[en] This volume brings together theorists, modelers and experimentalists working in the field of actinide science to present and discuss the latest breakthroughs in a field that spans materials science, condensed matter physics and chemistry

[en] The electronic structure of Pu chalcogenides is investigated making use of static around-mean field LDA+U and dynamical LDA+HIA (Hubbard-I) methods. The LDA+U calculations provide correct non-magnetic ground state for PuX (X S, Se, Te) with 5f-manifold non-integer filling (from approx. 5.6 in PuS to 5.7 PuTe). This is an indication of a mixed valence ground state which is a combination of f⁵ and f⁶ multiplets. The photoelectron spectra are calculated in good agreement with experimental data. The three-peak feature near E_F attributed to 5f-manifold is well reproduced by LDA+HIA, and follows from mixed valence character of the ground state. (authors)

[en] With the current level of actinide materials used in civilian power generation and the need for safe and efficient methods for the chemical separation of these species from their daughter products and for long-term storage requirements, a detailed understanding of actinide chemistry is of great importance. Due to the unique bonding properties of the f-elements, the lanthanides are commonly used as structural and chemical models for the actinides, but differences in the bonding between these 4f and 5f elements has become a question of immediate applicability to separations technology. This brief overview of actinide coordination chemistry in the Raymond group at UC Berkeley/LBNL examines the validity of using lanthanide analogs as structural models for the actinides, with particular attention paid to single crystal X-ray diffraction structures. Although lanthanides are commonly accepted as reasonable analogs for the actinides, these comparisons suggest the careful study of actinide materials independent of their lanthanide analogs to be of utmost importance to present and future efforts in nuclear industries. (authors)

[en] An yttria stabilised zirconia doped with plutonia and erbia has been selected as inert matrix fuel (IMF) at PSI. The results of experimental irradiation tests on yttria-stabilised zirconia doped with plutonia and erbia pellets in the Halden research reactor as well as a study of zirconia solubility are presented. Zirconia must be stabilised by yttria to form a solid solution such as MAz(Y,Er)_yPu_xZr_1-yO_2-ξ where minor actinides (MA) oxides are also soluble. (Er,Y,Pu,Zr)O_2-ξ (with Pu containing 5% Am) was successfully prepared at PSI and irradiated in the Halden reactor. Emphasis is given on the zirconia- IMF properties under in-pile irradiation, on the fuel material centre temperatures and on the fission gas release. The retention of fission products in zirconia may be stronger at similar temperature, compared to UO₂. The outstanding behaviour of plutonia-zirconia inert matrix fuel is compared to the classical (U,Pu)O₂ fuels. The properties of the spent fuel pellets are presented focusing on the once-through strategy. For this strategy, low solubility of the inert matrix is required for geological disposal. This parameter was studied in detail for a range of solutions corresponding to groundwater under near field conditions. Under these conditions the IMF solubility is about 109 times smaller than glass, several orders of magnitude lower than UO₂ in oxidising conditions (Yucca Mountain) and comparable in reducing conditions, which makes the zirconia material very attractive for deep geological disposal. The behaviour of plutonia-zirconia inert matrix fuel is discussed within a 'burn and bury' strategy. (authors)

[en] Plutonium, because of its self-irradiation by alpha decay, ages by means of lattice damage and helium in-growth. These integrated aging effects 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 weapons-grade plutonium to accelerate the aging process. This paper presents updated results of self-irradiation effects on enriched and reference alloys measured from 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 deg. 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. (authors)

[en] 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 nano-cluster 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. (author)

[en] Dynamic nonlinear localization, an emerging new area of materials physics, has the potential to fundamentally change our understanding of materials properties. These intrinsically localized modes (ILM) have been found forming in uranium above about 450 K. Comparisons with data from the literature shows that these ILMs influence many properties, including heat capacity, thermal transport, thermal expansion, and mechanical deformation. The existence of ILMs helps to explain many anomalies in uranium, some of which have been known for more than fifty years. Here, the possibility that ILMs may also play a role in the properties of plutonium is considered. The mechanism helps to explain the success of an 'Invar-like' two-level model for the thermal expansion of Pu without the need to invoke local magnetic states, which have been ruled out experimentally. It also helps to explain an excitation observed in δ-plutonium that has energy consistent with the two-level model, but momentum dependence consistent with lattice vibrations. This excitation, energy and momentum dependence, is consistent with the non-equilibrium generation of ILMs and the thermal excitation properties of these ILMs are consistent with a two-level model. High-temperature inelastic x-rays scattering measurements of the phonon dispersion curves of δ-plutonium are needed to test this hypothesis. (author)

[en] Results of radiation damage in Pu and Pu_1-xAm_x 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 4.3 at% 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 Pu_1-xAm_x 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 35 K. 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 Pu_1-xAm_x alloys. (authors)

[en] 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. (authors)

[en] By combining the local density approximation (LDA) with dynamical mean field theory (DMFT), we report a systematic analysis of the spectral properties of δ-plutonium with varying 5f occupancy. The LDA Hamiltonian is extracted from a tight-binding (TB) fit to full-potential linearized augmented plane-wave (FP-LAPW) calculations. The DMFT equations are solved by the exact quantum Monte Carlo (QMC) method and the Hubbard-I approximation. We show the strong sensitivity of the spectral properties to the 5f occupancy, which suggests using this occupancy as a fitting parameter in addition to the Hubbard U. By comparing with PES data, we conclude that the 'open shell' 5f⁵ configuration gives the best agreement, resolving the controversy over 5f 'open shell' versus 'close shell' atomic configurations in δ-Pu. (authors)