Table of contents

This volume of IOP Conference Series: Materials Science and Engineering consists of 98 papers that were presented at Actinides 2009, the 8th International Conference on Actinide Science held on 12–17 July 2009 in San Francisco, California, USA. This conference was jointly organized by Lawrence Livermore National Laboratory and Lawrence Berkeley National Laboratory.

The Actinides conference series started in Baden-Baden, Germany (1975) and this first conference was followed by meetings at Asilomar, CA, USA (1981), Aix-en-Provence, France (1985), Tashkent, USSR (1989), Santa Fe, NM, USA (1993), Baden-Baden, Germany (1997), Hayama, Japan (2001), and Manchester, UK (2005). The Actinides conference series provides a regular venue for the most recent research results on the chemistry, physics, and technology of the actinides and heaviest elements. Actinides 2009 provided a forum spanning a diverse range of scientific topics, including fundamental materials science, chemistry, physics, environmental science, and nuclear fuels. Of particular importance was a focus on the key roles that basic actinide chemistry and physics research play in advancing the worldwide renaissance of nuclear energy.

Editors Linfeng Rao Lawrence Berkeley National Laboratory (lrao@lbl.gov) James G Tobin Lawrence Livermore National Laboratory (tobin1@llnl.gov) David K Shuh Lawrence Berkeley National Laboratory (dkshuh@lbl.gov)

All papers published in this volume of IOP Conference Series: Materials Science and Engineering have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Various compounds with fluorite (cubic zirconia) and fluorite-derived (pyrochlore, zirconolite) structures are considered as promising actinide host phases at immobilization of actinide-bearing nuclear wastes. Recently some new cubic compounds — stannate and stannate-zirconate pyrochlores, murataite and related phases, and actinide-bearing garnet structure compounds were proposed as perspective matrices for complex actinide wastes. Zirconate pyrochlore (ideally Gd₂Zr₂O₇) has excellent radiation resistance and high chemical durability but requires high temperatures (at least 1500 °C) to be produced by hot-pressing from sol-gel derived precursor. Partial Sn⁴⁺ substitution for Zr⁴⁺ reduces production temperature and the compounds REE₂ZrSnO₇ may be hot-pressed or cold pressed and sintered at ~1400 °C. Pyrochlore, A₂B₂O_7−x (two-fold elementary fluorite unit cell), and murataite, A₃B₆C₂O_20−y (three-fold fluorite unit cell), are end-members of the polysomatic series consisting of the phases whose structures are built from alternating pyrochlore and murataite blocks (nano-sized modules) with seven- (2C/3C/2C), five- (2C/3C), eight- (3C/2C/3C) and three-fold (3C — murataite) fluorite unit cells. Actinide content in this series reduces in the row: 2C (pyrochlore) > 7C > 5C > 8C > 3C (murataite). Due to congruent melting murataite-based ceramics may be produced by melting and the firstly segregated phase at melt crystallization is that with the highest fraction of the pyrochlore modules in its structure. The melts containing up to 10 wt. % AnO₂ (An = Th, U, Np, Pu) or REE/An fraction of HLW form at crystallization zoned grains composed sequentially of the 5C → 8C → 3C phases with the highest actinide concentration in the core and the lowest — in the rim of the grains. Radiation resistance of the "murataite" is comparable to titanate pyrochlores. One more promising actinide hosts are ferrites with garnet structure. The matrices containing sometime complex fluorite structure oxide as an extra phase have leach and radiation resistance similar to the other well-known actinide waste forms.

Multi physics electrochemical modeling in a framework of Computational Fluid Dynamics (CFD) code was proposed and dealt with in detail to simulate the electro-transport behaviour that appears in a molten-salt electrolytic system. The modeling approach in this study is focused on the mass transport and current arising due to the concentration and the surface overpotential based on a cell configuration and electrolyte turbulence. This comprehensive modelling approach was applied and compared to electroplating model in a prepared rotating cylinder Hull (RCH) cell system.

Diffusion behaviours of oxygen and uranium were evaluated for bulk and grain-boundaries of uranium dioxide using the molecular dynamics (MD) simulation. It elucidated that oxygen behaved like liquid in superionic state at high temperatures and migrated on sub-lattice sites accompanying formation of lattice defects such as Frenkel defects at middle temperatures. Formation energies of Frenkel and Shottky defects were compared to literature data, and migration energies of oxygen and uranium were estimated by introducing vacancies into the supercell. For grain-boundaries (GB) modelled by the coincidence-site lattice theory, MD calculations showed that GB energy and diffusivities of oxygen and uranium increased with the misorientation angle. By analysing GB structures such as pair-correlation functions, it also showed that the disordered phase was observed for uranium as well as oxygen in GBs especially for a large misorientation angle such as S5 GB. Hence, GB diffusion was much larger than bulk diffusion for oxygen and uranium.

The phase states in the Pu-Si-O ternary system were investigated to understand the behaviour of Si impurity in MOX fuel and to assist in evaluating acceptable amounts of Si impurity in the fuel. Samples, which were mixed powders of PuO₂ and SiO₂ in three molar ratios, were annealed at 1623K-1973K as a function of oxygen potential. Two (Pu, Si) compounds, Pu_4.67Si₃O₁₃ and Pu₂Si₂O₇, were precipitated by annealing under a reducing atmosphere. The Pu_4.67Si₃O₁₃ phase was precipitated in a wider composition range as compared with Pu₂Si₂O₇.

Diffusion couples with polycrystalline urania and Am-MOX discs were annealed for 4.5 h at 1600 ° C under constant oxygen partial pressures. Concentrations of Pu and Am across the interfaces of the couples were measured using EPMA. The average diffusion coefficients of Pu and Am were estimated to be 10⁻¹⁵ and 10⁻¹⁴ m²/s by fitting their concentration profiles to Fick's law, and the difference between them was not significant. Grain boundary diffusion made the largest contribution to the diffusion coefficients. From the analysis of the diffusion depth based on a diffusion type classification, lattice diffusion coefficients are expected to be less than 10⁻¹⁷ m²/s at 1600°C.

Americium is a key element to design the FBR based nuclear fuel cycle, because of its long-term high radiological toxicity as well as a resource of even-mass-number plutonium by its transmutation in reactors, which contributes the enhancement of proliferation resistance. The present paper deals with the numerical analysis of the Am sample irradiation in Joyo to examine the transmutation performance of pure isotope in fast neutron environment during the irradiation, and deals with the comparison with the experimental result to evaluate the accuracy of current available numerical tool. In ²⁴¹Am pure isotope sample, the burn-up calculation of Am transmutation ratio and principal nuclides accumulation are agreed with the measured data within 1-σ uncertainty caused of cross-section covariance. Isomeric ratio of ²⁴²Am in total ²⁴¹Am capture reaction were calculated as 0.852±0.016 in the core and 0.85±0.025 in the axial and radial reactors. The current data and recently reported data by Koyama et. al 2008 support the latest version of nuclear data sets in ENDFB-VII and JENDL/AC-2008. From the view point of proliferation resistance, it was confirmed ²⁴¹Amp reduces un-attractive Pu to abuse from the beginning to the end of irradiation, and it would have important role to denature Pu in future FBR based nuclear fuel cycle.

Substituting Pu(IV) onto the Ca site and using Fe(III) as a charge balancing species, a series of 6 compositions of ²³⁹Pu doped zirconolite (of general formula (Ca_1−xPu_x)Zr(Ti_2-2xFe_2x)O₇) have been fabricated, where x = 0.1, 0.2, 0.3, 0.4, 0.6 and 0.7. Sintered pellets from each of these compositions have been characterised by XRD, SEM, EDX and Raman techniques in order to analyse the change in microstructure and determine the polytype boundaries as the doping level increases, showing that the zirconolite is stable in the natural 2M polytype up until x = 0.3, then adopting the 3T polytype from x = 0.3 to x = 0.4, but from there onwards an increasing degree of phase separation occurs.

The thermal conductivities of MOX fuel pellets stored for about 15 years and their recovery behaviours by pre-heating were investigated in two types of experiments. The experimental thermal conductivities approached the analytical curve derived from the thermal conductivities of non-self-irradiated specimens with an increase of pre-heating temperature. The experimental results were analyzed by the modified classical phonon transport model. The recovery processes between the thermal conductivities in this study and the lattice parameters of UO₂ and PuO₂ were compared. It was found that both recovery processes were similar to each other.

The reactivity of a polycrystalline UO₂ surface under alpha irradiation in contact with groundwater is investigated, in the hypothesis of direct disposal of spent fuel in a deep geological repository. Two series of plutonium-doped UO₂ samples (specific alpha activity of 18 and 385 MBq·g⁻¹_UO2) were leached in a synthetic Callovian-Oxfordian deep groundwater under anoxic conditions (Ar/CO₂ 3000 ppm, 3.5 bar relative pressure) to assess both the impact of alpha radiolysis of water and the complexing capacity of the groundwater ions on the dissolution of UO₂. This study follows a prior one performed in pure and carbonated waters. Firstly, technical developments were necessary for the analyses in the groundwater solution because of its high salt concentrations: quantification limits were determined for the measurement of uranium and radiolytic H₂O₂ traces in this medium. Secondly, given the very high reactivity of these samples in the presence of air and in order to minimize any prior surface oxidation, a strict experimental protocol was followed, based on high-temperature annealing in Ar + 4% H₂ with preleaching cycles. Each type of UO₂ pellet was then leached under static conditions for 30 days (anoxic conditions, deep groundwater solutions). Results on the evolution of uranium releases are presented. For the lowest alpha activity (18 MBq·g⁻¹_UO2), uranium releases in groundwater were below the quantification limit of 2 × 10⁻⁸ mol·L⁻¹ with a kinetic phosphorescence analyzer, even after 30 days. However, for higher alpha activity (385 MBq·g⁻¹_UO2) the uranium releases begin to exceed the quantification limit after 14 days of leaching and then increase exponentially. This increase is comparable to results previously obtained in carbonated solutions.

Transuranic elements have been simultaneously electro-deposited on a liquid cadmium cathode and decontaminated from fission products dissolved in molten 3LiCl-2KCl in the electrorefining of a pyrochemical reprocessing. Some lab-scale electrolysis experiments were carried out using uranium, plutonium and minor actinide elements in order to evaluate the performance of liquid cadmium cathodes. The results of several experiment confirmed that neptunium, americium and curium could be recovered together with Pu by the liquid cadmium cathodes through electrolysis operation. The separation factors of minor actinide vs. Pu were estimated to be about 0.5 to 2.5 and those of rare earth element vs. total actinides 18 to 32.

Nuclear fuel reprocessing schemes such as PUREX and UREX utilise HNO₃ media. An understanding of the corrosion of process engineering materials such as stainless steel in such media is a major concern for the nuclear industry. Two key species are cerium and chromium which, as Ce(IV), Cr(VI), may act as corrosion accelerants. An on-line analytical technique for these quantities would be useful for determining the relationship between corrosion rate and [Ce(IV)] and [Cr(VI)]. Consequently, a strategy for simultaneous quantification of Ce(IV), Cr(VI) and Cr(III) in the presence of other ions found in average burn-up Magnox / PWR fuel reprocessing stream (Fe, Mg, Nd, Al) is being developed.

This involves simultaneous UV-vis absorbance measurement at 620, 540, 450 nm, wavelengths where Ce and Cr absorb but other ions do not. Mixed solutions of Cr(VI) and Ce(IV) are found to present higher absorbance values at 540 nm than those predicted from absorbances recorded from single component solutions of those ions. This is attributed to the formation of a 3:1 Cr(VI)-Ce(IV) complex and we report on the complexation and UV-visible spectrophotometric characteristics of this species. To the best of our knowledge this is the first experimental study of this complex in aqueous nitric acid solution systems.

As the Hanford site undergoes remediation, it is noted that significant economies could be realized by minimizing the amount of aluminum deposited in High-Level Waste glass. Though such a step is not planned, an acidic scrub of the Hanford sludge could enhance Al removal. It is likely that the resulting Al(NO₃)₃ solution would contain measurable amounts of transuranic elements, thus the solution might require some secondary treatment to remove TRU contamination. Thus far, extraction chromatography (EXC) has shown promise [1] as an alternative to a liquid-liquid remediation of the Hanford site. Previous EXC studies have shown >99% of the Eu can be extracted from simulated Al/Cr waste. This study continues an examination of a hypothetical secondary cleanup of the waste by studying the removal of UO₂²⁺, NpO₂⁺, NpO₂²⁺ and Th⁴⁺ from using tri-n-octyl phospine oxide (TOPO) impregnated XAD7 resins. Neptunium was held in the V and VI oxidation states using ascorbic acid and chromate, respectively. Initial results show extraction following classical metal recovery trends, wherein an increased Z_eff correlates with increased distribution of the metal into the organic resin phase. The uptake of Eu³⁺ (representative of An³⁺) on a column of the same material was also investigated. Uptake kinetics were improved by wetting the TOPO-XAD7 resin with n-dodecane (TOPO-XAD7n). The presence of n-dodecane also provided consistency between batch mode and column mode metal recovery. Preliminary data show >99% recovery of metal ions with a Z_eff ≥ 3 under various simulated conditions.

The oxygen potentials of (Pu_0.81Am_0.08Nd_0.11)O_2−x were experimentally investigated by thermogravimetric analysis with H₂O/H₂ and CO₂/H₂ gas equilibriums at 1123 K, 1273 K and 1423 K. The oxygen potentials of (Pu_0.81Am_0.08Nd_0.11)O_2−x were extremely high above −200 kJ/mol near the maximum oxygen-to-metal ratio. From their high point, the oxygen potentials decreased monotonically with decreasing oxygen-to-metal ratio until the decreases of the oxygen potentials became very small before decreasing sharply again. The profiles of oxygen potentials of (Pu_0.81Am_0.08Nd_0.11)O_2−x were almost the same as those of (Pu_0.91Am_0.09)O_2−x, whereas the oxygen potentials of (Pu_0.81Am_0.08Nd_0.11)O_2−x were higher by approximately 100 kJ/mol than those of (Pu_0.91Am_0.09)O_2−x as a function of mean Am and Pu valences. Results were compared with those of related oxides and discussed from the viewpoint of the effects of Nd addition on the oxygen potentials.

The intention of the presented study is to elucidate the influence of noble metal inclusions (fission products) on the structure as well as on the electrochemical properties of spent nuclear fuel (SNF). To this aim, thin UO₂ films doped with metal inclusions such as Pd, Mo and Au are prepared by sputter deposition. The films are characterized by spectroscopic (XPS, EXAFS, XRD) as well as by microscopic (AFM, SEM) methods. In a next step the electrochemical properties of these model systems are comparatively investigated by cyclo voltammetry (CV). The sputter technique in combination with the heating treatment of the films allows the formation of a crystalline UO₂ matrix as it is found in SNF. The co-deposition with Au results in the dispersion of the pure metal in the oxide matrix. Pd as well as Mo are oxidized due to the deposition at RT. Heating the films involves a further oxidation of MoO₂ to MoO₃. By contrast Pd agglomerates and forms metallic -phases as it is found in SNF. Electrochemical investigations of the UO₂-Pd samples indicate an inhibiting influence of Pd on the oxidative dissolution of UO₂. When it comes to the formation of secondary phases under reducing conditions such influence is passivated. The precipitates finally dominate the overall redox behaviour of the model system.

The dependence of the oxygen potentials on oxygen nonstoichiometry (x) and temperature of Cm_0.09Pu_0.91O_2−x was measured by electromotive force (EMF) measurements. The galvanic cell type is shown: (Pt) air | Zr(Ca)O_2−x | Cm_0.09Pu_0.91O_2−x (Pt). The coulomb titration has been made for the sample at the intervals of 40 K between 1173 and 1333 K over the x range of 0.018 ≤ x ≤ 0.053. The oxygen potentials decreased gradually from −31.02 to −117.48 kJmol⁻¹ with increasing x from 0.018 to 0.045, and more rapidly decreased from −117.48 to −283.74 kJmol⁻¹ up to 0.053. The temperature dependence of the oxygen potentials was also measured between 1173 and 1333 K for several constant x values. The temperature dependences exhibited the smooth curves over the x and temperature ranges concerned. Systematic comparison of the oxygen potentials between Cm_0.09Pu_0.91O_2−x and those published for CmO_2−x and Am-containing oxides was also made. The oxygen potential of Cm₀₉Pu_0.91O_2−x at the equimolar ratio of Cm³⁺/Cm⁴⁺ was higher than those of Am_yPu_1−yO_2−x at the equimolar ratio of Am³⁺/Am⁴⁺ by approximately 150 kJmol⁻¹ when the Pu valence was assumed to be +4 in both oxides.

Phase separation behaviour was investigated to better understand the phase diagram in the U-Pu-O system. The effects of adding minor actinides and lanthanides on the phase separation behaviour were evaluated by using thermal analysis, X-ray diffraction analysis and microstructure observation. The maximum phase separation temperature of (U_0.7Pu_0.3)O_2−x was 633K. The amount of phase separation increased with decreasing O/M ratio from 2.00 to 1.92. The phase separation region expanded with Pu content and lower limit of Pu content was estimated to be about 20%. The effects of minor actinide and lanthanide addition on the phase separation temperature were also evaluated. It is concluded that the phase separation would not significantly affect the irradiation behaviour or pellet production.

The thermal diffusivities and heat capacities of transuranium nitride solid solutions, (Np,Am)N and (Pu,Am)N, were measured by using a laser flash method and a drop calorimetry, respectively. The thermal conductivities of these samples were determined from the measured thermal diffusivities, heat capacities and bulk densities. The thermal conductivities of (Np,Am)N and (Pu,Am)N increased with temperature over the temperature range investigated. The increases in the thermal conductivities were probably due to the increases of electrical components. In addition, the thermal conductivities of (Np,Am)N and (Pu,Am)N decreased with increasing Am contents. It could be considered that the decreases in the thermal conductivities with increasing Am contents correspond to the lowering of electronic contribution.

Basic research in actinide chemistry and physics is indispensable to maintain sustainable development of innovative nuclear technology. Actinides, especially minor actinides of americium and curium, need to be handled in special facilities with containment and radiation shields. To promote and facilitate actinide research, close cooperation with the facilities and sharing of technical and scientific information must be very important and effective. A three-year-program "Basic actinide chemistry and physics research in close cooperation with hot laboratories", ACTILAB, was started to form the basis of sustainable development of innovative nuclear technology. In this program, research on actinide solid-state physics, solution chemistry and solid-liquid interface chemistry is made using four main facilities in Japan in close cooperation with each other, where basic experiments with transuranium elements can be made. The ¹⁷O-NMR measurements were performed on (Pu_0.91Am_0.09)O₂ to study the electronic state and the chemical behaviour of Am and Cm ions in electrolyte solutions was studied by distribution experiments.

The surface oxidation of uranium metal has been studied by X-ray diffraction (XRD) and Rietveld method in the range of 50~300°C in air. The oxidation processes are analyzed by XRD to determine the extent of surface oxidation and the oxide structure. The dynamics expression for the formation of UO₂ was derived. At the beginning, the dynamic expression was nonlinear, but switched to linear subsequently for uranium in air and humid oxygen. That is, the growth kinetics of UO₂ can be divided into two stages: nonlinear portion and linear portion. Using the kinetic data of linear portion, the activation energy of reaction between uranium and air was calculated about 46.0 kJ/mol. However the content of oxide as a function of time was linear in humid helium ambience. Contrast the dynamics results, it prove that the absence of oxygen would accelerate the corrosion rate of uranium in the humid gas. We can find that the XRD and Rietveld method are a useful convenient method to estimate the kinetics and thermodynamics of solid-gas reaction.

The temperature range of the δ-phase field of plutonium can be expanded by alloying with Group IIIA elements. Ga is a particularly potent δ-stabilizer and effectively stabilizes the δ-phase to room temperature. Due to a strong propensity to wards s olute redistribution during cooling through the ε→δ phase field, regions of the material often do not contain enough solute to stabilize the δ-phase even after extensive homogenization annealing in the δ-phase field. The result is a small, but persistent, fraction of α-phase in the material. A technique using differential scanning calorimetry to measure the enthalpy of transformation of the plutonium α→β transformation is described which can detect and quantify α-phase in a δ-phase matrix at levels as low as ~0.1 wt. %. Complications arise due to interference from the pressure-induced α-phase, and a peak separation method was developed to accurately measure the heat signal from each phase. A set of δ-stabilized Pu-1.7 atomic % Ga alloys was examined using the technique and found to contain 0.32 ± 0.06 weight % α-phase. The onset temperature of the α→β transformation in these specimens was found to be 140.2°C, significantly higher than that for the transformation in pure plutonium, 126.2°C. This increase in onset temperature is a consequence of significant Ga content in the α-phase.

In the French long-lived radionuclide (LLRN) transmutation program, several irradiation experiments were initiated in the Phenix fast neutron reactor to obtain a better understanding of the transmutation processes. The PROFIL experiments are performed in order to collect accurate information on the total capture integral cross sections of the principal heavy isotopes and some important fission products in the spectral range of fast reactors. One of the final goals is to diminish the uncertainties on the capture cross-section of the fission products involved in reactivity losses in fast reactors. This program includes two parts: PROFIL-R irradiated in a standard fast reactor spectrum and PROFIL-M irradiated in a moderated spectrum. The PROFIL-R and PROFIL-M irradiations were completed in August 2005 and May 2008, respectively. For both irradiations more than a hundred containers with isotopes of pure actinides and other elements in different chemical forms must be characterized. This raises a technical and analytical challenge: how to recover by selective dissolution less than 5 mg of isotope powder from a container with dimensions of only a few millimeters using hot cell facilities, and how to determine analytically both trace and ultratrace elemental and isotopic compositions with sufficient accuracy to be useful for code calculations.

A thermodynamic database on a U-Pu-Zr-Np-Am-Fe alloy system is being constructed for developing metallic fuels containing minor actinides. In the first step, a ternary U-Pu-Zr alloy system is re-assessed by the CALPHAD method by taking some recent data into consideration, such as chemical activity of 8-phase for the U-Zr system, liquidus and solidus for the Pu-U system, vapour pressure of Pu in the Pu-U system and etc. Phase diagrams of three binary sub-system and a ternary system were then re-evaluated and some inconsistencies among the binary and ternary phase diagrams were adjusted by introducing some assumptions.

A thermodynamic database on a U-Pu-Zr-Np-Am-Fe alloy system is being constructed for developing metallic fuels containing minor actinides. The binary sub-systems containing Np, A m, and Fe were assessed by the CALPHAD method. The phase diagrams of ternary sub-systems were evaluated using both the assessed binary parameters and experimental information for some ternary systems, and then inconsistencies among the binary and ternary phase diagrams were adjusted. The assessed results were summarized as a database file for a thermodynamic calculation program such as Thermo-calc. The available experimental data on the binary, ternary, and quaternary sub-systems in the U-Pu-Zr-Np-Am-Fe system were fitted reasonably using the database.

Silicon nitride ceramics is a candidate for inert matrix, since it is very tolerant for neutron irradiation and it has relatively high thermal conductivity. For these reasons, Si₃N₄ ceramics containing large amounts of CeO₂, as a simulant of transuranium elements, were manufactured by sintering. The low-temperature sintering behavior and chemical and thermal properties of the obtained ceramics are reported. CeO₂ (16 or 30 mass%), SiO₂ (3 mass%) and MgO (5 mass%) were mixed with fine Si₃N₄ powder. The mixed powder was uniaxially pressed into a pellet under 60 MPa. These pellets were sintered at 1400~1750°C for 2~4 h in flowing N₂ (2 L/min). The pellet density rapidly increased after the sintering between 1400 and 1430°C in the case of 4 h keeping and bulk density of 3.34 g/cm³ was attained at 1450°C (Relative density ~95%), in the case of 16mass% CeO₂. Room temperature thermal conductivity increased with sintering temperature from ~10 to ~40W/mK after sintering at 1450°C and 1650°C, respectively. High temperature thermal conductivity of sintered ceramics at 1650°C was approximately four times as high as that of UO₂ up to 800°C. The dissolution rate of the sintered pellets for 3mol/L HNO₃ solution at 80°C was measured. After 200 h, almost 25% of grain boundary phase was eluted from the pellet containing 16mass% CeO₂.

The conversion of minor actinides to fuel starting materials for transmutation in a closed nuclear cycle is a big challenge for the next decades and the development of Gen(IV) nuclear systems. Conversion routes are numerous, but one needs to prove that they can be adapted to handle minor actinides. One of them is called the resin process and is particularly attractive because it stands for a "dustless" process as it produces microspheres of oxide or carbide after thermal treatment of the loaded resin. The study presented herein focuses on the experiments and tests which enable us to optimize the fixation of minor actinides onto ionic exchange resin and their carbonization into oxide type materials.

The hexacyanometallate family is well known in transition metal chemistry because the remarkable electronic delocalization along the metal-cyano-metal bond can be tuned in order to design systems that undergo a reversible and controlled change of their physical properties. We have been working for few years on the description of the molecular and electronic structure of materials formed with [Fe(CN)₆]^n- building blocks and actinide ions (An = Th, U, Np, Pu, Am) and have compared these new materials to those obtained with lanthanide cations at oxidation state +III. In order to evaluate the influence of the actinide coordination polyhedron on the three-dimensional molecular structure, both atomic number and formal oxidation state have been varied : oxidation states +III, +IV. EXAFS at both iron K edge and actinide L_III edge is the dedicated structural probe to obtain structural information on these systems. Data at both edges have been combined to obtain a three-dimensional model. In addition, qualitative electronic information has been gathered with two spectroscopic tools : UV-Near IR spectrophotometry and low energy XANES data that can probe each atom of the structural unit : Fe, C, N and An. Coupling these spectroscopic tools to theoretical calculations will lead in the future to a better description of bonding in these molecular solids. Of primary interest is the actinide cation ability to form ionic — covalent bonding as 5f orbitals are being filled by modification of oxidation state and/or atomic number.

For many decades, compounds containing oxygen atoms were excluded from the actinide-catalysis field because of the high oxophilic nature of these complexes. Pursuing the conceptual question about the potential activity of actinide-oxo bonds we were surprised to find that the coupling of aromatic aldehydes catalyzed by Cp*₂ThMe₂ and Th(NEtMe)₄ via thorium-alkoxide intermediates take place in high yields to produce the corresponding esters. Here we present our breakthrough results including comprehensive mechanistic, deuterium labeling, kinetic and thermodynamic studies. In addition, the tetrachloride salt of uranium reacts with one equivalent of Li₂[(C₅Me₄)₂SiMe₂] in DME to form the complex {[η⁵-(C₅Me₄)₂SiMe₂]UCl₂·2LiCl·2DME (13), which reacts with equimolar amounts of water in DME yielding the coordinative unsaturated bridged mono oxide and mono chloride uranium lithium salt complex {[η⁵-(C₅Me₄)₂SiMe₂]UCl}₂((μ-O)((μ-Cl)•Li(DME)₃•DME (14). The alkylation of complexes 14 with BuLi gives the mono bridged dibutyl complex {[η⁵-(C₅Me₄)₂SiMe₂]UBu}₂(μ-O) (16). Complex 16 is an active catalyst for the disproportionation metathesis of TMSC≡CH and the cross-metathesis of TMSC≡CH or TMSC≡CTMS with various terminal alkynes. PhSiH₃ reacts with complex 16 producing Ph₂SiH₂ and SiH₄(caution) indicating the cleavage of the trimethylsilyl group from the phenyl moiety and the formation of uranium-silyl intermediate.

Solid state chemistry of uranyl-containing inorganic compounds has been enriched recently by a multiplication of papers dealing with two and three dimensional inorganic materials. This paper is a review of the compounds structurally based on uranophane–type layers in uranyl silicates, phosphates, arsenates and vanadates systems. Depending on the nature and size of the metallic or organic cation used as charge compensators or structure directing agents, various geometric isomers are obtained and described herein. The cations occupy either the interlayer space between uranophane-type sheets or different types of cavities created by a three dimensional inorganic framework built from uranophane layers pillared by U(VI) and oxygen polyhedra. The number of UO₆ or UO₇ pillars by [(UO₂)(XO₄)] structural block units of the layer give a series of compounds with the following general formula A_2y/n{(UO₂)_1−y[(UO₂)(XO₄)]₂} with y=0,1/3,1/2 and 1.

Structural analyses of uranyl complexes with isomers of N,N'-diethyl-N,N'-ditolyl-dipicolinamide were carried out using IR spectroscopy and single crystal x-ray diffraction. From these analyses it was determined that complexation takes place through coordination with the carbonyl and pyridine nitrogen moieties. The uranium-oxygen and uranium-nitrogen bond distances for Et(p)TDPA are U(1)-O(1): 2.394(3), U(1)-O(2): 2.460(3), U(1)-N(1): 2.661(3) and for Et(o)TDPA U(1)-O(1): 2.415(5), U(1)-O(2): 2.432(4), and U(1)-N(1): 2.647(5).

A U(VI) complex with N,N'-disalicylidenediethylenetriaminate (saldien^2-) was characterized by single crystal X-ray analysis and X-ray absorption fine structure (XAFS) spectroscopy, and its electrochemical behavior in a DMSO solution was studied. The obtained U(VI)-saldien^2- complex recrystallized from DMSO was identified as orthorhombic U^VIO₂(saldien)·DMSO. All coordination sites in the equatorial plane of UO₂²⁺ are occupied by coordinating O and N atoms of saldien^2-. Comparing a k³-weighted U L_III-edge EXAFS spectra of U^VIO₂(saldien) in DMSO and DMF solutions with that in solid state, the molecular structure of U^VIO₂(saldien) remains even in the solutions. Quasi-reversible redox waves of U^VIO₂(saldien) were observed at E°' = -1.582 ± 0.005 V vs. Fc/Fc⁺ (ΔE_p = 0.080-0.170 V at v = 0.010-0.500 V·s⁻¹) in DMSO. UV-Vis-NIR absorption spectral change with the electrochemical reduction of U^VIO₂(saldien) using the spectroelectrochemical technique shows isosbestic points clearly, indicating that the electrochemical reaction of U^VIO₂(saldien) is only present. Using the absorbance change and the Nernstian equation, the electron stoichiometry in the reduction of U^VIO₂(saldien) in DMSO was determined as 0.929. This quantity close to unity reveals a redox reaction, U^VIO₂(saldien) + e⁻ = [U^VO₂(saldien)]⁻, i.e., U^VIO₂(saldien) without unidentate ligands results in the stable U(V) complex, [U^VO₂(saldien)]⁻, in DMSO. This U(V) species also shows the characteristic absorption bands of U(V) at 630, 700, 830, 1390, and 1890 nm as well as other U(V) complexes.

Such materials as polyethylene, polypropylene, polyisobutylene have about the same initial density and the same elemental composition (CH₂), only the structures of the initial molecules differ. As the analysis conducted shows, the behaviours of polyethylene and polypropylene under compression are similar and described with one and the same equation of state (with the same parameters). The correlation behaviour of compressibility of hydrocarbon and fluorocarbon compounds of CF₂ type is shown. This may be because of identical electron configuration of oxygen-like carbon ion in these compounds.

This paper summarizes efforts leading to selection of a new fluid for the determination of the density of large Pu parts. Based on an extended literature search, perfluorotributylamine (CF₃(CF₂)₃)₃N, trade name FC-43) was chosen for an experimental study. Plutonium coupon corrosion studies were performed by exposing Pu to deaerated and aerated solutions and measuring corrosion rates gravimetrically. Samples of deaerated and aerated (FC-43) were also irradiated with ⁶⁰Co gamma rays. The samples were extracted with NaOH and analyzed by Ion Chromatography (IC). In surface study experiments, Pu coupons were exposed to deaerated and aerated solutions of FC-43 and analyzed by X-ray photoelectron spectroscopy (XPS). The XPS data indicate that there is no detectable surface effect caused by the new fluid.

The purpose of this work is to precisely study the martensitic transformation in a plutonium-gallium alloy. Thus, the thermodynamics and kinetics of the δ→α'+δ phase transformation in a Pu-Ga alloy were studied under isochronal and isothermal conditions. The activation energy of the δ→α'+δ phase transformation at a constant cooling rate (0.5 K.min⁻¹) was determined by using Kissinger and Ozawa models. The average value of the activation energy was found to be at −56 kJ.mol⁻¹. Dilatometry measurement was also used to trace 'in situ' the entire transformation for several temperatures. The kinetics of the δ→α'+δ transformation were modelled under isothermal conditions in the theoretical frame of the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory. It is proposed that the transformation consists of three stages. The α' transformation begins with a nucleation of pre-existing embryos. Then, both nucleation and rapid growth of α' occurs simultaneously and finally, the plates width expend. Apparent activation energies for nucleation and growth transformation were determined from the temperature dependence of the constant K at respectively −34 kJ.mol⁻¹ and −60 kJ.mol⁻¹. Adler et al. [1] investigated also the thermodynamics and the kinetics of the martensitic transformation in Pu alloys. These nucleation energies were found by modelling of heterogeneous martensitic nucleation via strain interaction with observed superdislocation-like nucleation sites in PuGa alloys. The values obtain by this model was very close to those we find. Investigations in steels alloys indicate that these energies are of the same order for nucleation near dislocation. Then, it could be indicating a strong relationship between these dislocations and martensitic nucleation sites.

Under limited availability of transplutonium metals some special techniques and methods of their production have been developed that combine the process of metal reduction from a chemical compound and preparation of a sample for examination. In this situation the evaporation and condensation of metal onto a substrate becomes the only possible technology. Thin film samples of metallic ²⁴⁴Cm, ²⁴⁸Cm and ²⁴⁹Bk were produced by thermal reduction of oxides with thorium followed by deposition of the metals in the form of thin layers on tantalum substrates. For the production of ²⁴⁹Cf metal in the form of a thin layer the method of thermal reduction of oxide with lanthanum was used.

²³⁸Pu and ²³⁹Pu samples in the form of films were prepared by direct high temperature evaporation and condensation of the metal onto a substrate. For the production of ²⁴¹Am films a gram sample of plutonium-241 metal was used containing about 18 % of americium at the time of production. Thermal decomposition of Pt5Am intermetallics in vacuum was used to produce americium metal with about 80% yield. Resistivity of the metallic ²⁴⁹Cf film samples was found to decrease exponentially with increasing temperature. The ²⁴⁹Cf metal demonstrated a tendency to form preferably a DHCP structure with the sample mass increasing. An effect of high specific activity on the crystal structure of ²³⁸Pu nuclide thin layers was studied either.

A combination of a first-principles calculation, lattice dynamics and CALPHAD (CALculation of PHAse Diagrams) modeling is proven as a powerful tool so as to evaluate the Gibbs free energy and a phase equilibrium between compounds including large amount of vacancies. In this work, non-stoichiometric PuO_2−x (dioxide) and Pu₂O₃ (sesquioxide) has been studied. An electron cohesive energy was evaluated from a first-principles calculations to estimate total energy of the compounds and a vacancy formation energy, and the theory of statistical mechanics was applied to evaluate enthalpy/entropy change due to oxygen vacancies for the non-stoichiometry of the PuO₂ (i.e. PuO_2−x). Then a vacancy-vacancy interaction energy was determined by fitting to the experimental data of a quantity of non-stoichiometry of the PuO₂ compounds as a function of oxygen potentials at large deviation from stoichiometry. The resulting Gibbs free energy yields phase boundary between the phases with good agreement with to the experimental data.

Pressure-Composition-Temperature (PCT) data are presented for the plutonium-hydrogen (Pu-H) and plutonium-deuterium (Pu-D) systems in the solubility region up to terminal solubility (precipitation of PuH₂). The heats of solution for PuH_S and PuD_S are determined from PCT data in the ranges 350-625°C for gallium alloyed Pu and 400-575°C for unalloyed Pu. The solubility of high purity plutonium alloyed with 2 at.% gallium is compared to high purity unalloyed plutonium. Significant differences are found in hydrogen solubility for unalloyed Pu versus gallium alloyed Pu. Differences in hydrogen solubility due to an apparent phase change are observable in the alloyed and unalloyed solubilities. The effect of iron impurities on Pu-Ga alloyed Pu is shown via hydrogen solubility data as preventing complete homogenization.

The effect of deposited amorphous carbon on the reactivity of uranium towards hydridization has been investigated by means of optical (HSM), electron (SEM), Raman scattering and atomic force (AFM) microscopies. Clear preference was found towards hydrogen attack on the carbon covered area as mostly manifested by the formation of hollow blister-like hydrides with average height of ~1μm, and crust of few hundreds of nm.

NOTE: As a result of an inadvertent AN2009 editorial error that led to publication of non-finalized version the PDF was replaced with the correct version on 16 September 2010. The original PDF can be found in the supplementary data.

The common oxides of plutonium are the dioxide (PuO₂) and the sesquioxide (Pu₂O₃). The nature of an oxide on plutonium metal under air at room temperature is typically described as a thick PuO₂ film at the gas-oxide interface with a thinner Pu₂O₃ film near the oxide-metal substrate interface. In a reducing environment, such as ultra high vacuum, the dioxide (Pu⁴⁺; O/Pu=2.0) readily converts to the sesquioxide (Pu³⁺; O/Pu=1.5) with time. In this work, the growth and evolution of thin plutonium oxide films is studied with x-ray photoelectron spectroscopy (XPS) under varying conditions. The results indicate that, like the dioxide, the sesquioxide is not stable on a clean metal substrate under reducing conditions, resulting in substoichiometric films (Pu₂O_3-y). The Pu₂O_3-y films prepared exhibit a variety of stoichiometries (y~0.2-1) as a function of preparation conditions, highlighting the fact that caution must be exercised when studying plutonium oxide surfaces under these conditions and interpreting resulting data.

The diversity of microorganisms is still far from understood, although many examples of the microbial biotransformation of stable, pollutant and radioactive elements, involving Bacteria, Archaea and Fungi, are known. In estuarine sediments from the Irish Sea basin, which have been labelled by low level effluent discharges, there is evidence of an annual cycle in Pu solubility, and microcosm experiments have demonstrated both shifts in the bacterial community and changes in Pu solubility as a result of changes in redox conditions. In the laboratory, redox transformation of both U and Pu by Geobacter sulfurreducens has been demonstrated and EXAFS spectroscopy has been used to understand the inability of G. sufurreducens to reduce Np(V). Fungi promote corrosion of metallic U alloy through production of a range of carboxylic acid metabolites, and are capable of translocating the dissolved U before precipitating it externally to the hyphae, as U(VI) phosphate phases. These examples illustrate the far-reaching but complex effects which microorganisms can have on actinide behaviour.

In this report a complementary approach using powder x-ray diffraction (PXRD) and attenuated total reflection (ATR) IR spectroscopy is evaluated with an emphasis on (i) delineating isostructural (Na autunite (Na[(UO₂)(PO₄)]•1.5H₂O) and chernikovite (H₃O[(UO₂)(PO₄)]•4H₂O)) and structurally distinct (triuranyl diphosphate tetrahydrate (UO₂)₃(PO₄)₂•4H₂O) hydrated uranyl phosphates. Our results show that this complementary approach, when used in conjunction with elemental analysis, provides reliable identification and characterization of hydrated uranyl phosphates.

Uranium particles within the respirable size range pose a significant hazard to the health and safety of workers. Significant differences in the deposition and incorporation patterns of aerosols within the respirable range can be identified and integrated into sophisticated health physics models. Data characterizing the uranium particle size distribution resulting from specific foundry-related processes are needed. Using personal air sampling cascade impactors, particles collected from several foundry processes were sorted by activity median aerodynamic diameter onto various Marple substrates. After an initial gravimetric assessment of each impactor stage, the substrates were analyzed by alpha spectrometry to determine the uranium content of each stage. Alpha spectrometry provides rapid non-distructive isotopic data that can distinguish process uranium from natural sources and the degree of uranium contribution to the total accumulated particle load. In addition, the particle size bins utilized by the impactors provide adequate resolution to determine if a process particle size distribution is: lognormal, bimodal, or trimodal. Data on process uranium particle size values and distributions facilitate the development of more sophisticated and accurate models for internal dosimetry, resulting in an improved understanding of foundry worker health and safety.

Radionuclides from authorized low level radioactive effluent discharges from the nuclear fuel reprocessing plant at Sellafield, UK, are present in the Irish Sea sediments. The distribution of radionuclides in salt marsh sediment profiles can be related to the discharge history from Sellafield. Radioactive particles, from the intertidal salt marsh sediments in the Esk estuary (10 km from Sellafield), have been isolated and investigated. Autoradiography and heavy liquid density separation were used to find and isolate these particles. Scanning electron microscopy, combined with energy dispersive X-ray analysis (SEM-EDX), was used to obtain information on the morphology and elemental composition of the particles, and alpha spectrometry for radionuclide composition. Particles are typically 1 — 20 μm size. Elemental analysis suggests that they are composed mainly of uranium. Alpha spectrometry shows that they have been irradiated, and transuranium nuclides (Pu, Am, Cm) can be identified in them.

This work is a part of the joint Russian – American Program on Beneficial Use of Depleted Uranium. The production of nuclear fuels results in the accumulation of large quantities of depleted uranium (DU) in the form of uranium hexafluoride (UF₆), which is converted to uranium oxides. Depleted uranium dioxide (DUO₂) can be used as a component of radiation shielding and as an absorbent for migrating radionuclides that may emerge from casks containing spent nuclear fuel (SNF) that are stored for hundreds of thousands of years in high-level wastes (HLW) and SNF repositories (e.g. Yucca Mountain Project). In this case DU oxides serve as an additional engineered chemical barrier. It is known that the primary radioisotope contributor to the calculated long-term radiation dose to the public at the Yucca Mountain SNF repository site boundary is neptunium-237 (²³⁷Np). This paper describes the sorption of ²³⁷Np in various media (deionized water and J-13 solution) by DUO₂. Samples of DUO₂ used in this work originated from the treatment of UF₆ in a reducing media to form UO₂(DUO₂-1 at 600°C, DUO₂-2 at 700°C, and DUO₂-3 at 800°C). All species of DUO₂ sorb Np(V) and Np(IV) from aqueous media. Equilibrium was achieved in 24 hours for Np(V) and in 2 hours for Np(IV). Np(V) sorption is accompanied with partial reduction of Np(V) to Np(IV) and vice versa. The sorption of Np(V) onto DUO₂ surfaces is irreversible. The investigations on DUO₂ transformations were performed under dynamic and static conditions. Under static conditions the solubility of the DUO₂ samples in J-13 solution is considerably higher than in DW. When the pre-treatment temperature is decreased, the solubility of DUO₂ samples raises regardless of the media. The experiments on interaction between DUO₂ and aqueous media (DW and J-13 solution) under dynamic conditions demonstrated that during 30-40 days the penetration/filtration rate of DW and J-13 solution through a thin DUO₂ layer decreased dramatically, and then slowed and stabilized. The filtration rate of J-13 solution through DUO₂layer is several times lower than that of DW. If Np were sorbed by UO₂ in SNF rather than being transported to the site boundary, the site boundary dose would be more than an order of magnitude lower than that calculated. If this is so, the remaining primary contributors to site boundary dose would be ¹²⁹I and the decay products of ²³⁸U. One could provide an additional barrier, a chemical barrier, to radionuclide release by surrounding the SNF with UO2. The experiments also indicate that a relatively thin layer of UO₂ essentially stops water penetration. Such a barrier would deny water access to the SNF. Such a repository SNF configuration would provide reduced radionuclide transport from the drift as well as sorbing released nuclides from failed SNF pins.

The requirement for on-line and in-situ monitoring of analytes in process and effluent streams and in ground waters has become increasingly more important in recent years. We therefore describe the development of the transduction element for a fully automated online instrument for the detection of caesium. The sensor layer for this instrument employs an Ion Selective Conductimetric Microsensor (ISCOM) as the detector. This is based upon a plasticized polymeric membrane incorporating a selective ionophore, overlaying two interdigitated microelectrode arrays. A direct relationship has been observed between the bulk conductance (as determined by the microelectrodes) of the ionophore loaded membrane and the concentration of the primary ions in solution.

Caesium selective ISCOMs were prepared using an ion selective membrane containing the commercially available ionophore Calix [6]arene-hexaacetic acid hexaethyl ester, polyvinylchloride (PVC) and plasticiser Nitrophenylether (NPOE). The relative levels of membrane components have also been varied in order to further enhance the ISCOM response. We also present preliminary data concerning the caesium selectivity with respect to a range of possible interferents, including rubidium.

The band structures of heavy Fermion superconductors UPd₂Al₃ and UNi₂Al₃ in paramagnetic phase were studied by soft X-ray angle-resolved photoemission. The results were compared with the results of the band structure calculation treating all U 5f electrons being itinerant. We have found that their overall band structures are described by the calculation. This suggests that U 5f electrons have itinerant nature in these compounds and band structure calculation is a reasonable starting point to model their electronic structure.

AnPd₅Al₂ (An: actinide and rare earths) crystallizing in the tetragonal ZrNi₂Al₅-type structure are a new family of intermetallic compounds exhibiting exotic magnetic and superconducting properties. The first compound discovered in this family, NpPd₅Al₂, shows heavy-fermion superconductivity at the rather high temperature of 5 K. The uranium analog UPd₅Al₂ has a non-magnetic ground state in spite of the Curie-Weiss behavior at high temperatures. CePd₅Al₂ is an anisotropic antiferromagnet. Application of pressure on this compound leads to the suppression of antiferromagnetic ordering and finally superconductivity appears above 10 GPa.

The photophysical properties of the neptunyl (V) ion in aqueous solution have been studied using time-resolved luminescence spectroscopy. While any f-f transitions in emission are too weak to detect using available technology, the ligand to metal charge transfer state is emissive in the visible part of the spectrum. Both the aquo ion and its complexes with bidentate ligands exhibit biexponential decay kinetics, which can be rationalised by slow exchange on the timescale of the experiment.

U₃Co₄Ge₇ and U₃Co₂Ge₇ have been prepared as single crystals by solution growth from tin flux. U₃Co₄Ge₇ crystallizes in the tetragonal structure (I4/mmm) with lattice parameters a = 0,4116 nm and c = 2,749 nm and U₃Co₂Ge₇ possesses the orthorhombic structure (Cmmm) with a = 0,4151 nm, b = 2,498 nm, c = 0,4160 nm. All measurements document ferromagnetism in U₃Co₄Ge₇ below T_C = 21 K. The magnetization and magnetic susceptibility measurements revealed strong magnetocrystalline anisotropy. The c-axis has a strong ferromagnetic contribution to the magnetization and was found to be the easy-magnetization direction. U₃Co₂Ge₇ shows onset of magnetic ordering at 41 K. The b-axis is the easy magnetization direction with the saturated magnetization μ_at = 1 μ_B/U at 2 K. The magnetization curves show anomalous behavior; the virgin curve goes far out of the hysteresis loop and reaches higher value of saturated magnetization.

Selected electronic properties of Pu, Am, Cm and Bk are calculated with the aid of charge self-consistent LDA + Hubbard I method. Presented all-electron calculations are performed in the full-potential LAPW basis and incorporate spin-orbit interaction. The results are found to be in good agreement with experimental valence photoelectron spectra as well as with core XAS/EELS spectra of heavy actinides.

In the non-aqueous reprocessing process of spent nuclear fuels by the pyro-electrochemical method, a spent fuel is dissolved into molten LiCl-KCl and NaCl-CsCl eutectics and dissolved uranium and plutonium are collected as either metal or oxide. However, the binary alkali chloride mixture with the lowest melting point is the LiCl-RbCl eutectic. In this study, electronic absorption spectra of U³⁺ and U⁴⁺ in molten LiCl-RbCl eutectic at various temperatures between 673 and 973 K were measured by the UV/Vis/NIR spectrophotometry. We confirmed that these spectra were similar to those in molten LiCl-KCl and NaCl-CsCl eutectics. The sensitive absorption bands of U⁴⁺ in LiCl-RbCl eutectic were found at 22000, 16500, 14900, 8600, and 4950 cm⁻¹. The large absorption bands of U⁴⁺ over 25000 cm⁻¹ increased with increasing melt temperature, while absorption peaks at 15500-4000 cm⁻¹ decreased. The large absorption bands of U³⁺ in LiCl-RbCl eutectic were observed over 14000 cm⁻¹. The sensitive absorption bands of U³⁺ at Vis/NIR region were found at 13300, 11500-11200, 9800-9400, and 8250 cm⁻¹, and these peaks decreased with increasing temperature.

UTGe compounds form α-hydrides with a small H concentration and β-hydrides accommodating up to 2 H atoms/f.u. Hydrogen absorption has a significant impact on the 5f magnetism. The Curie temperature-T_C of suspected ferromagnetic superconductor UCoGe increases to 50 K. Magnetic susceptibility of spin fluctuator UFeGe increases, but long-range magnetic order is not achieved. For ferromagnetic URhGe only α-hydride could be obtained, which moderate increase of T_C and spontaneous moment. The α-hydride of UCoGe is surprisingly paramagnetic and non-superconducting despite of a small volume expansion (0.25 %).

In this work we present the results of the magnetization measurements of UNiGa (in magnetic fields applied along the c-axis) under hydrostatic pressures up to 0.8 GPa and uniaxial pressures (applied along the c-axis) up to 0.2 GPa in the temperature range 2 — 60 K and magnetic fields up to 2 T. The unmapped part of the magnetic phase diagram was investigated, especially the sensitivity of magnetism to the application of the uniaxial pressure along the c-axis, which is the direction governing the magnetic interaction in this compound. The presence of the history dependent magnetic phase and its increasing stability with application of the hydrostatic pressure is reported.

High resolution X-ray emission spectroscopy (HRXES) is becoming increasingly important for our understanding of electronic and coordination structures. The combination of such information with development of quantum theoretical tools will advance our capability for predicting reactivity and physical behavior especially of 5f elements. HRXES can be used to remove lifetime broadening by registering the partial fluorescence yield emitted by the sample (i.e., recording a windowed signal from the energy dispersed fluorescence emission while varying incident photon energy), thereby yielding highly resolved X-ray absorption fine structure (XAFS) spectra. Such spectra often display resonant features not observed in conventional XAFS. The spectrometer set-up can also be used for a wide range of other experiments, for example, resonant inelastic X-ray scattering (RIXS), where bulk electron configuration information in solids, liquids and gases is obtained. Valence-selective XAFS studies, where the local structure of a selected element's valence state present in a mixture of valence states can be obtained, as well as site-selective XAFS studies, where the coordination structure of a metal bound to selected elements can be differentiated from that of all the other ligating atoms. A HRXES spectrometer has been constructed and is presently being commissioned for use at the INE-Beamline for actinide research at the synchrotron source ANKA at FZK. We present the spectrometer's compact, modular design, optimized for attaining a wide range of energies, and first test measurement results. Examples from HRXES studies of lanthanides, actinides counter parts, are also shown.

Bremstrahlung Isochromat Spectroscopy (BIS) has a proven record for the probing of unoccupied electronic structure, including feasibility studies of actinides such as U and Th. A description of the BIS or Inverse Photoelectron Spectroscopy (IPES) process and of our reasoning concerning the potential importance of extending the application of BIS related techniques to the actinides, will be provided. To put this into the proper context, our past successes, using soft x-ray techniques to interrogate the electronic structure of Pu, will be briefly reviewed. Finally, the initial results of the calibration of the BIS device, including preliminary spectra from of the surrogate system CeOxide, will be presented.

Optical constants of a [111] UO₂ crystal, aged in air for 25.5 years, were measured in the range from .75 and 5 eV using ellipsometric spectroscopy. The ellipsometric data acquired at angles of incidence of 65, 70 and 75 were modelled by a Gauss-Lorentz and a Tauc Lorentz Oscillator, leading to dielectric constants that differ substantially from Schoenes' for vacuum-annealed [111] UO₂. Raman spectra taken at 632.8 nm at normal ( = 0°) as well as off-normal (=75°) incidence show no indication of a hyper-stoichiometric surface layer, suggesting that at room temperature oxidation of UO₂ to U₃O₇/U₄O₉ proceeds slower than extrapolation from higher temperature observations predict.

Third phase formation is a key issue in the extraction of plutonium in high concentrations by trialkyl phosphates. A number of parameters influence this phenomenon, among which the nature of the extractant (the carbon chain length, branching) is the important one. Studies on third phase formation in thorium extraction could provide insights into the phenomenon, given the challenges in making measurements on plutonium systems. However, the extrapolation of the results obtained for thorium extraction to plutonium systems is difficult in many instances. In the present paper, results of the extensive investigations carried out at IGCAR on third phase formation in the extraction of Th(NO₃)₄ by trialkyl phosphates (TalP) are presented. The effects of various parameters such as extractant concentration, temperature, structure of diluent, equilibrium aqueous phase acidity and extractant structure on third phase formation in the extraction of Th(NO₃)₄ by trialkyl phosphates are discussed. Empirical equations to predict Limiting Organic Concentration (LOC) with respect to various parameters for third phase formation in the extraction of Th(NO₃)₄ by trialkyl phosphates from nitric acid media are also derived and the calculated LOC values are compared with the experimental values. An effort is made to discuss Pu extraction systems based on the bank of data accumulated.

Many kinds of new extractants have been studied for the separation of minor actinides, Am and Cm in particular, from high-level liquid waste (HLLW) which is generated from spent fuel reprocessing for the recovery of U and Pu. The authors have developed a new type of extractant for the extraction of Am and Cm, N,N,N',N'-tetraoctyldiglycolamide (TODGA) which is one of the diamides and shows the tridentate feature. To apply such a new extractant to the separation process for Am and Cm from HLLW, many criteria should be investigated and satisfied; e.g., high separation factor between An(III) and fission products, chemical and radiolytic stability, high extraction capacity, fast kinetics, compatibility with hydrocarbon diluents, controllability for the behaviour of U, Pu and Np which exist as residue of the former step, and so on. TODGA is fully soluble in n-dodecane, but has a relatively low extraction capacity. Therefore, TODGA was modified and a new DGA extractant, N,N,N',N'-tetradodecyldiglycolamide, was developed, which can extract Ln with one-third of the extractant concentration. Since both TODGA and TDdDGA extract Zr and Pd, effective masking agents for them were examined and selected. To extract Np quantitatively, the method to reduce Np(V) to Np(IV) was studied. With those achievements, a counter-current extraction test with 0.1M TDdDGA in n-dodecane and simulated solution of HLLW was carried out using a small-scale mixer-settler. As results of the counter-current extraction test, very clear phase separation was observed without any crud formation during the operation and quantitative recovery of Nd which is a substitute for Am was obtained.

Molecular-scale chemical information about solutions is of primary importance in the understanding of liquid-liquid extraction phenomena. From this point of view, NMR spectroscopy is a useful tool. However, in the field of the nuclear fuel reprocessing, this technique needs to overcome certain intrinsic limitations, including the presence of both paramagnetic metals and radioactivity. Because of the experimental difficulties encountered, paramagnetic data about actinides is scarce but nevertheless required in order to take advantage of information contained in the electron-nucleus interactions. This study will present two speciation studies dealing with Am(III) and U(IV) complexes in solution. Am(III) paramagnetism was found to be weak enough to observe a complex formed with a tetrapodal hexadentate N,O ligand in an aqueous solution. Although U(IV) paramagnetism is stronger, due to a fast chemical exchange with the ionic liquid used it was possible to extract structural information arising from ¹H NMR spectra analysis. Results obtained in solution are consistent with X-Ray data which indicate that ligand-metal interactions mainly come from hydrogen bonding.

In order to understand the mechanisms involved in the extraction processes developed to separate minor actinides, the "ligand/metallic cation" complexes formed in the organic phases are characterized by electrospray ionization-mass-spectrometry (ESI-MS). This paper deals with the application of the ESI-MS technique to analyze americium complexes in organic solutions. Two extractant systems are investigated : 1/ organic solutions of nitrogen polydentate extractants such as 6,6'-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2'-bipyridines (BTBPs) and 2/ organic solutions composed of mixture of a malonamide and a dialkylphosphoric acid.

Redox potentials were measured in acidic aqueous solutions (-log₁₀[H⁺]=0.7) containing different fractions of tri- and tetravalent plutonium. Eh values measured directly by a Pt electrode vs Ag/AgCl reference electrode agree very well with the redox potential calculated from the oxidation state distribution Pu(III)/Pu(IV). By monitoring the solutions over 120 days the kinetics of redox state distribution and dissolution of initially present Pu(IV)-colloids were studied. In solutions of Eh>950mV colloids dissolve and form Pu(VI), whereas at lower Eh the dissolution of colloids leads to formation of Pu(III). These findings corroborate the assumption that colloids are an integral part of the aqueous Pu redox chemistry and that formation and dissolution can be fully understood by means of Eh / pH stability calculations.

Extraction behavior of neptunium (Np) by tri-n-butyl phosphate from calcium nitrate hydrate melt was investigated. Distribution ratio of Np was found to increase with the decrease of water content. Adding nitric acid into the system resulted in an increase of the distribution ratio. In order to understand the extraction trends, Np species in the hydrate melt were analyzed by Raman spectrometry and UV/Vis/NIR spectrometry. Major fraction was assigned to be NpO₂²⁺ of Np(VI) and small fraction to be NpO₂⁺ of Np(V). A shift of the v₁ symmetric vibrational frequency of NpO₂²⁺ in nitrate media was found in Raman spectra. This suggests a coordination circumstance change of NpO₂²⁺.

For the recovery of fissile materials from spent nuclear fuel, we have proposed a novel reprocessing process based on selective sulfurization of fission products (FPs). The key concept of this process is utilization of unique chemical property of carbon disulfide (CS₂), i.e., it works as a reductant for U₃O₈ but works as a sulfurizing agent for minor actinides and lanthanides. Sulfurized FPs and minor actinides (MA) are highly soluble to dilute nitric acid while UO₂ and PuO₂ are hardly soluble, therefore, FPs and MA can be removed from Uranium and Plutonium matrix by selective dissolution. As a feasibility study of this new concept, the sulfurization behaviours of U, Pu, Np, Am and Eu are investigated in this paper by the thermodynamical calculation, phase analysis of chemical analogue elements and tracer experiments.

The global energy context pleads in favour of a sustainable development of nuclear energy since the demand for energy will likely increase, whereas resources will tend to get scarcer and the prospect of global warming will drive down the consumption of fossil fuel. In this context, nuclear power has the worldwide potential to curtail the dependence on fossil fuels and thereby to reduce the amount of greenhouse gas emissions while promoting energy independence.

How we deal with nuclear radioactive waste is crucial in this context. In France, the public's concern regarding the long-term waste management made the French Governments to prepare and pass the 1991 and 2006 Acts, requesting in particular the study of applicable solutions for still minimizing the quantity and the hazardousness of final waste. This necessitates High Active Long Life element (such as the Minor Actinides MA) recycling, since the results of fuel cycle R&D could significantly change the challenges for the storage of nuclear waste. HALL recycling can reduce the heat load and the half-life of most of the waste to be buried to a couple of hundred years, overcoming the concerns of the public related to the long-life of the waste and thus aiding the "burying approach" in securing a "broadly agreed political consensus" of waste disposal in a geological repository.

This paper presents an overview of the recent R and D results obtained at the CEA Atalante facility on innovative actinide partitioning hydrometallurgical processes. For americium and curium partitioning, these results concern improvements and possible simplifications of the Diamex-Sanex process, whose technical feasibility was already demonstrated in 2005. Results on the first tests of the Ganex process (grouped actinide separation for homogeneous recycling) are also discussed.

In the coming years, next steps will involve both better in-depth understanding of the basis of these actinide partitioning processes and, for the new promising concepts, the studies necessary prior to industrial implementation of these processes are described.

Concerning the selective recovery of minor trivalent actinides (MA(III) = Am(III) and Cm(III)) from high level liquid waste (HLLW) by extraction chromatography, adsorption and elution behaviours of MA(III) and fission products (FP) in a nitric acid media were studied using iHex-BTP/SiO₂-P adsorbents, which is expected to show high adsorption affinity for MA(III) even in concentrated HNO₃ solution, such as HLLW. In the batch experiments, Pd showed strong adsorption on iHex-BTP/SiO₂-P adsorbents under any concentration of HNO₃. The MA(III) and heavy Ln(III) (Sm(III), Eu(III) and Gd(III)) were also adsorbed at the condition of high HNO₃ concentration, but they showed no adsorption under low HNO₃concentration. The separation factor for MA(III)/heavy Ln(III) took the maximum value (over 100) at around 1mol/dm³ HNO₃. It was difficult to elute MA(III) or heavy Ln(III) selectively by HNO₃ from the iHex-BTP/SiO₂-P adsorbents degradated by γ-ray irradiation. The chromatographic separation of real HLLW by an iHex-BTP/SiO₂-P column showed that MA(III) could be recovered selectively by adjusting the acidity of the feed solution, i.e. HLLW, to 1mol/dm³ and using H₂O as eluant. The adsorption of Pd(II) can be decreased by the addition of appropriate complexing reagents, e.g. DTPA, into HLLW without any effects on the MA(III) adsorption.

Tetravalent Pu reacts with Cs ions to form the crystalline precipitate of Cs₂Pu(NO₃)₆under certain chemical conditions during the U crystallization process. The Cs₂Pu(NO₃)₆precipitate reduces the decontamination factor (DF) of Cs to U in the crystal after being washed. The solubility and thermal properties of Cs₂Pu(NO₃)₆ were studied with the aim of providing a characterization estimate. The solubility of Cs₂Pu(NO₃)₆ increased with decreases in HNO₃ concentration. Loss in weight of the compound caused by thermal degradation of Cs₂Pu(NO₃)₆ to Cs₂PuO₂(NO₃)₄ was observed at 245 °C in thermal analysis. A uranyl nitrate hexahydrate (UNH) crystal was obtained by cooling irradiated fast reactor core fuel dissolver solution. The DF of Cs decreased with increasing the HNO₃ concentration of the mother liquor because more Cs₂Pu(NO₃)₆ precipitates with high concentration of HNO₃.

The separation of americium from the lanthanides and curium is a requirement if transmutation of americium is to be performed in advanced nuclear fuel cycles. Oxidation of Am³⁺ to AmO₂⁺ or AmO₂²⁺ may allow separation of Am from Ln and Cm in one step, since the lanthanides and curium do not have higher oxidation states as accessible. Two possible solid-liquid separation methods have been developed to address this difficult separation. Under acidic conditions using oxone or persulfate, the oxidation and retention of tracer Am in the aqueous phase has been observed with a separation factor of 11 ± 1. Most of these studies have been conducted using ²³⁷NpO₂(NO₃), ²³³UO₂(NO₃)₂, ²³⁸Pu(NO₃)₄ and ²⁴¹Am(NO₃)₃ at radiotracer concentrations. Lanthanides precipitate as the sodium or potassium europium double sulfate salt. Under basic conditions, ozone oxidation of Am(CO₃)OH_(s) solubilizes Am from a lanthanide carbonate hydroxide solid phase to the aqueous phase as the AmO₂(CO₃)₃^4-or AmO₂(CO₃)₃^5- species. For the ozone oxidation of the americium tracer a separation factor of 1.6 ± 0.8 and 47 ± 2 for the oxidation/separation in Na₂CO₃ and NaHCO₃ respectively.

Extraction of Am(III) and Cm(III) between tri-n-butyl phosphate solution and molten calcium nitrate hydrate Ca(NO₃)₂·RH₂O was investigated radiochemically. In the range of water content R = 3.5-8.0, the distribution ratio was found to increase with the decrease of water activity. The dependence of the distribution ratios on the water activity in the hydrate melt changes at around log a_H2O = −0.4, which corresponds to R = 5.0. The extraction behavior of Am(III) and Cm(III) was systematically discussed with the reported data of trivalent lanthanides.

Diamides of dipicolinic acid (N,N'-diethyl-N,N'-ditolyl-dipicolinamide, EtTDPA) were synthesized and evaluated for their extraction capability for actinides. In this work the extractions of neptunium(V), protactinium(V), and thorium(IV) with EtTDPA in a polar fluorinated diluent from nitric acid were investigated. EtTDPA shows a high affinity for Th(IV) even at millimolar concentrations. Np(V) and Pa(V) are both reasonably extractable with EtTDPA; however, near saturated solutions are required to achieve appreciable distribution ratios. A comparison with previously published actinide extraction data is given.

In order to establish a new technique to separate americium from curium and lanthanides in the treatment process of High Active Waste, the feasibility of the separation of Am by reduction to divalent state in chloride melts was studied. As a homologue of the formation of divalent Am and its reaction, electrochemical measurements and electrolysis of Nd were conducted using the LiCl-KCl eutectic melt. Based on the reported formal potentials and the thermodynamic values of the compound of related elements, the feasibility of the Am separation was evaluated. As a result, a rough concept of the new process to be attached to the downstream of the aqueous reprocessing process was proposed.

The sorption of americium (III) by sorbents on the basis of dibenzo-, dicyclohexano-18-crown-6, and their diisooktil- and ditert-butil- substitutors from solutions of HNO₃ of various concentrations and from solutions of HNO₃ contained trichloracetic acid was studied in the present investigation, including the kinetics of sorption. It was found, that the sorbents containing crown-ethers dibenzo-, and dicyclohexano-18-crown-6 without alkyl substitutes have the maximal sorption factors in solutions for 2M nitric acid and also in solutions closed to neutral. It was shown, that sorption of americium (III) by sorbents on the basis of dicyclohexano-18-crown-6 and their alkyl derivatives in the presence trichloracetic acid is higher, than by dibenzo-18-crown-6 and their ones, that, however, depends on a ratio of components in solution. Sorption of americium (III) by sorbents on the basis of dibenzo-, dicyclohexano-18-crown-6 from multicomponent solutions was investigated. It was shown, that using of macrocyclic polyethers for extraction of americium (III) from acid solutions is prospective technique.

The stability constant of the Pu(IV)-acetohydroxamic acid complex Pu(AHA)³⁺ at 1 M ionic strength (pH = 0) has been investigated by method of solvent extraction. Di(2-ethylhexyl) phosphoric acid (HDEHP) was used to extract Pu(IV) from perchloric and nitric acid media at various AHA concentrations. Distribution ratios over a range of ligand concentrations were used in conjunction with graphical methods to obtain logβ₁ = 14.3 ± 0.03 in perchloric acid. The stability constant determined from solutions in nitric acid was excluded because of the uncertainty in plutonium speciation.

The complex chemistry of plutonium under low nitric acid concentration can significantly affect the extraction of tetravalent plutonium by tri-n-butyl phosphate (TBP) in n-dodecane. At low HNO₃ concentrations, the main Pu(IV) species present in the aqueous solution are Pu(OH)³⁺ and Pu(OH)₂²⁺. Moreover, due to the disproportionation reaction of Pu(IV), a mixture of Pu(III), Pu(IV) and Pu(VI) must be considered. Also the colloidal Pu(IV) can be present under certain conditions. Vis-NIR spectroscopy revealed that in 0.1 M nitric acid, the formation of colloids and the disproportionation reaction of Pu(IV) are the main processes responsible for the distribution of plutonium between the organic and aqueous phases. Comparison of absorption spectra of Pu(IV) in TBP extracted from 0.4-10 M nitric acid concentrations confirms presence of two different Pu(IV) species. At lower nitric acid concentration (0.1 M), also colloidal Pu in TBP was observed.

The kinetics of reduction of NpO₂²⁺ to NpO₂⁺ by acetohydroxamic acid in 1 mol·L⁻¹perchloric acid media at 10 and 22°C were studied. The reaction rate was monitored using stopped-flow and standard infrared spectroscopy. Under conditions such that acetohydroxamic acid was in excess relative to Np, the reduction rate of NpO₂²⁺ is described by the following: where k = 2.57x10³ mol⁻¹·L·sec⁻¹ at 10°C. However, when neptunium is in a significant molar excess relative to acetohydroxamic acid, the reduction mechanism is dictated by two distinct reactions. An initial and incomplete reduction occurs as the result of the oxidation of AHA, while a slower and partial reduction of NpO₂²⁺ is likely caused by the oxidation products of AHA. The reaction rate of this first-order mechanism was calculated as 3.7x10⁻⁴ sec⁻¹ at 10°C and 0.001 sec⁻¹ at 22°C.

Management of the oxidation state of neptunium in the reprocessing of spent nuclear fuel by solvent extraction is very important. The kinetics of the oxidation of neptunium(V) by vanadium(V) in solutions of nitrate acid was investigated at constant ionic strength 4M. The reaction rate is first order with respect to Np(V) and V(V). The effects of proton concentration on the apparent second order rate constant k₁" was determined for temperature 25°C as k₁" = (0.99±0.03)·[H+]^1.21M⁻¹s⁻¹. Activation parameters associated with the overall reaction have been calculated; the standard reaction enthalpy and entropy were 52.6±0.9 kJ/mol and -55.8±0.9 J/K/mol respectively.

The solvent combination N,N,N'N'- tetraoctyl diglycolamide (TODGA)/tributyl phosphate (TBP)/odourless kerosene (OK) is examined as a potential solvent system for a Grouped Actinide Extraction (GANEX) process to separate all of the actinides from fission products when reprocessing spent nuclear fuel. A series of solvent extraction batch experiments were performed with a range of TODGA/TBP/OK solvent combinations to assess the sensitivity of distribution values for a number of key elements towards [TBP] (0 — 1.1M), [TODGA] (0.1-0.4M), [HNO₃] (0.1-5M) and heavy metal loading ([U] 0-200g/l). There is little impact on D_Am or D_Eu across the solvent range and no influence from U loading. Excellent D_Np values (> 10) are observed, increasing with increasing [TODGA], with [TBP] having little influence. Such high D_Np values may obviate the need for preconditioning of dissolved fuel feeds to control Np routing. High D_Tc values are found even at 5M HNO₃, therefore Tc is expected to remain in the solvent phase. Both Pu(III) and Pu(IV) are readily extracted with D_Pu(III) > D_Pu(IV). Uranium is extracted by both TBP and TODGA and TBP is shown to effectively compete with TODGA for uranium coordination sites. Third phase formation occurs at high [U] loading and [HNO₃] but is suppressed by increasing [TBP].

The ingenious combination of lactate and diethylenetriamine-N,N,N',N",N"-pentaacetic acid (DTPA) as an aqueous actinide-complexing medium forms the basis of the successful separation of americium and curium from lanthanides known as the TALSPEAK process. While numerous reports in the prior literature have focused on the optimization of this solvent extraction system, considerably less attention has been devoted to the understanding of the basic thermodynamic features of the complex fluids responsible for the separation. The available thermochemical information for both lactate and DTPA protonation and metal complexation reactions are representative of the behavior of these ions under idealized conditions. Significant departures from the speciation predicted based on reported thermodynamic values may be present in the TALSPEAK aqueous environment. Thus, thermodynamic parameters describing the separation chemistry of this process require further examination at conditions significantly removed from conventional ideal systems commonly employed in fundamental solution chemistry. In this report, calorimetric studies of lactate protonation equilibrium illustrate a distinct influence of nitrate, perchlorate, methylsulfonate and triflate on the thermodynamic parameters associated with TALSPEAK aqueous chemistry. Triflate is identified a closer non-complexing representative of lactate solution chemistry. The reported initial two stability constants for the complexation of americium and neodymium by lactate in triflate medium suggest that the identified medium effects do not significantly affect the speciation.

To know the behavior of plutonium in the fluoride volatility process (FLUOREX PROCESS) for the spent nuclear fuel, both UO₂ and PuO₂ are fluorinated by fluorine forming volatile UF₆ and PuF₆, respectively. Then PuF₆ is separated and recovered from UF₆ by using adsorption materials such as uranyl fluoride UO₂F₂. In this paper, adsorption behavior of PuF₆on UO₂F₂ was examined by the use of ²³⁶Pu tracer. First, the stability of UO₂F₂ in F₂atmosphere was analyzed by TG-DTA method showing that uranium volatilized completely over 350 °C by the formation of UF₆ and the adsorption of plutonium by UO₂F₂ should be done at temperatures lower than 250 °C. The behavior of PtF₆ as a chemical analogue of PuF₆ was also conducted for comparison and it showed that the deposition of PtF₄ on UO₂F₂ at 200 °C. When the ²³⁶Pu doped U₃O₈ was reacted with 10%F₂-He gas, the PuF₆ vaporized at ca. 600 °C. Then adsorption of ²³⁶Pu on UO₂F₂ was observed by α ray measurement. The adsorption mechanism of Pu on UO₂F₂ was discussed with experimental data and thermodynamic consideration.

The behaviors of reduction of NpO₂⁺ by controlled potential electrolysis were studied, and a unique time course of electrolysis current was observed. It was concluded that NpO₂⁺ was reduced by two reduction processes, which were the chemical reaction with Np³⁺and the electrocatalytic reduction by adsorbed hydrogen atom on platinum electrode surface. The time courses of current for controlled potential electrolysis of NpO₂⁺ under various conditions of the solution were investigated, and the effects of the concentration of H⁺ and NO₃⁻ on electrolysis behavior were explained by proposed reduction mechanisms. The Np⁴⁺was prepared from NpO₂⁺ in 3 mol dm⁻³ HNO₃ by electrolytic reduction at the potential where evolution of hydrogen gas and reduction of NO₃⁻ were inhibited. The electrolysis efficiency could be improved.

We have continued the studies on the trivalent ions of the 4f and 5f elements. In this paper, we compare the transport properties (self-diffusion coefficient) of the trivalent aquo ions over two ranges of concentrations (0 — 2×10⁻³M) and (2×10⁻³ — 1.5M). Self-diffusion coefficients, D, of the trivalent f-element aquo ion series have been determined in aqueous background electrolytes of Gd(NO₃)₃ and Nd(ClO₄)₃, at pH=2.5 (HNO₃, HClO₄) and at 25°C using the open-end capillary method (O.E.C.M.). This method measures the transportation time of ions across a fixed distance. In this paper, we complete a measurement of self-diffusion coefficient for terbium. We optimized the pH to avoid hydrolysis, ion-pairing and complexation of the trivalent 4f and 5f ions. The variation of D versus √C is not linear for dilute solutions (0 — 2×10⁻³M) and quasi-linear in moderate concentrations (C≤1.5 M). Similar behavior was observed for Tb, as compared with those for Bk, Eu and Gd. We complete the comparison variation of D/D° versus √C for all studied 4f and 5f elements from concentration 0 to 1.5M and we obtained the same variation with √C for all studied elements. All 4f and 5f elements studied follow the Nernst-Hartley expression.

Redox reactions of tetravalent uranium ion in calcium chloride hexahydrate CaCl₂·6H₂O melt ([CaCl₂] = 6.9 M) were studied electrochemically and spectrophotometrically. Cyclic voltammograms in CaCl₂·6H₂O melt containing UCl₄ were measured with a pyro-graphite carbon working electrode. A cathodic peak corresponding to the reduction of U⁴⁺ to U³⁺ was observed, and it was found to be controlled by the diffusion of U⁴⁺ in the melt. Although the concentration of H⁺ in the melt was negligible, the redox reaction of U⁴⁺ was observed without the disturbance of hydrolysis. The formal potential of the U⁴⁺|U³⁺ couple was determined to be -0.483 ± 0.005 V vs. NHE. The diffusion coefficient of U⁴⁺ in CaCl₂·6H₂O melt was determined to be 1.5 × 10⁻⁷ cm² s⁻¹ at 300 K. The anodic peak in the voltammogram was attributable to the oxidation of U⁴⁺ to UO₂²⁺, which was identified by using a technique based on the combination of electrolysis and spectrophotometry. Influences of the water content on chemical status of uranium ions in CaCl₂ hydrate melts were studied.

Simple hydroxamic acids (XHAs) are salt free, organic compounds with affinities for cations such as Np⁴⁺, Pu⁴⁺ and Fe³⁺. As such they have been identified as suitable reagents for the separation of either Pu and/or Np from U in modified or single cycle Purex based solvent extraction processes designed to meet the emerging requirements of Advanced Fuel Cycles. Acid catalyzed hydrolysis of free XHAs is well known and may impact negatively on reprocessing applications. The hydrolysis of metal-bound XHAs within metal ion-XHA complexes is less understood.

Using a model derived for the study of hydroxamic acid hydrolysis in the presence of non-oxidising metal ions (Np (IV) and Fe(III)), we review data pertaining to the hydrolysis of hydroxamic acids in the presence of the oxidising Pu⁴⁺ ion, under conditions where the influence of the redox processes may potentially be neglected.

Studies carried out at BARC, India on the development of new extractants for reprocessing of spent fuel suggested that while straight chain N,N-dihexyloctanamide (DHOA) is promising alternative to TBP for the reprocessing of irradiated uranium based fuels, branched chain N,N-di(2-ethylhexyl)isobutyramide (D2EHIBA) is suitable for the selective recovery of ²³³U from irradiated Th. In advanced fuel cycle scenarios, the coprocessing of U/Pu stream appears attractive particularly with respect to development of proliferation resistant technologies. DHOA extracted Pu(IV) more efficiently than TBP, both at trace-level concentration as well as under uranium/plutonium loading conditions. Uranium extraction behavior of DHOA was however, similar to that of TBP during the extraction cycle. Stripping behavior of U and Pu (without any reductant) was better for DHOA than that of TBP. It was observed during batch studies that whereas 99% Pu is stripped in four stages in case of DHOA, only 89% Pu is stripped in case of TBP under identical experimental conditions. DHOA offered better fission product decontamination than that of TBP. GANEX (Group ActiNide EXtraction) and ARTIST (Amide-based Radio-resources Treatment with Interim Storage of Transuranics) processes proposed for actinide partitioning use branched chain amides for the selective extraction of uranium from spent fuel feed solutions. The branched-alkyl monoamide (BAMA) proposed to be used in ARTIST process is N,N-di-(2-ethylhexyl)butyramide (D2EHBA). In this context, the extraction behavior of U(VI) and Pu(IV) were compared using D2EHIBA, TBP, and D2EHBA under similar concentration of nitric acid (0.5 — 6M) and of uranium (0-50g/L). These studies suggested that D2EHIBA is a promising extractant for selective extraction of uranium over plutonium in process streams. Similarly, D2EHIBA offered distinctly better decontamination of ²³³U over Th and fission products under THOREX feed conditions. The possibility of simultaneous stripping and precipitation of thorium (as oxalate) from loaded organic phase was explored using 0.05M oxalic acid. Ammonium diuranate (ADU) precipitation was performed on the oxalate supernatant for the recovery of uranium. Quantitative recovery (>99.9%) of Th as well as of U was achieved. Radiolytic studies suggested that irradiated DHOA and D2EHIBA behaved better with respect to fission product decontamination as compared to that of TBP.

First-principles density-functional theory (DFT) calculations have been used to investigate the electronic structure and total energy of Pu. In particular, we will present calculated electronic and elastic properties for several of its known phases. Generally, our obtained results compare favorably with the existing experimental data. Because of the limited availability of single crystals of plutonium, our calculated elastic constants are averaged to enable a comparison with data from polycrystal samples in some cases. The results presented suggest that the DFT model for plutonium is able to capture the main characteristics of the electronic structure, chemical bonding, and total energy.

We use the self-interaction corrected local spin-density approximation in order to describe localization-delocalization phenomena in the strongly correlated actinide materials. Based on total energy considerations, the methodology enables us to predict the ground-state valency configuration of the actinide ions in these compounds from first principles. Here we review a number of applications, ranging from electronic structure calculations of actinide metals, nitrides and carbides to the behaviour under pressure of intermetallics, and O vacancies in PuO₂.

We report ab initio calculations of the influence of gallium and aluminum substitution on the crystallographic and electronic structures of plutonium. Although ab initio calculations within standard density functional theory are unable to reproduce all the complexity of electronic structure of plutonium, we show here that this approach does give the major trends for unalloyed and alloyed plutonium. In particular, we present computed crystallographic structure and elastic moduli for Ga and Al substituted Pu alloys. For the theoretical equilibrium volume of the α phase, the shear modulus of the α phase containing 6.5 at. % Ga shows a large decrease, inducing a phase transformation to a new monoclinic structure.

The electronic structures and Kondo insulator state of the Pu monochalcogenides are computationally investigated, using the local density approximation (LDA), the LDA+U and dynamical mean field theory (LDA+DMFT) methods. We show that an enhanced hybridization of the Pu-5f state with the conduction bands occurs through the dynamical effect in the DMFT, which leads to the effective formation of a small energy gap around the Fermi level. Our LDA+DMFT calculations explain quantitatively the anomalous energy gap enhancement under pressure, observed for PuTe. The peculiar change of the energy gap of PuTe with pressure is found to result from a subtle crossover in the k-dispersion of the lowest excited states.

The effects of various chemical substitutions and induced lattice disorder in the Ce- and Pu-based 115 superconductors are reviewed, with particular emphasis on results from x-ray absorption fine structure (XAFS) measurements.

We will report the results of our recent inelastic neutron scattering study on β-US₂. This compound shows a semi-metallic or narrow gap semi-conducting behaviour at room temperature. A clear exponential up-turn of the resistivity in the order of ~10⁶ Ωcm has been observed below 100 K. We found a sharp inelastic peak at the excitation energy of about 7 meV at 8 K. The Q-dependence of the peak intensity is in good agreement with the magnetic form factor of U⁴⁺ ion and no clear dispersion relation has been observed. Therefore we concluded that this is a crystalline electric field (CEF) excitation peak. The excitation energy is in good agreement with the CEF level scheme obtained from the susceptibility data. The CEF peak intensity decreases with increasing temperature and becomes much weaker than the calculated temperature factor expected from the CEF level scheme. Furthermore a quasi-elastic response appears, and coexists with a broadened CEF peak at higher temperatures. The quasi-elastic component is not due to phonon, because the temperature dependence of the intensity is inconsistent with calculation. We concluded that this quasi-elastic response is a hybridization effect of U-5f electrons with, most likely, p-electrons of sulfur. It is highly interesting that the energy scale of the CEF peak (~7 meV) is very close to the conduction gap (90K), and the quasi-elastic component appears above the characteristic temperature of about 100 K. Our data strongly suggest that the crossover of 5f character plays an import role for the metal-insulating transition in β-US₂.

We studied the electronic states of three typical neptunium compounds, NpGe₃, NpRhGa₅ and NpCd₁₁. Among them, NpGe₃ and NpCd₁₁ with the cubic crystal structure are paramagnets without magnetic ordering, while NpRhGa₅ with the tetragonal structure is an antiferromagnet. At high temperatures, the 5f electrons in NpGe₃ are almost localized, and the magnetic susceptibility χ(T) approximately follows the Curie-Weiss law. With decreasing temperature, χ(T) shows a broad peak around 50 K, indicating a moderate heavy fermion state at lower temperatures. In fact, the results of the de Haas-van Alphen (dHvA) experiments for NpGe₃ are well explained by the 5f-itinerant band model; namely, the 5f electrons contribute to the Fermi surface and the cyclotron effective mass. The cyclotron mass is thus enhanced, ranging from 2.6 to 16 times the rest mass of the electron m₀. In the antiferromagnet NpRhGa₅, it was clarified from the results of dHvA experiments and energy band calculations that the 5f electrons contribute to the Fermi surface. The cyclotron mass varies from 8.1 to 11.7 m₀, and the magnetic moment is 0.89 μ_B/Np. In NpCd₁₁, the 5f electrons are localized in the whole temperature range and do not contribute to the Fermi surface. The corresponding cyclotron mass is thus light, below 1 m₀, revealing no hybridization between the localized 5f electrons and the conduction electrons. The Fermi surface consists of small closed Fermi surfaces, reflecting the small Brillouin zone associated to the large unit cell of the crystal structure in NpCd₁₁. The long Np-Np nearest-neighbor distance (6.568 Å) results in the well localized 5f⁴states. Magnetic susceptibility and magnetization curves are well explained in a crystalline electric field (CEF) scheme assuming a singlet ground state and an excited triplet state separated by a 120 K energy gap.

This contribution focuses on the structural and physical properties of U-based Laves phases. It starts with the structural description of the different type of Laves phases, followed by a brief description of the factors that affect their stability. The majority of the uranium Laves phases show a weakly paramagnetic behaviour. The reason is the compact structure of the phases that leads to small a U-U spacing as well as very high coordination numbers, regarding both the uranium and the ligands sublattices, which brings a strong hybridization with non-f states. However, there are some exceptions of uranium Laves phases that do order magnetically (UFe₂, UNi₂ and the recently discovered U₂Fe₃Ge compound). These exceptions are discussed in more detail in the present manuscript.

We succeeded in growing a high-quality single crystal of NpCd₁₁ with the cubic BaHg₁₁-type structure by the Cd-self flux method. The lattice parameter of a = 9.2968(2) Å and crystallographic positions of the atoms were determined by x-ray single-crystal structure analysis. From the results of the magnetic susceptibility and specific heat experiments, this compound is found to be a 5f-localized paramagnet with the singlet ground state in the crystalline electric field (CEF) scheme. Fermi surface properties were measured using the de Haas-van Alphen (dHvA) technique. Long-period oscillations were observed in the dHvA frequency range of 9.1 x 10⁵ to 1.9 x 10⁷ Oe, indicating small cross-sectional areas of Fermi surfaces, which is consistent with a small Brillouin zone based on a large unit cell. From the results of dHvA and magnetoresistance experiments, the Fermi surface of NpCd₁₁ is found to consist of many kinds of closed Fermi surfaces and a multiply-connected-like Fermi surface, although the result of energy band calculations based on the 5f-localized Np³⁺(5f⁴) configuration reveals the existence of only closed Fermi surfaces. The corresponding cyclotron effective mass is small, ranging from 0.1 to 0.7 m₀, which is consistent with a small electronic specific heat coefficient γ ≅ 10mJ/K²·mol, revealing no hybridization between the 5f electrons and conduction electrons.

The partial martensitic δ→α' transformation in plutonium alloys is sensitive to chemical composition, sample thermal history, as well as crystalline defects. The present work investigates the δ-Pu phase microstructure before and after the martensitic transformation δ→δ+α'. More precisely, microstructural modifications of the host δ-phase, resulting from the stress induced by a cell volume difference of 19% between the δ and α'-phases, were analysed. Microstructural information about crystallite size and microstrain of a highly homogenized Pu-Ga alloy was extracted from x-ray diffraction patterns using a three dimension crystallite size and microstrain model. This is available in Rietveld refinement software and consists in anisotropic broadening analysis of diffraction peaks. Crystallite size doesn't significantly change with the phase transformation contrary to microstrain that is multiplied, on average, by five. Furthermore, internal normal and shear microstress are multiplied, respectively, by 2 and 13 when α'-phase appears. Last, dislocation densities, calculated from crystallite size and microstrain, are compared to TEM results available in the literature.

Presented are results of the production and X-ray examination of micro-samples of americium-241 compounds with gold and copper produced by high-temperature condensation of metal americium vapor onto corresponding substrates. No mutual solubility of the investigated system components was revealed at room temperature. The following three intermetallic compounds were revealed in the Am-Au system: Au₆Am with tetragonal lattice of the Au₆Sm structural type, AuAm with orthorhombic lattice of the CuCe structural type and AuAm with cubic lattice. The Am-Cu system showed the intermetallic compound Cu₅Am (Cu₇Am) with a hexagonal lattice of the Cu₅Ca(Cu₇Tb) structure type. An effect of the ²⁴¹Am nuclide alpha-activity on the crystal structure of the produced intermetallide was studied.

Presented are results of the production and X-ray examination of micro-samples of curium-244 alloys with iron, cobalt and ruthenium produced by high-temperature condensation of metal curium vapor onto corresponding substrates. The investigated system components did not exhibit mutual solubility at room temperature. In the Cm-Fe system two intermetallic compounds were found: Fe₁₇Cm₂ (the Ni₁₇Th₂ structural type) and Fe₂Cm (the Cu₂Mg structural type). In the Cm-Co system three intermetallics were revealed: Co₁₇Cm₂ (the Ni₁₇Th₂structural type), Co₅Cm (the Cu₅Ca structural type) and intermetallide Co₂Cm (the Cu₂Mg structural type). In the Cm-Ru system intermetallides Ru₂Cm (the Zn₂Mg structural type) and Ru₃Cm (the Cu₃Au structural type) were detected. An effect of high alpha-activity of ²⁴⁴Cm nuclide on crystal structures of the obtained intermetallides was investigated.

Scientific and technical demand stimulates an extension of the practical implementation field of TPE, requirements to their ecological safety calling for the development of such materials which could be most resistant to the environment and most suitable for the production of a wide range of sources different in their application and design. Such materials can involve pure metals of transplutonium elements and their alloys with metals of platinum group as well as their chemically stable compounds (such as silicides, carbides etc.)

At SSC RIAR production processes of sources of different type and application have been implemented. Examples of the most recent developments of the sources are presented below. Presented is the analysis of the current state of issues related to designing, production and application of radionuclide research sources based on transplutonium elements. Examples of the development of the most up-to-date sources of alpha-, gamma- and neutron radiation and also fission ones are considered.

Plutonium is the element with the greatest number of allotropic phases. Thermally induced transformations between these phases are typically characterized by thermal hysteresis and incomplete phase reversion. With Ga substitutional in the lattice, low symmetry phases are replaced by a higher symmetry phase. However, the low temperature martensitic phase transformation (δ→α') in Ga stabilized δ-phase Pu is characterized by a region of thermal hysteresis which can reach 200°C in extent. These regions of thermal hysteresis offer a unique opportunity to study thermodynamics in inhomogeneous systems of coexistent phases. The results of thermophysical properties measured for samples of inhomogeneous unalloyed and Ga alloyed Pu will be discussed and compared with similar measurements of their single phase constituents.

UNiSi₂ orders ferromagnetically below T_Curie = 95 K. This material crystallizes in the orthorhombic CeNiSi₂-type structure. The uranium atoms form double-layers, which are stacked along the crystallographic b axis (the longest axis). From magnetization measurements the easy (hard) magnetization axis is the c axis (b axis). ²⁹Si-NMR measurements have been performed in the paramagnetic state. In UNiSi₂, two crystallographic Si sites exist with orthorhombic local symmetry. The Knight shifts on each Si sites have been estimated from these spectra of random and oriented powders. The transferred hyperfine couplings have been also derived. It is found that the transferred hyperfine coupling constants on each Si sites are nearly isotropic, and that their Knight shift anisotropy comes from that of the bulk susceptibility. The nuclear-spin lattice relaxation rate 1/T₁ shows temperature-independent behaviour, which indicates the existence of localized 5f electrons.

Elemental plutonium (Pu) assumes more crystal structures than other elements, plausibly due to bonding f electrons becoming non-bonding. Complex geometries hamper understanding of the transition in Pu, but calculations predict this transition in a system with simpler geometry: alternating layers either of plutonium and lead or of plutonium and indium. Here the transition occurs via a pairing-up of atoms within Pu layers. Calculations stepping through this pairing-up reveal valuable details of the transition, for example that the transition from bonding to non-bonding proceeds smoothly.