Symposium Organizers
David Shuh, Lawrence Berkeley National Laboratory
Ladia Havela, Charles University
Alexander Landa, Lawrence Livermore National Laboratory
Daniel Schwartz, Los Alamos National Laboratory
Symposium Support
Lawrence Livermore National Laboratory
EE13.1: Plutonium
Session Chairs
Alexander Landa
Per Soderlind
Tuesday PM, March 29, 2016
PCC North, 200 Level, Room 221 A
2:30 PM - *EE13.1.01
Density-Functional Theory for Plutonium: Phase Stability, Elasticity, Phonons, and Magnetic Structure
Per Soderlind 1,Fei Zhou 1,Alexander Landa 1,John Klepeis 1
1 Lawrence Livermore National Laboratory Livermore United States,
Show AbstractWe apply density-functional theory (DFT) to compute phase stability, elasticity, phonons, and magnetic structure for plutonium. The DFT model accurately predicts this very broad range of properties for plutonium because the character of the 5f electrons is very well captured by itinerant (band like) states that are perturbed by spin and orbital interactions. The DFT total energy is obviously quite accurate because otherwise phase stability, elastic constants, and lattice dynamics could not be computed realistically. Beyond that, the electronic structure itself compares well with experimental photoemission spectra while the long-standing controversy over the DFT prediction of magnetism is finally over because of results from recent neutron-scattering measurements. This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.
3:00 PM - EE13.1.02
The Mixed-Valent Ground State of delta-Pu Probed by Inelastic Neutron Scattering
Eric Bauer 1
1 Los Alamos National Laboratory Los Alamos United States,
Show AbstractPu is arguably the most complex elemental metal in the periodic table because its 5f electrons are tenuously poised at the edge between localized and itinerant configurations. This complex electronic structure leads to emergent behavior—all a direct consequence of its 5f electrons—including six allotropic phases, large volumetric changes associated with these transitions of up to 25%, and mechanical properties ranging from brittle alpha-Pu to ductile delta-Pu. Pu also exhibits a Pauli-like magnetic susceptibility, electrical resistivity, and a Sommerfeld coefficient of the specific heat that are an order of magnitude larger than in any other elemental metal. We have investigated the magnetic fluctuation spectrum of delta-Pu via inelastic neutron scattering using the ARCS spectrometer at SNS [1]. Our study reveals that the ground state of plutonium is governed by valence fluctuations, that is, a quantum-mechanical admixture of distinct 5f electronic configurations. Our results, which are in quantitative agreement with dynamical mean field theory calculations, show that the magnetism in Pu is not "missing" but is dynamic and driven by virtual valence fluctuations. Our measurements provide a straightforward interpretation of the microscopic origin of the large, Pauli-like magnetic susceptibility of delta-Pu. Finally, because the various valence configurations imply distinct sizes of the Pu ion, the valence-fluctuating ground state also gives a natural explanation for its complex structural properties and notably the large sensitivity of its volume to small changes in temperature, pressure or doping.
[1] Marc Janoschek, Pinaki Das, Bismayan Chakrabarti, Douglas L. Abernathy, Mark D. Lumsden, Jon M. Lawrence, Joe D. Thompson, Gerard H. Lander, Jeremy N. Mitchell, Scott Richmond, Mike Ramos, Frans Trouw, Jian-Xin Zhu, Kristjan Haule, Gabriel Kotliar, and Eric D. Bauer, “The valence fluctuating ground state of plutonium,” Science Advances 1, e1500188 (2015)
3:15 PM - *EE13.1.03
Racah Materials: Role of Atomic Multiplets and Intermediate Valence in f-Electron Systems
Alexander Lichtenstein 1,Alexander Shick 2,Jindrich Kolorenc 2,Mikhail Katsnelson 3
1 University of Hamburg Hamburg Germany,2 Institute of Physics ASCR Prague Czech Republic3 Radboud University Nijmegen Nijmegen Netherlands
Show AbstractTheoretical description of many actinide systems with with strongly interacting f-electrons is still far from being perfect. Local density approximation (LDA) scheme is often failed for correlated materials containing f-elements with complicated spectral function and intermediate valence state. Dynamical mean field theory (DMFT) in combination with the first-principle scheme (LDA+DMFT) which take into account full non-spherical local interaction vertex for f-shell can resolve the long-standing mystery of the nonmagnetic state of different intermediate valence f-electron ystems. Combination of atomic-like multiplets with spin-orbital coupling and pronounced hybridization to conducting bands are essential to describe complicated non-magnetic states of many actinide compounds. We found that one of the f-sub-bands has a well-pronounced multiplet structure in solids, and for another f-part of the spectrum, the multiplets are merged into a single quasiparticle sub-band. As example, we consider elemental actinide metals, plutonium hexaborides and light actinide dioxides. Comparison with experimental photoemission spectra support the crucial role of complex spin-orbital multiplets from mixed f-configurations differently hybridized with ligand states in such Racah materials.
4:15 PM - *EE13.1.04
Phase Transformations in PuGa 1at.% Alloy
Brice Ravat 1,Benoit Oudot 1,Fanny Lalire 1,Francois Delaunay 1,Aurelien Perron 1
1 CEA-Valduc Is sur Tille France,
Show AbstractThe metastable PuGa 1 at.% alloy exhibits low-temperature martensitic transformation. The kinetics of this process were studied experimentally via in situ XRD characterizations performed during isothermal holds. This revealed a double-C time–temperature–transformation diagram. The originality of our results lies in the demonstration of the existence of different martensite morphologies corresponding to the upper and lower parts of the TTT diagram. These microstructural variations seem to be the result of different accommodation mechanisms. The experimental nucleation rate study has suggested an autocatalytic character of the isothermal martensitic nucleation process as well as a large sensitivity to elastic and plastic strain. Indeed, the incubation period and subsequent increase in nucleation rate could be related to the appearance of new embryos rather than the growth of existing plates, while the partial character of the transformation may be attributed to interactions between plates that are being formed in the two-phase δ + α’ alloy. These hypotheses have been confirmed by the classical heterogeneous nucleation approach by Pati and Cohen, which takes into account the autocatalytic character of the transformation. This approach has also indirectly revealed the existence of restraining forces that reflect a high sensitivity of the energy barrier for nucleation to the α’ phase amount.
The influence of an applied external stress on martensitic transformation was also investigated. Special sample holders were developed to perform dilatometry and in situ XRD on samples under tensile and compressive loading. Results have revealed a good correlation between experimental Ms variations and those calculated considering Patel and Cohen theory.
After martensitic transformation, biphasic PuGa 1 at.% alloy behavior upon heating was studied highlighting activated mechanisms occurring during the whole reversion process. Indeed, results have revealed that the reverse transformation of the two-phase δ + α’ alloy during heating involves two competing modes, namely direct and indirect reversion. The latter is associated with Ga diffusion process that governs the ratio between these reversion modes. More precisely, our study demonstrates that the indirect reversion process consists of a Ga-enrichment of the remaining δ phase as well as the emergence of the β and γ phases of pure plutonium. In addition to these experimental results, thermodynamic calculations based on the CALPHAD method were performed and have contributed to the elucidation the origin of the competition between these two reversion modes, especially between direct reversion and the first step of indirect reversion. Indeed, they have revealed that if both reversion modes were possible, indirect reversion was more favorable and that the key aspects of reversion mechanisms, are the heating rate, initial α’ phase fraction and Ga content
4:45 PM - EE13.1.05
EXAFS Investigations of Radiation Damage in Plutonium
Daniel Olive 2,Corwin Booth 1,Alison Pugmire 2,Sarah Hernandez 2,Paul Tobash 2,Eric Bauer 2,Franz Freibert 2
1 Lawrence Berkeley National Laboratory Berkeley United States,2 Los Alamos National Laboratory Los Alamos United States,1 Lawrence Berkeley National Laboratory Berkeley United States2 Los Alamos National Laboratory Los Alamos United States
Show AbstractRadiogenic aging in plutonium systems involves a complex set of interrelated processes, including alpha-decay and He in-growth, radiation-induced defects and distortions in the crystal lattice, damage annealing, and phase instability. Local structure measurements, through Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy have been performed on delta-phase plutonium alloys. Local coordination and structural properties have been determined after a series of isochronal annealing experiments, designed to study the temperature regime in which the various damage recovery mechanisms activate to repair the lattice. These results are compared to simulated EXASFS spectra from spectra derived from simulations. That, along with information from complimentary techniques, can potentially be used to inform and benchmark molecular dynamics simulations, allowing for more useful predictions of materials properties over time.
5:00 PM - *EE13.1.06
Thermal Expansion of Delta-Phase Plutonium
Jeremy Mitchell 1,Franz Freibert 1,Scott Richmond 1,Daniel Schwartz 1
1 Los Alamos National Laboratory Los Alamos United States,
Show AbstractThe face-centered cubic δ-phase of pure Pu is stable from ~315-450 °C and has a mean thermal expansion coefficient (αm) of -9x10-6. Addition of as little as 1 atomic % Ga will stabilize δ-Pu below room temperature. This stabilization has a dramatic effect on thermal expansion as a function of Ga content, with αm ranging from 1x10-6 for Pu-2 atomic % Ga to 16x10-6 for Pu-12 atomic % Ga. Thermal expansion of both thermally- and solute-stabilized δ-Pu can be quite variable depending on factors such as prior thermal histories and microstructure. We have been studying other influences on the thermal expansion behavior of δ-Pu, and in this presentation we will discuss recent work on aging and hydrogen content effects coupled with bulk alloy composition.
5:30 PM - EE13.1.07
Time-Dependent Local and Average Structural Evolution of Pu-2at.%Ga Alloys
Alice Smith 1,Katharine Page 2,Olivier Gourdon 1,Joan Siewenie 2,Scott Richmond 1,Tarik Saleh 1,Michael Ramos 1,Daniel Schwartz 1
1 Los Alamos National Laboratory Los Alamos United States,2 SNS Oak Ridge National Laboratory Oak Ridge United States
Show AbstractPlutonium metal is a very unusual element, exhibiting six allotropes at ambient pressure, from room temperature to its melting point, a complicated phase diagram, and a complex electronic structure. Many phases of plutonium metal are unstable with temperature, pressure, chemical additions, and time. These strongly affect structure and properties, and become of high importance particularly when considering effects on structural integrity over long time periods. The fcc δ-phase deserves additional attention, not only in the context of understanding the electronic structure of Pu, but also as one of the few high-symmetry actinide phases that can be stabilized down to ambient pressure and room temperature by alloying it with trivalent elements.
Total scattering pair distribution function (TS-PDF) is a powerful tool for detecting subtle structural changes, utilizing not only the traditional Bragg scattering from a material, but also the diffuse scattering, and providing a good overview of the average structure, and information on the local structure. Room temperature/ambient pressure neutron total scattering measurements were conducted on the Neutron Powder Diffractometer (NPDF) at the Lujan Neutron Scattering Center, Los Alamos National Laboratory.
Results on a recent study on short-term aging of Pu-2at.%Ga alloy by neutron TS-PDF will be discussed. This work was funded by the US DOE-BES under FWP#2012LANLE389, 20110011DR, and NNSA LANSCE-LC FY2015 and FY2016.
Symposium Organizers
David Shuh, Lawrence Berkeley National Laboratory
Ladia Havela, Charles University
Alexander Landa, Lawrence Livermore National Laboratory
Daniel Schwartz, Los Alamos National Laboratory
Symposium Support
Lawrence Livermore National Laboratory
EE13.2/EE12.2/MD8.3: Joint Session: Actinide Materials—Radiation Damage
Session Chairs
Gianguido Baldinozzi
Thibault Charpentier
Blas Uberuaga
Gary Was
Wednesday AM, March 30, 2016
PCC West, 100 Level, Room 106 BC
9:30 AM - *EE13.2.01/EE12.2.01/MD8.3.01
Ion Irradiation for Studying Multiscale Radiation Effects in Structural Materials and Fuels
Gary Was 1,Jian Gan 2
1 University of Michigan Ann Arbor United States,2 Idaho National Laboratory Idaho Falls United States
Show AbstractUnderstanding the evolution of microstructures in irradiated materials is key to both the prediction of their future behavior and the development of advanced, radiation tolerant materials. Well controlled and carefully tailored ion irradiation has been successful at creating most of the features as well as their time and spatial evolution in LWR core structural materials such as stainless steels and zirconium alloys, and in fast reactor candidate materials such as ferritic-martensitic steels. Evolution of defect cluster distribution, loop size distribution, precipitate formation and growth, segregation to interfaces, and void nucleation and growth have all been captured using ion irradiation. The co-implantation of He to simulate transmutation is important in the procssess of void nucleation and growth, and co-injection of H accounts for uptake from the water in LWR components. Such techniques can also be applied to fuels in which fission gasses combine with radiation damage to play a key role in the evolution of microstructure and mechanical properties. This talk will focus on the application of carefully tailored ion irradiation as a means of capturing the multiscale nature of radiation effects in actinides.
10:00 AM - EE13.2.02/EE12.2.02/MD8.3.02
Radiation Induced Fission Gas Diffusion in UO2
Michael Cooper 2,David Andersson 2,Patrick Burr 1,Navaratnarajah Kuganathan 1,Michael Rushton 1,Robin Grimes 1,James Turnbull 3,Christopher Stanek 2
2 Materials Science and Technology Division Los Alamos National Laboratory Los Alamos United States,1 Materials Imperial College London London United Kingdom3 Independent Advisor London United Kingdom
Show AbstractThe release of fission gases during normal and accident conditions is of key importance for the safe operation of nuclear fuel. The release of fission gas can result in over pressurization of the fuel clad and can alter heat transfer from the fuel. At lower temperatures, such as those in the periphery of the pellet, the gas diffusivity is found to be athermal and is said to be driven by damage cascades. In fact, it is shown experimentally to be proportional to the fission rate. Underpinning this behavior are atomic scale processes that can be investigated through molecular dynamics. Firstly, potential parameters are developed for Xe and Kr that are consistent with a previously developed manybody potential for UO2 by force matching between molecular dynamics and density functional theory. Subsequently, we investigate the mobility of fission gases, Xe and Kr, during radiation damage cascades. By examining the effect of PKA energy and of multiple cascades occurring on the same region of crystal we attempt to link individual damage cascade simulations to the experimentally determined relationship between fission rate and gas diffusivity.
10:15 AM - EE13.2.03/EE12.2.03/MD8.3.03
Small Angle X-Ray Scattering Study of Helium Bubbles in Plutonium
Anthony Van Buuren 1,Jason Jeffries 1,Trevor Willey 1,Mark Wall 1,Jan Ilavsky 2
1 Lawrence Livermore National Lab Livermore United States,2 APS Argonne National Laboratory Argonne United States
Show AbstractThe evolution of inert gas bubbles in metals has important implications on the evolution of the mechanical properties of nuclear materials as well as materials in highly irradiating environments, such as those expected in next-generation nuclear reactors. The presence of gas bubbles in metallic lattices can profoundly alter the mechanical properties and strength of materials leading to embrittlement, swelling, and blistering. The behaviors of gas bubbles are thus important components of any evaluation of the effects of irradiation-induced aging in a material. The alpha decay of plutonium in PuGa alloys continually generates inert He atoms within the lattice of the PuGa matrix. In naturally aged Pu specimens, those He atoms form into bubbles, He-filled vacancy clusters, with a characteristic size from 2-10nm. Upon annealing, the He bubbles are subject to temperature induced changes which results in a coarsening of the bubble distribution yielding a lower bubble density but larger average bubble sizes up to 60nm. The formation of the He bubbles in PuGa alloys has been studied by TEM however concern has been raised that the preparation of very thin samples (> 1 micron) needed in the TEM experiment together with low number of voids in any particular TEM images may skew the measured He bubble concentration and distribution. To resolve these outstanding issues we have used a combination SAXS and USAXS to examine the formation and growth of He bubbles in aged and temperature annealed PuGa alloys. Development of non destructive volumetric probes for nuclear materials is needed to confirm TEM results and validate models of Pu aging.
10:30 AM - *EE13.2.04/EE12.2.04/MD8.3.04
He Bubble Structure Evolution and Effect on the Mechanical Properties of Metals Studied Using Novel Microscopy Techniques
Peter Hosemann 1,Zhangjie Wang 2,Frances Allen 1,David Frazer 1,Mehdi Balooch 1
1 Nuclear Engineering University of California-Berkeley Berkeley United States,1 Nuclear Engineering University of California-Berkeley Berkeley United States,2 State Key Laboratory for Mechanical Behavior of Materials Jiaotong University Xi'an China
Show AbstractThe materials deployed in many nuclear applications suffer from the buildup of helium generated as a result of neutron bombardment. Typically the He is not soluble in the target material and forms nano-sized bubbles within it. Due to the fact that studying the buildup of He bubbles in actual active materials is obviously difficult, surrogate materials and He implantation studies are utilized to understand the underlying effects. In this work we utilize the new ORION Nanofab, an He/Ne and Ga ion beam microscope, to implant He into Cu to develop an understanding of the formation of the He bubble superlattices and their effect on the mechanical properties of the material. In situ TEM nanocompression tests are performed to quantify the changes in the mechanical properties and to observe the evolution of the He bubble structure under stress. In addition, we present first results from correlative microscopy of the He implanted surfaces.
11:00 AM - EE13.2/EE12.2/MD8.3
BREAK
11:30 AM - *EE13.2.05/EE12.2.05/MD8.3.05
Radiation Damages in Nuclear Waste Glasses: An NMR Point of View
Thibault Charpentier 2,Sylvain Peuget 1,Alexandre Le Gac 3,Bruno Boizot 3,Cindy Rountree 4,Laura Martel 5,Joseph Somers 5
2 CEA, IRAMIS, NIMBE - UMR CEA-CNRS 3685 Gif-sur-Yvette France,1 CEA, DEN, LMPA Bagnols-sur-Cèze France1 CEA, DEN, LMPA Bagnols-sur-Cèze France,3 CEA, IRAMIS, LSI Gif-sur-Yvette France3 CEA, IRAMIS, LSI Gif-sur-Yvette France4 CEA, IRAMIS, SPEC - UMR CEA-CNRS 3680 91191 Gif-sur-Yvette France5 Institute for Transuranium Elements (ITU) European Commission, Joint Research Centre (JRC) 76125 Karlsruhe Germany
Show AbstractBorosilicate glasses have been recognized as valuable materials for the conditioning of nuclear wastes. An important issue for their long-term behaviour is radiation effects which may impact their performance and stability. To address these concerns, a fundamental understanding of the origin at the atomic scale of the macroscopic property evolutions must be established. Over the last decade, magic-angle spinning nuclear magnetic resonance (MAS NMR) has firmly established itself as one of the most powerful tool to investigate a glass’s structure. It offers several probes of the local structure, nuclei such as 11B, 23Na, 27Al, 29Si and 17O, to probe changes either in the glass network or in the alkali distribution.
Recently, using external heavy ions irradiation (Xe, Au, Kr) to simulate alpha decays,[1-3] dramatic changes in the local network structure were evidenced : conversion of tetrahedral BO4 units into planar trigonal BO3 units (11B), appearance of high-coordination aluminum units (AlO5, AlO6); glass depolymerisation (29Si) and changes in the distribution of alkali cations (23Na). Additionally, the spectra broaden globally which supports the hypothesis of an increased topological disorder after irradiation. All these structural changes are similar to those observed with increasing the glass temperature or quenching rate and support therefore the model of ballistic disordering fast quenching events which induce a new glassy state with higher fictive temperature. Effects of external electronic (beta) irradiations will be also discussed. If NMR spectra variations show similar trends -but much less pronounced- they are mainly engendered by alkali migration phenomena and formation of molecular oxygen.
Until recently, these studies were limited to externally irradiated samples (enabling the different components of irradiation to be dissociated for their precise investigation), but recently, the first MAS-NMR experiments could be performed on radioactive glasses (doped with 244Cm 0.1 % mol.) paving the way for future MAS NMR examinations of self-irradiation damages in glasses. Experiments were performed at the Joint Research Centre Institute for Transuranium Elements (JRC-ITU) where a commercial NMR spectrometer were integrated with a radioactive glovebox and a MAS commercial probe. First results will be presented. Competitive effects between the recoil nuclei and alpha decays were evidenced and the high resistance of the nuclear waste glasses corroborated.
[1] S. Peuget, C. Mendoza, E.A. Maugeri et al. Procedia Materials Science 7, (2014) 252-261
[2] C. Mendoza, S. Peuget, T. Charpentier et al., Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms 325 (2014) 5-65
[3] S. Peuget, E.A. Maugeri, T. Charpentier et al. J. Non-Cryst. Solids 378 (2013) 201-212.
12:00 PM - EE13.2.06/EE12.2.06/MD8.3.06
Effects of Radiation Fields on Actinide-Containing Materials
Steven Conradson 1,Janne Pakarinen 2,Mahima Gupta 3,Akhil Tayal 1
1 Soleil Saint-Aubin - BP48 France,2 Belgian Nuclear Research Centre Mol Belgium3 Morpho Detection Fremont United States
Show AbstractBecause of their internal radiation and their applications, nuclear materials are often subject to extreme radiation fields that affect their structures and properties over time. In plutonium, every atom is displaced from its lattice position once every ten years on average. Although almost all of the displaced nuclei rapidly return to the lattice quickly, some do not, becoming defects in the material. The conventional idea is that these will accumulate randomly, causing increasing disorder in the material that will eventually result in its becoming amorphous. Alternatively, these defects might interact strongly with each other and other defects or inhomogeneities in the material. If they do then the possibility exists that they will stabilize themselves and aggregate into defect-enriched domains until these move so far away from the original composition that they could potentially transofrm into domains with altered structures that are still trapped in the host lattice. This process describes the formation of helium bubbles from the emitted alpha particles, but also other such nanometer and larger scale structures. We have now observed exactly this type of phenomenon in delta plutonium-gallium alloys and also in ion irradiated uranium dioxide. Although delta plutonium eventually succumbs to accumulated radiation damage and does lose order, prior to that stage it displays a cycle based on the formation of particular locally ordered structures that deviate from the fcc one that is its long range average. These alternative structures are similar to the ones observed in new materials that are caused by strong interactions between the alloys atoms that cause it to cluster to form a quasi-intermetallic. Similarly, the propensity of adventitious O to cluster in uranium dioxide is emulated as the result of ion irradiation. Uranyl type species with higher valences are observed just as with oxidation to mixed valence compounds, although in the case of ion irradiation they must be mirrored by lower valence species as well. This complication demonstrates the substantial stability of these non-equilibrium structures. In the case of radiation damage, and also other forms of aging, this phenomenon of the formation of structures on increasingly large length scales is, in fact relatively common. The formation of these structures is coupled with the irreversibility of damage accumulation, with the formation of such structures corresponding to phase transtions. Aging effects may therefore be best described as non-equilibrium thermodynamic processes with these irreversible steps corresponding to critical points on the path.
12:15 PM - EE13.2.07/EE12.2.07/MD8.3.07
How Well Can Electronic Structure Calculations Describe Uranium Dioxide Properties
Marjorie Bertolus 1,Michel Freyss 1,Ram Devanathan 2,Matthias Krack 3
1 CEA, DEN St Paul-Lez-Durance France,2 Pacific Northwest National Laboratory Richland United States3 Paul Scherrer Institute Villigen PSI Switzerland
Show AbstractOne challenge for the development of Gen IV nuclear reactors is to improve significantly the effectiveness of the design and selection of innovative fuels. To this aim, multiscale modelling approaches are developed to build more physically based kinetic and mechanical mesoscale models to enhance the predictive capability of fuel performance codes. Atomic scale methods, in particular electronic structure calculations, form the basis of this multiscale approach. It is therefore essential to know the accuracy of the results computed at this scale if we want to feed them into higher scale models.
Electronic structure calculation methods, especially density functional theory (DFT), have been used extensively on molecular and solid systems during the last thirty years. Numerous assessments of these methods have been performed, which show that they are powerful tools yielding precise and predictive results for a large number of solid and molecular systems, therefore contributing to the understanding of numerous phenomena. The application to nuclear materials under irradiation and especially to fuels, however, is more delicate and calls for bespoke developments. A specific assessment of the atomic scale methods for the description of nuclear fuel under irradiation is therefore necessary.
We will present the result of the extensive assessment effort of the results of state-of-the-art electronic calculations on uranium dioxide performed in the framework of the Working Party on Multiscale Modelling of Fuels and Structural Materials for Nuclear Systems (WPMM) of the OECD/NEA.
12:30 PM - EE13.2.08/EE12.2.08/MD8.3.08
Development of a Multiscale Thermal Conductivity Model for Fission Gas in UO2
Michael Tonks 1,Xiang-Yang Liu 2,David Andersson 2,Aleksandr Chernatynskiy 3,Giovanni Pastore 4,Christopher Stanek 2
1 Pennsylvania State Univ University Park United States,2 Los Alamos National Laboratory Los Alamos United States3 Missouri Institute of Science and Technology Rolla United States4 Idaho National Laboratory Idaho Falls United States
Show AbstractModels used in fuel performance codes to predict the change in the fuel thermal conductivity are typically empirical fits to experimental data, and are independent of other models such as fission gas or grain size. As part of the Nuclear Energy Advanced Modeling and Simulation program, we are developing a system of new materials models for fuel performance that are based on microstructure rather than burn-up, for use in Idaho National Laboratory’s (INL’s) BISON code. In order to obtain a mechanistic model of thermal conductivity, we have developed a preliminary model that couples the fission gas release model to the thermal conductivity. Atomistic and mesoscale simulations were used to quantify the impact of three distributions of fission gas on the thermal conductivity: dispersed gas atoms, small intragranular gas bubbles, and grain boundary bubbles. The model was implemented in BISON and the results were compared to reactor test data.
12:45 PM - EE13.2.09/EE12.2.09/MD8.3.09
Fission Gas Diffusion in UO2 Nuclear Fuel by Extended Vacancy Cluster
David Andersson 1,Romain Perriot 1,Michael Cooper 1,Xiang-Yang Liu 1,Giovanni Pastore 2,Michael Tonks 3,Blas Uberuaga 1,Christopher Stanek 1
1 Los Alamos National Laboratory Los Alamos United States,2 Idaho National Laboratory Idaho Falls United States3 Pennsylvania State University University Park United States
Show AbstractIn UO2 nuclear fuel, the retention and release of fission gas atoms such as xenon (Xe) are important for nuclear fuel performance. We use multi-scale simulations to determine fission gas diffusion mechanisms as well as the corresponding rates in UO2 under both intrinsic and irradiation conditions. Density functional theory (DFT) calculations are used to study formation, binding and migration energies of small clusters of Xe and vacancies. Empirical potential calculations enable us to determine the corresponding entropies and attempt frequencies for migration as well as investigate the properties of large clusters or small fission gas bubbles. A continuum reaction-diffusion model is developed for Xe and point defects based on the mechanisms and rates obtained from atomistic simulations. Effective fission gas diffusivities are then obtained by solving this set of equations for different chemical, irradiation and microstructure conditions using the MARMOT phase field code. Emphasis is put on understanding how the diffusion rates evolve as function of the irradiation dose and its coupling to defect concentrations and microstructure. The predictions are compared to available experimental data. The importance of the large XeU3O cluster (a Xe atom in a uranium + oxygen vacancy trap site with two bound uranium vacancies) is emphasized, which is a consequence of its high mobility and high binding energy. However, all simple vacancy-mediated diffusion mechanisms underestimate the Xe diffusivity compared to the empirical radiation-enhanced model used in most fission gas release models. We investigate the possibility that diffusion of small fission gas bubbles or extended Xe-vacancy clusters may be responsible for the radiation-enhanced diffusion coefficient. These studies highlight the importance of U divacancies and a cluster composed of an octahedron coordination of uranium vacancies encompassing a Xe fission gas atom. The latter cluster can migrate via a multistep mechanism with a low effective barrier.
EE13.3: Nuclear Technology
Session Chairs
Stephane Gosse
Dennis Keiser
Wednesday PM, March 30, 2016
PCC North, 200 Level, Room 221 A
2:30 PM - *EE13.3.01
Influence of Plutonium on the Thermodynamic Properties and Phase Equilibria in Corium
Stephane Gosse 1,Christine Gueneau 1,Andrea Quaini 1,Patrick Bonnaillie 2,Dario Manara 3
1 DPC,SCCME,LM2T CEA, Centre de Saclay Gif-sur-Yvette France,2 DMN,SRMP CEA, Centre de Saclay Gif-sur-Yvette France3 Institute for Transuranium Elements Karlsruhe Germany
Show AbstractDuring a severe accident in a pressurized water reactor, very high temperatures can be reached (T>2500 K). In these conditions, the UO2 or mixed oxide (U,Pu)O2 nuclear fuel shall react with the Zircaloy cladding and then with the steel vessel, forming a complex mixture of solid and liquid phases called in-vessel corium. At very high temperature, the corium can be constituted of two metallic and oxide liquid phases due to the existence of a miscibility gap in the liquid state. The relative fraction and composition of these phases that form in the corium as a function of temperature are key input data for severe accident codes to predict corium thermal-hydraulics properties.
The TAF-ID thermodynamic database [1] coupled to software like Thermo-Calc or Open Calphad is a powerful computational tool to predict the thermodynamic data of nuclear fuel materials. The database is developed using the Calphad method on the basis of the available experimental data. In case of severe accident applications, experimental data are missing, especially on systems containing plutonium. New measurements of thermodynamic and phase diagram data on subsystems of the prototypic in-vessel corium U-Pu-Zr-Fe-O are required. Such experiments are particularly difficult to carry out due to radiotoxicity of the materials and to the very high temperature level. New measurements using advanced laser melting techniques will be presented. The models derived from these new experimental data will be described. Finally the influence of the presence of plutonium in the mixed oxide fuel on the thermodynamic properties and phase equilibria of the in-vessel corium will be investigated by thermodynamic calculations.
[1] https://www.oecd-nea.org/science/taf-id/
3:00 PM - EE13.3.02
Sintering of (U,Pu)O2 Mixed Oxide with Cr Addition
Jean-Marc Heintz 2,Regis Thomas 4,Chantal Riglet-Martial 4,Philippe Martin 4,Jean-Francois Silvain 1,Jacques Lechelle 3
1 ICMCB CNRS Pessac France,2 ENSCBP Bordeaux INP Pessac France,4 DEN/DEC CEA Cadarache Saint Paul Lez Durance France1 ICMCB CNRS Pessac France3 DEC/SESC/LCC CEA Cadarache Saint Paul Lez Durance France
Show AbstractOptimal use of the Mixed Oxide (U,Pu)O2 nuclear fuel (MOX) in pressurized water reactors could be reach by means of an optimized distribution of plutonium and large grains within the industrial ceramic product. For this purpose, addition of chromium sesquioxide during the manufacturing process is currently considered.
The objective of the present work is to obtain a general understanding of homogenization processes within UO2-PuO2 mixtures, doped with Cr2O3, as a function of plutonium content and sintering conditions, especially oxygen potential. First, new results concerning the speciation of solubilized and precipitated chromium in MOX were obtained using electron probe microanalysis (EPMA) and X-ray absorption spectroscopy (XAS). Second, it was verified whether the thermodynamic conditions of precipitate formation (such as PuCrO3) correspond to an optimal plutonium distribution and grain growth. Indeed, it was shown that the U-Pu interdiffusion kinetics is completely modified with chromium addition compared to pure MOX. However, sintering conditions which increase the U-Pu interdiffusion kinetics when chromium oxide is present do not necessarily correspond to optimal grain growth.
3:15 PM - EE13.3.03
Novel Synthesis Routes and Properties of Nanostructured UO2 and ThO2 Compacts
Vaclav Tyrpekl 1,Marco Cologna 1,Joseph Somers 1
1 EC JRC Institute for Transuranium elements Karlsruhe Germany,
Show AbstractDuring its life in a nuclear power plant the fuel (UO2) undergoes significant restructuring at the periphery of the pellet, and the grains (10 µm or more) of the fresh fuel convert to a highly (20%) porous structure with grain size of 100-300 nm, known as the high burnup structure (HBS). Due to the high radioactivity, however, investigations thereon have been limited. The focus of this work is the preparation of a surrogate material with this structure, to enable a deeper understanding of its properties. We report the synthesis of nanocrystalline UO2 and ThO2 powders using oxalate precipitation and controlled decomposition at low temperature, which yields a material with primary crystallites 10 nm in size. These oxide powders retain the morphology of initial oxalate particles, however, i.e. porous square sheets 0.5-2 μm in width and several tens of nm in depth. The key to consolidation of pellets retaining the nanometre character is short sintering times coupled to low sintering temperatures, which we achieve using spark plasma sintering (SPS) unit integrated in a glove box. During consolidation two steps are found. The first (~ 550°C) is due to sintering within the micron sized particle and the second (~750°C) to sintering of the agglomerates amongst each other. Remarkably, the final compacts have density > 95 % of theoretical value and by increasing the SPS pressure to 500 MPa, with suitable inserts, and reducing the maximum temperature to 800°C without dwell time, grain sizes in the compact below 40 nm have been obtained. The synthesis method will be reported in full, along with first mechanical property measurements. In future steps, controlled porosity will be introduced via precursors to simulate fully the HBS of irradiated fuel, along with full investigations on the effect of grain size on thermal conductivity, irradiation damage and gas behaviour.
4:00 PM - *EE13.3.04
Effects of Irradiation on the Microstructure of U-Bearing Alloys
Dennis Keiser 1,Jian Gan 1,Jan-Fong Jue 1,Brandon Miller 1,Adam Robinson 1,Walter Williams 1,James Madden 1
1 Idaho National Laboratory Idaho Falls United States,
Show AbstractDramatic changes occur in U-bearing alloys when they are irradiated in a nuclear reactor. The phenomena that occur during nuclear fission (e.g., fission spikes, fission damage) all have impacts on the starting microstructure of the nuclear fuel material. This has certainly been observed for the Material Managment and Minimization (M3) Program, wihch is responsible for developing new low-enriched uranium alloy fuels for use in research and test reactors. As part of the M3 Program, a variety of different U-bearing alloys have been irradiated in the Advanced Test Reactor and then microstructurally characterized. Examples of alloys that have been irradiated include: U-10Mo, U-10Mo-0.05Sn, and U-9Nb-3Zr. To perform characterization of different fuel materials after irradiation, recent work has utilized a focused ion beam for producing small, high-quality samples that can be used for SEM and TEM analysis. The quaiity of these samples is so improved over the mechanically-polished samples that were used in the past that they have been used to produce very unique images of the irradiated microstructures. This has allowed for breakthrough observations to be made about the effects of irradiation on the microstructural evolution of the materials of most interest. This talk will desribe features that have been observed in these high-quality samples and how they have been used to develop new understanding of how the microstructures of different U-bearing alloys respond to irradiation to high burn-up. This information is invaluable for developing the next-generation of nuclear fuels for use in different kinds of reactors.
4:30 PM - EE13.3.05
EBSD Study of Uranium Alloys
Daria Drozdenko 1,Peter Minarik 1,Mykhaylo Paukov 1,Ladislav Havela 1
1 Charles University Prague 2 Czech Republic,
Show AbstractBcc γ-Uranium alloys are relevant for technology of nuclear fuels. In addition, they exhibit interesting electronic properties, as conventional but field-resistant superconductivity [1], and they are also basis for various specific forms of UH3-based hydrides. Within the effort to synthesize bcc U alloys with diverse alloying elements and using different types of cooling, a phase analysis allowing to establish under which conditions the α-U phase can be avoided became indispensable. Conventional XRD can give some indications about the phase composition, but the sensitivity is not sufficient due to the overlap of dominating diffraction maxima in the U phases. The situation is further blurred due to surface contaminants, as the alloys cannot be crushed into powder. Conventional Scanning Electron Microscopy with a microprobe is not very informative, too, as different phases can have identical chemical composition. We show that in such situation the Electron Back Scatter Diffraction (EBSD) can provide vital information on the phase composition including maps of phase distribution, texture, grains size, twinning, and inclusions of spurious phases. For such technique a high surface quality is a prerequisite and focused ion beam (FIB) milling has to be applied to remove the oxide layer on the surface. Moreover FIB can be used for depth profiling, revealing that the microstructure of splat cooled U foils can be to some extent inhomogeneous. However, the FIB technique itself does not guarantee obtaining a diffracting surface in each case. Depending on the phase type and composition, it is convenient to combine FIB with other methods of surface preparation. Using different methods of surface preparation, we will show details of phase composition development particularly for the U-Mo and U-Nb phases. The study shows that Nb is inferior to Mo as effective γ-U stabilizer. In the U-Mo system, the splat cooled sample with as low as 11% Mo concentration has the α-U phase suppressed, while 15% Nb still shows α-U as a minority phase.
[1] I.Tkach et al., J. Alloys Comp. 534 (2012) 101.
4:45 PM - EE13.3.06
Radiation Aging of Nuclear Glasses Due to Alpha Decays Accumulation
Sylvain Peuget 1,H. Mir 1,J.M. Delaye 1,Thibault Charpentier 2,Laura Martel 3,Joseph Somers 3,Marcel Toulemonde 4,S. Bouffard 4,Christophe Jegou 1
1 CEA, DEN/DTCD/SECM Laboratoire d’Étude des Matériaux et Procédés Actif, Bagnols-sur-Cèze France,2 CEA, IRAMIS, NIMBE, UMR CEA-CNRS 3685 Gif-sur-Yvette France3 European Commission, Joint Research Centre(JRC) Institute for Transuranium Elements (ITU) Karlsruhe Germany4 CIMAP-GANIL (CEA-CNRS-ENSICAEN-Univ. Caen) Caen France
Show AbstractBorosilicate glasses, besides their numerous applications, have been recognized as valuable materials for the conditioning of nuclear wastes. Because alpha decay is the main source of atomic displacements in the glassy network under repository conditions, CEA has started a research program in this field. The effect of the radiation damage induced by alpha decay were investigated by examining glass specimens, doped with a short-lived actinide 244Cm, irradiated by light and heavy ions and by performing Molecular Dynamic simulation of ballistic damage.
These studies have shown that some macroscopic properties vary appreciably with the accumulation of alpha decay, but then stabilize after integrating doses of the order of 4 × 1018 α●g1. The glass density diminishes by about 0.6%, its Young’s modulus by about 15%, and its hardness by about 30%, while its fracture toughness increases by around 50%. Moreover the initial alteration rate of the glass is not significantly affected by the glass damage induced by alpha decays or heavy ions irradiations.
The analysis of the irradiated glassy structures with various spectroscopic studies (NMR, Raman, XANES) has identified some changes in the local order around some cations. Moreover a modification of the medium-range order has also been demonstrated through changes in the bond angles between network formers and broadening of the ring size distributions, indicating increasing disorder of the glass structure. This structural evolution induced by alpha decays would be driven by the reconstruction of the glass disorganized by displacement cascades of the recoil nuclei, freezing a glass structure with a higher fictive temperature. This “ballistic disordering (BD) fast quenching” or “ballistic induced vitrification” events induce a new glassy state characterized by a higher enthalpy state. Moreover it was recently shown that alpha particles induce a partial self-healing of the glassy structure damaged by heavy ions. This talk will illustrate how the final damaged glassy state of actinides doped glasses is controlled by both type of events and associated mechanisms, damage enhancement from recoil nuclei and self-healing from alpha particles.
Symposium Organizers
David Shuh, Lawrence Berkeley National Laboratory
Ladia Havela, Charles University
Alexander Landa, Lawrence Livermore National Laboratory
Daniel Schwartz, Los Alamos National Laboratory
Symposium Support
Lawrence Livermore National Laboratory
EE13.4: Bonding and Chemistry I
Session Chairs
Thursday AM, March 31, 2016
PCC North, 200 Level, Room 221 A
9:00 AM - EE13.4.01
Structural and Electronic Breaks in Berkelium and Californium
Thomas Albrecht-Schmitt 1
1 Florida State University Tallahassee United States,
Show AbstractBerkelium is one of the least explored elements in the actinide series, but there is both past and more very recent evidence that a structural break occurs in the actinide series at berkelium. All of the data point to the structural chemistry of berkelium paralleling that of californium. However, the electronic properties of these elements are quite different with f-d and f-f transitions dominating the absorption and photoluminescence spectra of berkelium; whereas charge-transfer transitions control the optical features of californium.
9:15 AM - EE13.4.02
Innovative (U,Am)O2 Synthesis Dedicated to Dustless Process for Americium Bearing Blankets Fabrication–Identification of the Chemical Steps through XRD and XAS Studies
Marie Caisso 1,Pascal Roussel 2,Christophe Den Auwer 3,Renaud Belin 1,Philippe Martin 1,Sebastien Picart 1,Florent Lebreton 1,Christoph Hennig 4,Andreas Scheinost 4,Kathy Dardenne 5,Joerg Rothe 5,Thibaud Delahaye 1,Andre Ayral 6
1 CEA Marcoule Bagnols sur Cèze France,2 UCCS Lille France3 ICN Nice France4 HZDR Dresden Germany5 KIT-INE Karlsruhe Germany6 IEM Montpellier France
Show AbstractOver the past few years, due to its high radiotoxicity in ultimate waste after plutonium recycling, americium (Am) transmutation in heterogeneous mode, through the use of U1-xAmxO2±δ dense pellets (AmBB), has progressively been considered as a reference. These fabrications are based on powder metallurgy routes which generate large amounts of radioactive dust. To envisage future industrial deployment, the development of dustless processes thus becomes mandatory. Among the different innovative routes currently considered, a promising process using micronic spherical precursors is studied. Through an adaptation of the weak acid resin (WAR) process, the general approach consists in synthetizing brittle mixed-oxide microspheres from ion exchange resin precursors. These nano-structured soft agglomerates were developed to combine the advantages of fine powders, with a high reactivity during sintering step, without the major drawback of pulverulent compounds, meaning high dissemination during handling. Moreover, the spherical precursor geometry was chosen to facilitate the filling of the compaction chamber and subsequent pelletization, required for green pellet fabrication. The final process is called Calcined Resin Microsphere Pelletization (CRMP) process and it has already been tested at the lab-scale, as a feasible AmBB fabrication route. It is divided in several steps, beginning by the fixation, in aqueous solution, of americium and uranyl cations into ion exchange resin microspheres. As loaded, they are then converted into U1-xAmxO2±δ mixed-oxide during two successive dedicated thermal treatments leading to the synthesis of porous microspheres which are finally employed as pelletization precursors. The main objective of this study is to control each step of the thermal conversion in order to optimize pelletization precursors before AmBB fabrication. Answering this need, an in-situ study has been initiated to understand mechanisms implied, for the first treatment performed under air, in carbon skeleton departure and in the formation of an Am-substituted U3O8 oxide, and for the following reductive conversion, in an U1-xAmxO2±δ mixed-oxide appearance. It was performed by using HT X-Ray diffraction (XRD) and HT X-Ray absorption spectroscopy (XAS). First actinide-based in-situ XANES spectra were thus acquired during the two thermal treatments, and combined to the key temperatures identified thanks to HT-XRD. Furthermore, the two final products, meaning intermediate Am-substituted U3O8 and U1-xAmxO2±δ solid solution were fully characterized at RT, thanks to XRD and neutron diffraction, XAS, Raman and infrared spectroscopies. Combination of the different characterization methods finally led to the determination of the local environment of U and Am, as well as the repartition of O atoms inside the cationic network of the two structures.
9:30 AM - *EE13.4.03
Recent Investigations of Solid State Chemistry of Lanthanides and Actinides at Soochow University
Shuao Wang 1
1 Soochow University Suzhou China,
Show AbstractDuring the past one year, progresses have been made on the solid state chemistry of lanthanides and actinides for several different projects. These include: (1) the first uranyl polycatenated framework that can effectively remove cesium from aqueous solutions; (2) several thorium based metal organic frmawork compounds with ultra-large channels and porosity as well as new thorium coordination features; (3) an "in-situ ion-exchange" strategy to create new hereobimetallic 4f-5f complexes in the vanadate system; (4) several extremely complicated uranyl phosphonates with unusual low-temperature phase transition features and combinations of uranyl coordination environments; (5) a special mixed valent Eu2+/Eu3+ complex showing luminescence upconversion and unprecedented luminescence thermometry applications between 9-300 K.
10:00 AM - *EE13.4.04
Unusual Temperature Dependence of Mössbauer Isomer Shift in NpF4
Itzhak Halevy 1
1 NRCN Beer-Sheva Israel,
Show AbstractWe report on unusual temperature dependence of Mössbauer isomer shift (IS) in the monoclinic NpF4 (c2/c symmetry). The crystal structure parameters from the fitted X-ray diffraction spectra utilizing Rietveld analysis area = 12.7234(5) Å, b = 10.8840(5) Å, c = 8.3621(5) Å with β = 126.15°. There are 8 fluorides nearest neighbors in antibprism structure.
The reaction to prepare the NpF4 is:
NpO2+4HF →900°C→ O2+ NpF4 + 2H2O
A special care was taken to using a very clean NpO2. The NpF4 was a light green powder material.Due to the low symmetry of the NpF4 we can be sure from the X-Ray diffraction that no NpO2 is present.
An interpretation of the low temperature absorption spectra of AnF4 (An=U, Np, Pu) was presented in Carnall work. Using an effective operator Hamiltonian with orthogonalized free ion operators and initializing crystal field parameter values based on a superposition model calculation for An4+sites with C2 symmetry, good agreement between the model calculations and experimentally observed absorption band structure was obtained.
When lowering temperature from 44 to 4.2 K the center of gravity of the Mössbauer spectra of the 60 keV is shifted positively by 1±0.05 mm/sec, indicating a decrease of the s-electron density at the Np nucleus. The source for the Mössbauer measurements is an Am(Th) source.In all previous Mössbauer measurements, temperature induced volume contraction is rather small and beyond the resolution of the Mössbauer IS technique. When lowering the temperature one would expect an increase of pressure as a result of a volume contraction and if at all a negative isomeric shift. Therefore, the present reported behavior of NpF4, an increase of the volume when reaching low temperature, is in rather surprising but in a good agreement with neutron inelastic scattering on UF4 and NpF4and AnF4 by Kern et. al. The Mössbauer spectrum of NpF4 could be fitted by taking into account two nonequivalent Npsites as its crystal structure demands. We assumed that the Np ions are tetravalent (Np4+) and exhibits 4I9/2 (Γ8(2)) ground state. In addition the Mössbauer spectra show some asymmetry. Our susceptibility measurements indicate that this compound is paramagnetic down to 4.2 K. Thus paramagnetic relaxation phenomena within the ground Kramer’s doublet (Δ=0) could explain this asymmetry.
10:30 AM - *EE13.4.05
Phosphides: A Paradigm to Study Trends in Actinide Behavior
Geng Bang Jin 1,S. Skanthakumar 1,L. Soderholm 1,Mark Antonio 1
1 Argonne National Laboratory Lemont United States,
Show AbstractThe electronic interactions between actinides and soft anions such as phosphide, give rise to materials with moderate 5f delocalization and a variety of chemical bonds featuring different degrees of covalency at the semiconductor/metal boundary. Because of the flexible redox and bonding capabilities of both metal and anions, actinide phosphides have displayed extremely rich structural diversity and electronic properties including semimetallic conductivity and strong magnetic coupling. Depending on the redox potential of the cation, the charge transfer between the metal and phosphide sublattices varies and, consequently, so do the structures and electronic properties of anions. Phosphides can capture gradual transitions of the 5f electronic states of actinides in comparable anionic environments. The difference among actinides can be then probed by studying both the metal sublattices and the phosphide sublattices. Therefore these materials provide a superb platform to study trends in actinide behavior. We have prepared a series of simple binary and ternary actinide (An = Th, U, Np) phosphides in single crystal form to elucidate the role of 5f electrons in the structure-property relationships of actinide materials. We have conducted extensive structural, spectroscopic, and physical property measurements to understand the underlying correlations. We also present some preliminary solid-state electrochemical experiments that provide a new approach to quantify relationships between electronic and thermodynamic properties as a function of 5f electron counts. This approach can also allow us to quantify relationships between structural and electrochemical behavior of actinides in these materials. This work was performed at Argonne National Laboratory, operated by UChicago Argonne LLC, and supported by the U.S. DOE, OBES, Chemical Sciences, Geosciences, and Biosciences Division, Heavy Elements Program, under contract DE-AC02-06CH11357.
EE13.5: Magnetism and Correlations I
Session Chairs
Thursday PM, March 31, 2016
PCC North, 200 Level, Room 221 A
11:30 AM - *EE13.5.01
Thermal Expansion of the Heavy-Fermion Superconductor PuCoGa5
Roberto Caciuffo 1,Nicola Magnani 1,Carlotta Giacobbe 2,Gerard Lander 1,Rachel Eloirdi 1
1 Joint Research Centre, ITU European Commission Karlsruhe Germany,2 European Synchrotron Radiation Facility Grenoble France
Show AbstractPuCoGa5 has the highest Tc (18.5 K) of any heavy-fermion superconductors. Twelve years after its discovery our understanding of this material remains at best confused [1]. We do know from NMR and point-contact spectroscopy measurements that the superconducting state has d-wave symmetry and that it is unlikely that the phonons are the driving mechanism in the formation of Cooper pairs. Form-factor measurements with neutrons [2] have shown that the ground state is not the conventional 5f5 state found in many Pu intermetallics. Recent theoretical efforts [3-5] have concluded that the driving mechanism for superconductivity is valence fluctuations. Calculations combining the local-density approximation with an exact diagonalization of the Anderson impurity model [6] show an intermediate 5f 5-5f 6-valence ground state and delocalization of the 5f 5 multiplet of the Pu atom 5f shell. The 5f local magnetic moment is compensated by a moment formed in the surrounding cloud of conduction electrons, leading to a singlet Anderson impurity ground state. The presence of valence fluctuations has been recently corroborated by resonant ultrasound spectroscopy, showing that the compressional elastic moduli exhibit anomalous softening upon cooling, which is truncated at the superconducting transition [7]. These results provide evidence for a valence transition at a TV
12:00 PM - EE13.5.02
Tuning of the 5f-Magnetism in UNi(Zn,Al) and Their Hydrides
Silvie Maskova 1,Stanislav Danis 1,Khrystyna Miliyanchuk 2,Olha Stelmakhovych 2,Barbora Vondrackova 1,Ladislav Havela 1
1 Charles University in Prague Prague Czech Republic,2 Ivan Franko National University of Lviv Lviv Ukraine
Show AbstractWe have synthesized a new ternary compound with the ZrNiAl structure type (hexagonal, s.g. P-62m), UNiZn [1], which is analogous to UNiAl (antiferromagnet with TN = 19 K) [2], but the smaller atomic radius of Zn comparing to Al leads to the loss of magnetic ordering and of U magnetic moments. The temperature dependence of magnetic susceptibility indicates that UNiZn has a paramagnetic ground state. Magnetic susceptibility is low (≈ 10-8 m3/mol) but temperature dependent. UNiZn can be considered as a spin fluctuator with its magnetic properties between two limiting cases, Pauli paramagnet and magnetically ordered material. H absorption reaching the stoichimetry UNiZnH2.3 can be seen as analogous to UNiAlH2.3. The lattice expansion, which is strongly anisotropic, produces antiferromagnetic order below TN = 50 K, lower comparing to UNiAlH2.3 (95 K). One of interesting trends is the variation of the γ-coefficient of electronic specific heat in the UNiZn1-xAlx series. The γ-value increases from 94 mJ/mol K2 in UNiZn to 100 mJ/mol K2 in the hydride. This tendency is opposite than for UNiAl (164 mJ/mol K2 in UNiAl and 67 mJ/mol K2 in UNiAlD2.1 [3]). The coefficient of electronic specific heat is in general expected to culminate somewhere close to the onset of magnetism, which is placed between non-magnetic UNiZn and antiferromagnetic UNiAl. Therefore we have synthesized several compounds from the UNiZn1-xAlx series to find the quantum critical point. UNiZn0.5Al0.5 was found antiferromagnetic with the Néel temperature TN = 10 K. Certainly the Sommerfeld coefficient of the substituted compound (175 mJ/mol K2) is higher than for the terminal phases. Upon hydrogenation the Néel temperature is shifted to TN ≈ 70 K and the Sommerfeld coefficient falls in between the values for the terminal hydrides. The system is therefore suitable for detailed exploration of the quantum critical region.
[1] S. Maskova, S. Danis, K. Miliyanchuk, O. Stelmakhovych, B. Vondrackova, A.V. Kolomiets, L. Havela, J. Alloys Comp. 646 (2015) 885-892.
[2] E. Brück, H. Nakotte, F.R. de Boer, P.F. de Châtel, H.P. van der Meulen, J.J.M. Franse, A.A. Menovsky, N.H. Kim-Ngan, L. Havela, V. Sechovsky, J.A.A.J. Perenboom, N.C. Tuan, J. Sebek, Phys.Rev. B 49 (1994) 8852.
[3] L. Havela,K. Miliyanchuk, A. Kolomiyets: Int.J.Mat.Res. 100, 1182-1186 (2009).
12:15 PM - EE13.5.03
Strong 5f Ferromagnetism in UH3-Based Materials
Ladislav Havela 1,Mykhaylo Paukov 1,Ilya Tkach 1,Zdenek Matej 3,Dominik Kriegner 1,Silvie Maskova 1,Ilja Turek 1,Daria Drozdenko 1,Miroslav Cieslar 1,Milan Dopita 1,Zuzana Molcanova 2,Marian Mihalik 2
1 Faculty of Mathematics and Physics Charles University Prague 2 Czech Republic,1 Faculty of Mathematics and Physics Charles University Prague 2 Czech Republic,3 Max IV Laboratory Lund University Lund Sweden2 UEF SAV Kosice Slovakia
Show AbstractUranium metal interacting with Hydrogen forms a fine pyrophoric powder of UH3, existing in two alotropic forms. β-UH3, the thermodynamically stable form, is known to be ferromagnet with Tc ≈ 170 K [1]. Magnetic order in its transient form, α-UH3, was seriously doubted [2], although the enhanced U-U separation (with respect to U metal) should yield magnetic order in both cases in the context of the Hill limit proximity. We succeeded to synthesize modified U-based hydrides when starting from γ-U alloys (bcc), in which a combination of dopants and/or ultrafast cooling suppresses the α-U (orthorhombic) phase. Such alloys (with e.g. Mo or Zr) behave as "stainless" Uranium, for which high H2 pressures are needed and the hydrides remain monolithic. The variations of composition lead to different structure modifications. The alloys with Zr exhibit stable α-UH3 structure [3]. Mo alloying [4] gives almost amorphous material with the grains size of ≈ 1 nm. Fe or Co leads to the common β-UH3 structure type. We have resolved some structure details by mean of TEM and and Pair Distribution Function study. The H concentration always corresponds to ≈ 3H/U atom, so the composition can be described by a general formula (UH3)1-xTx. The alloying of UH3 and the structure modification have little impact on magnetic properties, which is very surprizing considering the general sensitivity of the 5f states to any kind of variables. α-UH3 is indeed very similar to β-UH3 and the Tc values tend to be even enhanced by alloying, reaching over 200 K in the Mo case. This opens the question why ordering temperatures can be that high in the region of the Hill limit (330-360 pm), where the magnetic order should only set in. The fact, that structure modifications and U-U spacing are apparently not the most relevant tuning parameters, suggest that the U-H interaction can be dominant.
An insight is provided by ab-initio calculations, revealing a charge transfer towards H-1s states, depopulating the U-6d and 7s states and leaving almost pure 5f character around the Fermi level. The fact that electrical conductivity is low but keeps the metallic character corroborates such assumption. The calculations demonstrate large U orbital moments for the band 5f states and very large spontaneous volume magnetostriction, capturing the experimental value ΔV/V = 3.2*10-3. We suggest that other compounds of U with electronegative elements, which deplete the 6d and 7s states of U, may also produce high ordering temperatures. Preserving metallicity is though a prerequisite. Indeed e.g. U pnictides as U3As4 (TC = 198 K) [5] or UCu2P2 (216 K) [6] are high-Tc ferromagnets.
[1] R. Troc and W. Suski, J.Alloys Comp. 219 (1995) 1.
[2] A.C. Lawson et al., J.Appl.Phys. 69 (1991) 5112.
[3] I. Tkach et al., Phys.Rev. B 91 (2015) 115116.
[4] I. Tkach et al., Phys.Rev.B 88 (2013) 060407(R).
[5] J. Sternberk et al. J.Phys. (Paris) Suppl. 32 (1971) C1-744.
[6] D. Kaczorowski and R Troc, J.Phys.: Cond.Mat. 2 (1990) 4185.
12:30 PM - *EE13.5.04
NpFeAsO, NpPt2In7, Np2PdIn8 and NpV2Al20: Recently Discovered Np-Based Compounds
Tomasz Klimczuk 1,Helen Walker 2,Alexander Shick 4,Andrew Walters 5,Ross Springell 3,Michal Winiarski 1,Eric Colineau 6,Jean-Christophe Griveau 6,Rachel Eloirdi 6,Roberto Caciuffo 6
1 Gdansk University of Technology Gdansk Poland,2 ISIS Facility, Rutherford Appleton Laboratory Chilton, Didcot United Kingdom4 Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2 Prague Czech Republic5 Diamond Light Source, Harwell Science and Innovation Campus Didcot, Oxfordshire United Kingdom3 Royal Commission for the Exhibitial of 1851 Research Fellow, Interface Analysis Centre, University of Bristol Bristol United Kingdom6 European Commission, Joint Research Centre (JRC), Institute for Transuranium Elements (ITU) Karlsruhe Germany
Show AbstractNeptunium - the second artificially-synthesized element - remains mostly neglected and only few laboratories in the world are capable of working with it. Several new compounds that contain neptunium were recently synthesized and studied at Institute for Transuranium Elements (EC, JRC). In this lecture four of them will be discussed.
NpFeAsO is one of the few actinide-based iron-oxypnictide compounds. Although one may expect the physical properties of NpFeAsO to be similar to the superconducting lanthanide 1111 analogues, in reality this system behaves differently. In particular, we do not observe any structural transition, in agreement with the absence of high-temperature anomalies associated with in-plane magnetic ordering in the Fe-As layer. The temperature-dependent magnetic susceptibility, electrical resistivity, Hall coefficient, and specific-heat measurements reveal a long-range magnetic order below a critical temperature TN = 57 K. Below TN, powder neutron diffraction and Mössbauer spectroscopy measurements reveal an antiferromagnetic structure of the Np sublattice, with an ordered magnetic moment of 1.70 ± 0.07μB aligned along the crystallographic c axis.
The neptunium analogues of the layered, heavy-fermion superconductors CePt2In7 and Ce2PdIn8 have been synthesized and characterized by means of resistivity, magnetic susceptibility, and heat capacity techniques. Rietveld analysis of the powder x-ray diffraction patterns of NpPt2In7 and Np2PdIn8 confirm a tetragonal structure type for both compounds, with lattice parameters similar to those previously reported for CePt2In7 and Ce2PdIn8, respectively.
For NpPt2In7 an antiferromagnetic transition was observed with the Néel temperature TN = 23 K. Rather complex magnetism is revealed for Np2PdIn8 with both ferromagnetic and possibly antiferromagnetic transitions at TC = 9.5 K and TN = 8.5 K, respectively. For both NpPt2In7 and Np2PdIn8 a Curie-Weiss fit of the high-temperature magnetic susceptibility curve, χ(T), gives an effective magnetic moment as expected for trivalent Np.
The last compound to be discussed is Np1-xV2Al20, which forms in a complex cubic structure with the Np atoms located inside the icosahedral cages formed by Al atoms. Np1-xV2Al20 is one of the few known nonmagnetic Np compounds, and its 5f electrons seem to be itinerant, contrary to the 4f electrons in the lanthanide LnV2Al20 system.
This work has been performed at the Institute of Transuranium Elements within its “ActinideUser Laboratory” program, with support to users provided by the European Commission. The Np metal required for the fabrication of the compound was made available through a loan agreement between Lawrence Livermore National Laboratory and ITU in the framework of a collaboration involving Lawrence Livermore National Laboratory, Los Alamos National Laboratory, and the US Department of Energy. The support from the National Science Centre (Poland) grant no. DEC-2012/07/E/ST3/00584 is thankfully acknowledged.
EE13.6: Theory—Metals and Oxides
Session Chairs
Thursday PM, March 31, 2016
PCC North, 200 Level, Room 221 A
2:30 PM - *EE13.6.01
Thermal Evolution of Vibrational Properties of α-U
Johann Bouchet 1,Francois Bottin 1
1 CEA Arpajon France,
Show AbstractBy means of ab initio molecular dynamic calculations, the thermal evolution of vibrational proper-
ties in α-U is studied at low temperature. The phase transition undergone by this material around
50 K was previously studied extensively using ab initio calculations in the framework of the lin-
ear response at 0 K. Although these previous efforts capture successfully the complexity of the
experimental phonon spectrum at room temperature, in particular the soft-phonon mode and its
pressure dependence, they fail to reproduce the transition to the charge-density wave state at ambi-
ent pressure as a function of temperature. In the present work, by going beyond the quasi-harmonic
approximation and taking into account the temperature effects explicitly, we are able to reproduce
the behavior of both phonon spectrum and elastic constants of U-α as a function of temperature.
3:00 PM - EE13.6.02
Metal-Ligand Hybridization and Core-Level Spectra in Actinide and Rare-Earth Compounds
Jindrich Kolorenc 1,Alexander Shick 1
1 Institute of Physics, Czech Academy of Sciences Prague Czech Republic,
Show AbstractRecently, we have used the LDA+DMFT method to investigate the electronic structure of several actinide dioxides, UO2, NpO2, and PuO2 [1]. The theory indicates a large covalent mixing of the actinide 5f states with the 2p states of oxygen, which results in a substantially increased filling of the 5f orbitals away from the nominal integer occupancy. The core-level spectroscopy is known to clearly detect such intermediate valency in rare-earth compounds, including dioxides CeO2 and PrO2, and to distinguish this non-integer filling from an integer filling that is characteristic, for instance, to rare-earth sesquioxides [2,3]. The core-level spectra of the actinide dioxides, on the other hand, appear to be compatible with an integer rather than intermediate valency [4]. For example, the 4f x-ray photoemission spectra (XPS) show only small shake-up satellites, whereas the 3d XPS in the intermediate-valent CeO2 has a very different three-peak shape. We argue that this difference does not point to an integer valency in the actinide dioxides but to a reduced sensitivity of the core-level spectra to the filling of the 5f orbitals. Our large deviations from the nominal filling are in fact compatible with the small shake-up satellites in 4f XPS when a detailed calculation is performed [1]. To put our theoretical findings on an even firmer ground, we employ the LDA+DMFT method to calculate the electronic structure and the core-level spectra of selected rare-earth oxides with known intermediate and near-integer valency, and analyze possible reasons for the reduced sensitivity of the core spectra to the 5f electron count in the actinide oxides.
[1] J. Kolorenc, A. B. Shick, and A. I. Lichtenstein, Phys. Rev. B 92, 085125 (2015).
[2] A. Kotani and H. Ogasawara, J. Electron. Spectrosc. Relat. Phenom. 60, 257 (1992).
[3] A. Kotani, K. Kvashnina, S. Butorin, and P. Glatzel, Eur. Phys. J. B 85, 257 (2012).
[4] J. G. Tobin, et al., Phys. Rev. B 92, 035111 (2015).
3:15 PM - EE13.6.03
Defect Stability in Thorium Monocarbides: An Ab Initio Study
Cheng Cheng 1,Changying Wang 1,Han Han 1,Ping Huai 1
1 Shanghai Institute of Applied Physics, Chinese Academy of Sciences Shanghai China,
Show AbstractActinide carbides are considered to be one of the most promising nuclear fuel materials of Generation IV reactor. The relevant studies are concerning about both technological developments and fundamental scientific aspects. From the 1960s to 1970s, researchers have widely studied uranium carbide. [1-3] Through several decades’ intermission, the relevant experimental and theoretical studies for thorium carbide have attracted many attentions recently.
The elastic properties and point defects of thorium monocarbide (ThC) have been studied by means of density functional theory based on projector-augmented-wave method. Five types of point defects have been considered in our study including vacancy defect, interstitial defect, antisite defect, schottky defect and composition-conserving defect. The carbon vacancy defect has the lowest formation energy of 0.29 eV. This conclusion is consistent with the experimental phenomenon that the carbon vacancies are the predominant defects in nonstoichiometric ThC. The second most stable defect (0.49 eV) is one of composition-conserving defects in which one carbon is removed to another carbon site forming a C2 dimer. Our calculations have verified another experimental speculation that there is no antistructure defect in ThC. In addition, several kinds of carbon interstitial defects have been predicted that the carbon trimer configuration might be a transition state for a carbon dimer diffusion in ThC.
References
[1] Freyss M, 2010 Phys. Rev. B 81 014101
[2] Ducher R, Dubourg R, Barrachin M and Pasturel A 2011 Phys. Rev. B 83 104107
[3] Sahoo B D, Joshi K D and Gupta S C 2013 J. Nucl. Mater. 437 81
3:30 PM - EE13.6.04
Density-Functional Study of U-TRU-Zr and U-TRU-Mo Alloys
Alexander Landa 1,Per Soderlind 1,Patrice Turchi 1
1 Lawrence Livermore National Lab Livermore United States,
Show AbstractThe U-Zr and U-Mo alloys proved to be very promising fuels for liquid metal fast breeder reactors. The optimal composition of these alloys is determined from the condition that the fuel could remain stable in the bcc phase (γ-U) in the temperature range of stability of α-U phase. In other words, both Zr and Mo play a role of ‘γ-stabilizers’ helping to keep U in the metastable bcc phase upon cooling. In the present study we perform KKR-ASA-CPA and EMTO-CPA calculations of the ground state properties of γ-U-Zr and γ-U-Mo alloys and compare their heats of formation with CALPHAD assessments. Though the U-Zr and U-Mo alloys can be used as nuclear fuels, a fast rector operation on a closed fuel cycle will, due to the nuclear reactions, contain significant amount of TRU elements (Np, Pu, and Am). Above mentioned density-functional theory technique is extended to study ground-state properties of the bcc-based X-Zr and X-Mo (X = Np, Pu, Am) solid solutions. We discuss how the heat of formation correlates with the charge transfer between the alloy components, and how magnetism influences the deviation from Vegard’s law for the equilibrium atomic volume. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Work at LLNL was funded by the Laboratory Directed Research and Development Program under project tracking code 12-SI-008.
3:45 PM - EE13.6.05
Thermodynamic Properties of Point Defects in Delta-Plutonium from First Principles
B. Sadigh 1,Per Soderlind 1
1 Lawrence Livermore National Laboratory Livermore United States,
Show AbstractWe present extensive first principles calculations of structures and energies of point defects in the deltaphase
of plutonium at ambient pressure. The calculations incorporate orbital polarization (OP) and spinorbit
(SO) coupling within non-collinear spin-polarized density-functional theory as implemented using
the projector augmented wave (PAW) method.
We make detailed comparison with full-potential linear muffin-tin orbital (FPLMTO) calculations,
where SO-coupling and OP are implemented using the second variation method. We discuss the
formation energies and volumes of vacancies and self-interstitials in delta-Pu. We show that in stark
contrast to most close-packed metals, the equilibrium concentration of vacancies in delta-Pu is smaller
than the self-interstitials. Furthermore, the vacancy in this system induces an unusually large
compressive stress field, which is in magnitude comparable to the uncommonly small tensile stress field
around the self-interstitial. As a result, introduction of Frenkel pairs in delta-Pu leads to very little total
volume change.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore
National Laboratory under Contract DE-AC52-07NA27344.
EE13.7: Theory—Oxides
Session Chairs
Thursday PM, March 31, 2016
PCC North, 200 Level, Room 221 A
4:30 PM - *EE13.7.01
First-Principles Calculations of Structural and Electronic Modifications Induced by Point Defects in Mixed Actinide Oxides
Michel Freyss 1,Yaguang Li 1,Lei Shi 1,Emerson Vathonne 1,Marjorie Bertolus 1
1 CEA, DEN, DEC Cadarache, Saint-Paul lez Durance France,
Show AbstractEffort is still being put on the improvement of first-principles methods to study radiation effects in actinide-based nuclear materials. An accurate description of the electronic structure of the nuclear fuel material is required to get insight into elementary mechanisms of the material evolution at the atomic scale (atomic transport properties of point defects and fission products, for instance) and also to provide reliable structural and energetical data for the adjustment of parameters or potentials in empirical methods (classical molecular dynamics, kinetic Monte Carlo, etc.) at higher scales.
Most of the recent first-principles studies of radiation damage in actinide oxides are done using the DFT+U method in order to take into account the strong correlations of the actinide 5f electrons. By comparison with results using the DFT+DMFT method (DFT combined with dynamical mean field theory), we showed that DFT+U can capture a large majority of bulk properties of UO2.
The first-principles DFT+U method is then used to study structural, electronic and thermodynamic properties of mixed actinide oxides of interest for nuclear applications. One of the objectives is to determine the effect of the chemical composition and of the deviation from stoichiometry on the properties of these materials.
This approach is applied to the study of the actinide mixed oxides (U,Ce)O2 and (U,Pu)O2, the former being of interest as a weakly radioactive mixed oxide model material for separate effect experiments. We focus on oxygen defects with various chemical environments in mixed oxides of various compositions. The results are confronted to experimental data from the literature, obtained by X-ray absorption spectroscopy and X-ray diffraction, and to the results obtained in pure UO2.
5:00 PM - EE13.7.02
Electronic Structure Calculation on the Energetics of Nonmetallic Impurity Atoms in Plutonium Dioxide
Bingyun Ao 1
1 China Academy of Engineering Physics Mianyang China,
Show AbstractThe energetics of some typical nonmetallic impurity atoms (H, He, B, C, N, O, F, Ne, Cl, Ar, Kr and Xe) in PuO2 are calculated by means of a projector augmented-wave method in the frameworks of density functional theory. Hubbard parameter U and van der Waals corrections are selected for describing the strongly-correlated electronic behaviors of f electrons in Pu and weak interactions of rare gases, respectively. Three incorporation sites of the impurity atoms are considered: octahedral interstitial site, O vacancy and Pu vacancy. The main results show that the energetics of impurity atoms significantly depend on the incorporation sites and the properties of impurity atoms such as atomic radius and electron affinity. Almost all of the impurity atoms considered here are energetically unfavorable at the three incorporation sites, with exception of F atom at the octahedral interstitial sites and the O vacancy. The trends of incorporation energies of rare gas atoms generally address the size effects of impurity atoms. However, charge-transfer analysis reveals that the valence electrons can be polarized more easily with the increase in atomic number of rare gas elements. Moreover, electronic structures of these systems containing impurity atoms also indicate the general trends of their relative stabilities and chemical bonding characters.
5:30 PM - EE13.7.04
A First Principles Study of Impurities in PuO2
Sarah Hernandez 1,Edward Holby 1
1 Los Alamos National Laboratory Los Alamos United States,
Show AbstractWe will present results of the structural and electronic effects of impurities in bulk PuO2 using DFT+U as implemented in the Vienna Ab initio Simulation Package, VASP. Considered impurities were those that are known to be present in metallic δ-phase Pu. These impurities include Ga, Fe, C, and H, which were placed at various sites in the fluorite crystal structure of PuO2. Sites included an octahedral interstitial site, an interstitial site with twofold coordination with O, and O substitutional site, and a Pu substitutional site. Key results indicate that the incorporation energy was unfavorable for all sites except for the Pu substitutional site. When the impurities were placed in the Pu substitutional site, incorporation energies were not only favorable but complexes containing the impurity and O were formed. For instance, H migrated in the Pu oxide to form an OH structure with O-H bond of 0.98 Å and had incorporation energy of -2.62 eV. We will discuss the formation of these complexes and how they affected the structural and electronic properties of PuO2.
This work was funded by LANL LDRD program.
Symposium Organizers
David Shuh, Lawrence Berkeley National Laboratory
Ladia Havela, Charles University
Alexander Landa, Lawrence Livermore National Laboratory
Daniel Schwartz, Los Alamos National Laboratory
Symposium Support
Lawrence Livermore National Laboratory
EE13.8: Bonding and Chemistry II
Session Chairs
Friday AM, April 01, 2016
PCC North, 200 Level, Room 221 A
9:00 AM - *EE13.8.01
Achieving Actinide Separation over Lanthanides by Aluminium Cathode Based Electrolysis in LiCl-KCl Eutectic
Weiqun Shi 1
1 Institute of High Energy Physics, Chinese Academy of Sciences Beijing China,
Show AbstractPyrometallurgical process is one of the most promising options for the reprocessing of advanced nuclear fuels and transmutation blankets which are notable to possess high burn-up and high content of Pu and minor actinides. In a typical pyrometallurgical process, actinides are anodically dissolved in LiCl-KCl eutectic along with the active fission products. At the same time, predominant uranium is recovered onto a solid stainless steel cathode, whilst most remaining uranium, plutonium and minor actinides are deposited together at the liquid cadmium cathode. Generally, this well known process possesses good recovery rates for uranium and plutonium and is inherently nuclear proliferation resistant. Nevertheless, one of the drawbacks of this pyrochemical method is that significant amount (~6% wt) of rare earth elements remains in the liquid cadmium cathode. Therefore, it is still quite necessary to develop more efficient pyrometallurgical separation approaches toward actinides over lanthanides. As displayed by previous investigations, the deposition potential disparity of actinides and lanthanides on the solid Al cathode are much larger than those on other active solid or liquid cathodes, and therefore the separation of actinides from lanthanides by using a solid Al electrode should be more efficient and plausible. Keeping this in mind, the separation of actinides from lanthanides by the co-reduction of actinide cations and Al3+ was studied in the present work. The results showed that all Ln3+, Th4+and U4+ could be co-reduced with Al3+ through forming various Ln-Al intermetallic compounds. Efficient separation of actinides over lanthanides can be achieved with acceptable extraction efficiency by this method. Conceptual process design with respect to Al cathode based An/Ln separation is undergoing.
9:30 AM - EE13.8.02
The Complexation of CyM4-BTBP with Actinide Ions
Guoxin Tian 3,Suliang Yang 1,David Shuh 3
1 China Institute of Atomic Energy Beijing China,2 College of Nuclear Science and Technology Harbin Engineering University Harbin China,3 Chemical Sciences Lawrence Berkeley National Laboratory Berkeley United States,1 China Institute of Atomic Energy Beijing China3 Chemical Sciences Lawrence Berkeley National Laboratory Berkeley United States
Show AbstractThe complexation of Np(V), U(VI), Nd(III), and Th(IV) with CyMe4-BTBP has been studied by spectrophotometric titration method in 99% ethanol at varying temperatures. The 1:1 complexes for Np(V) and U(VI) are identified while 1:1 and 1:2 complexes are found for Nd(III) and Th(IV). Single crystals of the 1:1 complexes for Np(V) and U(VI), and the 1:2 complexes for Nd(III) and Th(IV) are grown from the corresponding solutions by slow evaporation. The crystal structures and formation constants provide helpful information for understanding the extraction behavior of the actinides with CyMe4-BTBP as extractant.
9:45 AM - *EE13.8.03
Three Important Factors of the 5f-Element Ion Recognition with Ligand
Tsuyoshi Yaita 1
1 Quantum Beam Science Center Japan Atomic Energy Agency Hyogo Japan,
Show AbstractCharacterization of complex structure and chemical bond of the f-elements with neutral N and/or O-donor ligands provides key information for design of new ligand for separation of trivalent actinides from lanthanides. Hence, we have studied the complex characterization with actinides: Th, U, Pu, Cm and lanthanides by the X-ray crystallography, EXAFS/XANES, XAS/XES and DFT calculation methods. From XAS/XES and the DFT calculation results, it was clarified that actinides having 5f-electron significantly interacted with N through both ionic and covalent interactions. Interestingly, 5f orbitals and the filled s and p orbitals would participate in covalent and ionic bonds, respectively. This is, it might mean that these two the interactions occur independently in the formation of chemical bond, because f, and s and p orbitals play important role independently for each interaction. The X-crystallography of lanthanides results have gradually clarified a rigid size of the ligand could recognise a special lanthanide or actinide size. For instance, the phenanthroline amide (PTA) showed the affinity for Nd to Sm. In this study, we carried out chemical formation dynamics study using TR-DXAFS in order to elucidate U(IV), Eu(III)-N donor ligand in solution. The TR-DXAFS provides time dependent EXAFS parameters: chemical shift, bond distance, debye-waller factor and so on, possibly giving us detailed information regarding chemical bond formation features about f-elements. The N-donor ligands used in this study were 1,10-phenanthroline (Phen) and PTA. The metal ion (U(IV, VI) or Eu(III)) in methanol was prepared as initial solution, and then concentrated ligand (Phen or PTA) solution was added by titration with remote control system, after EXAFS measurement started. The time dependent radial structural functions (RSF) of EXAFS for Eu(III)-PTA-methanol system. The EXAFS RSF after 200s consists of two peaks: peak1e around 2 Å and peak1e around 2.7 Å, arising from O, N(C=O, Phen) and C around N donor atoms, respectively. At first, oxygen of carbonyl group coordinated immediately replacing with water oxygen and the peak1e also appeared. After 5s, the peak2e slightly broadened and the peak2e slightly shifted for shorter distance, indicating that PTA coordination occurred by two steps coordination. The time resolved RSF of U(IV,VI)-PTA-methanol system. The EXAFS RSF after 2000s consists of three peaks: peak1u around 1.5 Å, peak2u around 2 Å, and peak3u around 3.1 Å, arising from O (axial oxygen), O, N of PTA, and C of PTA around N donor atoms, respectively. After mixing solution, although PTA coordination was already completed, it was observed that a part of water oxygen had changed to uranyl oxygen during oxidation of uranium. In this presentation, we will also present that time resolved EXAFS fitting parameters for complex formation dynamics of U(IV or VI) and Eu(III)-Phen, PTA solution system.
10:15 AM - EE13.8.04
Soft X-Ray Spectroscopy of Actinide Materials
David Shuh 1,Stefan Minasian 1,Chaitanya Pemmaraju 1,Anders Modin 2,Sergei Butorin 2,Jason Keith 3,Enrique Batista 3,David Clark 3,Stosh Kozimor 3,Richard Martin 3,Mich-To Suzuki 2,Johan Vegelius 2,Younsuk Yun 2,Lars Werme 2,Joseph Nordgren 2,Peter Oppeneer 2,Roy Copping 1,Tolek Tyliszczak 1,Andrew Canning 1,David Prendergast 1
1 Lawrence Berkeley National Lab Berkeley United States,2 Dept. of Physics and Astronomy Uppsala University Uppsala Sweden3 Los Alamos National Laboratory Los Alamos United States
Show AbstractSoft X-ray synchrotron radiation methodologies are being developed and employed at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory to elucidate the electronic structure of actinide materials. Results from these investigations have begun to provide improved fundamental knowledge that can be used as a scientific basis for the enhanced design of special-purpose actinide materials and the overall understanding of actinide materials. The experimental developments at the ALS have centered on the use of the Molecular Environmental Science (MES) scanning transmission X-ray microscope (STXM) at Beamline 11.0.2 for near-edge X-ray absorption spectroscopy (XAS), and on X-ray emission spectroscopy (XES) at several beamlines, focusing primarily on light atom constituents (C, N, O, F) for ligand K-edge XAS, and on metal-ion centers plus light-atom signals for XES. The spectromicroscopy capabilities of the STXM provide the means to investigate and determine the speciation in actinide materials and environmentally-relevant systems with spatial resolution that reaches to the true nanoscale. An absolutely critical and key enabling component for all of the soft X-ray investigations is the contribution of theory, that when combined with experiment, has firmly provided more detailed knowledge of electronic structure in actinide materials in terms of orbital composition and mixing, and oxidation state. The highlights of recent investigations of metallocenes at the carbon K-edge, uranyl complexes at the nitrogen K-edge, and actinide dioxides at the oxygen K-edge will be highlighted in this respect.
10:30 AM - *EE13.8.05
Chelating f-Elements in Nanomaterials for Theranostic Applications
Rebecca Abergel 1,Peter Agbo 1,Dahlia An 1,Stacey Gauny 1
1 Lawrence Berkeley National Lab Berkeley United States,
Show AbstractTargeted alpha-particle therapy holds tremendous potential as a cancer treatment, since it offers the potential of delivering a highly cytotoxic dose to targeted cells while minimizing damage to the surrounding healthy tissue, due to the short range and high linear energy transfer of alpha particles. A few actinide isotopes have recently emerged as promising short-lived radionuclides that emit multiple α particles in their decay chains, dramatically increasing the potential delivered dose. These isotopes can act as in vivo alpha-generator radionuclides and are of interest for new therapeutic applications. However, limited research efforts have been directed to the characterization of actinide coordination chemistry in biologically relevant species and on the development of new chelating platforms that are needed to bring the radionuclides to the desired sites. Our approach to this problem is to combine the use of new improved nano-scale platforms with the demonstrated selectivity and specificity of chelating agents that are known to form thermodynamically and kinetically stable chelates with f-elements. Such new ligand systems would increase the energy carried by the targeted constructs and would offer the possibility of concurrent targeted alpha-particle therapy with diagnostic imaging by inserting imaging functionalities through the use of other f-elements. Recent progress in the design of these nanomaterials will be presented and discussed.
EE13.9: Magnetism and Correlations II
Session Chairs
Friday PM, April 01, 2016
PCC North, 200 Level, Room 221 A
11:30 AM - *EE13.9.01
Investigation of Exotic Electronic Properties on Rare-Earth and Actinide Compounds under High Pressure
Fuminori Honda 1,Ai Nakamura 1,Dexin Li 1,Yoshiya Homma 1,Yusuke Hirose 2,Rikio Settai 2,Dai Aoki 1
1 Institute for Materials Research, Tohoku University Ibaraki Japan,2 Department of Physics Niigata University Niigata Japan
Show AbstractThe wide variety of f-electron compounds provides an ample opportunity for systematic studies of electronic properties. In rare-earth and actinide compounds, various kinds of electronic ground states such as magnetic ordering, heavy fermion, and unconventional superconductivity are realized as a result of RKKY interaction, Kondo effect, c-f hybridization etc. It is recognized that the electronic states in f-electron compounds can be tuned by pressure P. For example, in some Ce compounds, the magnetic ordering temperature Tord decreases with increasing P and becomes zero at a critical pressure Pc, where a heavy fermion state and, sometimes, pressure-induced unconventional superconductivity are formed. On the other hand, it is reported that non-magnetic Yb compounds are changed into the magnetically ordered state under high pressures. In the case of uranium compounds, it seems to me that pressure effect on electronic structures is more complicated. In order to investigate exotic electronic states of f-electron system, we extend our attention to several actinide compounds for studying wider pressure range.
CeIrGe3, which crystallizes in the BaNiSn3-type tetragonal structure without inversion symmetry, is an antiferromagnet with the Néel temperature TN1 = 8.5 K. With increasing pressure, TN1 shows a step-like decrease up to 20 GPa and suddenly disappears above 22 GPa. At 20 GPa, unconventional superconductivity appears below 1.5 K [1]. The upper critical field Hc2(0) at 24 GPa reaches more than 10 T for H || c-axis, reflecting the lack of inversion symmetry in its crystal structure. An antiferromagnet UIrSi3 with TN = 42 K also crystallizes with the same structure as that of CeIrGe3. On the other hand, an non magnetic heavy fermion compound YbIr2Zn20 exhibits a "super"-heavy fermion state, where the electronic specific heat coefficient exceeds 10 J/(K2 mol), around Pc ~ 5.2 GPa and an antiferromagnetic ordering above Pc [2]. While, in case of UIrSi3, TN monotonically increases with increasing pressure with a rate of 2.5 K/GPa up to 5 GPa. Recently, we have discovered a new heavy fermion compound UPd2Cd20, which orders antiferromagnetically below TN = 5 K. Pressure experiments on other uranium compounds will be presented and discussed.
This work was done in collaboration with Profs. I. Bonalde, K. Shimizu, Y. Onuki, and Y. Haga.
[1] F. Honda et al., Phys. Rev. B 81 (2010) 140507(R).
[2] F. Honda et al., J. Phys. Soc. Jpn. 79 (2010) 083709.
12:00 PM - EE13.9.02
Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x)
Steven Conradson 1,Akhil Tayal 1
1 Soleil Saint-Aubin - BP48 France,
Show AbstractBose-Einstein condensates composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic Bose-Einstein condensates in photo- and chemically doped UO2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. That some of these signatures of coherence in an atom-based system extend to ambient temperature suggests a novel mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. The dynamics and the condensate formation may both contribute to a substantial reduction in the size of the Mott gap, facilitating and as a result of the excitation. Such a mechanism would demonstrate that the use of ultra-low temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. A macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields.
12:15 PM - EE13.9.03
Novel 5f Electric Structure of Antiferromagnetic USb2 Studied by Angle-Resolved Photoemission Spectroscopy
Shiyong Tan 1,Donghua Xie 1,XInchun Lai 1
1 Institute of Materials, China Academy of Engineering Physics Jiangyou China,
Show AbstractActinide materials show various intriguing properties, such as heavy fermion states, unconventional superconductivities, and multiple orderings. It is generally believed that these properties mainly originate from the U 5f states. Up to now, intensive experimental efforts have been devoted to various actinide materials to study the complicated 5f electronic structure. Among various experimental methods, angle-resolved photoemission spectroscopy (ARPES) provides a direct probe of the band structure, and thus, it is a powerful method for studying the U 5f electronic states[1].
Antiferromagnetic USb2 (TN～203 K) is an excellent candidate to study the 5f electronic structure, as it is a moderately correlated electron system with a quasi-2D electronic structure[2]. Moreover, previous ARPES studies[3,4] observed a narrow heavy quasiparticle band below EF and the first kink structure of any actinide materials in USb2. However, they only reported the normal emission ARPES spectrum，the Fermi surface topology and band structure over the entire Brillouin zone are lacking, and the multiple gaps revealed by optical spectroscopy[5] are not found, which stimulate us to conduct our study of USb2 using ARPES.
Using helium discharging light source, we obtain the Fermi surface topology and complete band structures over the entire Brillouin zone for the first time. The observed valence bands and low energy electronic structure agree well with the first principle calculations in the literature [6]. While the 5f band around M point shows weak dispersion and is itinerant，we observe two straight-line shaped bands at -20 meV and -60meV below EF. These two bands can be seen over the entire Brillouin zone，which are angular independent, indicating that these two bands are localized 5f electron bands. Our ARPES result provide clear evidence that the 5f electron bands are partially localized and partially itinerant in USb2.
Then, we studied the mechanism of the antiferromagnetic transition of USb2. Possible Fermi surface nesting condition and partially opened gaps were observed on the 5f electron bands of USb2. The gaps are found to be associated with the antiferromagnetic transition in USb2. The gap size increases slightly with decreasing temperature, but doesn‘t follow the typical BCS formula. Our results provide important information about the electronic structure, magnetic properties and the complex emergent states in USb2.
Reference：
1. Damascelli, A., et al. Review of Modern Physics 75: 473-541(2003).
2. Aoki, D. Philosophical Magazine B 80: 1517-1514 (2000).
3. Guziewicz, E., et al. Physical Review B 69: 045102 (2004).
4. Durakiewicz, T., et al. Europhysics Letters 84: 37003 (2008).
5. Qi, J., et al. Physical Review Letters 111: 057402 (2013).
6. Yang, X., et al. Philosophical Magazine 89: 1893-1911 (2009).
EE13.10: Forensics
Session Chairs
Daniel Schwartz
Marianne Wilkerson
Friday PM, April 01, 2016
PCC North, 200 Level, Room 221 A
2:30 PM - EE13.10.01
Probing Forensic Signatures of Nuclear Materials
Marianne Wilkerson 1
1 Los Alamos National Laboratory Los Alamos United States,
Show AbstractChemical signatures correlated with nuclear processing may provide insight into sample provenance or history. Processes conducted to extract uranium out of natural ore, recover uranium from leach solutions, or purify feed materials are chemical nature. These activities provide the opportunity for chemical reagents or reaction intermediates to carry over into uranium oxide products. Subtle changes in chemical speciation as a function of controlled storage conditions may give additional information indicative of history. Plutonium oxide materials are readily formed in air, and studies reveal interesting chemical complexity over time. To better understand the usefulness of morphologic and chemical signatures from actinide oxides, we initiated studies to characterize a range of uranium oxide and plutonium oxide materials. Our ultimate goal is to be able to exploit this rich and complex information for understanding an unknown sample’s history.
Here, we present our investigation of measurable signatures from actinide oxides for forensic analyses using tools commonly employed to measure chemical structure and morphology. We characterized a series of both high-purity and legacy uranium powders that were stored under controlled conditions. In addition, we conducted initial studies on a high-purity plutonium oxide material to determine the ability to measure potential changes in structure. Chemical speciation was characterized by powder X-ray diffraction analysis and synchrotron-based X-ray Absorption spectroscopy, tools that provide complementary information, and morphologies were imaged by Scanning Electron Microscopy. LA-UR-15-28342
2:45 PM - EE13.10.02
Structural Characterization of Hydrolyzed Uranium Tetrafluoride Solids
Michael DeVore 1,Matthew Wellons 1
1 Savannah River National Laboratory Aiken United States,
Show AbstractTechnical nuclear forensics may include the characterization of nuclear materials produced from various uranium chemical conversion processes, such as oxides, fluorides, diuranates, and others. When these species are stored for long durations, environmental factors may induce chemical transformations within a sample with change in the temperature or humidity, or both. Uranium tetrafluoride (UF4) is an intermediate in both the processing of uranium ore, and the production of nuclear fuel. Published research focused on the uranium fluorine system, UF4 chemical changes induced by the environment are rare, in part due to its assumed chemical inertness. Additionally what published results on hydrolysis of UF4 are available are often contradictory. J. Dobratz et al reported UF4 almost completely decomposes in water at room temperature within 24 hours. Whereas A. Roberts et al reported that boiling water for 72 hours had no noticeable effect on UF4 solids.1 It has been proposed, and which previous work supports, that at elevated temperatures,UF4 will hydrolyze and oxidize to uranyl fluoride (UO2F2), but characterization of these reactions has not been clarified for typical environmental regimes.3
Anhydrous UF4 material is commercially available and can be manipulated by systematically changing the temperature and humidity such that both Raman spectroscopy and powder X-Ray Diffraction measurements can be made in-situ. Our efforts have focused on 1) determining the progeny of UF4 hydrolysis using elevated temperatures and relative humidities to expedite hydrolysis and determine final speciation, and 2) methodical control of temperature and humidity are used to identify intermediates and establish approximate kinetics for both temperature and humidity variances. Known UF4 Raman bands (130.7, 168.4, 296.9, and 360.8 cm-1), anhydrous UO2F2 bands (180, 442, and 915 cm-1), and hydrated UO2F2 bands (174 and 867 cm-1) are used to compare and contrast changes in time, temperature, and humidity.4 Results from this effort will validate/disprove the above decomposition pathway while providing a timeline for hydrolysis.
1 Nikolaev, N.S., Luk’yanychev, Yu.A., Atomnaya Energiya, 1961, 11, 1, 67-69
2 Wellons, M. Villa-Aleman, E., Smith, R., Journal of Raman Spectroscopy (submitted)
3 Katz, J.J., Rabinowitch, E. The Chemistry of Uranium, McGraw-Hill: New York, 1951, pg 374
4 Armstrong, D.P, Jarabek, R.J., Flether, W.H., Applied Spectroscopy, 1989, 43, 3, 461-468
3:00 PM - EE13.10.03
XPS Investigation on Changes in UO2 Speciation Following Exposure to Humidity
Scott Donald 1,M Davisson 1,Art Nelson 1
1 Lawrence Livermore National Lab Livermore United States,
Show AbstractIt is of interest in nuclear forensic science to understand the relationship between a sample’s history and the resulting chemical and physical characteristics. It may be possible to glean information on the processing and storage of uranium dioxide (UO2) from variations in the speciation of uranium. In this study, high purity UO2 powder samples were subjected to accelerated aging under controlled conditions with various relative humidities. Characterization of the chemical speciation of the products was accomplished using X-ray photoelectron spectroscopy (XPS). A shift to higher uranium oxidation states was found to be directly correlated to increased relative humidity exposure. It is thus expected that uranium oxide materials exposed to high relative humidity conditions during processing and storage would display a similar increase in average uranium valence.
3:15 PM - EE13.10.04
Characterization of Nuclear Fuel Pellets Using Scanning Electron Microscopy and Nanoscale Secondary Ion Mass Spectrometry for Nuclear Forensics
Ruth Kips 1,Michael Kristo 1
1 LLNL Livermore United States,
Show AbstractCeramic uranium oxide is the most common fuel type used in nuclear reactors worldwide, with standard fuel fabrication methods producing hundreds of uranium pellets per minute. Several cases of theft and illicit trafficking of nuclear fuel pellets have occurred in the past, aided by the large quantities of fuel pellets available and their low specific radioactivity. Uranium fuel pellets have been the subject of several inter-laboratory measurement evaluation exercises for nuclear forensics, including the recent CMX-4 exercise organized by the Nuclear Forensics International Technical Working Group (ITWG). These exercises aim to share best practices and advance our understanding of nuclear forensics analysis and interpretation by linking the material’s chemical, isotopic and morphological characteristics to the materials origin and process history.
LLNL has applied a wide range of analytical techniques to the analysis and identification of nuclear fuel pellets. In addition to the more commonly used techniques, LLNL has also pioneered the use of the CAMECA NanoSIMS for nuclear forensics analysis. This secondary ion mass spectrometer (SIMS) can analyze and map the elements/isotopes in the surface of the fuel pellets directly, with a spatial resolution typically an order of magnitude smaller than traditional SIMS. The instrument’s large dynamic range, as well as the relatively straightforward sample preparation process, make it a powerful technique for the measurement of isotopic and trace element abundances in inhomogeneous samples.
In this study, we will describe the analysis of four different fuel pellets at the microscale, using scanning electron microscopy (SEM) and NanoSIMS. Various microstructural attributes of a fuel pellet that influence the fuel properties and its subsequent behavior in a reactor may also be of value in a nuclear forensics investigation, potentially linking the fuel to a particular production process, feedstock material and/or fuel fabrication facility. The characterization of the fuel pellet grain size and grain structure, porosity, isotopic homogeneity and impurities will be described and evaluated, and where possible attributed to differences in their origin or production history.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (under contract DE-AC52-07NA27344).
3:30 PM - EE13.10.05
Nuclear Forensics of a Non-Traditional Sample: Neptunium
Jamie Doyle 1,Kevin Kuhn 1,Elmer Lujan 1,Alexander Martinez 1,Steven Myers 1,Donivan Porterfield 1,Khalil Spencer 1,Lisa Townsend 1,Daniel Schwartz 1,Lav Tandon 1
1 Los Alamos National Laboratory Los Alamos United States,
Show AbstractNuclear forensics is most commonly associated with plutonium and uranium; however by definition, nuclear forensics applies to any diverted nuclear material. A case study of a non-traditional actinide sample, neptunium oxide, will be presented. Within this case study, the results of the chemical analysis will be discussed with an emphasis on the morphological analysis. A comparison of this neptunium oxide morphology with others from different process conditions will be compared qualitatively as well as quantitatively. These oxides will be further compared with morphological observations of other more traditional nuclear materials.
4:15 PM - *EE13.10.06
Investigation of Selected Material Properties as Nuclear Forensic Signatures
Klaus Mayer 1,Maria Wallenius 1,Zsolt Varga 1,Doris Ho Mer Lin 2,Lorenzo Fongaro 1
1 European Commission - Joint Research Centre Karlsruhe Germany,2 DSO National Laboratories Singapore Singapore
Show AbstractNuclear forensic science is an evolving discipline which aims at re-establishing the history of nuclear material of unknown origin by using measurable material properties. Initially, nuclear forensic science focused on chemical and radiochemical parameters, such as isotope ratios, chemical composition, chemical impurities or products of radioactive decay for deriving information on the intended use of the material or its place and date of production. Such information may be relevant for non-proliferation, for countering nuclear terrorism, for combating illicit trafficking of nuclear or other radioactive materials and for nuclear security in general. Obviously, this may involve law enforcement aspects as well as scientific aspects. In order to provide credible hints on the origin and the history of the material, useful parameters or a combination of several parameters (referred to as "nuclear forensic signature") need to be identified. The paper will review the signatures that have been identified for various types of nuclear material. Particular attention will be given to recent investigations on morphological aspects and different options for their evaluation.
4:45 PM - EE13.10.07
Forensic Analysis of Uranium Materials by Scanning Transmission X-Ray Microscopy
Joseph Pacold 1,Stefan Minasian 1,Tolek Tyliszczak 1,David Shuh 1
1 Lawrence Berkeley National Laboratory Berkeley United States,
Show AbstractNuclear material carries physical and chemical signatures that can often be used to determine its origin and process history. The field of nuclear forensic analysis is concerned with quantifying these signatures and applying them to characterize specimens of unidentified nuclear material. Initial results from studies of uranium materials by soft X-ray scanning transmission X-ray microscopy (STXM) are presented, demonstrating the utility of STXM as a nuclear forensic analysis technique. STXM combines 25-nm or better spatial resolution with X-ray absorption spectroscopy, making it possible to generate detailed compositional and speciation maps of a specimen. Operating in the soft X-ray regime provides access to the NIV,V-edges of the actinides and the K-edges of carbon, nitrogen, oxygen, and fluorine. Sensitivity to the chemical state of actinides in nuclear material is derived from the absorption spectra of both the actinides and the light atoms present. The oxygen K-edge, as an example, has spectral features that can be used as fingerprints of a broad range of actinide compounds and minerals and their hydrates. STXM data can consequently be used to directly evaluate the composition, species present, and homogeneity of a nuclear forensic sample, providing information on process history that is complementary to bulk-averaged data from, for example, mass spectrometry and X-ray fluorescence. Nuclear forensics-targeted developments in STXM operation at Beamline 11.0.2 of the Advanced Light Source are briefly described; fluorescence-mode detection has been implemented to improve sensitivity to dilute species, and software has been developed to streamline the acquisition of data from highly heterogeneous materials.
5:00 PM - EE13.10.08
Advanced Microstructural Analysis Methods for Nuclear Materials Characterization and Technical Nuclear Forensics Applications
Matthew Wellons 1,Michael DeVore 1,Taghi Darroudi 2
1 Nonproliferation Technology Section Savannah River National Laboratory Aiken United States,2 Clemson University Anderson United States
Show AbstractTraditionally the nonproliferation and technical nuclear forensics communities have been focused on characterization of the isotopic fingerprint of nuclear materials. However if no unique isotopic signature is found or mixed materials are present other physical characterization strategies are required for classification and or identification. Characterization of a nuclear material’s microstructure can provide probative information; particularly for nuclear materials originating from intermediate processing steps. These species may possess characteristics indicative of a chemical process or manufacturing including unique grain sizes, particle sizes, particle morphologies, unusual grain stress/strain, pore size distributions and others. Current efforts have focused on the characterization of bulk powders (i.e. XRD) for grain size information and their sub specimens via SEM and TEM for homogeneity/structural information, but new modern techniques in microanalysis now allow much more detailed characterization with decrease amounts of test material.
We have explored the use of advanced electron diffraction techniques and associated sample processing for the characterization of micron-sized nuclear materials via Electron backscatter diffraction (EBSD) and transmission kikuchi diffraction (TKD). As a preliminary study our aims were to determine: 1) a simple demonstration of the methods on uranium materials in practice; in order to identify material specific challenges, 2) whether nonmetallic uranium bearing materials were conducive to electron diffraction characterization or would characterization artifacts become induced during preparation and analysis, 3) understand potential limitations, such as the pattern fitting for structural identification. Electron diffraction methods rely on comparison between known crystalline structure diffraction patterns to measured species with various fit function. With the analysis of several different uranium compounds we have demonstrated the feasibility of commercial fit functions and the need to rely on the corresponding EDS information.
Test compounds within our efforts included various uranium oxides, uranium tetrafluoride, and uranyl oxalate compounds; all were processed via traditional ion milling techniques and subsequent characterized by electron diffraction. To date demonstration of EBSD and TKD have been accomplished on both fluoride and oxalate compounds with successful identification and characterization of internal grain structure. Additionally, initial results indicate that no measurable chemical structural damage occurred during sample preparation or analysis. These efforts and additional work on various uranium oxides is ongoing and will be presented.
5:15 PM - EE13.10.09
Morphological Analysis of Uranium Ore Concentrate Particles for Forensics Purposes
Daniel Schwartz 1,Lav Tandon 1,William Kinman 1
1 Los Alamos National Laboratory Los Alamos United States,
Show AbstractActinide metals are susceptible to rapid and catastrophic oxidation, and when collected from sites exposed to atmospheric conditions are frequently found in the form of small (< 100 µm diameter) oxide particles. We are investigating the plausibility of morphological and chemical analysis of such actinide particles for identifying the source, intended purpose, and processing route for field-collected particle sets. Scanning electron microscopy coupled with energy dispersive spectroscopy is a powerful tool for analyzing these types of particles, as these techniques yield both quantitative morphological information and chemical information rapidly and with relative ease.
We examined uranium oxide ore concentrates from two known sources, the Key Lake uranium deposit in Canada, and the Rössing uranium deposit in Namibia. These U ore concentrates were chosen because they are well-characterized materials with known pedigree. Raw U ore undergoes chemical-mechanical processing to concentrate it into yellowcake, which is orthorhombic U3O8 in powder form. X-ray diffraction showed both sets of powder to be single-phase orthorhombic U3O8 within the XRD detection limits. The two ore concentrate particles sets were qualitatively similar and key features will be compared and contrasted between the sets.
SEM images were produced from ~ 500 particles for each type of U3O8 powder. Morphological measurements were made on these images using MAMA (Morphological Analysis for Material Attribution) software developed at Los Alamos National Laboratory to quantify area, perimeter, and diametral parameters for each particle. By amassing a large morphological dataset, we were able to explore the statistical distributions of each measured morphological parameter as a potential identifying characteristic for the ore concentrate type. The morphological parameters and the statistical sets analyzed in this way will be discussed in detail.
Ensuring that the 500 particle datasets for each specimen do in fact represent a random sampling of the powder particles is non-trivial. Bias towards specific particle shapes and sizes can easily occur during handling and mounting of the particles for SEM observation. Methods for minimizing and recognizing biases will be discussed and illustrated.