High-pressure studies have been performed on heavy rare earth metals Terbium (Tb) to 155 GPa and Holmium (Ho) to 134 GPa in a diamond anvil cell at room temperature. The following crystal structure sequence was observed in both metals hcp ⟶ Sm-type ⟶ dhcp ⟶ distorted fcc (hR-24) ⟶ monoclinic (C2/m) with increasing pressure. The last transformation to a low symmetry monoclinic phase is accompanied by a volume collapse of 5 % for Tb at 51 GPa and a volume collapse of 3 % for Ho at 103 GPa. This volume collapse under high pressure is reminiscent of f-shell delocalization in light rare earth metal Cerium (Ce), Praseodymium (Pr), and heavy actinide metals Americium (Am) and Curium (Cm). The orthorhombic Pnma phase that has been reported in Am and Cm after f-shell delocalization is not observed in heavy rare earth metals under high pressures.

In situ analyzes of gaseous atmospheres could be performed by FT-IR spectroscopy in order to study the corrosion reactions of actinides. Nevertheless experimental conditions and the nature of studied species have a strong effect on IR absorption laws. Thus a prior calibration of our set-up is required to obtain an accurate estimation of gas concentration. For this purpose, the behavior of several air pure gases has been investigated according to their concentration from IR spectra. Reproducible results revealed subsequent increases of the most significant peak areas with gas pressure and small deviations from Beer Lambert's law. This preliminary work allowed to determine precise absorption laws for each studied pure gas in our in situ experimental conditions. Besides our FT-IR set-up was well suitable to quantitative analysis of gaseous atmosphere during corrosion reactions. Finally the effect of foreign gas will be investigated through more complex air mixtures to obtain a complete calibration network.

The electronic structure of the actinide metals, Th, U, Np, Pu, Am, and Cm, is investigated using electron energy-loss spectroscopy (EELS) in a transmission electron microscope, together with many-electron spectral calculations. At the N4,5 edge, sum rule analysis gives the angular part of the spin-orbit interaction per hole, showing that while light metals (Th and U) follow LS coupling, heavier metals (Pu, Am, and Cm) follow intermediate coupling of the 5f states. The intermediate coupling is near the jj limit for Pu and Am, but strongly shifted towards the LS coupling limit for Cm. At the O4,5 edge many-electron spectral calculations show that the prepeak corresponds to a “forbidden” transition.

We are developing the technique of spin-polarized photoelectron spectroscopy as a probe of electron correlation with the ultimate goal of resolving the Pu electronic structure controversy. Over the last several years, we have demonstrated the utility of spin polarized photoelectron spectroscopy for determining the fine details of the electronic structure in complex systems such as those shown below.

Unusual phase transitions driven by electron correlation effects occur in many f-electron metals (lanthanides and actinides alike) from localized phases to itinerant phases at high pressures. The dramatic changes in atomic volumes and crystal structures associated with some of these transitions signify equally important changes in the underlying electronic structure of these correlated f-electron metals. Yet, the relationships among the crystal structure, electronic correlation and electronic structure in f-electron metals have not been well understood. In this study, utilizing recent advances in third-generation synchrotron x-ray spectroscopies and high-pressure diamond-anvil cell technologies, we describe the pressure-induced spectral changes across the volume collapse transition in Gd at 60 GPa and well above. The spectral results suggest that the f-electrons of high-pressure Gd phases are highly correlated even at 100 GPa – consistent with the Kondo volume collapse model and the recent experimental evidence of strong electron correlation of α-Ce.

Nuclear transmutation reactions are based on the absorption of a smaller particle as neutron, proton, deuteron, alpha, etc. The resulting compound nucleus gets out of its initial lattice mainly by taking the recoil, also with help from its sudden change in chemical properties. The recoil implantation is used in correlation with thin and ultra thin materials mainly for producing radiopharmaceuticals and ultra-thin layer radioactive tracers. In nuclear reactors, the use of nano-particulate pellets could facilitate the recoil implantation for breeding, transmutation and partitioning purposes. Using enriched 238U or 232Th leads to 239Pu and 233U production while using other actinides as 240Pu, 241Am etc. leads to actinide burning. When such a lattice is immersed into a radiation resistant fluid (water, methanol, etc.), the recoiled product is transferred into the flowing fluid and removed from the hot area using a concentrator/purifier, preventing the occurrence of secondary transmutation reactions. The simulation of nuclear collision and energy transfer shows that the impacted nucleus recoils in the interstitial space creating a defect or lives small lattices. The defect diffuses, and if no recombination occurs it stops at the lattices boundaries. The nano-grains are coated in thin layer to get a hydrophilic shell to be washed by the collection liquid the particle is immersed in. The efficiency of collection depends on particle magnitude and nuclear reaction channel parameters. For 239Pu the direct recoil extraction rate is about 70% for 238UO2 grains of 5 nm diameters and is brought up to 95% by diffusion due to 239Neptunium incompatibility with Uranium dioxide lattice. Particles of 5 nm are hard to produce so a structure using particles of 100 nm have been tested. The particles were obtained by plasma sputtering in oxygen atmosphere. A novel effect as nanocluster radiation damage robustness and cluster amplified defects rejection will be discussed. The advantage of the method and device is its ability of producing small amount of isotopic materials easy to separate, using the nuclear reactors, with higher yield than the accelerator based methods and requiring less chemistry. It also represents a reliable candidate for nuclear fuel breeding reducing the cost of super-grade Plutonium and Thorium toward the price of urania and thoria.

Results of radiation damage in Pu and Pu1-xAmx alloys studied with magnetic susceptibility, χ(T), and resistivity are presented. Damage accumulated at low temperatures increases χ(T) for all measured alloys, with the trend generally enhanced as the lattice expands. There is a trend towards saturation observable in the damage induced magnetic susceptibility data. that is not evident in similar damage induced resistivity data taken on the same specimen. A comparison of isochronal annealing curves measured by both resistivity and magnetic susceptibility on a 4.3at% Ga stabilized δ-Pu specimen show that Stage I annealing, where interstitials begin to move, is largely transparent to the magnetic measurement. This indicates that interstitials have little impact on the damage induced increase in the magnetic susceptibility. The isochronal annealing curves of the Pu1-xAmx alloys do not show distinct annealing stages as expected for alloys. However, samples near 20% Am concentration show an unexpected increase in magnetization beginning when specimens are annealed to 35K. This behavior is also reflected in a time dependent increase in the magnetic susceptibility of damaged specimens indicative of first order kinetics. These results suggest there may be a metastable phase induced by radiation damage and annealing in Pu1-xAmx alloys.

Under ambient conditions, a Pu-2.0 at.% Ga alloy is retained in the metastable δ phase. Upon cooling to approximately -120 °C, the face-centered-cubic δ phase partially transforms to the metastable monoclinic α′ phase via a martensitic transformation. The kinetics of the δ⟶α′ transformation are reported to have double-C curve kinetics in a time-temperature-transformation (TTT) diagram, but the mechanisms responsible for this unusual behavior are not understood. Our work focuses on determining the underlying cause of the two noses. Optical microscopy has been used to investigate the role of “conditioning”—an isothermal hold at sub-anneal temperatures—on the δ⟶α′ transformation and to illuminate any disparities in transformation products. Conditioning was found to affect substantially the amount of transformation that occurs at particular points corresponding to both the upper- and lower-C of the TTT diagram.

In almost all materials, compression is accompanied naturally by stiffening. Even in materials with zero or negative thermal expansion, where warming is accompanied by volume contraction it is the volume change that primarily controls elastic stiffness. Not so in the metal plutonium. In plutonium, alloying with gallium can change the sign of thermal expansion, but for the positive-thermal-expansion monoclinic phase as well as the face-centered-cubic phase with either sign of thermal expansion, and the orthorhombic phase, recent measurements of elastic moduli show soften on warming by an order of magnitude more than expected, the shear and compressional moduli track, and volume seems irrelevant. These effects point toward a novel mechanism for electron localization, and have important implication for the pressure dependence of the bulk compressibility.

Electrical resistivity measurements performed under applied hydrostatic pressure and in magnetic fields have been used to probe the hidden order (HO) and superconducting (SC) states of URu2Si2, which have ambient-pressure transition temperatures TO = 17.5 K and Tc = 1.5 K, respectively. TO increases with applied pressure and a distinct kink in its pressure dependence is observed at 15 kbar; this feature is associated with the onset of antiferromagnetism. The pressure dependence of the SC upper critical field has been measured with the external field aligned parallel to both crystalline axes. The SC phase is smoothly suppressed to a critical pressure of about 15 kbar and no qualitative change in the critical field curves is observed. The co-evolution of the HO and SC phases is discussed within the context of a model in which the two phases compete for Fermi surface fraction.

The potential environmental and health concerns surrounding actinides and the use of nuclear fuels limits the acceptance of nuclear power by the public. This in turn, hinders the capability of this country to take advantage of nuclear power. Expanding our fundamental knowledge of actinide coordination chemistry will allow for the development of improved actinide sensors, new separations methods, or new means of radioactive waste remediation. We have designed and optimized a solution-phase parallel method for the synthesis of a library of symmetrical 2-quinoxalinol salens, Schiff-base type ligands with a 2-quinoxalinol incorporated into the salen backbone. This combines the rigid salen coordination framework with the quinoxaline properties that impart properties for use in colorimetric or fluorescent sensors. These have now been incorporated into organic soluble resins for metal extraction.

Computational analysis and modeling of spectroscopic properties of trivalent uranium in crystals of hexagonal symmetry have been conducted with inclusion of the crystal-field induced orbital hybridization between the 5f3 and 5f26d configurations. It is shown that, in the absorption spectrum with energy above 20,000 cm-1, the mixing of 5f3 and 5f26d states is significant. The spectrum in this region cannot be interpreted by the conventional model of crystal field theory. The Judd-Ofelt theory is completely failed in predicating the intensities of optical absorption from the ground state to the configuration mixed excited states. A new Hamiltonian including the odd ranks of crystal field interaction is diagonalized on the bases of all 5f3 and 5f26d states. A simulation of absorption spectrum is optimized in comparison with the experimental spectrum for determination of the Hamiltonian parameters.

Previous in situ examination of U(VI) spiked concrete indicated that uranyl-oxyhydroxide phases that were initially formed, later led to the formation of mixed uranyl-oxyhydroxide/silicates, which subsequently transformed into uranyl-silicates, and finally altered into mixed uranyl-silicate/phosphate and uranyl-phosphate phases. We conducted solubility studies of the identified final uranyl-phosphate phase (calcium meta-autunite) in phosphate solutions ranging in concentration from 0.001 – 0.1M as a function of pH. These studies indicated a secondary phosphate phase that formed during the solubility of meta-autunite regulated the uranium concentrations at relatively low levels under high pH conditions (>12) typically encountered in cement pore waters. The importance of uranyl-phosphate minerals in concrete waste forms has, to date, been neglected because of the minimal amount of phosphorus present in most concrete compositions. However, because concrete is a continuously reacting solid, the thermodynamic stability of uranyl minerals that form at the later stages of reaction may have a substantial impact on the long-term fate of uranium in the waste forms. This study suggests that any future investigations should consider the potential benefit of including phosphorus in concrete waste forms.

Plutonium, because of its self-irradiation by alpha decay, ages by means of lattice damage and helium in-growth. These integrated aging effects will result in microstructural and physical property changes. Because these effects would normally require decades to measure, studies are underway to asses the effects of extended aging on the physical properties of plutonium alloys by incorporating roughly 7.5 wt% of highly specific activity isotope 238Pu into the weapons-grade plutonium to accelerate the aging process. This paper presents updated results of self-irradiation effects on enriched and reference alloys measured from the immersion density, dilatometry, and mechanical tests. After nearly 90 equivalent years of aging, both the immersion density and dilatometry show that the enriched alloys at 35°C have decreased in density by ∼0.19 % and now exhibit a near linear density decrease, without void swelling. Both tensile and compression measurements show that the aging process continues to increase the strength of plutonium alloys.

Most of the exothermic nuclear reactions transfer the mass defect or binding and surplus energy into kinetic energy of the resulting particles. These particles are traveling through material lattices, interacting by ionization and nuclear collisions. Placing an assembly of conductive-insulating layers in the path of such radiation, the ionization energy is transformed into charge accumulation by polarization. The result is a super-capacitor charged by the moving particles and discharged electrically. Another more promising solution is to use bi-material nanoparticles organized such as to act like a serial connection and add the voltage. A spherical symmetry fission products source coated in several nano-layers is desired for such structures. The system may operate as dry or liquid-immersed battery, removing the fission products from the fissile material. There is a tremendous advantage over the current heat flow based thermal stabilization system allowing a power density up to 1000 times higher.

The fundamental characterization and understanding of 5f electron behavior in actinide complexes is imperative to provide an enhanced basis for the rational and accelerated development of improved processes relevant to nuclear energy. Soft x-ray absorption spectroscopy utilizing the scanning transmission x-ray microscope (STXM) at the Advanced Light Source-Molecular Environmental Science (ALS-MES) Beamline 11.0.2 has been used to probe the electronic characteristics of a nitrogen donor ligand 2,6-Bis(2-benzimidazyl)pyridine (BBP) and its resulting U(IV) complex. The nitrogen K- and carbon K-edges have been collected from both ligand and uranium complex, as well as the uranium 4d-edge from the complex. Upon complexation, the light element absorption spectra change markedly and the uranium spectra from the complex is compared to the reference spectrum obtained from U(IV)Cl4. The evolution of the spectral features are described and interpreted within a simple conceptual framework. Based on spectral evidence alone, the uranium is bound through the pyridine-like nitrogens and the oxidation state of the uranium is consistent with a U(IV) species.

Experimental measurements have shown that plutonium alloys exhibit changes of their macroscopic as well as microscopic properties. For example, a swelling of plutonium alloys was observed with aging with dilatometry and X-ray diffraction. The main idea to explain these changes rises in self irradiation undergoing by those materials. Plutonium α decay is at the origin of displacements cascades creating a large amount of structural defects. These later by anihilation and recombination give rise to larger defects such as voids and clusters. The aim of this work is to study the occurrence of such phenomena combining ab-initio, molecular dynamic and Monte Carlo methods in a coherent multi-scale approach which would help to understand long term behavior of structural defects and consequences of self irradiation. We show that plutonium does not seem to behave like other metals under ion irradiation. We discuss results obtained for high energy displacements cascade simulations. After parametric study of displacements cascade simulations combining temperature and cascade energy has been exposed, superposition of low energies displacements cascades is discussed as a method to construct realistic defect microstructures and to reach a rational use of computational time. At the end, we will present results of preliminary Monte Carlo simulations based on our molecular dynamic data which show that the spatial correlation of the stable defects populations created by the cascades seems to have a great influence on the predicted swelling.