Transition Metals Separation with Commercial Neutral Extractants – A Review

Nanotechnology applications in nuclear waste management: challenges and limitations

Lanthanide-containing luminescent molecular edifices

Abstract. The DECOVALEX Task SAFENET is dedicated to advancing the understanding of fracture nucleation and evolution processes in crystalline rocks, with applications in nuclear waste management and geothermal reservoir engineering. Further improvements to fracture mechanics models are required in two distinct areas. Firstly, there is a need to enhance numerical methods for fracture mechanics under varying thermo-hydro-mechanical (THM) conditions. Secondly, there is a requirement to develop applied tools for performance and safety assessment in the context of nuclear waste management, as well as for reservoir optimisation in geothermal applications. Building on the achievements of SAFENET, which concentrated on benchmarking fracture models and experimental laboratory analyses, SAFENET-2 is dedicated to extending and validating models from the laboratory to the field scale. This paper gives a detailed description of the SAFENET-2 experimental programme work plan and modelling exercises. The experiments will be carried out at the rock mechanics laboratories of the University of Edinburgh and Chongqing University. For field data, the STIMTEC experiment at the Reiche Zeche teaching and research mine (Technische Universität Bergakademie Freiberg) is used. The individual steps of the Task are described in detail in this paper. As a result of SAFENET, the benchmark suite will be made available as interactive exercises via a web portal, thus promoting the concept of open science. The paper is a tool for teams to organise their work efficiently and is also an overview and insight for the community.

The first heterobimetallic uranium(IV)/vanadium(III) phosphite compound, Na2UV2(HPO3)6 (denoted as UVP), was synthesized via an in situ redox-active hydrothermal reaction. It exhibits superior hydrolytic and antioxidant stability compared to the majority of structures containing low-valent uranium or vanadium, further elucidated by first-principles simulations, and therefore shows potential applications in nuclear waste management.

Understanding the behavior of radioactive nuclide elements in different environmental conditions is an active area of research. In this work, we have investigated the possible interaction mechanism between carbon nanotubes and uranyl using density functional theory. It is shown that functionalized carbon nanotubes can be used to bind uranyl ions much more efficiently as compared to their unfunctionalized counterpart. The uranyl binding energies are sensitive to the nature of the functional groups rather than the carbon nanotube itself. The binding takes place preferably at the functionalized sites, although pH could determine the strength of uranyl binding. Our predicted results correlate well with the recent experimental uranyl sorption studies on carbon nanotubes. These finding are new and can open up a new era for actinide speciation and separation chemistry using carbon nanotubes.

Laser-driven relativistic electrons can be focused onto a high-Z convertor for generating high-brightness γ-rays, which in turn can be used to induce photonuclear reactions. In this work, photo-transmutation of long-lived radionuclide 135Cs induced by laser–plasma–interaction-driven electron source is demonstrated using Geant4 simulation (Agostinelli et al., 2003 Nucl. Instrum. Meth. A506, 250). High-energy electron generation, bremsstrahlung, as well as photonuclear reaction are observed at four different laser intensities: 1020, 5 × 1020, 1021, and 5 × 1021 W/cm2. The transmutation efficiency depends on the laser intensity and target size. An optimum laser intensity, namely 1021 W/cm2, was found, with the corresponding photonuclear reaction yield reaching 108 J−1 of the laser energy. Laser-generated electrons can therefore be a promising tool for transmutation reactions. Potential application in nuclear waste management is suggested.

For application in nuclear waste management, it is essential to study the self-irradiation effect in long-term deep geological disposal repository. In this study, accelerated irradiation experiment was conducted on Nd2Zr2O7 pyrochlore matrix by using 0.5 MeV He2+ ions with fluences ranging from 1 × 1014 to 1 × 1017 ions/cm2. A series of results figure out that Nd2Zr2O7 matrix transforms from pyrochlore into fluorite after radiation experiment and some weak structural disordering is led with intensified irradiation. Moreover, the surface micrography shows slight changes after irradiation.

Some example applications are presented, in which the peculiar Raman fingerprint of PuO2 can be used for the detection of crystalline Pu4+ with cubic symmetry in an oxide environment in various host materials, like mixed oxide fuels, inert matrices and corium sub-systems. The PuO2 Raman fingerprint was previously observed to consist of one main T2g vibrational mode at 478 cm−1 and two crystal electric field transition lines at 2130 cm−1 and 2610 cm−1. This particular use of Raman spectroscopy is promising for applications in nuclear waste management, safety and safeguard.

Muonium (Mu = μ+e-), which can be considered a light isotope of the H atom, has been observed for the first time in supercritical CO2 (ScCO2). It is unreactive on a time scale of a few microseconds and over a wide density range from well below to well above the CO2 critical density ρc = 0.47 g/cm3. The fraction of muon polarization in muonium, PMu, does not vary significantly at low densities but changes quickly at the highest densities, approaching zero. This density dependence is reflected in a concomitant increase observed in the lost fraction of polarization, PL, demonstrating that the dynamics of Mu formation and depolarization in ScCO2 is a direct probe of radiolysis effects in the terminal muon radiation track. In marked contrast to previous studies in hydrogen-containing solvents, C2H6 and H2O, over comparable density ranges, the diamagnetic fraction, PD, was found to be almost independent of density in CO2, attributed to the formation of the stable solvated MuCO2+ molecular ion in this hydrogen-free solvent. The differing density dependences of both the Mu and the diamagnetic fraction in CO2, in comparison with the rather similar trends seen for both in C2H6 and H2O, supports previous claims of a significant role played by proton (muon) transfer reactions in the competing processes involved in Mu formation in hydrogen-containing solvents. In addition to this being the first report of radiolysis effects accompanying energetic positive muons stopping in ScCO2, it is the only report of end of track effects in this solvent, which has many applications in nuclear waste management and green chemistry. With a mass intermediate between that of the electron, which has provided most radiation−chemistry studies in ScCO2 to date, and the proton (or alpha-particle), implanted muons provide a unique data set, characteristic of higher LET radiation, that may be relevant to radiolysis effects induced in ScCO2 by alpha decay from heavy nuclei, for which there are no comparable studies.

Activated carbon derived from avocado seeds (AVSAC) was evaluated for its ability to adsorb and desorb Thorium(IV) ions, targeting applications in nuclear waste management and environmental cleanup. Extensive characterization (FTIR, XRD, SEM, TGA/DSC, BET) confirmed structural changes upon Th(IV) uptake; notably, FTIR indicated hydroxyl and aromatic groups participate in binding, while SEM and BET showed significantly reduced porosity and surface area, consistent with effective adsorption. At pH 3.0, a fixed-bed column (0.50 g AVSAC; flow rate 0.25 mL min−1; residence time 4 min mL−1) treated 50 mL of 750 mg L−1 Th(IV), achieving 97.3% removal (36.5 mg captured; 73 mg g−1 working capacity). The adsorption was remarkably fast, sequestering 94% of Th(IV) within five minutes. Kinetic data fit a pseudo-second-order model well, and equilibrium data aligned with the Freundlich isotherm, consistent with PSO behavior on a heterogeneous surface; overall uptake is predominantly physical (thermodynamics/D–R), with localized Th–O coordination contributions. Thermodynamic analysis revealed a spontaneous and endothermic process. Regeneration studies showed that 1.00 M nitric acid could recover 70.5% of the adsorbed thorium. Overall, this work highlights AVSAC as a highly promising, efficient, and regenerable adsorbent for removing Th(IV) from aqueous solutions, offering valuable insights for treating contaminated water streams.

CNUCTRAN: A program for computing final nuclide concentrations using a direct simulation approach

This study reports the synthesis and characterization of a novel composite material, TiO 2 -ZrO 2 /PA/AC (titanium dioxide, zirconium dioxide, phosphonic acid, and activated carbon), fabricated via the sol-gel method for radionuclide removal. Characterization (XRD, SEM, FTIR, EDX) confirmed the successful integration of components and a functional surface structure. The composite’s adsorption behavior toward Cs(I), Sr(II), Pu(IV), and U(VI) was investigated in aqueous solution. Adsorption efficiency was observed to increase with pH and temperature. Isotherm analysis revealed the Langmuir model as the best fit, suggesting monolayer coverage, with the maximum adsorption capacity (Q 0 ) being highest for Sr(II) (467.83 mg/g at 310 K). Kinetic analysis confirmed the process is governed by the pseudo-second-order model, indicating a dominant chemisorption mechanism. The diffusion coefficients were found to increase with temperature, reinforcing the endothermic nature of the process and suggesting faster intraparticle transport at elevated temperatures. Furthermore, desorption studies demonstrated the composite’s excellent reusability, maintaining approximately 80% recovery efficiency after four cycles with HNO 3 . These findings establish the TiO 2 -ZrO 2 /PA/AC composite as a highly promising, stable, and efficient adsorbent for practical application in nuclear waste management. The composite establishes an efficient, stable, and reusable adsorbent for practical nuclear waste management.

Study’s Excerpt/Novelty This study uses density functional theory (DFT) simulations to investigate the structural and electrical properties of gadolinium zirconate pyrochlore (Gd2Zr2O7), a compound considered for high-level nuclear waste immobilization. The research provides detailed insights into the lattice parameters, band structure, and density of states, revealing the conductive behavior of Gd2Zr2O7 and highlighting its resistance to amorphization. These findings enhance the understanding of Gd2Zr2O7's potential as a robust material for nuclear waste containment, offering a scientific basis for future ab initio investigations and practical applications in nuclear waste management. Full Abstract Nuclear energy is an alternative low CO2 emission strategy anticipated to mitigate future high energy demand. Radioactive wastes generated from spent nuclear fuel are the major challenge of utilizing nuclear reactors as a source of energy. Pyrochlore compounds are among the rigorous nuclear waste forms considered for High-level waste immobilization. Density functional theory (DFT) based on first-principles simulations was used to study gadolinium zirconate pyrochlore's structural and electronic characteristics (Gd2Zr2O7). The lattice parameters of optimized Gd2Zr2O7 are α = β = γ = 60.0 ° and a = b = c = 7.635A. The conduction band minimum and valence band maximum structure was discovered to be stable and approached the experimental lattice constant. The overlapping of the conduction and valence bands in Gd2Zr2O7 indicates its conductive behavior in terms of its electrical characteristics. Due to a usual underestimating of band gap energy in DFT based on electron exchange handling, the estimated band gap energy of 0.09 eV differed from experimental measurements. In addition to band gap energy computation, the computed total density of states and projected density of states show different orbital dominations and energy levels. The findings showed that the Gd2Zr2O7 ceramic compound had good resistance to amorphization and could be used for further ab initio investigations.

This report presents a study on the diffusion of Americium-241 (Am-241) through a capsule. The primary goal is to model the transport mechanism of Am-241 and analysed its behaviour under various conditions. The simulation incorporates factors such as diffusion rates, capsule material properties, and temperature variations. Results demonstrate the efficiency of the diffusion process and provide insights into the containment effectiveness of the capsule. The findings are relevant for applications in nuclear waste management and radiation shielding. Future work may focus on improving the accuracy of the model and exploring alternative containment materials.

The knowledge of radionuclides sorption behavior of various site-specific heterogeneous geosystems is essential for developing different clean-up strategies and predicting the radiological risks for long term. The present study is aimed at understanding the mineralogical and textural characteristics of natural shale rock (sampled from Kachchh Basin of Gujarat, India) and its correlation with cesium (Cs) sorption behavior. The modal mineralogical composition, textural attributes, petrophysical properties, surface functionalities and morphology of shale were evaluated. Clay minerals (smectite, kaolinite and illite) constitute more than 40% of the shale along with the major component- quartz. A comprehensive Cs batch sorption study performed at varying experimental parameters demonstrated that the maximum Cs retention of shale was 34.80 ± 2.85 mg g−1 in the studied concentration range. Sorption equilibrium data agreed well with Freundlich isotherm, highlighting the heterogeneity of shale. Variation in solution pH (in the range of 6–10) during sorption demonstrated the buffering of solution in near neutral range indicating the role of cations (available in the interlayers of clay minerals) in Cs uptake. Alternatively, the presence of illite mineral in the shale with known frayed edge sites contributed to the irreversibility of sorption event. The present studies illustrate the potential of shale as host rock for its application in nuclear waste management.