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The history of chemistry has not once seen representations of the periodic system that have not received proper attention or recognition. The present paper is dedicated to a nearly unknown version of the periodic table published on the occasion of the centenary celebration of Mendeleev's birth (1934) by V. Romanoff. His periodic table visually merges Werner's and Janet's periodic tables and it is essentially the spiral periodic system on a plane. In his 1934 paper, Romanoff was the first one to introduce the idea of the actinide series, a decade before Glenn T. Seaborg, the renowned creator of the actinide concept. As a consequence, another most outstanding thing about Romanoff's paper occurs towards its very end: he essentially predicted the discovery of elements #106, #111 and #118. He theorized that, had uranium not been the "creative limit", we would have met element #106, a "legal" member of group 6, element #111, a precious metal, "super-gold" and element #118, a noble gas. In 2019, we take it for granted that elements #106, #111 and #118 indeed exist and they are best known as seaborgium, roentgenium and oganesson. It is fair to say that Romanoff's success with the prediction of correct placement and chemical properties of seaborgium, roentgenium and oganesson was only made possible due to the introduction of an early version of the actinide series that only had four elements at that time. Sadly, while Professor Romanoff was imprisoned (1938–1943), two new elements, neptunium (element #93) and plutonium (element #94) were discovered. While Professor Romanoff was in exile in Ufa (1943–1953), six further elements were added to the periodic table: americium (element #95), curium (element #96), berkelium (element #97), californium (element #98), einsteinium (element #99) and fermium (element #100). The next year after his death, in 1955, mendelevium (element #101), was discovered. Romanoff's version of the periodic table is an unparalleled precursor to the contemporary periodic table, and is an example of extraordinary anticipation of the discovery of new chemical elements. [ABSTRACT FROM AUTHOR]

Mathematical techniques for modeling and simulating dangerous or complex systems, such as nuclear technology systems, often require high-performance computing to process and analyze available data. In this paper, simple and quick method to support studies and research related to nuclear fuel is presented. This reasonably simple method helps to predict different concentrations of actinides and fission products in nuclear fuels without the need for expensive specialized programs and highly-trained researchers. The great importance of this approach is the speed of predicting the components of nuclear fuel concentrations, which in turn leads to quick decision-making, such as the possibility of operating fuel at higher burnup values, predicting the amount of gases resulting from nuclear fission (which may accumulate and cause problems in nuclear fuel such as volume swells), and other important decisions in nuclear fuel technology. The predicted equations have been generalized for higher values of burnup and compared with comparable results from MCNP codes. The equations deduced in calculating the different concentrations of xenon and krypton isotopes resulting from fission in burnup of nuclear fuel showed very precise results with discrepancies (magnitude of an error between the data points and the corresponding predicted ones) less than 2%. The suggested method offers a great advantage for researchers, which are the use one of any simple or common computational programs available to most researchers and do not need much experience to deal with, such as MATLAB, Excel that are easy to use for regression analyses. In this paper, the advantages of the proposed method are explained along with the limitations of its use. [ABSTRACT FROM AUTHOR]

Actinide minor is a reactor waste with high toxicity and a long half-life. Minor actinides can be reduced by reusing them as fuel mixtures in reactors. This research uses PWR reactors with the primary fuel UN-PuN or Uranium Plutonium Nitride with a burning time of 5 years. The fuel consists of enriched Uranium, reactor-grade Plutonium from LWR waste, and minor actinides including Neptunium-237, Americium-241, and Curium-244. The purpose of this study was to find a design that is effective in reducing minor actinide waste. There are six designs or cases used in the addition of minor actinides. Each case has six minor actinide pins in each assembly. The addition of minor actinides is arranged in heterogeneous cores. The analysis was carried out by observing the values of k-eff, excess reactivity, and mass of minor actinides obtained from simulations using OpenMC code 0.13.2 and the ENDF/B-VIII library. The homogeneous core obtained an excess reactivity of 9.7 % with a percentage of plutonium of 8 %. The results of the homogeneous core are used as a reference for preparing a heterogeneous core. The heterogeneous core obtained an excess reactivity of 9.9 % with a percentage of plutonium F1: 5.5 %, F2: 8 %, and F3: 10.5 %. Np-237 can be reduced by 53 kg, and Am-241 can be reduced by 61 kg with minor actinide pins in case 1. Cm-244 can be reduced by 363 kilograms with minor actinide pins in case 6. Excess reactivity in the addition of Np-237 and Am-241 decreased to 5.3 %, while the accumulation of Cm-244 increased to 12.1 %. [ABSTRACT FROM AUTHOR]

Selective separation of an individual actinide of interest from other actinides and accompanying lanthanides is a challenging task in radiochemistry and radioanalytical chemistry. This paper illustrates a dual column technique (i.e., stacked columns of two appropriate resins) to separate an individual actinide of interest, where the selection of two resins and a common effluent running through the stacked columns are key parameters in design of an appropriate dual column. This paper describes the dual column design and practice with two examples, one for a heavy actinide 249Bk and the other for a light actinide 230U. In the former case, stacked columns of anion exchange (AX) resin and LN resin replaced the traditional CX-AHIB method used at Oak Ridge National Laboratory for 60 years. In the latter case, an elution process with an AX column followed with a stacked column of AX resin and a DGA resin was applied, instead of traditional methods, e.g., PUREX or U-TEVA methods. Application results of the dual column method to the two example actinides are displayed, while the considerations in method design and the required conditions are discussed. [ABSTRACT FROM AUTHOR]

A novel method has been developed for the simultaneous determination of difficult-to-measure (DTM) nuclides 93Zr, 237Np, 232Th, 230Th and 228Th using a DGA resin® (containing N,N,N′,N′-tetra-n-octyl-diglycolamide) column for simultaneous separation of Zr and actinides followed by purification of Zr, Np and Th on a TEVA resin® (containing Aliquat 336) column. Samples are destroyed by fusion with sodium hydroxide or by acid destruction using HNO3, HCl and HF. Pre-concentration procedure tailored to the extraction chromatography is based on co-precipitation of Zr and actinides and removal of alumina, silica, iron and calcium. The concentrations of 93Zr, 237Np and Th nuclides are determined by ICP-MS and α spectrometry, respectively. High chemical recoveries (≥ 73%) and separation factors were obtained for Zr, Np and Th both in evaporation concentrates of an NPP and various samples of mineral origin such as soil and concrete. The procedure can be easily combined with the simultaneous separation of other actinides (Pu, Am, U) using the same DGA column that has been described in our previous papers (Cassette et al. in Appl Radiat Isot 68:122–130, 2010 and Groska et al. in J Radioanal Nucl Chem 309(3):1145–1158, 2016). [ABSTRACT FROM AUTHOR]

This paper describes the sequential separation of actinides such as U, Pu, Am, and Sr in urine samples. Urine bioassay is one of the preferred methods for assessing low level of internal contamination in radiation workers. Any special monitoring case necessitates the completion of sample analysis as soon as possible. Hence, in this work, efforts have been made to reduce the overall analysis time for the estimation of actinides and strontium in urine samples. In the described method, TRU and Sr-spec resins are used in tandem for the separation of actinides and strontium. The proposed method is very convenient to handle, rapid, and robust when compared with ion exchange and other extraction chromatography work. Radiochemical recoveries of 232U, 242Pu, 243Am, and 90Sr obtained are in the range of 66%-89%, 63%-99%, 63%-96%, and 61%-79% with an average and standard deviation of 77.2% ±7.2, 79.8% ±11.4, 80.9% ±11.2, and 71.8% ±5.9, respectively. [ABSTRACT FROM AUTHOR]

The paper shows the usage of destructive assay data from PWR fuel samples for the validation of the NFCSS burnup system developed by the IAEA. The results of radiochemical measurements of spent fuel isotopic composition were compared with the results of numerical modelling. In total, 254 samples from 15 PWRs, incorporated in the SFCOMPO database, were applied in the validation study. The paper shows the trends observed in the calculated-to-experimental ratios for eight major actinides and six minor actinides present in spent nuclear fuel. The data were quantified and analysed considering the enrichment, burnup and origin. The obtained results were compared with other studies on burnup validation using different numerical tools. In general, the results of numerical modelling for major actinides show rather good consistency with radiochemical measurements, while the results for minor actinides are less accurate. [ABSTRACT FROM AUTHOR]

Separation of lanthanide (Ln) and minor actinide (MA) elements and mutual separation between minor actinide elements (e.g. Am(III) and Cm(III)) represent a crucial undertaking. However, separating these elements poses a significant challenge owing to their highly similar physicochemical properties. Asymmetric N-heterocyclic ligands such as N-ethyl-6-(1H-pyrazol-3-yl)-N-(p-tolyl)picolinamide (Et-p-Tol-A-PzPy) and N-ethyl-N-(p-tolyl)-1,10-phenanthroline-2-carboxamide (ETPhenAm) have recently received considerable attention in the separation of MAs over Ln from acid solutions. By changing the central skeleton structures of these ligands and introducing substituents with different properties on the side chains, their complexation behavior with Am(III), Cm(III), and Eu(III) may be affected. In this work, we explore four different asymmetric N-containing heterocyclic ligands, namely Et-p-Tol-A-PzPy (L¹), N-ethyl-6'-(1H-pyrazol-3-yl)-N-(p-tolyl)-[2,2'-bipyridine]-6-carboxamide (L²), N-ethyl-9-(1H-pyrazol-3-yl)-N-(ptolyl)-1,10-phenanthroline-2-carboxamide (L³), and ETPhenAm (L4) using density functional theory (DFT). The calculated results demonstrate the potential of ligands L¹-L4 for the extraction and separation of Am(III), Cm(III), and Eu(III). Ligand analysis shows that ligand L³ binds more easily to the central metal atom, in line with the stronger extraction capacity of L³. In spite of the higher covalence between the side chain and the central metal atom for complexes with L¹-L³, the main chain seems to control the stability of the extraction complexes. The preorganized 1,10-phenanthroline backbone also further enhances the extraction performance of L³ and L4. The difference in coordination ability between the side chain donors of these ligands and metal ions may affect their separation efficiency. This work presents theoretical insights into synthesizing novel ligands for separating trivalent actinides by adjusting N-heterocyclic ligands. [ABSTRACT FROM AUTHOR]

In recent years, evidence has emerged that actinide (An) uptake at the enhanced actinide removal plant (EARP) at the UK's Sellafield nuclear site occurs via An interactions with an α-Fe13 Keggin molecular cluster during ferrihydrite formation. We here study theoretically the substitution of aquo complexes of the actinides Th–Pu onto a Na-decorated α-Fe13 Keggin cluster using DFT at the PBE0 level. The optimised Pu–O and Pu–Fe distances are in good agreement with experiment and Na/An substitutions are significantly favourable energetically, becoming more so across the early 5f series, with the smallest and largest ΔrG° being for Th and Pu at −335.7 kJ mol−1 and −396.0 kJ mol−1 respectively. There is strong correlation between the substitution reaction energy and the ionic radii of the actinides (Δrε0R2 = 0.97 and ΔrG° R2 = 0.91), suggesting that the principal An-Keggin binding mode is ionic. Notwithstanding this result, Mulliken and natural population analyses reveal that covalency increases from Th–Pu in these systems, supported by analysis of the occupied Kohn–Sham molecular orbitals where enhanced An(5f)–O(2p) overlap is observed in the Np and Pu systems. By contrast, quantum theory of atoms in molecules analysis shows that U-Keggin binding is the most covalent among the five actinides, in keeping with previous studies. [ABSTRACT FROM AUTHOR]

Etidronic acid (1-Hydroxyethylidene-1,1-diphosphonic acid, HEDP, H4L) is a proposed decorporation agent for U(VI). This paper studied its complex formation with Eu(III), an inactive analog of trivalent actinides, over a wide pH range, at varying metal-to-ligand ratios (M:L) and total concentrations. Combining spectroscopic, spectrometric, and quantum chemical methods, five distinct Eu(III)−HEDP complexes were found, four of which were characterized. The readily soluble EuH2L+ and Eu(H2L)2− species with log β values of 23.7 ± 0.1 and 45.1 ± 0.9 are formed at acidic pH. At near-neutral pH, EuHL0s forms with a log β of ~23.6 and, additionally, a most probably polynuclear complex. The readily dissolved EuL− species with a log β of ~11.2 is formed at alkaline pH. A six-membered chelate ring is the key motif in all solution structures. The equilibrium between the Eu(III)–HEDP species is influenced by several parameters, i.e., pH, M:L, total Eu(III) and HEDP concentrations, and time. Overall, the present work sheds light on the very complex speciation in the HEDP–Eu(III) system and indicates that, for risk assessment of potential decorporation scenarios, side reactions of HEDP with trivalent actinides and lanthanides should also be taken into account. [ABSTRACT FROM AUTHOR]

Studies on the recovery of trivalent metal ions such as Nd3+Eu3+(taken as homologs of Am(III)) from solid oxide (Nd2O3), Thorium concentrate (obtained from Monazite ore processing), tissue paper/surgical gloves (rubber), and plant samples have been carried out by supercritical fluid extraction (SFE) using supercritical CO2and ethanol/nitric acid.N,N,N’,N’-tetraoctyl diglycolamide (TODGA) was used as the extractant in these studies. The results showed that the recovery of Nd increased with TODGA concentration from 50% (no TODGA) to 70% (10% TODGA) at 3 M HNO3in ethanol. However, the extraction of Nd at 1 M HNO3was invariant with 1-3% (v/v) TODGA concentration (73 ± 4%). Interestingly, REEs recovery from Th concentrate was ˜ 60% even without TODGA using ethanol/3 M HNO3mixture. On the other hand, quantitative recovery of152,154Eu from tissue paper and surgical gloves sample could be achieved using 3 M HNO3/ethanol mixture. This suggested that it would be possible to decontaminate the contaminated laboratory waste papers using SFE technique. [ABSTRACT FROM PUBLISHER]

The modern databases on the thermodynamic properties of individual substances were reviewed to determine applicability of databases for solving problems in the field of thermodynamic modeling of physicochemical processes of radiochemical technologies. The paper considers database packages of computational tools FactSage, Thermo-Calc, HSC Chemistry, MTDATA, IVTANTERMO, TeDy, as well as a specialized SmartDB database. The lack of data was revealed on the thermodynamic properties of some compounds of actinides, part of organic compounds, characteristic of radiochemical technologies. Based on the results of the comparison, the databases most suitable for use in modeling radiochemical operations were determined. [ABSTRACT FROM AUTHOR]

Plutonium-specific supported liquid membranes were developed and reported for the first time. The studies included in this paper are on the supported liquid membrane transport behavior of Pu(IV), Am(III) and U(VI) investigated using two tripodal amides viz. N,N,N,'N,'N,"N"-hexa-n-octylnitrilotriacetamide (HONTA) and N,N,N,'N,'N,"N"-hexa-n-dodecylnitrilotriacetamide (HDDNTA). The feed phase consisted of 3 M HNO3 while 0.5 M oxalic acid +0.5 M HNO3 was used as the strip phase. The SLM studies indicated 78.2% and 86.2% transport of plutonium(IV) after 4 h using 0.08 M concentrations of HONTA and HDDNTA, respectively, and the transport of Am(III) and U(VI) was <1% under identical feed acid conditions indicating a possible highly selective separation of Pu(IV) using HONTA as the carrier ligand from a mixture of Pu(IV), Am(III) and U(VI). The stability of the membrane was reasonably good up to 9 days. The activation energy of the transport process was determined using temperature variation studies with HONTA and HDDNTA indicating the transport process being kinetically as well as diffusion controlled. This work is highly relevant for the separation of Pu from radioactive feeds containing other actinide elements such as U and Am. [ABSTRACT FROM AUTHOR]

This paper is an attempt to find out thorium oxide dissolution mechanism in HNO3-HF mixture. In a previous paper, several parameters effects on thorium oxide dissolution have been described, with specific focus on hydrofluoric acid effect, which can lead to an increase of the dissolution rate if present in small amount, but precipitates as ThF4 at higher content. Based on this previous study, experimental data were fitted using several dissolution models in order to find out the best one. Finally, a revisited model based on literature and considering the ThF4 formation was proposed. It describes the main steps of dissolution and is able to fit the experimental data for a wide range of solution compositions. This point is crucial since it allows considering an extrapolation of the established model to not-yet-studied conditions. [ABSTRACT FROM AUTHOR]

Summary: Fluoride‐salt‐cooled solid‐fuel fast reactor (LSFR) with thorium‐based fuel could complete a self‐sustaining core that fulfills long‐term energy demands. This paper further investigated the LSFR core sustainability of breeding thorium and the spent fuel characteristics for closed fuel cycle. Two fuel recycle strategies were proposed in this paper, including U recycling and U/Pu/MA recycling, to evaluate the physical effects caused by these recycling some highly radiotoxic and heat producing minor actinides. Based on the two fuel management strategies, the sustainability of breeding thorium and the spent fuel characteristics from the 0th cycle core to the 8th cycle core were assessed, including radioactivity, radiotoxicity, and decay heat. It was found that both recycle strategies accomplished good breeding performance and reduced the 233U fuel inventory, implying that recycling nuclides could partially replace 233U. The U/Pu/MA recycling scheme possessed slightly better advantages in lower 233U loading and breeding performance, but this scheme accumulated more transuranium elements with cycle burnup because the LSFR core could not transmute MA for its relatively soft fast energy spectrum. In spite of this, the level of radioactivity, radiotoxicity, and decay heat for the discharge fuel in the 8th cycle core was either lower than or comparable to that of traditional PWR. It is worthwhile mentioning that between 1000 and 100 000 years the radioactivity, radiotoxicity, and decay heat production tend to grow again, which might require sophisticated storage design for LSFR core with thorium‐based fuel in the future. [ABSTRACT FROM AUTHOR]

Covalency in actinides has emerged as a resounding research topic on account of the technological importance in separating minor actinides from lanthanides for spent nuclear fuel processing, and utilization of their distinct bonding properties has been realized as a route towards overcoming this challenge. Because of the limited radial extent of the 4f orbitals, there is almost no 4f electron participation in bonding in lanthanides; this is not the case for the actinides, which have extended 5f orbitals that are capable of overlapping with ligand orbitals, although not to the degree of overlap as in the d orbitals of transition metals. In this concept paper, a general description of covalency in actinide compounds is provided. After introducing two main approaches to enhance covalency, either by exploiting increased orbital overlap or decreasing energy differences between the orbitals causing orbital energy degeneracy, the current state of the field is illustrated by using several examples from the recent literature. This paper is concluded by proposing the use of actinide chalcogenides as a convenient auxiliary tool to study covalency in actinide compounds. [ABSTRACT FROM AUTHOR]

N,N-Dialkyl diglycolamic acid (HDRDGA) derivatives with alkyl groups varying from n-hexyl to n-dodecyl were synthesized, and the promising ligands such as N,N-dioctyl diglycolamic acid (HDODGA) and N,N-didecyl diglycolamic acid (HD2DGA) were investigated for the mutual separation of trivalent lanthanides and actinides from dilute nitric acid solution. Since diglycolamic acid is strongly polar, it was dissolved in a traditional diluent, n-dodecane, with the help of an isodecyl alcohol (IDA) phase modifier. Nevertheless, the hexyl and didodecyl derivatives were sparingly soluble even in the presence of 30% (v/v) IDA in n-dodecane, and therefore, the extraction behavior of the lanthanide and actinide representatives, Eu(III) and Am(III), respectively, was studied only in a solution of HDODGA or HD2DGA present in 30% (v/v) IDA/n-dodecane. The cation-exchange mechanism of extraction and the stoichiometry of trivalent metal to HDRDGA were elucidated from the slope analysis of the extraction data. Since the stoichiometry of the metal to ligand complex in the organic phase was unusually varied from 1 : 3 to 1 : 6 depending upon the Nd(III) loading into the organic phase, the reverse micellar aggregation behavior and the coordination chemistry of Nd(III) in the organic phase were probed by dynamic light scattering and visible spectroscopy, respectively. The results revealed that three molecules of anionic DRDGA were coordinated to Nd(III) in the inner-sphere at lower metal concentrations, and also three more molecules of HDRDGA in the outer-sphere at higher metal concentrations. The good separation factor achieved with the use of these ligands showed their potential ability to separate lanthanides from actinides in nitric acid medium. [ABSTRACT FROM AUTHOR]

Hybrid donor extractants are a promising class of compounds for the separation of trivalent actinides and lanthanides. In this paper, we present a new ligand from the bipyridyl-dicarboxylic acid diamide family—N,N'-diethyl-N,N'-bis(2,4,5-trimethylphenyl)-[2,2'-bipyridine]-6,6'-dicarboxamide. The synthesis of N-ethyl-2,4,5-trimethylaniline from pseudocumene by selective acetylation is presented. The target ligand was obtained using this aminylene. Chemical synthesis of its complexes with Ln(NO3)3 and their spectroscopic analysis showed that the structure of the complexes is near to the corresponding structures of well-known di-methylated dianilides. A series of studies on the photophysical, complexing, and extraction properties of this ligand and its complexes were carried out. It was shown that the extraction system based on this ligand can selectively isolate americium from the solution of high-level waste imitator. [ABSTRACT FROM AUTHOR]

The observations of GW170817/AT2017gfo have provided us with evidence that binary neutron star mergers are sites of r -process nucleosynthesis. However, the observed signatures in the spectra of GW170817/AT2017gfo have not been fully decoded, especially in the near-infrared (NIR) wavelengths. In this paper, we investigate the kilonova spectra over the entire wavelength range with the aim of elemental identification. We systematically calculate the strength of boundâ€"bound transitions by constructing a hybrid line list that is accurate for important strong transitions and complete for weak transitions. We find that the elements on the left side of the periodic table, such as Ca, Sr, Y, Zr, Ba, La, and Ce, tend to produce prominent absorption lines in the spectra. This is because such elements have a small number of valence electrons and low-lying energy levels, resulting in strong transitions. By performing self-consistent radiative transfer simulations for the entire ejecta, we find that La iii and Ce iii appear in the NIR spectra, which can explain the absorption features at λ ∼ 12000â€"14000 Ă... in the spectra of GW170817/AT2017gfo. The mass fractions of La and Ce are estimated to be >2 Ă— 10âˆ'6 and ∼(1â€"100) Ă— 10âˆ'5, respectively. An actinide element Th can also be a source of absorption as the atomic structure is analogous to that of Ce. However, we show that Th iii features are less prominent in the spectra because of the denser energy levels of actinides compared to those of lanthanides. [ABSTRACT FROM AUTHOR]

In this paper, we employ the density-dependent relativistic mean-field theory to study how the triaxiality and pairing interaction affect the inner fission barriers of actinide nuclei. It was found that the triaxiality reduced the inner barriers and improved agreement with experimental values for many actinides. However, about 1–2 MeV discrepancy to the experimental values still remained for some of the considered nuclei. Such a discrepancy could be made further smaller by increasing the BCS pairing strength parameter. In this work, we demonstrated that adjusting the paring strength was effective in reproducing the experimental inner fission barriers as well as "pairing rotational energy" and binding energy in a consistent manner for nuclei where the effect of the triaxiality on the inner barriers was significant. [ABSTRACT FROM AUTHOR]

Although the multimessenger detection of the neutron star merger event GW170817 confirmed that mergers are promising sites producing the majority of nature’s heavy elements via the rapid neutron-capture process (r-process), a number of issues related to the production of translead nuclei—the actinides—remain to be answered. In this short review paper, we summarize the general requirements for actinide production in r-process and the impact of nuclear physics inputs. We also discuss recent efforts addressing the actinide production in neutron star mergers from different perspectives, including signatures that may be probed by future kilonova and γ -ray observations, the abundance scattering in metal-poor stars, and constraints put by the presence of short-lived radioactive actinides in the Solar system. [ABSTRACT FROM AUTHOR]

In this paper, we develop a nonadiabatic collective model for even–even nuclei with effective triaxial quadrupole and octupole deformations. The model describes three-dimensional quadrupole–octupole rotation coupled with axial quadrupole–octupole vibrations. The moment-of-inertia tensor depends on the angular part of the polar coordinates in the quadrupole–octupole space, the values of which are determined from the ground state of the nucleus. In this model framework, the collective states of the yrast-alternating-parity band in the lanthanides 1 5 4 Sm, 1 5 4 , 1 6 0 Gd, 1 5 6 Dy and the actinides 2 2 8 , 2 3 0 , 2 3 2 Th, 2 3 0 , 2 3 2 , 2 3 6 , 2 3 8 U, 2 3 8 Pu are studied. [ABSTRACT FROM AUTHOR]

This paper provides an introduction for non-experts to first-principles electronic structure methods that are widely used in condensed-matter physics. Particular emphasis is placed on giving the appropriate background information needed to better appreciate the use of these methods to study actinide and other materials. Specifically, the underlying theory is described in sufficient detail to enable an understanding of the relative strengths and weaknesses of the methods. In addition, the meaning of commonly used terminology is explained, including density functional theory (DFT), local density approximation (LDA), and generalized gradient approximation (GGA), as well as linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods. Methodologies that extend the basic theory to address specific limitations are also briefly discussed. Finally, a few illustrative applications are presented, including quantum molecular dynamics (QMD) simulations and studies of surfaces, impurities, and defects. The paper concludes by addressing the current controversy regarding magnetic calculations for actinide materials. [ABSTRACT FROM AUTHOR]

Due to the limited abundance of the actinide elements, computational methods, for now, remain an exclusive avenue to investigate the periodic trends across the actinide series. As every actinide element can exhibit a +3-oxidation state, we have explored model systems of gas-phase actinide trihalides, phosphates, and arsenates across the series to capture the periodic trends. By doing so, we were able to capture the periodic trends down the halogen series as well, and for the first time we are reporting a study on actinide astatides. Using scalar and spin–orbit relativistic Density Functional Theory (DFT) calculations, we have explored the variations in bond lengths, bond angles, and the charges on actinides (An). Despite the use of different sets of ligands, the trends remain similar. The properties of trivalent Pa, U, Np, and Pu are nearly identical; similar ionic radii could be the reason. The actinide elements show a tendency to exhibit a pre-Pu and a post-Cm behaviour, with Am acting as a switch. This could be due to the change in the behaviour from d–f-type to f-filling/d-type at around Pu–Cm in the actinides as already proposed in the previous literature. Bond lengths in the AnX3 increase down the halide series, and the atomic charges decrease on the actinide elements. [ABSTRACT FROM AUTHOR]

Monitoring of radionuclide concentration in natural samples is important for assessing environmental safety. The low concentration of long-lived radionuclides require concentration from large volumes of natural water samples. This paper presents a method for sequential separation and simultaneous determination of radioisotopes of U, Pu, Am and Tc in water samples. Actinides and technetium were pre-concentrated by coprecipitation with iron hydroxides from the aqueous sample. Separation of actinides and Tc was achieved by extraction chromatography. The developed method allows separation of actinide and technetium from 100 L water with chemical yields between 40 and 70%. [ABSTRACT FROM AUTHOR]

The long-lived minor actinides (MA); americium, neptunium, and curium are main contributors to the long-term radiotoxicity of used fuel. Thus, the transmutation of these MAs is considered as an alternative to direct burial. Until now, no unambiguous internationally recognized quantitative criterion for the effectiveness of MA transmutation has been developed, although this would be highly desirable. The absolute and relative decrease in the total mass of MA is completely inadequate, since they ignore the accumulation of higher radiotoxic MA from the transmuted nuclide. In this paper, we propose a new criterion for the efficiency of MA transmutation in nuclear reactors and demonstrate its efficiency when comparing two molten salt reactors; Single-fluid Double-zone Thorium-based Molten Salt Reactor (SD-TMSR) and Small Molten Salt Fast Reactor (SMSFR). In addition, the proposed criterion takes into account the mass of all useful MA, short-lived MA, and short-lived fission products (FPs). We present a new approach to loading MA in SD-TMSR and SMSFR. The total change in the mass of actinides and FPs during irradiation was calculated using SERPENT-2 Monte Carlo code. The results show that the transmutation efficiency of 241Am (a major candidate for transmutation) in SD-TMSR is much higher than in SMSFR. After 1500 days of irradiation, the transmutation efficiency reaches 82.6% for SD-TMSR, but for SMSFR it reaches 52.5%. [ABSTRACT FROM AUTHOR]

Nuclear Material Balance code version 4.0 (NMB4.0) has been developed through collaborative R&D between TokyoTech&JAEA. Conventional nuclear fuel cycle simulation codes mainly analyze actinides and are specialized for front-end mass balance analysis. However, quantitative back-end simulation has recently become necessary for considering R&D strategies and sustainable nuclear energy utilization. Therefore, NMB4.0 was developed to realize the integrated nuclear fuel cycle simulation from front- to back-end. There are three technical features in NMB4.0: 179 nuclides are tracked, more than any other code, throughout the nuclear fuel cycle; the Okamura explicit method is implemented, which contributes to reducing the numerical cost while maintaining the accuracy of depletion calculations on nuclides with a shorter half-life; and flexibility of back-end simulation is achieved. The main objective of this paper is to show the newly developed functions, made for integrated back-end simulation, and verify NMB4.0 through a benchmark study to show the computational performance. [ABSTRACT FROM AUTHOR]

In this paper, the transitions between symmetric and asymmetric modes are investigated for the fission of actinides within the scission point model. All effective energies in fission are investigated in detail, separately. This indicates that the interaction energy and the liquid-drop energy do not change much in the symmetric region, so they cannot play a major role in the transition of actinide fission modes. Additionally, the sum of shell correction of complementary fragments at zero excitation energy is plotted over the fission fragment mass numbers. Also, the mass distributions of actinides fission are calculated within the scission point model. There is a good agreement between the calculated mass distribution and the total shell correction distribution. This indicates that the minimum total shell correction energy at the excitation energy corresponds to the maximum mass distribution for actinides fission, especially for the fermium 258 fission. Therefore, the main reason for the formation of fission mode in the actinides fission is the total shell correction energy of the complementary fission fragments at the zero excitation energy. [ABSTRACT FROM AUTHOR]

The THermally Evaporated Spray for Engineered Uniform particulateS (THESEUS) production platform was developed to generate highly uniform mixed actinide oxide particles. The particulate synthesis platform builds on previous efforts and utilizes an aerosol-based technology to generate, calcine, characterize, and aggregate a monodisperse oxide phase particle product. In this study, particles comprised of uranium oxide, incorporated with varying compositions of thorium, were produced. Th/U test materials with 232Th concentrations between 1 ppm and 10%, ratioed to 238U, were successfully generated with in situ calcination at 600 °C and characterized by in situ aerodynamic particle size spectrometry and ex situ microanalytical methods. Populations of monodisperse particulates (geometric standard deviation – GSD < 1.15) with an average diameter near 1 μm were generatated and micro-Raman spectroscopy of individual particles identified U3O8 as the primary material phase for the range of Th/U samples analyzed. Single particle measurements and automated particle analyses by secondary ion mass spectrometry (SIMS) were performed. Uniform inter-particle elemental and isotopic homogeneity for uranium and thorium isotopes was characterized by SIMS, and a 232Th/238U relative sensitivity factor of 0.53 was determined. SIMS results demonstrated differences in the 232Th/238U profiling behavior for Th/U particulates with increased Th content (>1%). Despite the observed profiling behavior, single particle measurements of the 10% Th sample indicate inter-particle homogeneity. This work represents the first systematic study of Th/U microparticulate reference materials generated and intended for nuclear safeguards applications and serves as a demonstration of THESEUS to support a sustained capability for the production mixed-element particulate reference materials. [ABSTRACT FROM AUTHOR]

In this paper, a simple semi-empirical formula is proposed for angular momentum-dependent fission barriers of actinides (8 9 ≤ Z ≤ 1 0 3). This formula produces angular momentum-dependent fission barriers with the simple inputs of atomic number (Z), mass number (A) and angular momentum (ℓ). The fission barriers produced by the present formula are compared with that of experiments and other models. There is a good agreement between the present formula and experiments. The present formula could be used to evaluate the angular momentum-dependent fission barriers of actinides. [ABSTRACT FROM AUTHOR]

2019, which was proclaimed by the United Nations as the International Year of the Periodic Table, sees one hundred years since Alfred Werner, the first Swiss to receive a Nobel Prize in chemistry, passed away. The undoubted father of coordination chemistry, he is also well‐known for influencing many other fields of chemistry, including organic, inorganic, organometallic, bioinorganic, and stereochemistry. However, one of his more rare and unique contributions to chemistry, his 1905 version of the periodic system, to this day remains overlooked. The simple and elegant idea which he used to construct his periodic table has not been communicated to the English‐speaking world, because Alfred Werner published his only original paper on the periodic table in German. Werner's simple mathematical approach lead to overwhelming success with anticipating the future f‐block. He managed to predict almost perfectly the number of lanthanides, which was hotly debated at that time. Werner's genius vision was considerably ahead of its time. It was not until the 1940s and the discovery of actinide series when the idea of representing the elements as a 32‐column periodic table finally became justified. [ABSTRACT FROM AUTHOR]

Summary: Transmutation of minor actinides (MAs) is an effective solution to reduce the long‐term radiotoxicity of nuclear waste. Online refueling and no fuel rod fabrication in thorium‐based molten salt reactors (TMSR) are two remarkable advantages of MA transmutation. However, MA solubility limit of the fuel salt and the neutron spectrum in the core are two key parameters that have a strong impact on MA transmutation capability. In this paper, three types of carrier salt with different MA solubility limits and various salt volume fractions (SVFs) are introduced in a TMSR core to evaluate the MA transmutation characteristics. The results indicate that the Flibe salt with the best neutron economy can obtain the highest MA transmutation rate (TR), while the Flinak salt with the largest MA inventory can achieve the highest specific MA transmutation consumption (STC). STC and TR for the case with the Flibe salt and 5% SVF are about 200 kg/GWth.yr and 82%, respectively, which indicates that it can consume the annual MA yields from about 3.37 typical pressurized water reactors (PWRs). Meanwhile, the STC and TR for the case with the Flinak salt and 40% SVF are about 366 kg/GWth.yr and 75%, respectively, which indicates that it can consume the annual MA yields from about 50 typical PWRs. In addition, the total radiotoxicity of MAs after 50‐year operation in TMSR can be lowered by as high as about 50%. The significant production of Pu isotopes can be reused as nuclear fuel in fast reactors. In particular, Pu‐238, with the mass fraction of more than 60% in Pu isotopes, is a useful material for many nuclear applications. In conclusion, it is feasible to transmute MAs in TMSR and thus achieve the goals of reduction of MA's long‐term radioactive hazards. [ABSTRACT FROM AUTHOR]

This paper focuses on major phosphate-based ceramic materials relevant for the immobilisation of Pu, minor actinides, fission and activation products. Key points addressed include the recent progress regarding synthesis methods, the formation of solid solutions by structural incorporation of actinides or their non-radioactive surrogates and waste form fabrication by advanced sintering techniques. Particular attention is paid to the properties that govern the long-term stability of the waste forms under conditions relevant to geological disposal. The paper highlights the benefits gained from synergies of state-of-the-art experimental approaches and advanced atomistic modeling tools for addressing properties and stability of f-element-bearing phosphate materials. In conclusion, this article provides a perspective on the recent advancements in the understanding of phosphate based ceramics and their properties with respect to their application as nuclear waste forms. [ABSTRACT FROM AUTHOR]

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Determining the amount, chemical form, physical shape, and multiplication of the fissile material in an unknown assembly is a challenging problem that is of great importance in a number of national security contexts. The discrimination of plutonium in metal versus oxide form in special nuclear materials is crucial and yet remains a challenge for current methods. It has previously been shown that the $\alpha $ -ratio for un-moderated plutonium oxides can be rapidly determined by comparing the fast neutron spectrum measured with a liquid scintillator with pure fission and ( $\alpha $ ,n) neutron spectra measured with the same liquid scintillator. In this paper we show that the chemical form can be obtained for moderated nuclear materials using fast neutron detection systems. We describe a new method to distinguish moderated plutonium metal from oxide using liquid scintillators, neutron spectroscopy and neutron correlations. [ABSTRACT FROM PUBLISHER]

There has been discussion within industry for a number of years regarding standards for shipping uranium concentrates from producers (mine/mill operations) to uranium conversion facilities. Although the standard way of transporting ore concentrates is in drums (nominally 200–210 L size), the specific packing and securing methods for sea transport vary considerably. A major initiative was recently launched within the World Nuclear Transport Institute with the setting up of a task force to examine the aspects of the transport of uranium concentrates that include a marine component. These aspects were grouped into three areas of interest as follows: the drums used for packaging, the sea International Standards Organisation (ISO) containers themselves and the restraint of the drums in the ISO containers. The objective of the task force has been to explore the concept of standard good industry practices for uranium concentrates packaging and shipping in ISO containers. Based on the findings of the Task Force, the present paper shares the lessons learned. It discusses good industry practices, which can be used as a basis to establish common methodology for the transport uranium concentrates. It considers the value of adopting a common approach and in this regard, the present paper highlights the current variations in drum design and the range of difficulties this can pose. In addition, the present paper describes drum restraint systems within the container, explaining the way in which securing methods have had to change due to restrictions on the use of wood dunnage. The importance of using containers satisfying ISO 1496 standard and the Convention for Safe Containers is discussed. Based on industry experience, important operational procedures to ensure well packaged secure loads are also discussed. [ABSTRACT FROM AUTHOR]

In this paper, the coprecipitation methods of selected radionuclides in connection with solid-state scintillation counting were explored. The calcium phosphate co-precipitation method exhibited best results from all investigated methods reaching almost absolute detection efficiencies for selected actinides and more than 60% for Sr/Y-90. The linear response of the measurement was in the range of 0.4 to 411.5 Bq for alpha/beta separation mode, respective 0.4 to 2000 Bq nuclear counting (high activity mode). Computed and optimized MDA values exhibited better results in comparison with previous works. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present results of fast neutron behavior analysis within the chloride salts environment using simulations based on Monte Carlo method (MCNP 6.2). Three non-fueled salts (NaCl, KCl, MgCl2) and two salts containing fissile material (UCl3, ThCl4) were studied. Results of this theoretical study will be used for design of an experimental assembly, which will serve to achieve goals of the international research project ADAR (Accelerator Driven Advanced Reactor). One of the project objectives is to investigate chloride salts as potential coolant and a dissolved fuel carrier of advanced nuclear reactor cooled by molten salts and driven by an accelerator. [ABSTRACT FROM AUTHOR]

Thermal reactors have been considered as interim solution for transmutation of minor actinides recycled from spent nuclear fuel. Various studies have been performed in recent decades to realize this possibility. This paper presents the neutronic feasibility study on transmutation of minor actinides as burnable poison in the VVER-1000 LEU (low enriched uranium) fuel assembly. The VVER-1000 LEU fuel assembly was modeled using the SRAC code system, and the SRAC calculation model was verified against the MCNP6 calculations and the available published benchmark data. Two models of minor actinide loading in the LEU fuel assembly have been investigated: homogeneous mixing in the UGD (Uranium-Gadolinium) pins and coating a thin layer to the UGD pins. The consequent negative reactivity insertion by minor actinides was compensated by reducing the gadolinium content and boron concentration. The reactivity of the LEU assembly versus burnup and the transmutation of minor actinide nuclides were examined in comparison with the reference case. The results demonstrate that transmutation of minor actinides as burnable poison in the VVER-1000 reactor is feasible as minor actinides could partially replace the functions of gadolinium and boric acid for excess reactivity control. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

Capillary electrophoresis (CE) was hyphenated to Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) to perform isotope ratio measurements for actinides (U, Pu, Am, and Cm) and lanthanide fission products (Nd, Sm, Eu, and Gd) in a spent nuclear fuel sample. A capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS) method was developed using either α-HMBA or α-HIBA as electrolytes, demonstrating the ability of alpha-hydroxycarboxylic acids to perform the concurrent separation of actinides and lanthanides in a simulated sample and a spent Mixed Oxide (MOX) fuel sample. Isotope ratios for U, Pu, Am, and Cm as well as Nd, Sm, Eu, and Gd were then determined by CE-MC-ICP-MS in two injections of approximately 30 nL of the spent MOX fuel sample. The relative standard deviations were in the per-mil range, similar to the ones obtained by two-step offline chromatography followed by Thermal Ionisation Mass Spectrometry (TIMS). The use of CE as the separation method lowered the sample quantity (in the pg range for Pu, Am, Cm and lanthanides, in the ng range for U) and waste volume production (a few hundred μL) as compared to commonly used chromatography methods. CE-MC-ICP-MS therefore makes it possible to measure multiple isotope ratios at a per-mil level of uncertainty without the need for prior offline chemical separation. [ABSTRACT FROM AUTHOR]

This paper results from my introductory talk at the symposium “Frontiers of Organo-f-Element Chemistry.” Although my active research in organoactinide and -lanthanide chemistry ended early in my career, it led to an interest in actinide coordination chemistry that continues to this day; I am a member of the actinide research group of the Chemical Sciences Division of the Lawrence Berkeley National Laboratory. My remarks will be somewhat personal and are intended to provide a perspective on the history of this field, but I hope to connect it to what has become a new and very active area of research; this class of compounds is now associated with what are essentially quantum confined multiconfigurational molecules. [ABSTRACT FROM AUTHOR]

In the study presented here, the initial (that is, before the start of the process of natural hydrochemical influence) mineral formula of metamict polycrase in the composition of granite pegmatites of the Baltic Shield, applying an uranium natural half-leaching period, was calculated. To investigate the characteristics of immobilization of actinides in the studied polycrase, the absolute and relative uranium contents are compared with the corresponding uranium contents in the original betafite of the same deposit and age. It has been shown that over its geological history, betafite has lost up to 80% of its original uranium content. The proportion of uranium preserved in polycrase is twice as high. It is concluded that the difference in the relative content of uranium (27.3 wt% in polycrase and 31.6 wt% in betafite) cannot be the only reason for the complete oxidation of uranium in betafite, given that in polycrase 30% of uranium is preserved in the tetravalent state. It is more likely that the oxidation of uranium in betafite was primarily a result of the low ionicity of the chemical bonds compared to that in polycrase. This allows us to consider minerals of the euxenite group to be quite promising as matrix materials for the immobilization of actinides. At the same time, an opinion was expressed on the advisability of further comparative studies of Nb–Ta–Ti-oxides of the mineral groups AB2O6 and A2B2O7 for their use at the final stage of the nuclear fuel cycle. [ABSTRACT FROM AUTHOR]

The mutual separation of Am and Cm is conducted using an alkyl-diamide amine (ADAAM(EH)) extractant. ADAAM(EH) exhibits an extremely high separation factor (SF) with respect to Am and Cm separation (SF = 5.9) in an HNO3-n-dodecane system. The batch-wise multistage extractions are performed using a system containing 0.2 M ADAAM(EH) and 1.5 M HNO3, with their distribution ratios (D) of the system for Am and Cm equal to 2.55 and 0.434, respectively. In this multistage extraction, 3 stages of feed, 9 stages involving scrubbing, and 11 stages involving the use of an organic solvent give 96.5% and 1.06% yields of Am and Cm, respectively. After the mutual separation, the aqueous and the organic phases including actinides increase four times in volume compared to the feed solution. Additional extraction steps are to reduce the volume of the solutions including actinides. We use tetraethyl diglycolamide (TEDGA)/water for Am concentration, tetraoctyl diglycolamide/n-dodecane for the intermediate extraction, and TEDGA/water for stripping in the Cm concentration step. Taking the additional steps, Am and Cm can be recovered in just two or three stages in the aqueous phases. [ABSTRACT FROM AUTHOR]