Pu Atoms Research Articles

Exploring constituent redistribution in irradiated U-19Pu-14Zr fuel via electron probe microanalysis

The phenomena of constituent redistribution, wherein a previously homogeneous metallic fuel forms discrete, radially concentric compositional zones upon irradiation was investigated by examining an irradiated U-19Pu-14Zr fuel (where numbers represent wt. %) with a burnup of 11.5 at.% with electron probe microanalysis (EPMA) and quadruple inductively coupled plasma mass spectroscopy (Q-ICP-MS).EPMA-generated U, Pu, and Zr compositional data obtained from a diameter traverse of the sample was converted to mass and was used to: 1) compare the overall fuel element analysis results between the two methods, 2) determine the number of compositionally distinct zones forming as a result of constituent redistribution; and 3) quantify the post-irradiation loss or gain of U, Pu, and Zr atoms in each distinct compositional zone.Weight percent concentrations of U, Pu, and Zr for the overall cross section compare favorably between the two analytical methods, suggesting that the spatially resolved EPMA analysis complements bulk chemical analysis.Among the four identified compositional zones, post-irradiation quantification of U, Pu, and Zr elemental atom content changes shows that the quantity of U atoms lost from the innermost zone is slightly less than the quantity of U atoms gained by the middle two zones, and the quantity of Zr atoms lost from the high-U third zone is slightly less than is gained by the two innermost zones. Pu is lost from all four zones, although the innermost zone and the high-U third zone lose a significantly higher percentage (> 22 %) of their initial Pu atoms than the other two zones. For all three elements, EPMA cannot distinguish between atoms lost due to transport to a different zone from atoms lost due to nuclear processes; however, the insight gained from using this process can be used to experiment with new modeling techniques to predict constituent redistribution in U-Pu-Zr fuels.

Structural, magnetic, mechanical, thermodynamic, and electronic properties of PuAlO3: A first-principles study

Based on the Coulomb hybrid density functional with spin–orbit coupling (SOC) effect and generalized gradient approximation (GGA) + U method, the structural, magnetic, and electronic properties of PuAlO3 (Pnma and Imma) have been studied. The value of magnetic moment (μs) with the GGA + U method is maximum, the GGA + U + SOC method is minimum, and the GGA method is centered. The phonon curve of the two phases with ferromagnetic (FM) is almost identical to that of the antiferromagnetic (AFM) state. Pu atoms primarily contribute to the low-frequency phonon branches. In contrast, lighter O atoms are mainly responsible for the high-frequency phonon modes, and Al atoms are predominantly distributed in the middle part of the compound. For the mechanical properties, the volume modulus B of the V-R-H scheme agrees with the Birch–Murnaghan equation of state fitting results. Moreover, the bulk modulus is anisotropic, and the remaining parameters are isotropic. According to the electronic calculation, FM has a wider bandgap than AFM. In part of the state density diagram, it can be observed that the main contributors are Pu and O atoms. Bader charge calculation revealed that the charge of Pu and Al atoms transfers to O atoms.

Adsorption properties of black phosphorene for actinides U, Th, and Pu: A first‐principles study

AbstractDensity functional theory (DFT) calculations were carried out in this work to systematically investigate the adsorption properties of monolayer black phosphorene (BP) for actinide uranium (U), thorium (Th), and plutonium (Pu) atoms. More specifically, the linear response method was used and the HubbardUvalues of 2.97 and 2.61 eV were fitted describing the strong lattice point Coulomb interactions of the U and Pu 5forbitals, respectively. From the DFT + Ucalculations, it was demonstrated that the U, Th, and Pu atoms can be favorably adsorbed on the hollow sites of the BP surface, with an adsorption energy of 3.48, 4.93, and 0.98 eV, respectively. By analyzing the electronic structure, charge transfer, and highest occupied molecular orbital, it was revealed that the U and Th adatoms can induce the generation of impurity states within the band gap of BP and stabilize their adsorption by strongp‐dcoupling with the phosphorus atoms. In addition, from the electron–phonon coupling calculations, it was revealed that the temperature for the stable adsorption of the U and Th adatoms can reach as high as 500 and 673 K. By using the adsorption rate equation, the critical temperature for the adsorption–desorption transition of U and Pu adatoms was estimated to be 632 and 185 K, respectively, while the Th adatom did not tend to desorb. Our results clearly indicate that BP is an ideal adsorption and separation material for actinides with promising potential applications, such as uranium extraction from seawater.

Effects of fission product doping on the structure, electronic structure, mechanical and thermodynamic properties of uranium monocarbide: A first-principles study

A first-principle approach within the framework of density functional theory was employed to study the effect of vacancy defects and fission products (FPs) doping on the mechanical, electronic, and thermodynamic properties of uranium monocarbide (UC). Firstly, the calculated vacancy formation energies confirm that the C vacancy is more stable than the U vacancy. The solution energies indicate that FPs prefer to occupying in U site rather than in C site. Zr, Mo, Th, and Pu atoms tend to directly replace U atom and dissolve into the UC lattice. Besides, the results of the mechanical properties show that U vacancy reduces the compressive and deformation resistance of UC while C vacancy has little effect. The doping of all FPs except He has a repairing effect on the mechanical properties of U1-xC. In addition, significant modifications are observed in the phonon dispersion curves and partial phonon density of states (PhDOS) of UC1-x, ZrxU1-xC, MoxU1-xC, and RhxU1-xC, including narrow frequency gaps and overlapping phonon modes, which increase the phonon scattering and lead to deterioration of thermal expansion coefficient (αV) and heat capacity (Cp) of UC predicted by the quasi harmonic approximation (QHA) method.

Oxidation of Pu alloys stabilized in δ–phase: Study of Ga alloying element behavior by using EXAFS analysis and Reverse Monte Carlo simulation

Studies were performed to improve the knowledge about Ga behavior during oxidation of Pu alloys stabilized in δ–phase. The coupling of EXAFS experiments with Reverse Monte Carlo (RMC) simulation of 3D material structure has achieved the characterization of the atomic local environment around Pu and Ga atoms in the outer PuO2 layer formed on a δ−PuGa 1 at% alloy. No formation of Ga aggregates or Ga oxides was detected. The RMC analysis of experimental data has revealed the presence of Ga atoms within the lattice of the oxide scale in Pu substitutional sites or octahedral sites. Nevertheless, this incorporation leads to a large local disorder with a displacement of Ga atoms from their initial high symmetry crystallographic site. Finally, the results obtained bring new insights explaining the destabilization of the δ−phase by the diffusion of Ga atoms likely into Pu vacancies in PuO2 lattice during oxidation.

Insight into the interfacial interactions of CO2 with PuH2 (100), (110), and (111) surfaces from first-principles calculations

The interface interaction behavior and mechanism between CO2 molecule and PuH2 (100), (110), and (111) surfaces were investigated by GGA + U method. It is found that both strong chemical adsorption and weak physical adsorption exist between CO2 and PuH2 surfaces. In all the adsorption configurations considered in this study, the adsorption energy results suggest that CO2 may have relatively strong reactivity with (110) surface. In the strongest adsorption, the C–O bonds can be extended from about 1.176 Å in gas phase to about 1.287 Å, and the bond angle bends from 180° to 120.78°. The CO2 adsorption configurations on the surfaces reveals that the adsorbed CO2 is captured by surface Pu atoms, and new Pu–O and Pu–C bonds are generated on the hydride surface. The surface work function could increase from about 2.007 eV of clean surface to about 3.239 eV of CO2/slab system. The vibration frequencies and electronic properties indicate that the reduction of vibrational frequencies and the prolongation of C–O bonds of CO2 are attributed to the charge transfer between the CO2 and surface atoms during adsorption. The research can offer useful details for the adsorption morphology and interfacial reaction behavior of CO2 on hydride surface.

Atomistic simulation of helium diffusion and clustering in plutonium dioxide.

This study uses molecular dynamics and barrier searching methods to investigate the diffusion and clustering of helium in plutonium dioxide. Such fundamental understanding of helium behaviour is required because radiogenic helium generated from the alpha decay of Pu nuclei can accumulate over time and storage of spent nuclear fuel needs to be safe and secure. The results show that in perfect PuO2, interstitial He is not mobile over nanosecond time scales at temperatures below 1500 K with the lowest diffusion barrier being 2.4 eV. Above this temperature O vacancies can form and diffusion increases. The He diffusion barrier drops to 0.6 eV when oxygen vacancies are present. High temperature simulations show that the key He diffusion mechanism is oxygen vacancy assisted inter-site hopping rather than the direct path between adjacent interstitial sites. Unlike oxygen vacancies, plutonium vacancies act as helium traps. However, isolated substitutional He at Pu sites can be easily ejected through displacement by neighbouring interstitial Pu atoms. High temperature MD simulations show that helium can diffuse into clusters with the majority of helium clusters which form over nanosecond time scales having a He : vacancy ratio below 1 : 1. Further static calculations show that a ∼3.5 : 1 He : vacancy ratio is the largest possible for an energetically stable helium cluster. Schottky defects act as seed points for He cluster growth and a high local concentrations of He can create such defects which then pin the growing He cluster.

The evolution of radiation-induced point defects near symmetrical tilt Σ5 (3 1 0) 〈0 0 1〉 grain boundary in Ga stabilised δ-Pu: A molecular dynamics study

Molecular dynamics (MD) simulations were performed to investigate the evolution of radiation-induced point defects affected by the symmetrical tilt Σ5 (310) 〈001〉 grain boundary (GB) in Ga stabilised δ-Pu. From the perspective of formation energy, the formation energy of vacancies had no prominent change in the whole region, but it was lower than the formation energy of interstitial atoms. The formation energy of interstitial atoms near GB was lower than that in the bulk. On the other hand, the average formation energy of interstitial Pu atoms was greater than that of interstitial Ga atoms. Furthermore, by comparing the evolution of radiation-induced point defects when primary knock-on atom (PKA) was located at −25 Å and 25 Å far from the GB, respectively, and analyzing the tendency of the number of remaining defects with the distance between PKA and GB changing, it could be found that interstitial atoms were more easily trapped in Σ5 (310) 〈001〉 GB than vacancies for Pu-Ga alloy. Simultaneously, the influence of temperature on the number of point defects near GB was taken into consideration, and the results displayed that the number of residual point defects in Pu-Ga alloy with Σ5 (310) 〈001〉 GB showed a decreasing trend with temperature increasing because temperature had an effect on the diffusion of point defects. Remaining interstitial atoms rather than remaining vacancies, moreover, are more severely affected by temperature, for interstitial atoms were more easily absorbed by GB.

Features of actinide contraction in AnХ crystals (X = S, Se or Te)

Using Voronoi–Dirichlet polyhedra, the features of actinide contraction in chalcogenides AnX, where An is Th, U, Np, Pu, Am, or Cm, and X is S, Se, or Te, were revealed and discussed. The characteristics of AnX and isostructural chalcogenides LnX, where Ln is lanthanide, were compared. It was found that, in contrast to LnX, which exhibit the effect of lanthanide contraction, in AnX crystals with increasing atomic number of An some characteristics change nonlinearly: in many cases the volume of Voronoi–Dirichlet polyhedra of An atoms as well as the length of An–X bonds and An–An contacts increase instead of decreasing. It was shown that the detected anomalies can be considered a consequence of the bonding 5f interactions, which are characteristic of U, Np, and Pu atoms, but are absent in the case of Th and transplutonium actinides. Using AnX and LnX as examples, a crystal-chemical method for evaluating the covalence of An–X and Ln–X bonds has been tested.

First-Principle Study of Co-Adsorption Behavior of H2O and O2 on δ-Pu (100) Surface

The surface corrosion of plutonium in air is mainly the result of the interaction with O2 and H2O in air. In this paper, the co-adsorption behavior of O2 and H2O on a δ-Pu (100) surface is studied by the first-principle method. Two different cases of preferential adsorption of H2O and O2 are considered, respectively. Bader charge analysis and adsorption energy analysis are carried out on all stable adsorption configurations, and the most stable adsorption configurations are found under the two conditions. The results of differential charge density analysis, the density of states analysis and Crystal Orbital Hamilton Populations (COHP) analysis show that the two molecules can promote each other’s adsorption behavior, which leads to the strength and stability of co-adsorption being far greater than that of single adsorption. In the co-adsorption configuration, O atoms preferentially interact with Pu atoms in the surface layer, and the essence is that the 2s and 2p orbitals of O overlap and hybridize with the 6p and 6d orbitals of Pu. H atoms mainly form O–H bonds with O atoms and hardly interact with Pu atoms on the surface layer.

Unraveling 5f correlated electronic states in paramagnetic PuSn3

Plutonium-based compounds establish an ideal platform for exploring the interplay between long-standing itinerant-localized 5f states and strongly correlated electronic states. In this paper, we exhaustively investigate the 5f correlated electronic states of PuSn3 dependence on temperature by means of a combination of the density functional theory and the embedded dynamical mean-field theory. It is found that the spectral weight of narrow 5f band grows significantly and remarkable quasiparticle multiplets appear around the Fermi level at low temperature. A striking c–f hybridization and prominent valence state fluctuations indicate the advent of coherence and itinerancy of 5f states. It is predicted that a 5f localized to itinerant crossover is induced by temperature accompanied by the change in Fermi surface topology. Therefore itinerant 5f states are inclined to take in active chemical bonding, suppressing the formation of local magnetic moment of Pu atoms, which partly elucidates the intrinsic feature of paramagnetic PuSn3. Furthermore, the 5f electronic correlations are orbital selective, which manifested themselves in differentiated band renormalizations and electron effective masses. Consequently, the convincing results remain crucial to our understanding of plutonium-based compounds and promote ongoing research.

Stabilization of Plutonium(V) Within a Crown Ether Inclusion Complex

Crystalline coordination complexes of actinides, especially in atypical oxidation states, are not only fundamentally important for expanding the notably limited knowledge on the bonding nature of a...

Unveiling the energetic and structural properties of Pu doped zircon through electrochemical equilibrium diagram from DFT+U calculations

Zircon (ZrSiO4) mineral is a sustainable and promising material to store of radioactive waste that has received extensive attention by material, geochemical and environmental scientists. Although the incorporation of actinide elements in zircon lattices has been experimentally studied, bare fundamental work are carried out to systemically assess the structural and chemical stabilities of Pu doped zircon. The primary aim to unveil the Pu immobilization mechanism and assess the stability of PuxZr1−xSiO4 is carried out by calculating the formation energies, electron and hole affinities, and electronic levels of Pu doped zircon based on density functional theory. Our results reveal under μ = μO−poor condition PuSi4+, PuZr1+ and PuZr0 are respectively energetically favorable to form with increasing the electronic chemical potential. Besides, PuZr4+ is energetically favorable in an n-type environment under all these three conditions (i.e., μ = μO−poor, μ = μPu/Zr, μ = μPu/Si). In addition, Pu doping will induce local structural distortion. Intriguingly however, self-repairing the symmetry of [ZrO8] polyhedra is first observed via the structural distortion in PuZr4+ configuration, which in turn could enhance the structural stability of PuxZr1−xSiO4. Ab initio molecular dynamic simulations demonstrate the configurations with negative formation energies are thermal stable at 500 K. The charge density difference and charge transfer are investigated to describe the chemical bonding nature. It is demonstrated Pu(5f)-O(2p) hybridization is more profound for interstitial Pu. Moreover, the bonding character of surrounding Zr atoms along [010] direction is almost identical to the pristine one, while it is distinctly changed towards [100] and [001] directions, showing remarkable anisotropy of PuxZr1−xSiO4. Oppositely, the ionicity in Pu–O bond is mainly featured when Zr or Si sites are substituted by Pu atoms which becomes stronger with increasing the hole doping process.

Studies on magnetic and electronic properties of [formula omitted]-Pu[formula omitted] ([formula omitted] = Al, Ga, In, and Tl) compounds

The magnetic properties of δ-PuX3 (X = Al, Ga, In, and Tl) are investigated using first-principles calculations. Non-zero magnetism is found in Pu atoms, resulting from the sum of the spin magnetic moment and orbital magnetic moment which is opposite to the former. The origin of the orbital moment is revealed by the occupation of f orbitals with different magnetic quantum numbers, which also accounts for the larger magnetization in PuAl3 compared to those in other PuX3 compounds. Moreover, the stable magnetic orderings are explored, showing that the in-plane antiferromagnetic arrangement with the axial ferromagnetic arrangement is the most favorable magnetic configuration for all the four compounds. Besides, the decomposed electronic band structures with p, d, and f projections as well as the phonon dispersions for the PuX3 compounds are also present.

Ab initio predictions for the reaction mechanism and orbital topological properties of the formation of Neptunimine, Plutonimine, and its side products.

Exploring the different mechanisms involved in the application of actinide is necessary to obtain a more comprehensive understanding of actinide science. In this study, the mechanisms of gas-phase Np and Pu atoms dissociating NH3 molecules forming Neptunimine and Plutonimine complexes were systematically investigated using different approaches of density functional theory. A new dehydrogenation channel was discovered. The results reveal that the intermediates HAn-NH2 are the lowest energy in the overall reaction, and the direct planar evolution dehydrogenations are the lowest energy reaction path. Besides, the mechanism of the initial complexation process is discussed on the electron localization function, atoms-in-molecules, atomic dipole moment corrected Hirshfeld atomic charges, and electron density difference analysis. The results indicate that An-N in complex I exhibits a very weak covalent interaction, and it comes down to pulling the original dipole moment of the NH3 molecule and stretched between An atom and three H atoms. Graphical abstract.

Electron elastic collisions with Pu, Am and Lr actinide atoms

SynopsisThe robust Regge-pole methodology which embeds the crucial electron correlations and the vital core-polarization interaction is used to explore negative-ion formation in the actinide atoms Pu, Am and Lr through the electron elastic total cross sections (TCSs) calculation. The TCSs are found to be characterized by ground, metastable and excited anionic formation, whence we extract the anionic binding energies and compare them with existing electron affinities. The TCSs exhibit both atomic and molecular behavior in addition to polarization-induced metastable TCSs.

Crystal Structure of An(VI) Complexes with Succinate Anions, [PuO2(C4H4O4)(H2O)] and Cs2[(AnO2)2(C4H4O4)3]·H2O (An = U, Np, Pu)

Actinide(VI) complexes with succinate anions [PuO2(succ)(H2O)] and Cs2[(AnO2)2(succ)3]·H2O (An = U, Np, Pu), where succ = [C4H4O4]2 −, were synthesized and studied by single crystal X-ray diffraction. The compound [PuO2(succ)(H2O)] is isostructural with [UO2(succ)(H2O)] [1] and forms a three-dimensional electrically neutral framework in the crystal. The equatorial plane of the Pu(VI) pentagonal bipyramid is constituted by the O atoms of four [C4H4O4]2− anions and one water molecule. The [C4H4O4]2− anions are bridging; each anion is bound in the monodentate fashion with four Pu atoms. The structure of the complexes Cs2[(AnO2)2(succ)3]·H2O is based on an anionic framework. The equatorial plane of the An(VI) hexagonal bipyramid is constituted by O atoms of three [C4H4O4]2− anions, with each anion acting as a chelating and bridging ligand binding two An(VI) atoms. The electronic absorption spectra of [PuO2(succ)(H2O)] and Cs2[(PuO2)2(succ)3]·H2O were measured.

Probing Magnetism in the Vortex Phase of PuCoGa_{5} by X-Ray Magnetic Circular Dichroism.

We measure x-ray magnetic circular dichroism (XMCD) spectra at the Pu M_{4,5} absorption edges from a newly prepared high-quality single crystal of the heavy-fermion superconductor ^{242}PuCoGa_{5}, exhibiting a critical temperature T_{c}=18.7 K. The experiment probes the vortex phase below T_{c} and shows that an external magnetic field induces a Pu 5f magnetic moment at 2K equal to the temperature-independent moment measured in the normal phase up to 300K by a superconducting quantum interference device. This observation is in agreement with theoretical models claiming that the Pu atoms in PuCoGa_{5} have a nonmagnetic singlet ground state resulting from the hybridization of the conduction electrons with the intermediate-valence 5f electronic shell. Unexpectedly, XMCD spectra show that the orbital component of the 5f magnetic moment increases significantly between 30 and 2K; the antiparallel spin component increases as well, leaving the total moment practically constant. We suggest that this indicates a low-temperature breakdown of the complete Kondo-like screening of the local 5f moment.

Influence of Ga on H Reactivity with Ga-Stabilized δ-Pu Alloys

The influence of Ga on the adsorption and solubility of H on Ga-stabilized δ-Pu alloys is investigated using density functional theory and experimentally via a Sieverts’ apparatus. All-electron DFT calculations, with spin–orbit coupling and full relaxations of the surface, are implemented to calculate H adsorption on δ-Pu–Ga alloy (111) surfaces. Chemisorption energies indicate that H prefers a 3-fold hollow site that binds strongly to a Pu-rich environment regardless of Ga concentration of the surface. Sites that include a Ga–H bond yield an increase in chemisorption energies as opposed to chemisorption energies when the H is only bonded to Pu atoms. Also, solution energies for interstitial sites are less exothermic than surface adsorption energies. Experimentally, H-vacancy binding is more exothermic than interstitial binding, and since vacancy binding is the analogue of surface binding, the DFT results are in agreement. Both DFT and experimental results show that with increasing Ga content to 7 at. % Ga there is an increase in H solution energies, thus reducing H solubility. The maximal reduction of H solubility is between 4 and 5 at. % Ga stabilized δ-Pu. The bonding nature of H on the Pu–Ga surface, via analysis of the partial density of states, shows weak hybridizations between the Pu 6d and H 1s states, with a slight decrease of the Pu 5f states near the Fermi level. Overall, Ga will affect the surface adsorption and solubility of H in δ-Pu–Ga alloys.

Laser ablation absorption spectroscopy for isotopic analysis of plutonium: Spectroscopic properties and analytical performance

Spectroscopic properties of atomic species of plutonium were investigated by combining laser ablation and resonance absorption techniques for the analysis of a plutonium oxide sample. For 17 transitions of Pu atoms and ions, the absorbance, isotope shift, and hyperfine splitting were determined via Voigt profile fitting of the recorded absorption spectra. Three transitions were selected as candidates for analytical use. Using these transitions, we investigated the analytical performance that was attainable and determined a correlation coefficient R2 between the absorbance and plutonium concentration of 0.9999, a limit of detection of 30–130ppm, and a relative standard deviation of approximately 6% for an abundance of 240Pu of 2.4%. These results demonstrate that laser ablation absorption spectroscopy is applicable to the remote isotopic analysis of highly radioactive nuclear fuels and waste materials containing multiple actinide elements.