Real-time monitoring of fissile material concentration in molten salt reactors (MSRs) is essential for ensuring operational safety, maintaining reactivity control, and fulfilling nuclear safeguards requirements. This study presents a simple and economical method to estimate salt composition from phase-transition temperatures measured during a cooling process. Temperature-time profiles recorded with thermocouples are differentiated (dT/dt) to identify phase transition temperatures, which are then mapped to a validated reference phase diagram to infer composition without composition-specific empirical sensor-to-composition calibration. The method has been experimentally validated in three molten salt systems: LiCl-KCl, LiCl-KCl-NaCl, and UCl3-KCl. In particular, UCl3-KCl experiments were conducted at uranium concentrations up to 88.2 wt% UCl3, representing the high-concentration regime relevant for liquid-fueled MSRs. Results from independent experiments performed at Seoul National University and the Korea Atomic Energy Research Institute showed high reproducibility and strong agreement between measured and actual concentrations. While further development of phase diagram databases is needed for broader application to complex actinide and fission product-containing salts, the proposed approach represents a technically mature and operationally feasible method for reliable, real-time material accounting in liquid-fueled MSRs.

Pyroprocessing is efficient for recycling spent nuclear fuel, enabling the recovery of useful elements and minimizing waste. However, a key challenge is the difficulty in selectively separating U and Ln. This study investigates the feasibility of directly separating U and Ln elements (Nd, Ce, La) in LiCl-KCl molten salt using Bi and Cd as liquid metal electrodes. The electrochemical behaviors of U and Ln elements, as well as the formation of intermetallic compounds, were investigated using electrochemical measurements. The results revealed that in the presence of BiCl3, U formed intermetallic compounds with Bi. However, no such interactions were observed with CdCl2, indicating weaker interactions between U and Cd. For the Ln elements, Bi consistently formed intermetallic compounds with Nd, Ce, and La, whereas Cd showed stronger interactions with Nd and Ce than with La. Electrodeposition experiments demonstrated that U was deposited prior to the Ln elements in Bi and Cd media, with Ce and Nd preferentially deposited compared to La. Dissolution experiments showed that Ln elements dissolved before U in Bi, whereas in Cd, simultaneous dissolution of U and Ln was observed. These results demonstrate the feasibility of Bi as an effective medium for the electrochemical recovery of U and Ln. Conversely, Cd prevents their separation, supporting nuclear non-proliferation by maintaining U and Ln in a mixed state.

The reduction of graphene oxide (GO) is essential for maximizing its energy storage performance. Although numerous studies have reported the fabrication of electrochemically reduced graphene oxide (ERGO), achieving a high specific capacitance remains a critical challenge. In this study, the parameters of electrolyte concentration and temperature were systematically investigated to elucidate their influence on the removal of oxygen-containing functional groups and the subsequent enhancement of electrochemical performance. To gain a comprehensive understanding of these mechanisms, the morphologies, surface characteristics, oxygen-to-carbon (O/C) atomic ratios, and electrical properties of the prepared ERGO materials were meticulously analyzed. The optimized ERGO film, reduced at 60 °C in a saturated NaNO3 solution, exhibited the highest specific capacitance; however, prolonged durability tests revealed a definitive trade-off between the enhanced initial capacity and long-term cycling stability. Overall, this study offers a practical optimization strategy for the electrochemical reduction of GO, while emphasizing the critical necessity of balancing initial electrochemical metrics with long-term cyclability for the strategic development of high-performance supercapacitors.

Uranium (III) chloride (UCl3) is a crucial component of a potent nuclear recycling technology-pyroprocessing-and next-generation molten salt reactors. It is usually synthesized by reacting metallic uranium with chlorinating agents (e.g., CdCl2 and PbCl2) in molten chloride salts. In this study, we report the unexpected formation of UCl3 from metallic simulated fuel (simfuel) immersed in impure molten LiCl-KCl salt (in the presence of a small amount of residual H2O) in a stainless-steel (SS) crucible, without a chlorinating agent. We investigated various factors influencing UCl3 formation, including fuel type (metallic simfuel, pure U, oxide simfuel, or no fuel), crucible material (SS or alumina), salt composition (LiCl-KCl or LiCl), temperature (773 K or 923 K), and contact between fuel and SS crucible. UCl3 only formed when metallic fuels (simfuel or pure U) were immersed in molten salt in the SS crucible, with higher concentrations at elevated temperatures. Oxide fuels did not produce UCl3, nor did contact with the crucible affect formation. Our findings suggest that impurities, particularly moisture in the salt, corroded the SS crucible, releasing iron and chromium chlorides that reacted with metallic U to form UCl3. UCl3 formation was more pronounced in LiCl-KCl than in LiCl, and thermodynamic calculations helped establish the mechanism.

Pyroprocessing is a critical technology for recycling spent nuclear fuel, which enhances the sustainability of nuclear power generation. This process begins with metal oxides, which must be converted into metal chlorides to facilitate further processing, including electrorefining and electrowinning. In this work, we investigate the chlorination of lanthanide (Nd, Gd) and actinide (Th, Np) oxides in LiCl-KCl molten salt and confirm the chlorination through electrochemical and spectroscopic analyses. Nd2O3 and Gd2O3 are chlorinated using NH4Cl, with electrochemical measurements demonstrating the electrodeposition and dissolution currents of Nd3+ and Gd3+ ions. Th and Np chlorides are prepared using AlCl3 as a reactant. The reaction between ThO2 and AlCl3 produces ThCl4, as evidenced by the electrodeposition-dissolution currents of Th4+. For the chlorination of NpO2, NpO2Cl is first prepared by dissolving NpO2 in acidic solutions and then drying. Subsequently, the reaction of NpO2Cl and AlCl3 in molten LiCl-KCl yields NpCl4. Electrochemical and UV–Vis spectroscopic measurements confirm the redox reactions of Np4+/Np3+/Np0 and the presence of NpCl4 in the molten LiCl–KCl, respectively.

The radioactive cesium species (e.g., 137Cs) in radioactive waste have necessitated the development of strategies for its selective removal from contaminated water. In this study, we synthesized nickel-modified Prussian blue/maghemite (NiPB/γ-Fe2O3) composite materials exhibiting high selectivity for Cs ions. The composites were synthesized via a facile hydrothermal reaction, and their magnetism was confirmed through an X-ray magnetic circular dichroism measurement. The composites selectively separated Cs from solutions containing alkali and alkaline earth metal cations, with a removal efficiency of ≥ 99.7 %. The synthesis mechanism involved the hydrothermal reaction, including partial oxidation and subsequent γ-Fe2O3 formation. The maximum adsorption capacity of the NiPB/γ-Fe2O3 composites, assuming successful magnetic separation, was determined to be 102 mg g−1 using the Langmuir adsorption model. The powder X-ray diffraction patterns revealed enhanced crystallinity in the composites compared to NiPB, with a distorted structure framework from face-centered cubic to rhombohedral. XAS spectra showed changes in vibration peaks due to hydrothermal treatment, indicating partial oxidation of Fe(Ⅱ) to Fe(Ⅲ). The composites exhibited superparamagnetism, whereas NiPB showed no magnetization. These findings highlight the potential of NiPB/γ-Fe2O3 composites in environmental remediation and radioactive waste management, providing an effective solution for Cs removal from contaminated systems.

Radioactive Cs+ + and I-- ions are major components of nuclear wastewater, typically existing as counter ions. Due to their high water solubility and mobility, these ions can spread through contaminated water and soil into ecosystems, necessitating continuous removal and management. In this study, we synthesized a reusable bifunctional Ni@Pt/K2NiFe(CN)6 2 NiFe(CN) 6 composite that can simultaneously remove radioactive Cs+ + and I-- ions and, for the first time, enable their separate recovery in aqueous solutions. In this material, K2NiFe(CN)6 2 NiFe(CN) 6 acted as an electrochemically switched ion exchanger, controlling the adsorption/desorption of Cs+, + , while Pt enabled the spontaneous adsorption and electrochemical desorption of I-,- , and the magnetic Ni core allowed for efficient adsorbent recovery. The adsorption isotherms of both Cs+ + and I-- were best fitted using the Langmuir model, and the corresponding adsorption capacities were comparable to those of conventional adsorbents used for the separate removal of Cs+ + and I-.- . Furthermore, the composite demonstrated stability over 100 sorption cycles, maintaining high recovery efficiencies of 97.9 % for Cs+ + and 99.7 % for I-,- , thereby proving its reusability. Thus, the developed composite holds great promise for radioactive wastewater treatment and environmental restoration.

Self-assembly-based structural transition has been explored for various applications, including molecular machines, sensors, and drug delivery. In this study, we developed new redox-active metal-organic frameworks (MOFs) called DGIST-10 series that comprise pi-acidic 1,4,5,8-naphthalenediimide (NDI)-based ligands and Ni2+ ions, aiming to boost ligand-self-assembly-driven structural transition and study the involved mechanism. Notably, during the synthesis of the MOFs, a single-crystal-amorphous-single-crystal structural transition occurred within the MOFs upon radical formation, which was ascribed to the fact that radicals prefer spin-pairing or through-space electron delocalization by pi-orbital overlap. The radical-formation-induced structural transitions were further confirmed by the postsynthetic solvothermal treatment of isolated nonradical MOF crystals. Notably, the transient amorphous phase without morphological disintegration was clearly observed, contributing to the seminal structural change of the MOF. We believe that this unprecedented structural transition triggered by the ligand self-assembly magnifies the structural flexibility and diversity of MOFs, which is one of the pivotal aspects of MOFs.

Pyrochemical processing and molten-salt reactors have recently garnered significant attention as they are promising options for future nuclear technologies, such as those for recycling spent nuclear fuels and the next generation of nuclear reactors. Both of these technologies require the use of high-temperature molten salt. To implement these technologies, one must understand the electrochemical behavior of fission products in molten salts, lanthanides, and actinides. In this study, a rotating-disk-electrode (RDE) measurement system for high-temperature molten salts is constructed and tested by investigating the electrochemical reactions of Sm3+ in LiCl-KCl melts. The results show that the reduction of Sm3+ presents the Levich behavior in LiCl-KCl melts. Using the RDE system, not only is the diffusion-layer thickness of Sm3+ measured in high-temperature molten salts but also various electrochemical parameters for Sm3+ in LiCl-KCl melts, including the diffusion coefficient, Tafel slope, and exchange current density, are determined.

Understanding the redox reactions of fission products in molten salts is crucial for developing pyroprocessing techniques for used nuclear fuel. A rotating disk electrode is useful for investigating the electrochemical reactions with controlled mass transfer conditions, but its application has been limited in high-temperature corrosive molten salts. This study employs a tungsten (W) rotating disk electrode (RDE) to measure the electrochemical and kinetic properties of the Sm(III)/Sm(II) redox reaction in a LiCl-KCl eutectic molten salt. The properties of the Sm(III)/Sm(II) redox reaction, including diffusion coefficients, exchange current densities, charge transfer coefficients, activation energies, and Tafel slopes, were determined over a temperature range of 723-803 K using limiting currents in linear sweep voltammetry at various rotating speeds and mass transfer-corrected Tafel plots. The kinetic parameters obtained using the rotating disk electrode system can be useful for optimizing the design of pyroprocessing techniques.

In this paper, the reaction of SrO in molten chloride and fluoride systems is investigated using Raman spectroscopy, combined with density functional theory calculations. The formation of Sr4OCl6 was observed in various salt compositions, including LiCl, LiCl-KCl, and LiCl-LiF, at temperatures ranging from 298 K to 923 K. Thermodynamic calculations estimated that Sr4OCl6 is more stable than SrO and SrCl2, while no stable strontium oxyfluoride compound was found. The results were also supported by X-ray analyses: Extended X-ray absorption fine structure analysis indicated that the local structure of Sr in LiCl-KCl and LiCl-LiF consists of one oxygen and six chlorides, corresponding to a complex with a similar local structure of Sr4OCl6. Additionally, Sr4OCl6 was found in LiCl-LiF, and no strontium compound was observed in LiF-KF using X-ray diffraction. These results provide a comprehensive understanding of the dissolution structures of strontium oxyhalide in molten chloride and fluoride systems.

Real-time monitoring of uranium concentration in molten salt reactors (MSR) is crucial for reactor operation and safety. However, conventional analytical methods cannot provide accurate results when uranium concentrations exceed approximately 4 wt

Performing accurate electrical conductivity measurements in harsh environments (such as high temper-atures and corrosive conditions) or highly conductive liquids, which exhibit significant polarization, remains challenging. Thus, a rapid, simple technique involving two-electrode capillary cells and microsecond-scale staircase voltammetry was devised to effectively determine the electrical conductiv-ities of highly conductive liquids and high-temperature molten salts. The maximum currents generated in response to the voltage applied on a short microsecond timescale were free from polarization-induced interference. Thus, solution resistances were accurately determined from the slope of the simple, linear plot between the maximum peak current and applied voltage, and the electrical conductivities were determined using cell constants estimated using an aqueous 3 M KCl solution at room temperature. Validation was performed using a highly corrosive eutectic LiCl-KCl molten salt, whose conductivities in the temperature range of 657-915 K and conductivity range (1.1-2.5 S cm-1) were accurately known. Multiple steps of large-amplitude voltages facilitated measurements of liquids with a wide range of con-ductivities. Moreover, the measurements were performed within a few tens of microseconds, highlight-ing the potential of the method for real-time on-line monitoring of processes involving highly conductive molten salts.(c) 2022 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chem-istry.

A microelectrode is useful to determine electrochemical parameters such as diffusion coefficient, exchange current density, and Tafel slope without the limitations of ion diffusion. This study aims to develop a new microelectrode for use in high-temperature molten salts, which has been evaluated by determining the parameters of the Sm(III)/Sm(II) reaction in a LiCl–KCl eutectic molten salt. The electrochemical and kinetic properties of the samarium ion in the temperature range 723–823 K were calculated using the limiting current from cyclic voltammograms and the Allen–Hickling equation. The results imply that kinetic parameters (exchange current density and charge transfer coefficient) critical for designing pyroprocesses can be obtained using the developed microelectrode.

Deep eutectic solvents (DESs) could make uranium recycling processes greener than using conventional solvents, owing to their inherent advantages such as being biodegradable and non-toxic. However, the chemistry of uranium ions in DES systems, particularly the mechanism of direct anodic dissolution of uranium metal, remains unclear. The anodic dissolution of uranium metal in choline chloride (ChCl)- ethylene glycol (EG) DES was conducted by applying a constant current. The oxidation state of uranium in ChCl-EG DES was uranium(IV) when compared to concentration and applied charge. Absorption spectra showed 8 coordinated U(IV) centered complexes formed in the ChCl-EG DES, regardless of the uranium source (i.e. uranium chloride or metallic uranium anodic dissolution). The in situ spectroelectrochemistry during potentiostatic electrolysis, cyclic voltammograms, and absorption spectra of different times of po-tentiostatic electrolysis showed U(IV) oxidized to U(V), and then the U(V) disproportionated into U(IV) and U(VI) species. Understanding fundamental uranium speciation in DES systems and electrochemical properties could facilitate the development of an eco-friendly nuclear fuel cycle and nuclear uranium recycling process using green DESs. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

90Sr is one of the most heat-generating fission products in used nuclear fuel. Because of its chemical stability as an oxide, it is tricky to separate Sr from used nuclear fuel without separating nuclear materials. Here we report on thermodynamic behavior of one of the primary contributors of decay heat, SrO, by investigating the reactions in molten salt systems. We study the respective influences of the KCl molar fraction and temperature on the dissolution behavior of SrO in molten LiCl-KCl salts: a widely used-salt composition owing to its low melting point and wide electrochemical window. Our results reveal that the solubility of SrO is relatively low in the eutectic LiCl-KCl at 773 K, compared to the other temperatures (823 K to 923 K) and the solubility decreased with increasing molar fraction of KCl (0 to 0.6) in LiCl at 923 K. Sr4OCl6 is produced by the dissolution of SrO in LiCl-KCl, and was confirmed by applying X-ray analyses. The results can be utilized to design a molten salt leaching process to separate high heat-generating fission products without proliferation issues, thereby reducing the environmental footprint during final waste disposal.

Environmental damage from serious nuclear accidents should be urgently restored, which needs the removal of radioactive species. Radioactive iodine isotopes are particularly problematic for human health because they are released in large amounts and retain radioactivity for a substantial time. Herein, we prepare platinum-coated iron nanoparticles (Fe@Pt) as a highly selective and reusable adsorbent for iodine species, i.e., iodide (Gamma), iodine (I2), and methyl iodide (CH3I). Fe@Pt selectively separates iodine species from seawater and groundwater with a removal efficiency >= 99.8%. The maximum adsorption capacity for the iodine atom of all three iodine species was determined to be 25 mg/g. The magnetic properties of Fe@Pt allow for the facile recovery and reuse of Fe@Pt, which remains stable with high efficiency (97.5%) over 100 uses without structural and functional degradation in liquid media. Practical application to the removal of radioactive 129I and feasibility for scale-up using a 20 L system demonstrate that Fe@Pt can function as a reusable adsorbent for the selective removal of iodine species. This systematic procedure is a standard protocol for designing highly active adsorbents for the clean separation and removal of various chemical species dissolved in wastewater.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.