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Synthesis, FTIR spectral study, and X-ray diffraction analysis of single crystals of (CH3)4N[UO2(mba)3] (I), (CH3)4N[NpO2(mba)2(NO3)] (II), (CH3)4N[PuO2(mba)2(NO3)] (III), and (CH3)4N[NpO2(mba)(NO3)2] (IV), where mba is a monobromoacetate ion (CH2BrCOO-), were conducted. The main structural units of crystals I-IV are mononuclear anionic complexes of the [AnO2(mba)3]-, [AnO2(mba)2(NO3)]-, or [AnO2(mba)(NO3)2]- composition. All these complex units are characterized with the same crystal-chemical formula AB013 (A = AnO22+ and B01 = CH2BrCOO- or NO3-). Using the method of molecular Voronoi-Dirichlet polyhedra, the contributions of various types of noncovalent interactions into the formation of supramolecular structures of the obtained complexes were characterized. The analysis of coordination modes of all monobromoacetate-containing compounds from the Cambridge Structural Database was accomplished. Actinide contraction in the studied compounds is discussed.

The structure of a new type of polyoxo cluster complex that contains thirteen uranium atoms, {U13}, is reported. The complex crystallized from methanol containing tetravalent uranium (UIV) with a basic organic ligand, and was characterized as dichloridooctacosa-μ2-methanolato-octakis(methanolato)octa-μ4-oxido-tridecauranium, [U13(CH3O)35.7Cl2.3O8] or [U13(μ4-Ooxo)8Cl x (MeO)38–x ] (x = 2.3, MeO = methoxide) (I), by single-crystal X-ray diffraction. The characterized {U13} polyoxo cluster complex (I) possesses a single cubic uranium polyhedron at the centre of the cluster core. To the best of our knowledge, this is the very first example of a polyoxo actinide complex that bears a single cubic polyhedron in its structure. The cubic polyhedron in I is well comparable in shape with those in bulk UO2. The U—O bonds in the cubic polyhedron of I are, however, significantly shorter than those not only in bulk UO2 but also in another analogue in the {U38} cluster. This shortening of U—O bonds, together with BVS calculations and the overall negative charge (2−) of I, suggests that the central uranium atom in I, which forms the single cubic coordination polyhedron, is presumably oxidized to the pentavalent state (UV) from the original tetravalent state (UIV). Complex I is, hence, the first example of a polyoxo cluster possessing a single cubic coordination polyhedron of UV.

In this work, the resin capacity factors of Ac, Am and Th on the DGA extraction chromatographic resin have been investigated between 0.5 and 2.0 M nitric acid without and with addition of elevated concentrations of the selective tetravalent complexant, 343HOPO. The resin capacity factors decreased with increasing 343HOPO concentration but remained high enough to support a selective removal of a tetravalent element. The Ac and Am capacity factors were also investigated under Th loading which yields generally reduced uptake on the resin. It was shown that loading effects could be fully scavenged by the addition of 343HOPO complexant. These results indicate that separation steps for Ac involving significant amounts of Th can be handled by selective tetravalent complexation with the DGA system.

We have studied the alpha decay properties of actinides using seven different proximity potentials MP 77, MP 81, Bass 77, Prox 13, Ng80, DP00 and Prox 00. The values produced by the present work are compared with experiments. Decay chains of actinides are presented. The present work is useful in the study of decay modes of actinides.

Radiation stability is one of the key properties to enable the efficient use of extractants in spent nuclear fuel with high radioactivity. The last several decades have witnessed a rapid progress in the radiation chemistry of extractants. A variety of studies and reviews pertinent to the radiation stability of extractants have been published. However, a thorough summary for the alpha radiolysis results of extractants is not available. In this review, we survey the development of alpha radiolysis of extractants for actinide lanthanide separation and compare their radiolysis behaviors induced by alpha particles and gamma rays. The discussion of alpha radiolysis of extractants is divided into three parts according to the functional groups of extractants (i.e., phosphine oxide, amide and bis-triazinyl bipyridines). Given the importance of radiation source to carry out alpha irradiation experiment, we first give a brief introduction to three practicable alpha radiation sources including alpha emitting isotopes, helium ion beam and reactor. We hope this review will provide useful information and unleash a broad palette of opportunities for researchers interested in radiation chemistry.

Solutions of two nitrilotriacetamide (NTA) ligands, viz., N,N,N’,N’,N”,N”-hexa-n-butylnitrilotriacetamide (HBNTA) and N,N,N’,N’,N”,N”-hexa-n-hexylnitrilotriacetamide (HHNTA) in 20% isodecanol–80% n-dodecane were employed for the extraction of U(VI), Np(IV), Pu(IV), and Am(III) from nitric acid feed solutions. Limitations of ligand solubility and third-phase formation when contacted with nitric acid solutions led to the choice of the diluent composition of 20% isodecanol and 80% n-dodecane. The results of the solvent extraction studies indicated poor extraction of the metal ions with HBNTA as compared to that with HHNTA as the extractant and hence, major part of this work involved HHNTA. Slope analysis suggested extraction of 1:1 (ML) species with Np(IV) and Pu(IV) at 3 M HNO3 and mixed 1:2 (ML2) and 1:3 (ML3) species with U(VI) at pH 2. At 0.5 M HNO3, the observed trend for extraction was Pu(IV) > Np(IV) >> Am(III) > U(VI).

Density functional theory calculation is applied to predict the stability constants for Eu3+ and Am3+ complexes in aqueous solution for molecular modelling of novel separation agents for minor acti...

N,N′-dioctyl-N,N′-di-dodecyl-3-oxapentane-1,5-diamide ((DdO)2DGA) is a novel unsymmetrical diglycolamide. Herein, we analyzed the third phase formation and extraction behavior of trivalent actinides and lanthanides with (DdO)2DGA in kerosene. Moreover, FT-IR and UV/Vis spectra of the extracted phase of Nd(III) with (DdO)2DGA were analyzed. The third phase is not formed by the extraction of Nd(III) with 0.10 mol/L (DdO)2DGA at 298 K. The metal ion distribution ratios increase with increased acidity and extractant concentration. Moreover, thermodynamic analysis demonstrates that the extraction is an exothermic reaction with ΔH = − 64.94 kJ/mol and ΔS = − 144.42 J/(mol·K). Both slope and spectroscopic analysis suggest that the extracted species is Nd(NO3)3·3(DdO)2DGA and the change in the acidity or extractant concentration will not change the extracted species.

Due to its associated low CO2 emissions, nuclear energy production is rapidly growing. In this context, the treatment of high-level liquid waste (HLLW) of nuclear plants is of high concern to both scientific and industrial communities. Specifically, the separation of An(III) and Ln(III) cations when processing nuclear fuel is a vitally important, yet challenging, step within HLLW because An(III) and Ln(III) have similar chemical properties in solution. To guide the choice of relevant ligands, anions, and solvents for this separation step, in this work, we calculate and compare the free energy of formation of different Am(III) and Eu(III) complexes (which are typical and important An(III) and Ln(III) cation examples), involving two different ligands and three different counter ions in four different solvents. Based on our calculations, we predict that the chosen solvent is a key factor in the extraction of Am(III) and Eu(III) in treatment of HLLW. This study supports a systematic, computation-assisted screening of solvents and extractive ligands with counter anions as a proficient method to optimize the separation of Ln(III) and An(III).

The properties and stability of ozone in aqueous solutions of various compositions in the рН range of 0–14 were considered. The effect of anions and cations, which are involved in the redox reactions of actinides, on the stability of ozone and its reactivity has been studied. The reactions of О3 with ions of d- and f-elements were analyzed. Depending on the solution composition and рН value, the reaction can occur directly with the O3 molecule (direct mechanism) and/or with short-lived ion-radical products (•OH, HO 2 • / O 2 − • ${\text{HO}}_{2}^{{\bullet}}/{\text{O}}_{2}^{-{\bullet}}$ , H2O2/ HO 2 − ${\text{HO}}_{2}^{-}$ , O 3 − • ${\text{O}}_{3}^{-{\bullet}}$ ) formed upon ozone decomposition in water (indirect mechanism). Ions with inert coordination sphere react with О3 in the outer-sphere fashion with electron transfer. Polyvalent ions with labile coordination spheres are oxidized in acidic medium via О atom transfer, possibly, with intermediate peroxy addition (H2O2, HNO4, H2SO5, etc.). In alkaline medium, О3 is converted to the O 3 − • ${\text{O}}_{3}^{-{\bullet}}$ radical ion, which is the key oxidant for actinides. The results of studies and the mechanisms of reactions of ozone and its intermediates decomposition products with U, Np, Pu, and Am in various oxidation states and with some transition metals (Fe, Mn, Ag, Co, etc.) in aqueous solutions are presented and discussed.

Monitoring and quantification of the photoresponsive behavior of metal-organic frameworks that respond to a light stimulus are crucial to establish a clear structure-activity relationship related to light regulation. Herein, we report the first azobenzene-modified photoresponsive thorium-organic framework (Th-Azo-MOF) with the formula [Th6O4(OH)4(H2O)6L6] (H2L = (E)-2'-p-tolyldiazenyl-1,1':4',4'-terphenyl-4,4″-dicarboxylic acid), in which the utilization of a thorium cluster as a metal node leads to one of the largest pore sizes among all the azobenzene-containing metal-organic frameworks (MOFs). The phototriggered transformation of the trans isomer to the cis isomer is monitored and characterized quantitatively by comprehensive analyses of NMR and UV spectroscopy, which reveals that the maximum isomerization ratio of cisTh-Azo-MOF in the solid state is 19.7% after irradiation for 120 min, and this isomerization is reversible and can be repeated several times without apparent performance changes. Moreover, the isomerization-related difference in the adsorption of the Rhodamine B guest is also illustrated and a possible photoregulated mechanism is proposed. This work will shed light on new explorations for constructing functionalized actinide porous materials by the elegant combination of actinide nodes with tailored organic ligands and furthermore will provide a comprehensive understanding of photoisomerization processes in MOF solids and insight into the mechanism on photoregulated cargo adsorption and release by photoactive MOFs.

Quaternary ammonium salt functionalized silica gel (QA/SiO2) was synthesized and used to remove uranium from the alkaline solution. Batch experiments showed that the saturated adsorption capacity of QA/SiO2 to uranium was 370 mg/g at pH > 8.0. The isothermal adsorption confirms to the Langmuir model. Different co-existing anions have been studied, QA/SiO2 showed a high affinity for uranium. The interaction mechanism is anion exchange. Because of its low cost, operable large particle size and high adsorption capacity, it has a prospect of large-scale industrial application.

In light of the importance of helium production in influencing the behaviour of fast reactor fuels, in this work we present a burn-up module with the objective to calculate the production of helium in both in-pile and out-of-pile conditions tracking the evolution of 23 alpha-decaying actinides. This burn-up module relies on average microscopic cross-section look-up tables generated via SERPENT high-fidelity calculations and involves the solution of the system of Bateman equations for the selected set of actinide nuclides. The results of the burn-up module are verified in terms of evolution of actinide and helium concentrations by comparing them with the high-fidelity ones from SERPENT, considering two representative test cases of (U,Pu)O2 fuel in fast reactor conditions. In addition, a code-to-code comparison is made with the independent state-of-the-art module TUBRNP (implemented in the TRANSURANUS fuel performance code) for the same test cases. The herein presented burn-up module is available in the SCIANTIX code, designed for coupling with fuel performance codes.

The mobility of heavy metal contaminants and radionuclides in the environment is directly controlled by their interactions with charged mineral surfaces, hence an assessment of their potential toxicity, e.g. in the context of nuclear waste disposal sites, requires understanding of sorption processes on the molecular level. Here, we investigate the sorption of a variety of rare earth elements (REE) and trivalent actinides (Am, Cm) on K-feldspar using batch sorption and column transport experiments, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and a surface complexation model. Initially, a reliable pKa for K-feldspar’s surface deprotonation reaction was determined as 2.5 ± 0.02, in excellent agreement with a measured pHIEP of 2.8. Batch sorption experiments over a broad range of experimental conditions in terms of mineral grain size, pH, [M3+], ionic radius, solid/liquid ratio, ionic strength, and equilibration procedures were carried out to quantify macroscopic immobilization. Similar pH-dependent uptake behavior was found for all investigated trivalent REE and actinides. In parallel, spectroscopic investigations provided insight into surface speciation. Cm TRLFS spectra indicate the formation of three inner-sphere sorption complexes with increasing hydrolysis. Additionally, a ternary K-feldspar/Cm/silicate complex was found for pH > 10, and batch and spectroscopic data at low pH (< 4) point to small amounts of outer sphere sorption complexes. Based on TRLFS data, batch sorption, and titration data, a generic geochemical sorption model was developed, that describes sorption edges for all investigated M3+/K-feldspar systems satisfactorily. The derived stability constants for the binary sorption complexes (logK1-4 = −3.6, −7.7, −11.5, and −17.4, respectively) are in good agreement with previous studies on similar systems, and could successfully be used to reproduce literature data. The stability constants obtained for the surface complexes were included into the database for the Smart Kd-concept, which will further improve the safety assessment of potential repositories for radioactive waste.

U(VI) was found to form intrinsic colloids in the natural groundwater. Fluorescence spectra, TEM, SEM techniques and thermodynamic calculation were used to identify the species of U(VI) and characterize the intrinsic uranium colloidal particles in the groundwater. The effect of pH on the formation of U(VI) colloidal particles was studied. It was found that under near-neutral and strong alkaline conditions, several elements, mainly Ca, Na and Si were responsible for the formation of intrinsic U(VI) colloid, and under weak alkaline conditions, U(VI) colloidal particles were not formed due to the formation of calcium uranyl carbonate complex.

A new process was developed to recover high specific activity (no carrier added) 99Mo from electron-accelerator irradiated U3O8 or uranyl sulfate targets. The process leverages a novel solvent extraction scheme to recover Mo using di(2-ethylhexyl) phosphoric acid following uranium and transuranics removal with tri-n-butyl phosphate. An anion-exchange concentration column step provides a final purification, generating pure 99Mo intended for making 99Mo/99mTc generators. The process was demonstrated with irradiated uranium targets resulting in more than 95% 99Mo recovery and without presence of fission products or actinides in the product.

We report a high sensitivity study of actinides content in water and sediment matrices performed for the first time along the Garigliano river, near the nuclear power plant currently undergoing decommissioning, and in the marine environment surrounding the river mouth up to a depth of 100 m. Ultrasensitive accelerator mass spectrometry measurements were carried out to estimate the absolute values of 236U, 238U, 239Pu, and 240Pu concentrations and 236U/238U, and 239Pu/240Pu ratios. The accuracy of the measurements and the spatial distribution of the radionuclides enable us to discriminate the anthropogenic from the natural radionuclide’s contribution to the environmental radioactivity. The results indicate that the contribution to the anthropogenic contamination of past power plant operations is, in most of the examined environmental compartments, negligible compared to fallout. High resolution γ-ray spectrometry measurements for 137Cs and 40K show interesting correlations with the actinides results.

We report a series of uranium complexes stabilized by the pentakis-benzyl-derivatized cyclopentadienyl ligand, CpBn5. Treatment of [UCl4] and [UI3(1,4-dioxane)1,5] with 2 equiv of the potassium salt, CpBn5K, yielded the corresponding complexes [(CpBn5)2UIV(Cl)2] (1) and [(CpBn5)2UIII(I)] (4). Subsequently, tetravalent 1 is either methylated to give [(CpBn5)2UIV(Me)2] (2) or reduced to form trivalent [(CpBn5)2UIII(μ-Cl)2K(OEt2)3] (3). Oxidation of 4 with AgI yields [(CpBn5)2UIV(I)2] (5), which was found to generate rarely observed, linear uranium metallocenes [(CpBn5)2UIV(NCMe)5][X]2 (X = PF6– (6), BPh4– (7)) upon abstraction of the iodide ligands with thallium salts in acetonitrile. All complexes were characterized by 1H NMR spectroscopy, CHN elemental analysis, UV–vis–NIR spectroscopy, and SQUID magnetization measurements. The solid-state molecular structures of 1–7 were determined by single-crystal X-ray diffraction analysis. An in-depth computational analysis revealed the peculiar electronic structure of the linearly coordinated title complex 7 and its closely related, parent [(Cp*)2UIV(NCMe3)5]2+ dication.

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A new class of actinide complexes [(L)An(N{SiMe3}2)3] (An = Th or U) (Th1–Th3 and U1–U3) supported by highly nucleophilic seven-membered N-heterocyclic iminato ligands were synthesized and fully characterized by single-crystal X-ray diffraction. These complexes were successfully exploited as powerful catalysts for the addition of alcohols to carbodiimides to yield the corresponding desirable isourea products at room temperature with short reaction times and excellent yields. Thorough stoichiometric, thermodynamic, and kinetic studies were carried out, allowing us to propose a plausible mechanism for the catalytic reaction.

Two phosphoramide extractants, namely, hexapropyl phosphoramide (HPPA) and hexabutyl phosphoramide (HBPA), were developed in our laboratory for their application toward actinide separations. Prelim...

Encapsulating a certain guest molecule in an assigned molecular compartment and then endowing the corresponding potential remains a huge challenge for metal-organic frameworks. To this end, we demonstrate a good example, for the first time, based on an actinide-based MOF. The used MOF (namely, ECUT-300) shows a unique uranyl-TPE anionic skeleton with three distinct cages, viz., mesopore A (2.8 nm), mesopore B (2.0 nm), and micropore C (0.9 nm). Through solid-liquid reaction, a RhB+ molecule can be encapsulated into ECUT-300 with the exact location in mesopore B, whereas the encapsulation of a metal-organic cation of [Fe(tpy)2]3+ was observed with the location in micropore C, suggesting unprecedented classified encapsulation. Impressively, the potential of the resulting guest@MOF composites is also highly dependent on the type of encapsulated guest molecules, for example, white-light emission for RhB+ and selective adsorption of C2H2 over CO2 for [Fe(tpy)2]3+.

99Tc is a long-lived radionuclide present in large amounts as TcO4- anion in used nuclear fuel. Its removal from the waste stream is highly desirable because of its interference capability with actinide separation and its volatile nature during the nuclear waste vitrification process. Despite the progress achieved in the past few years, the design of anion-exchange materials with optimized Tc uptake property and improved stability under the extreme condition, is still a research goal beneficial for reducing the volume of secondary radioactive solid waste generated during the waste partitioning process. However, their design philosophy remains elusive, with challenges coming from charge repulsion, steric hindrance, and insufficient reactive sites within the materials. Herein, we present a design philosophy of cationic polymer network materials for TcO4- separation by systematic precursor screening and structure prediction. This affords an optimized material, SCU-CPN-2 (SCU=Soochow University), with extremely high positive charge density while maintaining high radiation resistance. SCU-CPN-2 exhibits a record high adsorption capacity (1,467 mg/g towards the surrogate ReO4-) compared to all anion-exchange materials reported up to date. In addition to ultrafast adsorption kinetics, SCU-CPN-2 has remarkable selectivity over nitrate and sulfate, and facile recyclability.

We report an extraction chromatography-based method via Actinide Resin for the isolation of radio- manganese from both natural chromium and isotopically enriched iron targets for cyclotron production of (52g)Mn and (51)Mn. For the separation of (52g)Mn from (Nat)Cr, a decay-corrected radiochemical yield of 83.7 ± 8.4% was achieved. For (51)Mn from (54)Fe, a decay-corrected radiochemical yield of 78 ± 11% was achieved. This automatable method efficiently isolates both radionuclides from accelerator target material.

Catalysis remains one of the final frontiers in molecular uranium chemistry. Depleted uranium is mildly radioactive, continuously generated in large quantities from the production and consumption of nuclear fuels and accessible through the regeneration of “uranium waste”. Organometallic complexes of uranium possess a number of properties that are appealing for applications in homogeneous catalysis. Uranium exists in a wide range of oxidation states, and its large ionic radii support chelating ligands with high coordination numbers resulting in increased complex stability. Its position within the actinide series allows it to involve its f-orbitals in partial covalent bonding; yet, the U–L bonds remain highly polarized. This causes these bonds to be reactive and, with few exceptions, relatively weak, allowing for high substrate on/off rates. Thus, it is reasonable that uranium could be considered as a source of metal catalysts. Accordingly, uranium complexes in oxidation states +4, +5, and +6 have been studied extensively as catalysts in sigma-bond metathesis reactions, with a body of literature spanning the past 40 years. High-valent species have been documented to perform a wide variety of reactions, including oligomerization, hydrogenation, and hydrosilylation. Concurrently, electron-rich uranium complexes in oxidation states +2 and +3 have been proven capable of performing reductive small molecule activation of N2, CO2, CO, and H2O. Hence, uranium’s ability to activate small molecules of biological and industrial relevance is particularly pertinent when looking toward a sustainable future, especially due to its promising ability to generate ammonia, molecular hydrogen, and liquid hydrocarbons, though the advance of catalysis in these areas is in the early stages of development. In this Perspective, we will look at the challenges associated with the advance of new uranium catalysts, the tools produced to combat these challenges, the triumphs in achieving uranium catalysis, and our future outlook on the topic.

The organic solution composed of N,N,N′,N′-tetraoctyldiglycolamide (TODGA) and n-dodecane is extensively studied for the removal of trivalent actinides from the high-level liquid waste arising from nuclear industry. Present work deals with the evaluation of density and viscosity of TODGA/n-dodecane as a function of absorbed gamma radiation dose, temperature and composition. In addition, volumetric and viscometric properties like excess molar volume, apparent molar volume, viscosity deviation, activation energy for the viscous flow, enthalpy and entropy changes of activation of this binary mixture were also estimated. Based on these derived thermodynamic properties, the inter-molecular interactions of this binary liquid solution were predicted. Redlich–Kister type equations were employed to correlate excess volume and viscosity deviation, and the coefficients of fourth degree polynomial that fitted well with the experimental data were estimated. Present study indicated the stable nature of hydrodynamic behaviour of TODGA/n-dodecane system with respect to physical properties up to 500 kGy of absorbed gamma radiation dose.

Introduction. Treatment and disposal of radioactive wastes as well as monitoring of radioactive isotope content in environmental objects are actual tasks in the developed world. Lanthanide and transuranium element removal from spent nuclear fuel of nuclear power plants allows decreasing waste amount to be dumped and diminishing the risk of environmental pollution by radionuclides. Problem Statement. Considering extreme radiotoxicity of transuranium elements and tight standards restricting their activity in air and water, there is an urgent need to develop accurate and highly sensitive methods for pollution control. Purpose. Development of solid phase extractants (SPEs) based on porous polymers impregnated with multidentate chelating ligands for lanthanide, uranium and transuranium element removal from aqueous solutions. Materials and Methods. The materials used are porous divinylbenzene polymers of POROLAS brand and styrene-divinylbenzene copolymers from Smoly SE (Kamianske); multidentate chelating ligands of actinides and lanthanides such as N,N,N´,N´-tetra-n-octyl-oxapentane-1,5-diamide (TODGA) and carbamoyl phosphine oxides (CMPO); sorbent from TrisKem (France) based on TRU Resin (Eichrom Industries, Inc.). The research techniques are inductively coupled plasma atomic emission spectrometry, IR spectroscopy, scanning electron spectroscopy, spectrofluorimetry. Results. The solid-phase extractants (SPEs) for actinide and lanthanide removal from aqueous solutions have been synthesized by impregnation of porous polymeric POROLAS matrices and TODGA, CMPO-(PhOct) and CMPO-(Ph2). Sorption kinetics has been studied and capacity values for the different sorbents have been estimated. Extractive columns for uranium and europium concentration have been manufactured. Conclusions. SPEs studied demonstrate a high efficiency in removing uranium and europium from aqueous solutions. Due to their characteristics obtained materials may be used for preconcentration of target ions in radioecologycal monitoring procedures.

Nuclear characterization of the spent nuclear fuel in a reactor core is essential, especially in case of severe accidents. The radionuclide inventory and its activity can assist in the management of spent fuel handling, transport, or reprocessing. In this paper, the core of the Fukushima Daiichi Unit-1(FD-U1) accident was modeled using the Monte Carlo code (MCNPX 2.7) linked to the depletion calculation code CINDER'90 and ENDF/B-VII.0 cross-section data library. The isotopic inventory and the activity of the radionuclides for the burned fuel were calculated. The input to the code depends on the previous evolution of the reactor core configurations, dimensions and material of the fuel assemblies, initial uranium enrichment, fuel burn-up, and reactor core operational history. The calculations were validated with experimental measurements which were carried out by the Japan Nuclear Energy Safety Organization (JNES) and verified with published results using ORIGEN2-code by Japan Atomic Energy Agency (JAEA). The masses, activities, specific activities, half-lives, and decay schemes for the actinides and fission products were calculated at the time of the accident and after 50 years of cooling time. The calculations showed that the total activity of the burned fuel in the core at the time of the accident was 9.86E+19Bq and after 50 years was 1.89E+17Bq and the higher inventory concentration in the fuel was dominated by the trans-uranic elements. Also, the specific activity in the core at the time of the accident and after 50 years of cooling time was found to be 1.84E+15Bq/g and 5.86E+12Bq/g, respectively.

A common advanced radiochemical technique is the use of the AG® 1-X8 anion exchanger, Cl2− form (from Bio Rad), to separate uranium and/or thorium from a sample by ion exchange. This method is used to separate elements by chemical elution from an ion exchange column via a precipitate of substances (co-precipitation), with Nd3+ as a thin layer of smooth fluoride particles on a membrane filter, then using α-spectrometry to measure uranium and thorium. The obtained data showed that the column could be reused, at least twelve times, safely in separating uranium and thorium from environmental samples, before observing any change in the performance of the exchanger.

Abstract Refractory ‘stuffed’ pyrochlores such as Gd2TiO5 are of interest for nuclear applications, including as matrices for actinide disposition and as neutron absorbers in control rods. Here, we report the results of a preliminary comparative investigation of the synthesis of Gd2TiO5 by molten salt and conventional solid-state synthesis. We show that synthesis of Gd2TiO5 proceeds from the pyrochlore phase Gd2Ti2O7 which is first formed as a kinetic product. Molten salt synthesis afforded single phase Gd2TiO5 at 1300 °C in 2 h, via a template growth mechanism, and is effective for the synthesis of these refractory materials. This work demonstrates molten salt mediated synthesis of ‘stuffed’ pyrochlore for the first time. Graphic abstract

A zirconium-based metal–organic framework (DUT-69) was fabricated via a hydrothermal synthesis for U(VI) removal in aqueous solutions. Experimental results showed that the maximum adsorption capacity for U(VI) was 362.32 mg·g−1 at 303 K, pH = 6 and initial U(VI) concentration of 80 mg L−1. The adsorption process fit well with the pseudo-second-order kinetic and Langmuir models. Various characterizations indicated that complexation interactions was the central adsorption mechanism and electrostatic was the secondary. The carboxyl, Zr–O, and C–S bonds in the framework participated in the adsorption process. Reusability experiments showed that 80.34% adsorption rate could be maintained after 5 cycles.

The results of a study of the effect of the homogeneous addition of 237Np, 241Am, 243Am into the fuel on the neutronics characteristics of a lead-cooled fast reactor are reported. The reasons for the change in the delayed- neutron fraction and the effective delayed-neutron fraction, breeding ratio, density effect of reactivity, and residual energy release of the fuel unloaded from the core are analyzed. The transmutation efficiency was determined for the starting actinide fraction 3–5% h.a. mass in the fuel.

U(VI) and Eu(III), as representative elements of the hexavalent actinide and trivalent lanthanides (always as a chemical analogue for trivalent actinide), respectively, have attracted more and more attentions due to the widespread use of nuclear energy. Much effort has been focused on developing versatile materials for their uptake from aqueous solution. For the first time, we report here UiO-66 and its mono- (UiO-66-COOH) and di-carboxyl (UiO-66-2COOH) functional derivatives as robust adsorbents for efficient U(VI) and Eu(III) removal. It is found that the introduction of carboxyl groups greatly reduces the surface charge of UiO-66, thus guaranteeing excellent adsorption capacity at low pH. At pH = 3, for example, the adsorption capacity of UiO-66-2COOH for U(VI) and Eu(III) is more than 100 and 60 mg/g, respectively, while almost no adsorption occurs for pristine UiO-66. At pH = 4, both UiO-66-COOH and UiO-66-2COOH show high performance on U(VI) and Eu(III) removal. UiO-66-COOH has adsorption capacities of 80 and 43 mg/g for U(VI) and Eu(III), respectively, while the values for UiO-66-2COOH reach 150 and 80 mg/g, respectively. Also, all these materials achieve adsorption equilibrium within 100 min. More importantly, combining the needs of practical applications and the characteristics of high stability, high porosity, and excellent adsorption performance of UiO-66-2COOH, dynamic adsorption column experiments were successfully conducted; ∼99% U(VI)/Eu(III) can be efficiently adsorbed, and >90% adsorbed U(VI)/Eu(III) can be re-collected with dilute nitric acid solution, even after four adsorption-desorption cycles. The findings of this work demonstrate the application potential of metal-organic framework materials to remove radionuclides from environmental samples or nuclear waste liquids.

A new sample stage for characterizing radioactive materials by X-ray powder diffraction was developed at the ATALANTE facility (CEA Marcoule, France) using a conventional (non-nuclearized) Bruker D8 goniometer mounted in Bragg–Brentano geometry. The setup consists of a removable, fully hermetic sample stage, with a 200 µm-thick beryllium window, that can be plugged onto a glove-box, allowing the sample to be introduced in an hermetic medium that also encapsulates the glove-box atmosphere throughout the analysis process. The whole setup is thus hermetically unplugged from the glove-box and positioned on the centre of the goniometer. No preliminary decontamination and/or decontainment of the sample is necessary. The device was developed to avoid an expensive and time-consuming nuclearization of the diffractometer while also keeping it easily accessible for maintenance. Ultimately, keeping the diffractometer out of a glove-box also limits the volume of the final nuclear wastes, and thus the removable sample stage is the only `active' part. X-ray diffraction results of two NIST standards LaB6 and α-Al2O3 as well as five actinide dioxides ThO2, UO2, NpO2, PuO2 and AmO2 are presented to show the efficiency of the setup.

High-throughput computational studies of lanthanide and actinide chemistry with density-functional theory are complicated by the need for Hubbard U corrections, which ensure localization of the f-electrons, but can lead to metastable states. This work presents a systematic investigation of the effects of both Hubbard U value and metastable states on the predicted structural and thermodynamic properties of four uranium compounds central to the field of nuclear fuels: UC, UN, UO2, and UCl3. We also assess the impact of the exchange-hole dipole moment (XDM) dispersion correction on the computed properties. Overall, the choice of Hubbard U value and inclusion of a dispersion correction cause larger variations in the computed geometric properties than result from metastable states. The weak dependence of structure optimization on metastable states should simplify future high-throughput calculations on actinides. Conversely, addition of the dispersion correction is found to offset the repulsion introduced by the Hubbard U term and provides greatly improved agreement with experiment for both cell volumes and heats of formation. The XDM dispersion correction is largely invariant to the chosen U value, making it a robust dispersion correction for actinide systems.

A combined method of high-resolution gamma spectroscopy and thermal ionization mass spectroscopy without chemical separation was applied for plutonium assay in pure Pu and U–Pu mixed solutions collected at the Rokkasho Reprocessing Plant, Japan. The relative biases of Pu assay results determined by the combined method to the conventional IDMS are less than 0.01% in the pure Pu and the U–Pu mixed solutions. The combined method can be used as an alternative rapid method for Pu assay as a backup to the conventional IDMS method and K-edge densitometry without any loss of precision and accuracy.

Isotope dilution mass spectrometry using traceable standards as spikes coupled with isotope ratio measurements by thermal ionization or inductively coupled plasma mass spectrometer instruments is the preferred methodology for element content determinations and isotopic composition measurements in a variety of applications, especially those involving highly radioactive isotopes like the actinide elements. This assay measurement technique takes advantage of the sensitivity of modern mass spectrometry instrumentation to minimize the amount of material utilized for the measurement and enables the measurement sequence to be automated, with minimal intervention from analyst during the measurement process. LA-UR-20-28878.

To reduce the damage of minor actinides to the environment, the separation selectivity of new chiral extractant (E)-5-(((1H-prrazol-3-yl) methtlene)amino)acridine-1,4-dione (PMAAD) to Am(III)/Eu(III) was investigated by all-electron DKH2-DFT calculations. The results indicated that the position of nitrate ions in complex plays a important role in affecting PMAAD to form three types complexes with Am(III)/Eu(III) and the ligands’s structures in complexes. The selectivity coefficient of PMAADs to Am(III) was increased by 11.7% at least when types 1 as chiral-at-Am(III)/Eu(III) complexes generated by two diffrent chiral PMAADs. The preorganization level of ligands was quantitatively determined. The newly designed chiral ligands could coordinate with Am(III)/Eu(III) to form three types complexes, among them, type 2 and 3 complexes formed by single chiral ligands and type 1 complex formed by two different chiral ligands. Furthermore, the ligands within type 2 complexes in which nitrate ions are located between two quinone planes show maximum deformation but have lowest Gibbs free energy. However, within type 1 complexes called chiral-at-Am(III)/Eu(III) complexes, the ligands show less deformation and high selectivity to Am. The selectivity coefficient (Ks) between type 1 complexes and the other two types complexes increased by 11.70% at least.

Covalency is often considered to be an influential factor in driving An3+ vs. Ln3+ selectivity invoked by soft donor ligands. This is intensely debated, particularly the extent to which An3+ /Ln3+ covalency differences prevail and manifest as the f-block is traversed, and the effects of periodic breaks beyond Pu. Herein, two Am complexes, [Am{N(E=PPh2 )2 }3 ] (1-Am, E=Se; 2-Am, E=O) are compared to isoradial [Nd{N(E=PPh2 )2 }3 ] (1-Nd, 2-Nd) complexes. Covalent contributions are assessed and compared to U/La and Pu/Ce analogues. Through ab initio calculations grounded in UV-vis-NIR spectroscopy and single-crystal X-ray structures, we observe differences in f orbital involvement between Am-Se and Nd-Se bonds, which are not present in O-donor congeners.

Neutral arenes such as benzene have never been considered suitable ligands for electropositive actinide cations, yet we find that even simple UIII UX3 aryloxide complexes such as U(ODipp)3 bind and reduce arenes spontaneously at room temperature, forming inverse arene sandwich (IAS) complexes XnU(μ-C6D6)UXm (X = ODipp, n=2, m=3; X = OBMes2 n=m=2 or 3) (ODipp = OC6H3iPr2-2,6; Mes = 2,4,6-Me3-C6H2). In some of these cases, further arene reduction has occured as a result of X ligand redistribution. These unexpected spontaneous reactions explain the anomalous spectra and reported lack of further reactivity of strongly reducing UIII centers of U(ODipp)3. Phosphines that are not considered suitable ligands for actinides can catalyze the formation of the IAS complexes. This enables otherwise inaccessible asymmetric and less congested IAS complexes to be isolated and the bonding in this series compared.