and PXRD techniques. These analyses revealed that the polymers are amorphous in nature and have a low surface area. The iodine uptake capacities of POPSP-1, POPSP-2, and POPSP-3 were measured to be 4.13, 5.25, and 5.65 g g−1, respectively, at a temperature of 75 °C due to the increased density of the adsorption sites. Furthermore, the POPSPs exhibit exceptional adsorption performance in iodine/n-hexane solution and their effectiveness in removing iodine is excellent. This work provides a novel approach for the development of sulfur-rich porous organic polymers (POPs) as effective adsorbents for iodine capture. [ABSTRACT FROM AUTHOR]

The Strategic Research Agenda (SRA; https://www.ejp-eurad.eu/publications/eurad-sra) of the European Joint Programme on Radioactive Waste Management (EURAD; https://www.ejp-eurad.eu/) describes the scientific and technical domains and sub-domains and knowledge management needs of common interest between EURAD participant organizations. Theme number 7 is entitled "Performance assessment, safety case development and safety analyses." A list of research and development priorities and activities of common interest to be addressed within EURAD for theme 7 have been established. Amongst others, the Understanding and modelling of multi-physical Thermo-Hydro-Mechanical-Chemical coupled processes (THMC) occurring in radioactive waste disposal is a major and permanent issue to support optimization of design and safety case abstraction. To tackle this challenge a research work package entitled "DONUT: Development and improvement of numerical methods and tools for modelling coupled processes" has been conducted within the EURAD join programming initiative. The purpose of this work package is to improve/develop methods or numerical tools in order to go a step further in development of (i) relevant, performant and cutting-edge numerical methods that can easily be implemented in existing or new tools, in order to carry out high-performance computing to facilitate the study of highly coupled processes in large systems, (ii) numerical scale transition schemes for coupled processes, (iii) innovative numerical methods to carry out uncertainty and sensitivity analyses. In this paper the work carried out within the DONUT work package is put in perspective regarding the existing concept and literature on the field. It does not pretend to be exhaustive but rather to put emphasis on particular issues tackled during the project. [ABSTRACT FROM AUTHOR]

Iron phosphate glasses, known for their exceptional chemical durability and potential applicability in nuclear waste management, have gained significant attention over the years. The structures of these glasses are complicated by the coexistence of Fe3+ and Fe2+, which plays a crucial role in determining their structures and properties. This work uses molecular dynamics simulations to study the structural changes in Na2O–Fe2O3–P2O5 glasses with varying glass composition and Fe2+/Fe3+ redox ratio. It was found that the redox ratio and modifier contents significantly affected the short‐range and medium‐range orders in the glasses. Significant changes in the local environments around P5+ and Fe3+ were observed, as reflected by the bond distances and coordination numbers. Na+ cations are found to preferentially associate with Fe3+ (rather than Fe2+),  whereas Fe2+ has stronger association with P5+ than Na+, confirming the structural role of Fe2+ as a glass modifier. The disruptions in P–O–P linkages upon increasing FeO suggest that FeO causes glass depolymerization. These glasses achieved higher connectivity with increasing Fe3+/(Fe3++Fe2+)${\mathrm{Fe}}^{3+}/({\mathrm{Fe}}^{3+}+{\mathrm{Fe}}^{2+})$ ratios, conerting phosphorous Q2 to Q3 units and iron Q5 units to Q4 units. The decrease of nonbridging oxygen fractions with increasing Fe3+/(Fe3++Fe2+)${\mathrm{Fe}}^{3+}/({\mathrm{Fe}}^{3+}+{\mathrm{Fe}}^{2+})$ ratios, through creating P–O–Fe linkages, is the main reason of enhanced network connectivity. Quantitative structure–property relationship analyses with different structural descriptors were used to correlate with measured properties. The analyses provided valuable insights into structure–property relationships, emphasizing the importance of choosing relevant energy parameters and defining glass network connectivity, particularly in Fnet descriptors. It was found the Fe–O–P linkage density exhibits strong correlations to measured dissolution rates, supporting the importance of these linkages in improving the chemical durability in iron phosphate glasses. [ABSTRACT FROM AUTHOR]

Selective separation of 137Cs is significant for the sustainable development of nuclear energy and environmental protection, due to its strong radioactivity and long half-life. However, selective capture of 137Cs+ from radioactive liquid waste is challenging due to strong coulomb interactions between the adsorbents and high-valency metal ions. Herein, we propose a strategy to resolve this issue and achieve specific Cs+ ion recognition and separation by modulating the stacking modes of layered perovskites. We demonstrate that among niobate-based perovskites, ALaNb2O7 (A = Cs, H, K, and Li), HLaNb2O7 shows an outstanding selectivity for Cs+ even in the presence of a large amount of competing Mn+ ions (Mn+ = K+, Ca2+, Mg2+, Sr2+, Eu3+, and Zr4+) owing to its suitable void fraction and space shape, brought by the stacking mode of layers. The Cs+ capture mechanism is directly elucidated at molecular level by single-crystal structural analyses and density functional theory calculations. This work not only provides key insights in the design and property optimization of perovskite-type materials for radiocesium separation, but also paves the way for the development of efficient inorganic materials for radionuclides remediation. Selective capture of radiocaesium is challenging due to strong coulomb interactions between adsorbents and high valent metal ions. Here, authors propose a strategy of modulating the stacking modes of layered perovskites to achieve specific Cs+ recognition and separation. [ABSTRACT FROM AUTHOR]

With the increasing demand for sustainable energy sources, the management of radioactive iodine, a byproduct of nuclear energy, has become critical for environmental safety and human health. This study presents the design and synthesis of non-porous amorphous polymers, specifically PEI-PD, derived from polyethylenimine (PEI) and pyromellitic dianhydride (PD), for the adsorption of iodine from aqueous and gaseous environments. The adsorbent exhibits high efficiency in capturing iodine, with a remarkable adsorption capacity of 4.43 g g–1 for volatile iodine and 1.43 g g–1 for liquid iodine. The adsorption process is governed by a pseudo-second-order kinetic model and follows the Langmuir isotherm, indicating a chemisorption mechanism driven by electrostatic attraction. The mechanism of iodine adsorption by the adsorbent was investigated using infrared spectroscopy and independent gradient modeling (IGMH), which helped to clarify types of weak interaction between the adsorbent and iodine and the adsorption sites. The study highlights the potential of PEI-PD as an effective material for the removal of radioactive iodine, contributing to the safe and sustainable management of nuclear waste. Non-porous amorphous polymers demonstrate exceptional iodine adsorption capacities of 4.43 g g–1 for volatile iodine and 1.43 g g–1 for liquid iodine. Insights into the adsorption mechanism were gained through FT-IR analysis and independent gradient model based on Hirshfeld partition (IGMH), elucidating the adsorption sites and weak interactions with iodine. (Image credit: Chang Sun.) [ABSTRACT FROM AUTHOR]

Ruthenium quantities in borosilicate glasses, used in vitrification process to nuclear waste immobilization, is uncertain due to the volatility of ruthenium oxide. In this work, a quantitative method was developed to determinate the content of ruthenium in the borosilicate glasses containing nuclear waste tracer nuclides by inductively coupled plasma mass spectrometry (ICP-MS). The research showed that the ruthenium in borosilicate glasses can be completely decomposed by NaOH at 350 °C for 8 h. A recovery of no less than 95% and a detection limit of 0.4 mg kg−1 were obtained. The method has been successfully applied for the determination of actual samples. [ABSTRACT FROM AUTHOR]

A granular manganese oxide-based sorbent was synthesized. One volume of the sorbent decontaminates 125–145 volumes of hardness water from strontium radionuclides to background values of radioactivity. The synthesis includes interaction of MnSO4 with KMnO4 in aqueous medium at [Mn2+]/[MnO4−] = 1.8, followed by the precipitation, aging the precipitate at pH = 11, and calcining it at 160 °C. Characteristics of the sorbent obtained were as follows: the distribution coefficient of the tracer 85Sr radionuclide in 0.01 mol dm−3 CaCl2 solution of 1.6 × 104 cm3 g−1, the batch capacity by Ca2+ of 1.10 mol g−1, and the Sr/Ca pair separation coefficient of 65. [ABSTRACT FROM AUTHOR]

The spent alum sludge was employed for the removal of specific fission products including 137Cs, 85Sr, 152+154Eu, 99Mo, and 99Tc radionuclides from radioactive waste. The physicochemical features of spent alum sludge were investigated. The results illustrated that the uptake percentages were 94.2, 90.5, 87.6, 87.1, and 76.6%, correspondingly, for 99Mo, 152+154Eu, 99Tc, 85Sr, and 137Cs. The kinetic studies illustrated that the adsorption process obeyed Langmuir kinetics which is a combination of first-order and second-order expressions. The findings demonstrated that the spent alum sludge can be applied successfully as a low-cost and effective adsorbent for the treatment of radioactive waste. [ABSTRACT FROM AUTHOR]

Low-permeability rock is suitable as the host rock of an underground repository for radioactive waste disposal; however, minor faults might develop there. Investigating the shear capability (= shear compliance) of those faults is crucial because they could be elastically sheared by the thermal effect of the waste to damage the waste's engineered barriers. This study performed constant-head step-injection tests along with a recently developed packer-pressure-based extensometer method for assessing the applicability of this method to investigate the shear capability of minor faults. Herein, two neighboring minor faults (A and B) in siliceous mudstone were evaluated. The results showed that fault A, with centimeter-thick fault breccia, exhibited high shear capability, whereas fault B, with millimeters or less-thick fault breccia, displayed low shear capability despite containing an incohesive fault rock. An elastic shear displacement occurred for fault A during injection and reached 15–66 mm when the test-section pressure increased from 4.1 to 4.3 MPa. Here, the shear capability was 101 mm/MPa or more. Conversely, fault B had cohesion, and no shear displacement was detected even when the test-section pressure increased from 4.0 to 6.0 MPa. In this case, the shear capability was 10−1 mm/MPa or less. The estimated shear capabilities were consistent with the results from previous shear experiments, and therefore, the applied method helps investigate the shear capabilities of minor faults. Highlights: The packer-pressure-based extensometer method was applied to two neighboring minor faults to investigate their shear capability. The estimated shear capability was corroborated with the results from previous shear experiments. The applied method helps investigate the shear capability of minor faults. [ABSTRACT FROM AUTHOR]

MX80 bentonite pellet/powder mixture has been considered as a candidate sealing/filling material in geological high-level radioactive waste disposal. As a single pellet can play an important role in the global hydro-mechanical behaviour of the mixture, the compression behaviour of a single MX80 pellet was investigated by performing uniaxial compression tests on cylinder-shaped pellets at different initial suctions, imposed by the vapour equilibrium technique. Large cracks were observed at suctions ≤ 9 MPa. Results from the compression tests showed that the axial strain εaxial contributed to the contractancy, whereas the lateral strain εlateral contributed to the dilatancy. The uniaxial shear strength σa, max, the crack closure (CC) stress σcc, the crack initiation (CI) stress σci, the crack damage (CD) stress σcd and the Young's modulus E were found to decrease with decreasing suction, providing evidence of the suction effect through softening and cracking. CI was considered as the inflection point of Δεlateral and the onset of dilatancy. Because of the combined effects of suction and wetting-induced cracks, the Poisson's ratios v increased until the suction decreased to 38–25 MPa, and then decreased with further suction decrease. Loading closed the wetting-induced horizontal cracks at suctions ≤ 9 MPa, leading to a drop of εlateral before CC. [ABSTRACT FROM AUTHOR]

The Beishan Exploration Tunnel (BET) is a facility built to develop technologies associated with the safety of China's first high‐level radioactive nuclear waste(HLW) disposal. The surrounding rock discontinuity identification is a key research topic in BET, which could provide essential geological data for future HLW disposal stability and integrity research. This article presents the rock discontinuity identification research progress in BET based on Structure from Motion (SfM) photogrammetry technology. The discontinuity identification algorithm is improved by introducing the region‐growing algorithm to optimize the candidate subplane. This algorithm automatically picks the seed, avoids human intervention, and thus increases the work efficiency of the discontinuity identification. The FCM method is improved by embedding with the CFSFDP algorithm in the discontinuity sets grouping. The CFSFDP algorithm coincides well with the Fisher distribution of discontinuity orientations, which is suitable for the Beishan situation. A parallel scheme is used when implementing the method, which accelerates the discontinuity calculation. This improved rock discontinuity identification method was tested on a slope above the BET and applied in the BET. The discontinuity identification results were compared with the results from the manual field measurement and the open‐source software DSE. The results show that the improved discontinuity identification method obtains reliable discontinuity data and costs less time and human workload than the other two methods. The surrounding rock discontinuity identification research provides a powerful tool for the Beishan HLW disposal geological investigation. [ABSTRACT FROM AUTHOR]

Extracting uranium from water bodies is urgently needed whether from a waste nuclear resource utilization or a new energy exploration perspective. Herein, a novel robust hierarchical porous CAP membrane was fabricated from the nucleophilic condensation of phenolphthalein and 2,6-difluorobenzonitrile, followed by classical amidoximation and nonsolvent-induced phase separation (NIPS) methods. Fast uranium uptake kinetics with sorption equilibrium at a mere 12 h was demonstrated, and the uranium uptake capacity was found to be 499 mg g−1. The significant improvement in uranium enrichment performance was probably endowed by the outstanding hydrophilic surface and the hierarchical pores throughout the cross-sectional CAP membrane. Meanwhile, it was confirmed that the CAP molecular backbone may endure polymer degradation during amidoximation, and the amount of hydroxylamine used should be strictly controlled. The sorption mechanism was explored, and practical testing experimentally indicated the excellent desorption, reusability and selectivity properties of the CAP membrane. Overall, the easy processability, robustness and outstanding uranium sorption performance made the CAP membrane an ideal candidate for uranium enrichment from water bodies. [ABSTRACT FROM AUTHOR]

Uranium (U) is a radiologically and chemically toxic element that occurs naturally in water, soil, and rock at generally low levels. However, anthropogenic uranium can also leach into groundwater sources due to mining, ore refining, and improper nuclear waste management. Over the last few decades, various methods for measuring uranium have emerged; however, most of these techniques require skilled scientists to run samples on expensive instrumentation for detection or require the pretreatment of samples in complex procedures. In this work, a Schiff base ligand (P1) is used to develop a simple spectrophotometric method for measuring the concentration of uranium (VI) with an accurate and affordable light-emitting diode (LED) spectrophotometer. A test for a higher-order polynomial relationship was used to objectively determine the calibration data's linearity. This test was done with a Python program on a Raspberry Pi computer that captured the spectrophotometer's calibration and sample measurement data. [ABSTRACT FROM AUTHOR]

The efficient capture and monitor of radioactive iodine are crucial for managing radioactive nuclear waste and protecting human health. Herein, three metal–organic coordination compound‐mediated supramolecular organic frameworks (MSOFs) are reported with distinct electron‐rich structures for efficient iodine capture with fluorescence response. The electron‐rich adsorption sites play crucial roles for electron‐deficient iodine capture via charge transfer interactions, where π donors contribute greater than nitrogen heteroatom. Among three MSOFs, MSOF‐3 with the maximum numbers of electron‐rich π donors exhibited the highest iodine uptake capacity (3.70 g mmol−1). Prominently, the charge transfer interactions between iodine and MSOFs result in distinct fluorescence response during iodine uptake, establishing a real‐time fluorescence monitoring system. To facilitate the personal health protection toward practical application, a mask with high iodine removal efficiency (99.1%) and real‐time fluorescence response is successfully developed. This study underscores the great promise of electron‐rich fluorescent MSOFs for capture and sensing of radioactive iodine, offering substantial prospects for the advance of protective equipment in the nuclear industry. [ABSTRACT FROM AUTHOR]

The MOS model (acronym coming from the French MOdèle Simplifié) was born from the desire to have a simple tool that can quantify the contribution of the diffusive reactive environment to the alteration of a vitrified nuclear waste package in deep geological disposal conditions. In the model, this environmental contribution consists partly of the ability of iron, metallic casing corrosion products, and argillite to consume silicon, and partly of the brake on diffusive transport provided by silicon through the successive layers of environmental material. It is a modeling tool serving as an intermediary between operational modeling for the calculation of the source term from the glass, mathematically more simple and giving higher upper margins, and models that use geochemistry and transport, giving greater accuracy for the interactions between glass and its environment. The goal of the MOS model is to calculate the possible impact of silicon reactive diffusion on the alteration rate within the different layers of material surrounding nuclear glass. This article lists the simplifying hypotheses on which the MOS is based, presents the digital resolution method for an environment consisting of several successive layers with different reactivity and transport properties, and explains the model's implementation. [ABSTRACT FROM AUTHOR]

Because of its swelling capacity, compacted bentonite clay is a suitable buffer material in deep geological repositories for high-level nuclear waste. However, this only applies if the swelling capacity is maintained. Accordingly, bentonites have to be stable to changing temperature, humidity, infiltrating fluids or microbial activity. In batch experiments, we investigated combined microbial and thermo-hydro-geochemical effects on the swelling capacity of uncompacted bentonite MX-80. Bentonite was exposed to fluids of different ionic strength and the bacterium Stenotrophomonas bentonitica. Bacterial growth was monitored by counting colony-forming units while the swelling capacity of bentonite was evaluated using in situ XRD at varied temperatures and humidity. The presence of bentonite prolonged the survival of S. bentonitica. However, electron microscopy, XRD and ICP-OES analyses showed neither an interaction of S. bentonitica with bentonite, nor significant changes in the swelling capacity or element composition. The swelling capacity and diffraction peak intensity were, however, strongly reduced by the ionic strength of the fluid and the exposure time. The study highlights that bentonite is affected by thermo-hydro-geochemical and microbial processes to different degrees and that the complexity of different co-occurring factors in potential nuclear waste repositories is important to consider in safety assessments. [ABSTRACT FROM AUTHOR]

This study focuses on the influence of low-concentration additions of NiCl2 on the overall properties of lead arseborate oxide glasses. In this regard, small amounts, in grams, of NiCl2 were added, separately, to the main constituents of the lead-arseboarte glass, according to the chemical formula [23 wt% B2O3–11 wt.% Na2O–20 wt. CaO–23 wt.% PbO–23 wt.% As2O3] % + x NiCl2, where x = 0.25, 0.5, 0.75, and 1 g, to prepare a glass series of four samples using the fast quenching technique. The structural and optical characterizations of the prepared samples have been described based on X-ray diffraction (XRD) measurements, Fourier transform infrared charts (FTIR), and UV–Vis spectra. The X-ray diffraction (XRD) patterns did not contain any crystalline peaks but only two broad humps which revealed that all samples possess short-range order structures. At the same time, the FTIR charts showed different structural units. The UV–Vis spectra demonstrated that the absorption edge spectra changed to a higher wavelength with an increase in NiCl2 dopants, accompanied by a drop in optical transmittance, particularly in the visible range. As the NiCl2 dopants increased, the values of the optical energy gaps reduced while the mass attenuation remained constant, and the effective atomic number, bulk density, microhardness, absorption index, and characteristic relaxation time increased. Regardless of sample thickness, a novel methodology has been proposed to determine both the optical band gaps and the optical loss. The novel method and the widely used one (Tauc relation) demonstrated excellent agreement. The results suggest the NiCl2-rich sample is a primary material for radiation shielding applications as a carrier for radioactive sources and preserving them, or for preserving radioactive waste and high-reflection and UV-blocking glass coating. [ABSTRACT FROM AUTHOR]

This paper focuses on the highly radioactive, long-lasting nuclear waste produced by the currently operating fission reactors and on the sensitive issue of spent fuel reprocessing. Also included is a short description of the fission process and a detailed analysis of the more hazardous radioisotopes produced either by secondary reactions occurring in the nuclear installations or by decay of the fission fragments. The review provides an overview of the strategies presently adopted to minimize the harmfulness of the nuclear waste to be disposed, with a focus on the development and implementation of methodologies for the spent fuel treatments. The partitioning-conditioning and partitioning-transmutation options are analyzed as possible solutions to decrease the presence of long-lived highly radioactive isotopes. Also discussed are the chemical/physical approaches proposed for the recycling of the spent fuel and for the reusing of some technologically relevant isotopes in industrial and pharmaceutical areas. A brief indication is given of the opportunities offered by innovative types of reactors and/or of new fuel cycles to solve the issues presently associated with radioactive waste. [ABSTRACT FROM AUTHOR]

An advanced solvent has been developed for application in the extraction of cesium from alkaline nuclear waste. Four lipophilic guanidines have been compared to arrive at a more hydrolysis-resistant suppressor component of the solvent. Plans call for deployment of the Next-Generation Caustic Side-Solvent Extraction (NG-CSSX) process at industrial scale for separation of radioactive Cs-137 from the legacy salt waste stored at the US Department of Energy Savannah River Site (SRS). In the solvent used in NG-CSSX, an alkyl guanidine "suppressor" component facilitates efficient stripping of the loaded cesium from the solvent. However, as typical of guanidine compounds, the suppressor previously used in the NG-CSSX solvent, N,N',N"-tri(3,7-dimethyloctyl)guanidine (TiDG), suffers from hydrolytic degradation under process conditions. Recently, the sterically hindered alkyl guanidine N,N'-dicyclohexyl-N"-(10-nonadecyl)guanidine (DCNDG) has been found to offer 8 to 44 times greater hydrolysis resistance than TiDG. Here, the process performance characteristics of the NG-CSSX solvent incorporating DCNDG are determined in comparison with TiDG and two other guanidine suppressors. The solvent has been adjusted in density to accommodate use in the SRS Salt Waste Processing Facility and tested under aggressive bench-scale conditions intended to increase plant throughput. Experiments include the effect of ageing at normal and off-normal temperatures of the distribution of Cs+ through the NG-CSSX process, the fate and effects of guanidine degradation products, suppressor capacity, coalescence times for aqueous-solvent dispersions, tendency for emulsification, third-phase formation, and degree of protonation of the guanidine in stripping. While the chosen structures of the four compared guanidines mainly effect differences in stability, subtle differences in other system properties such as emulsion formation and suppressor capacity provide insight into the function of this important solvent component. In comparison with TiDG and two other guanidines, DCNDG provides greatly increased stability while not compromising the excellent functional properties of the NG-CSSX solvent. [ABSTRACT FROM AUTHOR]

In deep tunneling and mining, high-level radioactive waste repositories, and geothermal reservoirs, the rock fractures are typically in the thermal–mechanical coupled condition. It is crucial to precisely replicate the geoenvironment in the lab, including stress, temperature, boundary conditions, and other factors, to derive trustworthy strength estimates for rock fractures. Utilizing the recently developed shear apparatus, we performed direct shear tests on rough granite fractures under thermal–mechanical coupled loading (room temperature to 400 °C, 1–30 MPa) to address the effects of normal stress and high in-situ temperature on the shear behavior of rough granite fractures, and the sequence of heating and normal loading on the strength parameters is also examined. Results show that the acoustic emission is more active if the fracture is heated under a large normal stress, while the expansion in the normal direction is more restricted. Besides, the shear strength tends to increase with increasing temperature, particularly if the fracture is heated under a large normal stress; at the greatest temperature, the shear strength is deteriorated. The strengthening of rock fracture upon heating is associated with the time- and temperature-dependent asperity contact creep which increases the real contact area of the macroscopically mated fracture surfaces. The sequence of heating and normal loading prominently affects the shear properties of granite fractures; the shear strength, post-peak stress drop and stick–slip amplitude are greater for granite fractures which were normal loaded first than heated first. The post-peak stress drop and stick–slip stress drop, which are vital parameters to estimate the seismic event intensity, are related to the corresponding dynamic slip and loading system stiffness. Highlights: Direct shear tests were conducted on granite fractures with a newly developed apparatus equipped with real-time heating capability. The thermal expansion is smaller while the AEs are more active when the fractures were heated under a larger normal stress. The shear strength of granite fractures first increases and then decreases with increasing temperature when heated under a large normal stress. The shear strength, post-peak stress drop and stick–slip are greater for granite fractures which were normal loaded first than heated first. The strengthening of fractures heated under a large pre-set normal stress is related to increase in fracture contact area due to asperities creep. [ABSTRACT FROM AUTHOR]

The joints of buffer material composite blocks as potential weak parts in the engineering barrier system of a high-level radioactive waste (HLW) repository must be studied in depth. Therefore, a laboratory experiment device suitable for unsaturated composite bentonite samples was developed. The evolution of temperature and volumetric water content at different locations of Gaomiaozi (GMZ) composite bentonite samples with time before and after simulated water inflow was measured by the experiment device. According to the experimental results, the thermal conductivity and hydraulic conductivity of the joint location after healing of the composite bentonite samples were obtained. The experimental results show that the change in the internal temperature of the composite bentonite samples is mainly affected by the temperature boundary and that the change in the internal water has little effect on it. In a short period of time, the loading of hydraulic boundary conditions only makes the volumetric water content of the soil near the hydraulic boundary increase significantly but has little effect on other locations. And, affected by the temperature boundary, the volumetric water content of the soil near the temperature boundary gradually decreases with time. The process of hydration swelling of the composite bentonite sample is accompanied by the adjustment of stress. The composite bentonite samples are continuously squeezed to the joint area after hydration swelling, the whole composite samples are generally homogenized, and the joints between the composite bentonite samples tend to heal. The thermal conductivity and permeability of the joint location after healing can meet the requirements of the engineering barrier of the HLW repository. [ABSTRACT FROM AUTHOR]

This document is a calendar of upcoming conferences, workshops, and symposiums related to materials and corrosion. The events cover a wide range of topics and will be held in different countries around the world. Some of the topics include heat treatment, corrosion control, electric steelmaking, copper alloys, sustainable development, condition monitoring, thermal spray coatings, and solar structure durability. The document provides contact information and links for more information about each event. [Extracted from the article]

• The adsorption capacity of ZnFC-PA/PSF composite spheres for Cs+ was 305.38 mg/g. • Its practicability is superior than of most previously reported adsorbents. • A fixed bed reactor loaded with ZnFC-PA/PSF spheres was used for cesium removal. • The effects of operating parameters on the breakthrough curves were investigated. Radioisotope leaking from nuclear waste has become an intractable problem due to its gamma radiation and strong water solubility. In this work, a novel porous ZnFC-PA/PSF composite sphere was fabricated by immobilization of ferrocyanides modified zinc phytate into polysulfone (PSF) substrate for the treatment of Cs-contaminated water. The maximum adsorption capacity of ZnFC-PA/PSF was 305.38 mg/g, and the removal efficiency of Cs+ was reached 94.27% within 2 hr. The ZnFC-PA/PSF presented favorable stability with negligible dissolution loss of Zn2+ and Fe2+ (< 2%). The ZnFC-PA/PSF achieved high-selectivity towards Cs+ (K d = 2.24×104 mL/g) even in actual geothermal water. The adsorption mechanism was inferred to be the ion-exchange between Cs+ and K+. What's more, ZnFC-PA/PSF worked well in the fixed-bed adsorption (E = 91.92%), indicating the application potential for the hazardous Cs+ removal from wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

Previous studies have indicated that acid-washed pyrite is inert toward aqueous U(VI) under most pH conditions at ambient temperature, even though insoluble UO 2 is the thermodynamically predicted product for the reduction of U(VI) by pyrite. Considering the exothermic nature of nuclear waste, the interaction between uranyl nitrate/acetate and natural pyrite was studied at temperatures ranging from 25 °C to 85 °C and at pH values between ∼4.0 and ∼9.5, to simulate the scenarios encountered in a high-level radioactive waste repository. The results revealed that the reactivity of pyrite toward aqueous U(VI) significantly increased with rising temperature, and the reaction could be described by a pseudo-first-order kinetic equation. Activation energies were calculated to be 79.4 ± 10.6 and 45.7 ± 3.8 kJ⋅mol−1 for the reduction of uranyl nitrate, and 78.2 ± 5.2 and 42.2 ± 5.8 kJ⋅mol−1 for the reduction of uranyl acetate, at pH values of ∼4.5 and ∼5.0, respectively. These values indicate that the reaction is controlled by the surface chemical processes. In addition, the complete reduction of aqueous U(VI) to UO 2 product was first observed for the reactions at pH ∼4.0 to ∼5.5 when the temperature was ≥75 °C. Conversely, non-stoichiometric UO 2+x (s) (0 < x ≤ 0.67) was found at lower temperatures within the same pH range, and also at 85 °C with a reaction pH of ∼9.5. Moreover, the ratio of reduced U(IV/V) on pyrite surfaces increased gradually over time, indicating that reaction time played a significant role in the reduction products. The findings are essential not only for the safety assessment of the high-level radioactive waste repository, but also for understanding the metallogenic mechanism of U(IV)-bearing ore deposits under the relevant anaerobic and hydrothermal conditions. [ABSTRACT FROM AUTHOR]

The development of density functional theory (DFT) has significantly enhanced the use of computational chemistry as a tool in the design and development of ligands for the separation of actinides (An) and lanthanides (Ln) in the nuclear waste management. In the past, identifying new ligands involved either making incremental structural changes to existing ligands or conducting extensive laboratory testing of numerous compounds. However, these experimental methods are often costly and time-consuming. With the advancements in hardware and software, theoretical and computational chemistry has become a powerful and cost-effective approach in nuclear waste management research. The density functional theory (DFT), in particular, has played a pivotal role by enabling scientists to accurately predict the effectiveness of ligands based on electronic and molecular properties, as well as reactivity indices. This computational approach provides valuable insights into the separation efficiencies of ligands without the need for extensive experimental efforts. This review highlights the role of computational chemistry in the design of ligands for the separation of lanthanides and actinides in spent nuclear fuel processing. It discusses various design strategies and computational analyses used in ligand optimization, highlighting the potential applications of computational tools in guiding ligand design and improving separation processes. The work emphasizes the synergy between computational insights and experimental observations in lanthanide/actinide chemistry, which enhances understanding of complex phenomena and aids in the interpretation of experimental results. It also explores different design approaches that allow for fine-tuning of ligand properties and selectivity toward specific metal ions, ultimately improving separation efficiency. In this review, we will discuss some widely used computational tools in chemistry without delving into complex mathematical formulas. This will be particularly helpful for researchers who come from an experimental background and may not be as familiar with advanced mathematical concepts. The tools covered are bond order analysis, population analysis, quantum theory of atoms in molecules (QTAIM) analysis, Energy Decomposition Analysis (EDA), and thermodynamic analysis. These methods are explored in a more accessible manner for non-theoretical researchers. They provide valuable insights into bonding, binding, stability, non-bonding interactions, coordinating abilities and selectivity of organic ligands in extraction of actinides and lanthanides, thus providing useful information in the designing of ligands to enhance separation strategies. This review serves as an excellent resource for future ligand design, offering valuable insights into computational techniques used to understand the coordination and complexation behaviors of ligands. Also an attempt has been made to understand the role of DFT functionals in the calculations. It provides a foundation for researchers to comprehend and apply computational tools effectively in their investigations. [ABSTRACT FROM AUTHOR]

Bentonite is an integral part of the engineered barrier system (EBS) in deep geological repositories (DGR) for nuclear waste, but its indigenous microorganisms may jeopardize long-term EBS integrity. To predict microbial activity in DGRs, it is essential to understand microbial reactions to the early hot phase of DGR evolution. Two bentonites (BCV and MX-80) with varied bentonite/water ratios and saturation levels (compacted to 1600 kg.m− 3 dry density/powder/suspension), were subjected to heat (90–150 °C) and irradiation (0.4 Gy.h− 1) in the long-term experiments (up to 18 months). Molecular-genetic, microscopic, and cultivation-based techniques assessed microbial survivability. Exposure to 90 °C and 150 °C notably diminished microbial viability, irrespective of bentonite form, with negligible impacts from irradiation or sample type compared to temperature. Bentonite powder samples exhibited microbial recovery after 90 °C heating for up to 6 months but not 12 months in most cases; exposure to 150 °C had an even stronger effect. Further long-term experiments at additional temperatures combined with the mathematical prediction of temperature evolution in DGR are recommended to validate the possible evolution and spatial distribution of microbially depleted zones in bentonite buffer around the waste canisters and refine predictions of microbial effects over time in the DGR. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The application of Phalaris seed peel (PSP) for the production of biochar involves the pyrolysis process in an N2 environment, resulting in the creation of a cost-effective sorbent. Two distinct modifications were conducted on the existing biochar (BC), employing just silicate (BC/SiO2) and in combination with iron-silicate (BC/SiO2/Fe). Several analytical methods were used to look at the modified biochar's physical and chemical properties. These included scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis-differential thermal analysis (TGA-DTA), and surface area analysis. Based on the initial investigations, it has been revealed that the use of silica and iron as the second modification is a more suitable approach for effectively retaining 133Ba from liquid radioactive waste streams. The investigation of sorption kinetics and isotherms was conducted to enhance our understanding of the process. The Langmuir isotherm model demonstrates the most optimal correlation for sorption, yielding a maximum sorption capacity (Qmax) of 31 mg/g. Furthermore, an evaluation was performed on the BC/SiO2/Fe sorbent material by subjecting it to a mixture of simulated radioactive liquid waste, which included 133Ba, 60Co, and 137Cs.The experimental results indicate that BC/SiO2/Fe exhibits a comparatively higher sorption capacity for 133Ba when compared to 60Co and 137Cs as competing ions. [ABSTRACT FROM AUTHOR]

Thermal plasma is a versatile technology that can be used to treat various types of wastes, including vegetal and mineral oils, solvents, plastics, paper and cardboard, glasses, bricks and rocks, metals, clothes, and mixtures of these materials. In this study, we utilized a commercial plasma cutter as a thermal plasma source to decrease the volume of a simulated low-level radioactive mixed solid waste. The simulated waste included papers, plastics, clothes, gloves, metals, and stable Co, Cs, Sr, and Ce additives as surrogates of 60Co, 137Cs, 90Sr, and 144Ce, respectively, the latter being typical contaminants in nuclear LLW. As a result of the process, two products were obtained: a solid phase, on which we focused this work, and a gaseous phase. To retain as many as surrogates as possible in the solid final phase, crushed glass from broken bottles was included as a vitrification additive to the original waste. After undergoing heat treatment, a dense vitreous slag was produced along with ashes. The process resulted in a volume reduction of 70%, indicating the successful gasification of organic excess materials. The surrogate elements were retained in the process and were found in the ashes composition: Co (3.4% w/w), Cs (37.7% w/w), and Ce (0.6% w/w) and in the glass matrix composition of Co, Cs, Sr and Ce: 72.4 ± 14.7, 32 ± 18.2, 125.3 ± 31.6, 80 ± 13.1% w/w, respectively. For the actual experimental conditions, retention efficiencies were estimated for cobalt (Co) at 72.4 ± 14.7%, cerium (Ce) at 80 ± 13.1%, strontium (Sr) at 125.3 ± 31.6%, and notably cesium (Cs) at 32 ± 18.2%. [ABSTRACT FROM AUTHOR]

The leachability of low-level radioactive waste was meticulously evaluated to determine the efficacy of a cement–vermiculite matrix for immobilisation. Laboratory-scale blocks, with a cement-to-vermiculite ratio of 1:0.1, were subjected to the IAEA-recommended semi-dynamic leaching test using rainwater (RW) from the disposal site and demineralised water (DW) for comparative analysis. The experimental data elucidated the transport phenomena governing Cs-137 release from the matrix. A strong positive correlation was observed between pH, conductivity, and Cs-137 activity release, indicating their interdependent dynamics. This research derived mathematical equations for both single-source term models describing the entire leaching process and the most fitting combination models, based on statistical parameters. Key leaching parameters, including a diffusion coefficient of 5.83E-07 cm2/d, a dissolution velocity of 4.93E-05 cm/d, and a first-order kinetic rate constant of 8.00E-05 d−1, were established and used to identify the optimal leaching model. These parameters are crucial for future radiological impact assessments of the area. Various physico-chemical observations during the leaching period were documented, with efforts to elucidate their underlying causes. The cumulative Cs-137 release of less than 1% over the study period and a leachability index of 7.2 confirmed the matrices' suitability for immobilising the studied waste. Research highlights: Cs-137 is the major long-lived radionuclide present in low-level radioactive waste. Waste is immobilized in cement–vermiculite matrix and disposed in reinforced concrete trenches at disposal site, Tarapur. Cs-137 leaching from cement-waste products using rainwater and demineralised water is studied using IAEA standard leaching test. Integrity of block is studied and Leaching parameters are evaluated from observed cumulative leach fraction. Using statistical parameter, Index of agreement, best-fit leaching mechanism for Cs-137 was established. The efficiency of the matrix in immobilising low-level waste is found suitable with Leachability Index > 6. Diffusion is the underlying controlling leaching mechanism. [ABSTRACT FROM AUTHOR]

Magnesium silicate hydrate (M‐S‐H) represents a promising alternative to traditional cement, particularly for low‐pH construction applications such as nuclear waste encapsulation and carbon dioxide injection. The durability of construction materials, a critical aspect of their suitability for various purposes, is primarily governed by the kinetics of dissolution of the binder phase under service conditions. In this study, we employed in situ atomic force microscopy to assess the dissolution rates of M‐S‐H in water equilibrated with air. Quantitative analysis based on changes in volume and height revealed dissolution rates ranging from 0.18 to 3.09 × 10−12 mol/cm2/s depending on the precipitate Mg/Si ratio and morphology. This rate surpasses its crystalline analogs, talc (Mg3Si4O10(OH)2) and serpentine (Mg3(Si2O5)(OH)4), by about three to five orders of magnitude. Interestingly, oriented M‐S‐H dissolved faster than non‐oriented M‐S‐H. Spatially resolved assessments of dissolution rates facilitated a direct correlation between rates and morphology, showing that edges and smaller crystallites dissolve at a faster pace compared to facets and larger crystallites. The outcomes of this study provide insights into the mechanisms governing the dissolution of M‐S‐H and the factors dictating its durability. These findings hold implications for the strategic design and optimization of M‐S‐H for various applications. [ABSTRACT FROM AUTHOR]

Glassy materials form the basis of many modern applications, including nuclear waste immobilization, touch‐screen displays, and optical fibers, and also hold great potential for future medical and environmental applications. However, their structural complexity and large composition space make design and optimization challenging for certain applications. Of particular importance for glass processing and design is an estimate of a given composition's glass‐forming ability (GFA). However, there remain many open questions regarding the underlying physical mechanisms of glass formation, especially in oxide glasses. It is apparent that a proxy for GFA would be highly useful in glass processing and design, but identifying such a surrogate property has proven itself to be difficult. While glass stability (GS) parameters have historically been used as a GFA surrogate, recent research has demonstrated that most of these parameters are not accurate predictors of the GFA of oxide glasses. Here, we explore the application of an open‐source pre‐trained neural network model, GlassNet, that can predict the characteristic temperatures necessary to compute GS with reasonable performance and assess the feasibility of using these physics‐informed machine learning (PIML)‐predicted GS parameters to estimate GFA. In doing so, we track the uncertainties at each step of the computation—from the original ML prediction errors to the compounding of errors during GS estimation, and finally to the final estimation of GFA. While GlassNet exhibits reasonable accuracy on all individual properties, we observe a large compounding of error in the combination of these individual predictions for the PIML prediction of GS, finding that random forest models offer similar accuracy to GlassNet. We also break down the performance of GlassNet on different glass families and find that the error in GS prediction is correlated with the error in crystallization peak temperature prediction. Lastly, we utilize this finding to assess the relationship between top‐performing GS parameters and GFA for two ternary glass systems: sodium borosilicate and sodium iron phosphate glasses. We conclude that to obtain true ML predictive capability of GFA, significantly more data needs to be collected. [ABSTRACT FROM AUTHOR]

Understanding mass transport in the alteration layers of glass surfaces is a crucial component of the safety assessment of nuclear waste glass. In this work, we model such an alteration layer as a silicate gel with water through a molecular dynamics (MD) simulation with a reactive force field. Gels with various water contents (WCs) ranging from 5.1 to 30.7wt%$30.7 \,{\rm wt}\%$ are produced via high‐temperature annealing with water and silica. It is found that an increase in the water content destroys the polymerized structure of the silicate network and promotes the formation of silanol groups. The pore size and water connectivity formed by the silicate networks are investigated for the modeled gels. Gel with a WC of 5.7wt%$5.7 \,{\rm wt}\%$ is composed of isolated water in the pores; in contrast, pores filled with interconnected water are formed in gel with a WC of 30.7wt%$30.7 \,{\rm wt}\%$. The water diffusivity in the modeled gel is calculated using the mean‐squared displacement at various temperatures. An attempt is made to formulate a linear relationship between the water diffusivity and porosity derived from the MD simulation. The porosity is calculated using a probe atom with a radius, which was optimized from a linear relationship between the water diffusivity and porosity. This approach successfully explains the water diffusivity in terms of the porosity. Random walk (RW) simulations for the structures derived from the MD simulations are performed to determine the geometrical effects of the pores. The diffusivity obtained from RW simulation is compared with the results of the MD simulations, which include chemical interactions such as the formation and breakage of hydrogen bonds. This comparison highlights how geometrical effects and chemical interactions contribute to water diffusivity depending on the WC. [ABSTRACT FROM AUTHOR]

We study a parameter estimation problem which arises from measurements with QUANTOM, a measurement facility utilizing PromptGamma Neutron Activation Analysis (PGNAA) to analyze elemental masses in 200-l nuclear waste drums. The presence of neutron flux measurements in QUANTOM offers additional information for elemental composition reconstruction, motivating an alternative to the standard iterative approach. Therefore, the measurement is modelled using approximate models for neutron and photon transport. We introduce a mathematical formulation for solving the resulting parameter estimation problem of QUANTOM measurements and employ an adjoint-based method to determine the elemental composition. Uniqueness of solutions in this context is studied, and the results offer novel insights for PGNAA applications. [ABSTRACT FROM AUTHOR]

Complexes formed between the heaviest and lightest elements in the periodic table yield the f-block hydrides, a unique class of compounds with wide-ranging utility and interest, from catalysis to light-responsive materials and nuclear waste storage. Recent developments in syntheses and analytics, such as exploiting low-oxidation state metal ions and improvements in X-ray diffraction tools, have transformed our ability to understand, access and manipulate these important species. This perspective brings together insights from binary metal hydrides, with molecular solution phase studies on heteroleptic complexes and gas phase investigations. It aims to provide an overview of how the f-element influences hydride formation, structure and reactivity including the sometimes-surprising power of co-ligands to tune their behaviour towards a variety of applications. [ABSTRACT FROM AUTHOR]

Nanostructure titanium carbide MXene (Ti3C2Tx) was modified with KH2PO4 and chitosan to effectively remove strontium from nuclear wastewater. Nuclear waste includes radionuclides of uranium, thorium, strontium, and cesium, which are classified depending on the concentration of radionuclides. Nuclear waste with a high strontium concentration is the production waste of radiopharmaceutical production centers. Ti3C2Tx was synthesized from Ti3AlC2 using HF40% and HF in situ (MILD-Ti3C2Tx) in 24 h at 313.15 and 333.15 K. Morphology, structure, and functional groups were investigated using the XRD, SEM, EDS, FTIR, and BET analyses. The Sr(II)'s adsorption capacity on Ti3C2Tx-HF and Ti3C2Tx-HF in situ was obtained as 61.9 and 253.5 mg g−1, respectively (temperature, 298.15 K; pH, 7.00; contact time, 180 min; and Sr(II) concentration, 150 mg l−1). Ti3C2Tx-HF in situ showed fourfold adsorption due to more hydroxyl functional groups and larger interlayer spacing. Ti3C2Tx was modified with KH2PO4 and chitosan to investigate the mechanism of change of Sr(II)'s adsorption capacity, which increased to 370 and 284 mg g−1, respectively. The structural results of modified Ti3C2Tx showed that the surface functional groups increased when modified with chitosan. In addition, modification with KH2PO4, through encapsulating large amounts of KH2PO4 between Ti3C2Tx layers, increased the possibility of Sr(II) diffusion between layers and electrochemical interactions with hydroxyl groups, and thus, increased its adsorption. Some experiments were designed to investigate the effect of parameters like initial concentration of Sr(II), contact time, temperature, and pH solution, as well as modified- and unmodified-Ti3C2Tx on adsorbent. The results revealed that the adsorption process of Sr(II) with pristine and modified-Ti3C2Tx follows pseudo-second-order kinetics and Freundlich heterogeneous isotherm model. Freundlich model isotherm indicates the presence of various functional groups on the surface and between the pristine and modified Ti3C2Tx layers. Electrostatic reactions and intra-sphere complexation were the two dominant mechanisms of the adsorption process. [ABSTRACT FROM AUTHOR]

This paper presents an optimized design approach using nonlinear dynamic analysis and finite element methods to ensure the structural integrity of square-shaped containers made from ductile cast iron for intermediate- and low-level radioactive waste packaging. Ductile cast iron, with its spherical graphite structure, effectively distributes stress throughout the material, leading to a storage capacity increase of approximately 18%. Considering the critical need for containers that maintain integrity under extreme conditions like earthquakes, the design focuses on mitigating stress concentrations at the corners of square structures. Nonlinear dynamic analyses were conducted in five drop directions: three specified by ASTM-D5276 standards and two additional directions to account for different load patterns. Fractures were observed in four out of the five scenarios. For each direction where fractures occurred, equivalent loads causing similar displacement fields were applied to linear static models, which were then used for multi-load topology optimization. Three optimized models were derived, each increasing the volume by 1.4% to 1.6% compared to the original model, and the design that best met the structural integrity requirements during drop scenarios was selected. To further enhance the optimization process, weights were assigned to different load conditions based on numerical analysis results, balancing the impact of maximum stress, average stress, and plastic deformation energy. The final model, with its increased storage capacity and enhanced structural integrity, offers a practical solution for radioactive waste management, overcoming limitations in previous designs by effectively addressing complex load conditions. [ABSTRACT FROM AUTHOR]

Fabricating efficient adsorbent for the removal of nuclear waste is of vital importance from the viewpoint of both environmental protection and resource reclamation. Published research has yielded several adsorbents; however, these reported materials do not possess a high removal performance for different types of nuclear waste. In this work, it is shown for the first time the synthesis of a boron‐functionalized covalent organic framework (COF) and its ionic borate counterpart. These boron‐functionalized COFs are found to show large potential for handling various nuclear wastes, including alkaline nuclear wastewater, uranium‐containing nuclear wastewater, and I2 nuclear off‐gas. The developed COF has a record NaOH uptake of 2 g g−1, an ultrahigh uranium extraction ability of 1.77 g g−1, and an ultrahigh I2 capture capacity of 9.4 g g−1. Moreover, the materials have low cost and are reusable, and thus have significant potential for handling nuclear wastes. [ABSTRACT FROM AUTHOR]

Flash sintering can prepare ceramics in extremely short time, which can significantly improve fabrication efficiency and is promising for processing nuclear waste. Herein, simulated TRPO waste (16 components containing low-melting components) was directly added into as-prepared Gd 2 Zr 2 O 7 , and a series of waste forms were successfully prepared by flash sintering at 950 °C for only 3 min. It was demonstrated that samples prepared by flash sintering showed almost no loss of simulated low-melting-point radionuclide, while samples prepared by pressureless sintering have certain losses of simulated low-melting-point radionuclide. The 42 d leaching rates of Mn, Ce, Nd, and Gd of the flash sintered samples were 8.21 × 10−5, 5.31 × 10−7, 4.04 × 10−6, and 1.04 × 10−6 g m−2 d−1, respectively, showing excellent chemical durability. This work proves that flash sintering technology can effectively suppress nuclear leaks during immobilization, along with excellent chemical durability. [ABSTRACT FROM AUTHOR]