Symposium : E
Actinide compounds and properties
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| 09:00 | Introduction | |
| Actinide alloy and compound properties : P. Oppeneer & M. Mazzaniti | ||
| 09:20 | Point Contact Spectroscopy Investigation of the PuCoGa5 Superconducting Phase Authors : D. Daghero1, M. Tortello1, G.A. Ummarino1, J.-C. Griveau2, E. Colineau2, R. Eloirdi2, A. B. Shick2, J. Kolorenc3, A. I. Lichtenstein4, and R. Caciuffo2 Affiliations : 1 Dipartimento di Fisica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy; 2 European Commission, Joint Research Centre, Institute for Transuranium Elements, Postfach 2340, D-76125 Karlsruhe, Germany; 3 Institute of Physics, ASCR, Na Slovance 2, CZ-18221 Prague, Czech Republic; 4 University of Hamburg, Jungiusstrasse 9, 20355 Hamburg, Germany Resume : PuCoGa5 is a 5f-electron superconductor exhibiting a number of interesting properties, including the highest critical temperature among heavy-fermion materials (Tc = 18.5 K). Despite extensive experimental and theoretical work, the nature of the Cooper pairing mediator
and the role of magnetism in determining the physical
origin of the superconducting behavior in this compound are still a matter of debate. Here, we report the results of point-contact Andreev-reflection measurements in
PuCoGa5 single crystals. Andreev reflection structures are clearly observed in the low-temperature spectra, and prove that the wave function of the paired electrons has a d-wave symmetry. The amplitude of the gap and its temperature dependence are reproduced within the Eliashberg theory for superconductivity by assuming a spin-fluctuation-like shape for the spectral function of the mediating bosons. The analysis shows that the peak energy of the spectral function falls in the range of spin-fluctuation energies as determined by NMR. Electronic structure calculations, combining the local density approximation with an exact diagonalization of the Anderson impurity model, provide a hint about the possible origin of the fluctuations that would involve a time-dependent 5f local moment dynamically compensated by a moment formed in the surrounding cloud of conduction electrons. | 1 1 |
| 10:00 | Coffee Break | |
| 10:20 | Electronic structure theory and magnetic character of Np_2Co_17. Authors : A. B. Shick(1,2), A. Hen(1), N. Magnani(3), E. Colineau(1), R. Eloirdi(1), J.-C. Griveau(1), J.-P. Sanchez(4), R. Caciuffo(1) Affiliations : (1) European Commission, Joint Research Centre, Institute for Transuranium Elements, Postfach 2340, D-76125 Karlsruhe, Germany; (2) Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, CZ-182 21 Prague, Czech Republic; (3) Lawrence Berkeley National Laboratory, Chemical Sciences Division, 1 Cyclotron Road, Berkeley, CA 94720-8175, USA; (4) SPSMS, UMR-E CEA/UJF-Grenoble 1, INAC, F-38054 Grenoble, France Resume : We report the results of a study performed to investigate the magnetic properties of the newly discovered Np_2Co_17 compound. This material belongs to the group of R$_{2}$T$_{17}$ (R = rare-earth, T = transition-metal) intermetallic compounds which were extensively studied during the past decades. The spin-polarized local spin density
approximation (LSDA) as well as LSDA plus Hubbard U (LSDA+U) calculations, using the experimental lattice parameters for
the ideal Th_2Ni_17-type structure. All calculations are performed making use of the full-potential linearized augmented
plane wave (FP-LAPW) method, and includes all relativistic effects: scalar-relativistic and spin-orbit coupling (SOC).
The comparison between first-principle electronic structure calculations and experimental data shows the necessity to go
beyond the local spin density approximation for correctly describing the magnetic properties of this family of Np
compounds, and that a satisfactory level of accuracyis obtained already by fully-relativistic LSDA+U approaches. | 1 2 |
| 10:40 | Spin-orbital hybridization and the origin of hidden order in URu2Si2 Authors : P. M. Oppeneer, S. Elgazzar, J. Rusz, T. Durakiewicz, J. A. Mydosh Affiliations : Dept. of Physics and Astronomy, Uppsala University, S-75120 Uppsala, Sweden; Physics Dept., Johannesburg University, South Africa; Los Alamos National Laboratory, Los Alamos, NM 87545, USA; Kamerlingh Onnes Laboratory, Leiden University, NL-2300 RA Leiden, The Netherlands Resume : The intermetallic uranium compound URu2Si2 undergoes a mysterious phase transition to an unknown phase below 17.5 K. Here we analyze the Fermi surface nesting properties of URu2Si2 with particular focus on their implication for the "hidden order" phase. We show that there exist two Fermi surfaces that exhibit a strong nesting at the antiferromagnetic wavevector, Q0=(0, 0, 1). The corresponding energy dispersions fulfill specific relations at eight FS hotspot lines.
The spin-orbital characters of the involved 5f states are distinct
(jz=±5/2 vs ±3/2) and hence the occurring degenerate Dirac crossings
are symmetry protected in the nonmagnetic normal state.
Dynamical symmetry breaking through an Ising-like spin-orbital excitation mode with ∆ jz=±1 induces a hybridization of the two states, causing substantial Fermi surface gapping.
Concomitant spin and orbital currents in the uranium planes give rise to a rotational symmetry breaking in the hidden order state. | 1 3 |
| 11:00 | The first-principles treatment of the electron-correlation and spin-orbital effects in uranium mononitride nuclear fuels Authors : D. Gryaznov1,2, E. Heifets2, E. A. Kotomin1,2 Affiliations : 1) Max Planck Institute for Solid State Research, Stuttgart, Germany 2) Institute for Solid State Physics, Riga, Latvia Resume : The DFT+U calculations were employed in a detailed study of the strong electron correlation effects in promising nuclear fuel – uranium mononitride (UN). A simple method for solving the multiple minima problem in DFT+U simulations and insure obtaining the correct ground state is suggested and applied. The crucial role of spin-orbit interactions in reproduction of the U atom total magnetic moment is demonstrated. Basic material properties (the lattice constants, the spin- and total magnetic moments on U atoms, magnetic ordering, and the density of states) were calculated varying the Hubbard U-parameter. Varying the tetragonal unit cell distortion, the meta-stable states have been carefully identified and analyzed. The difference of the magnetic and structural properties obtained for the meta-stable and ground states are discussed. The optimized effective Hubbard parameter Ueff =1.85 eV reproduces correctly the UN anti-ferromagnetic ordering, and only slightly overestimates the experimental total magnetic moment of U atom and the unit cell volume. This approach could be applied to a wide class of strongly correlated systems. | 1 4 |
| 11:20 | Uranium Carbide Material Investigations at CERN-ISOLDE and at the Swiss Light Source Authors : A. Gottberg, T. Stora, C. Degueldre, D. Grolimund Affiliations : CERN, CH-1211 Genève 23, Switzerland; CERN, CH-1211 Genève 23, Switzerland; Paul Scherrer Institut, 5232 Villigen PSI, Switzerland; Paul Scherrer Institut, 5232 Villigen PSI, Switzerland Resume : Although uranium carbide targets are commonly used in pin-type nuclear fuel elements and for radioactive ion-beam production in various facilities such as CERN-ISOLDE, only very little is known about the influence of microstructure in terms of crystallography, morphology and chemistry on the isotope release properties. Systematic investigations of phase and chemical evolution of this material in the length scale of its crystallographic grains, both before and after pulsed high energy proton irradiation, in combination with methodical variation of surfactants and micro structure, will provide important missing insights for the synthesis of future target materials required for next generation isotope mass separation online facilities. Therefore a campaign for a thorough analysis of this material has been launched within a large international collaboration; various investigations, such as EXAFS, XFS, and micro XRD using synchrotron radiation have already been achieved on a high density UC monophasic material.
This contribution will present a number of material studies performed on uranium carbide and reveal outstanding impact of their results on exotic radioactive ion beam production in the near future. Furthermore the first X-ray absorption spectrum ever taken from this exotic material will be presented. | 1 5 |
| 11:40 | Atomistic simulation of the UO2 polymorphs Authors : Fossati P., Van Brutzel L., Crocombette J.-P., Devincre B. Affiliations : CEA DEN/DANS/DPC/SCCME, CEA DEN/DANS/DPC/SCCME, CEA DEN/DANS/DMN/SRMP, ONERA LEM Resume : Uranium dioxide (UO2) is widely used as a nuclear fuel for pressurized water reactors around the world.
Despite its industrial interest, little is still known about its behaviour under reactor conditions, because of the technical difficulties to set up realistic experiments.
As such, Molecular Dynamics (MD) simulations are a valuable tool to explore the behaviour of this material under high temperature, pressure and radiation level.
The ground structure at room pressure and temperature is the Fluorite structure.
In this study, we observed some other possible structures for UO2 in high pressure conditions, using both DFT and empirical potentials calculations.
We also and described the related strain-induced phase transitions.
Then we used these results to interpret larger-scale simulations of fracture propagation in a UO2 monocrystal. | 1 6 |
| 12:00 | Lunch | |
| 13:40 | Thorium characterisation in plutonium uranium mixed oxide fuel by x-ray absorption Authors : C. Cozzo, A. Orlov, C. Borca, C. Degueldre Affiliations : NES & SYN, Paul Scherrer Institute, 5232 Villigen, Switzerland Resume : Plutonium uranium mixed oxide (MOX) fuels are currently used in nuclear light water reactors. Thorium can be found in pristine as well as irradiated MOX samples as an impurity. Since in non-extreme redox environment this element presents only one stable oxidation state (IV), its characterization can be used as a solid base for the study of the other actinides with the same oxidation state An(IV).
In this work the structure and next-neighbour atomic environment of thorium within irradiated (60 MWd kg-1) MOX samples was analysed by micro-X-ray absorption fine structure (µ-XAFS) spectroscopy measured in transmission mode. The experimental spectra were obtained from the peripheral (rim) and central zones on the fuel cross-section. In addition, spectra of pure thoria (ThO2) powder samples were recorded to serve as reference. The experimental data were also compared to XAFS calculations for thorium. It was found that thorium is only present in its most common state (tetravalent) in both pristine and irradiated fuel. | 2 11 |
| 14:00 | URANIUM CLUSTERS WITH NEW TOPOLOGIES AND UNUSUAL MAGNETIC PROPERTIES Authors : Victor Mougel, Biplab Biswas, Jacques Pécaut, Marinella Mazzanti Affiliations : CEA-Grenoble, INAC/SCIB/RICC Resume : The design of multinuclear molecular actinide complexes is of high current interest because of their efficiency to provide practical models to understand the uranium mobility in the environment and to investigate the magnetic interaction and the electronic structure of actinide materials. Accordingly we have become interested in studying the redox reactivity of uranium compounds as a route to new polynuclear architectures. Two main directions have been explored: the hydrolysis of trivalent uranium in non-aqueous conditions and Cation-Cation Interactions (CCI).
Thus, the controlled hydrolysis of UI3(THF)4 in presence of biologically relevant organic acids and strong bases lead to the isolation of a new family of discrete clusters with the U6O8 core and with the unprecedented U10O14 and U16O24 topologies. We experimentally demonstrates that these cluster can be formed in the course of the disproportionation reaction of uranyl(V) in organic media, providing good molecular model for the U(IV) clusters formed in the bacterial reduction of U(VI).
On the other hand, the synthesis of stable pentavalent uranyl with CCI’s provides a route to the self assembly of multinuclear uranium complexes trough the mutual coordination of the UO2+ groups. Such assemblies show interesting magnetic properties which can be tuned by appropriate structural modifications. The structure and magnetic properties of new polymetallic assemblies of uranium and uranyl(V) will be presented. | 1 8 |
| 14:20 | On the Controlled Synthesis of Uranium and Thorium Oxides Nanocrystals. Authors : D. Hudry, C. Apostolidis, T. Gouder, E. Courtois, C. Kübel, O. Walter. Affiliations : D. Hudry; C. Apostolidis; T. Gouder; O. Walter; European Commission, Joint Research Center – Institute for Transuranium Elements, P.O. Box 2340, 76125 Karlsruhe, Germany E. Courtois; C. Kübel; Karlsruhe Institute of Technology, Institute of Nanotechnology, Hermann-von-Helmholtz-Platz 1, Building 640, 76344 Eggenstein-Leopoldshafen, Germany Resume : Within the last 10-20 years, there has been a huge interest in the controlled synthesis of nano-objects, their assembly into 2- and 3-dimensional objects and their structural and physical characterization. The ongoing revolution in nanoscience is providing a powerful approach to tune materials properties. Whereas nanoscience is a very active field for a wide range of stable elements, it is still neglected for actinides. So far, there have never been conclusive studies on size and shape effects on the physical and chemical properties of actinide compounds. We are convinced that there are no scientific reasons for which actinides nanoscience should be neglected. To investigate potential size and shape effects, a synthesis and characterization strategy should be implemented based on the two decades of intense efforts for stable elements. Our main goal is to open a new field of research in basic actinides science. In this presentation, we report a non-hydrolytic method for the controlled synthesis of uranium and thorium oxides nanocrystals. We synthesized uranium oxide nanodots and thorium oxide nanorods which crystallize in the fluorite structure (Fm-3m) of the corresponding bulk materials. Our results strongly suggest that the nature of the actinide precursor and / or the nature of the actinide centre dramatically influence the reactivity and hence the characteristics of the final actinide oxides nanocrystals. | 1 9 |
| 14:40 | Vibrational spectroscopy of actinide dioxides: a comparison between Raman spectra of UO2, NpO2 and PuO2 Authors : D. Manara, J.-Y. Colle, O. Beneš, R. Böhler Affiliations : European Commission, Joint Research Centre - Institute for Transuranium Elements (ITU) P.O. BOX 2340 G-76125 Karlsruhe, Germany Resume : Raman spectra of UO2, NpO2 and PuO2 have been measured with a Jobin-Yvon T64000 spectrometer using two excitation sources at different energies: one at 2.41 eV (Ar+ laser at 514 nm) and the other at 1.65 eV (Kr+ laser at 752 nm). Actinide oxide samples were encapsulated in a special alpha-shielding container equipped with a quartz window through which confocal measurements were carried out with a long focal microscope objective. The two sets of spectra recorded with higher or lower excitation energies display systematic differences, which can help the interpretation of some vibrational modes of uncertain origin, particularly in the wavelength range around 1150 cm-1. Independently of the excitation energy, the fundamental Raman-active T2g mode (An-O symmetrical stretching) was clearly identified for the three compounds between 445 and 475 cm-1. The wavenumber shift observed for this mode from an oxide to another is related to the different atomic masses of the different actinides, and to the stiffness of the actinide-oxygen and the oxygen-oxygen bonds in the three compounds. | 1 10 |
| 15:00 | Thermal expansion of PuO2 Authors : Teppei Uchida, Takeo Sunaoshi, Kenji Konashi, Masato Kato Affiliations : Japan Atomic Energy Agency; Tohoku university Resume : Experiment and simulation studies on physical properties of actinide oxides have been carried out. Thermal expansion is important data to evaluate the various properties from molecular dynamics (MD) simulation. In this study, thermal expansion of PuO2 was evaluated by experiment and MD simulation.
In the experimental study, a PuO2.00 sintered pellet of 95.0 % TD was used, which was obtained by sintering at 1923 K for 5 h in Ar/H2 atmosphere and annealling at 1123 K for 3 h in air. Dilatmeter was employed in the measurement. Thermal expansion of PuO2.00 was determined in the temperature range of 300 - 1923 K.
In the MD simulation, Born-Mayer-Huggins interatomic potential with a partially ionic model and Morse potential were employed. Potential parameters were determined by fitting the literature data of lattice constants, thermal expansion and melting point of PuO2. Lattice constants of PuO2 were evaluated in the temperature range from 300K to 2800K by MD simulation, and thermal expansion was evaluated.
The experimental data of thermal expansion was good agreement with that of the MD simulation in the temperature range from 300 K to 1923 K. Evaluation formula for thermal expansion of PuO2 in the temperature range from 300 K to2800 K was derived from both data. | 1 11 |
| 15:20 | Coffee Break | |
| 15:40 | Basic properties and anomalous thermal expansion of the first actinide based iron oxyarsenide compound: NpFeAsO Authors : T. Klimczuk1;2, H. C.Walker3, R. Springell4, A. B. Schick1, A. H. Hill3, P. Gaczy´nski1, K. Gofryk5, S. A. J. Kimber3, C. Ritter6, E. Colineau1, J.-C. Griveau1, D. Bou¨exi`ere1, R. Eloirdi1, R. J. Cava7 and R. Caciuffo1 Affiliations : 1 European Commission, JRC, Institute for Transuranium Elements, Postfach 2340, 76125 Karlsruhe, Germany; 2 Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Narutowicza 11/12, 80-952 Gdansk, Poland; 3 European Synchrotron Radiation Facility, BP220, F-38043 Grenoble Cedex, France; 4 London Centre for Nanotechnology and Department of Physics and Astronomy; University College London, London WC1E 6BT, United Kingdom; 5 Los Alamos National Laboratory, Los Alamos, NM, USA; 6 Institut Laue-Langevin, 38042 Grenoble Cedex, France; 7 Department of Chemistry, Princeton University, Princeton NJ 08544, USA; Resume : We report on the synthesis of NpFeAsO and PuFeAsO, the first actinide based oxyarsenide. This new compound is isostructural to the RFeAsO system (R=Rare Earth), possessing lattice parameters, Fe-As interatomic distances, and Fe-As-Fe bond angles falling within the empirical ’optimum’ for the observation of the highest superconducting transition temperatures.
A series of bulk measurements performed on the parent NpFeAsO compound, including susceptibility, heat capacity, Hall effect and resistivity, show no evidence for the expected spin density wave (SDW) formation, nor antiferromagnetic (AFM) ordering of the iron sublattice. Instead, a distinct antiferromagnetic ordering occurs at TN = 57 K. In order to identify the nature of the magnetic ordering, 237Np Mossbauer spectroscopy and powder neutron diffraction (D20, ILL) experiments were undertaken. These studies clearly show that the Np moments order below 60K and are aligned along the c-axis, with a ferromagnetic
coupling within the basal plane, and an antiferromagnetic coupling between the planes.
Low temperature high resolution X-ray synchrotron powder diffraction measurements on NpFeAsO was performed using ID31 at the ESRF. In contrast to all of the RFeAsO compounds, on cooling to 5 K no orthorhombic distortion was observed within the resolution of our NpFeAsO data. Our results reveal an anomalous thermal expansion below 60K, as the system undergoes antiferromagnetic ordering. | 1 13 |
| 16:00 | Structural characterization of new An(IV)-An(III) actinide oxalates (An= U,Pu and/or Am), precursors of oxide solid solutions. Authors : Christelle TAMAIN, Bénédicte ARAB CHAPELET, Murielle RIVENET, Stéphane GRANDJEAN, Francis ABRAHAM Affiliations : CEA, Nuclear Energy Division, Marcoule, RadioChemistry & Process Department, Separation Process Chemistry Service, Actinides Chemistry and Conversion Laboratory, F-30207 Bagnols sur Cèze ; CEA, Nuclear Energy Division, Marcoule, RadioChemistry & Process Department, Separation Process Chemistry Service, Actinides Chemistry and Conversion Laboratory, F-30207 Bagnols sur Cèze ; UCCS, Solid Chemistry Unit, UMR CNRS 8181, ENSCL-USTL, BP 90108, 59652 Villeneuve d’Ascq Cedex, France ; CEA, Nuclear Energy Division, Marcoule, RadioChemistry & Process Department, Separation Process Chemistry Service, Actinides Chemistry and Conversion Laboratory, F-30207 Bagnols sur Cèze ; UCCS, Solid Chemistry Unit, UMR CNRS 8181, ENSCL-USTL, BP 90108, 59652 Villeneuve d’Ascq Cedex, France Resume : Oxalic acid is a well-known reagent to recover actinides in the solid state thanks to the very low solubility of An(IV) and An(III) oxalate compounds in acidic solution. Moreover, considering homogeneous incorporation of minor actinides in mixed-oxide fuel or targets/blankets for transmutation, oxalic co-precipitation is particularly convenient to synthesize controlled mixed oxalate compounds, precursors of oxide solid solutions.
Up to now, only U(IV)-Ln(III) oxalate solid solutions have been completely structurally described from single-crystals. The extent of this study on powder compounds allowed to examine the influence of An(IV) and An(III) nature. The switch of actinide’s nature causes unexpected structural modifications underlining the specificity of transuranium chemistry and the need to pursue studies directly on single crystal of these actinides.
As the existing oxalate single crystal syntheses are not adaptable to the actinide-oxalate system, several original crystal growth methods allowing the formation of mixed actinide oxalate crystals were first developed. Applied to the mixed actinide systems, they led to the formation of the first mixed An(IV)-An(III) oxalate single crystals. These novel results, including the structural resolution, are presented here. | 1 14 |
| 16:20 | Secondary Phase Characterization of the Corrosion Products of U3Si2-Al Fuel Elements Authors : A. Neumann, M. Klinkenberg, G. Kaiser, H. Curtius, D. Bosbach Affiliations : Institute of Energy and Climate Research – Nuclear Waste Management and Reactor Safety IEK-6, Forschungszentrum Jülich (Germany) Resume : Corrosion experiments of non-radiated U3Si2-Al research reactor fuel elements were carried out under repository relevant conditions. During the corrosion secondary phases are formed which have to be identified and determined quantitatively. This analysis is important for the safety assessment of final repositories. In detail the experiments were carried out in glass autoclaves at 90 °C in repository relevant solutions under reducing conditions.
After termination of the corrosion period X-Ray Diffraction and Rietveld analysis were the major methods being applied for the identification and quantification of the crystalline and amorphous corrosion products which were subdivided into different grain size fractions previously.
The corrosion products, i. e. the secondary phases of the research reactor fuel elements, were identified via “Search/Match” database retrieving. The identified phases were lesukite, which has been observed for the first time under such experimental conditions, Layered Double Hydroxides (LDH) structures, iron, residues of uncorroded nuclear fuel, iron oxyhydroxides and chlorides.
The quantitative analysis showed that LDH compounds and lesukite are the major crystalline phases being observed. Rietveld analysis also revealed the content of amorphous phases. Considering future prospects of this research it will be important to characterize the amorphous content which is expected to include the uranium. | 2 15 |
| Poster: Preview 14-5/View&Vote 15-5/ End 16-5 : C. Degueldre & P. Arnold | ||
| 17:00 | Molecular dynamics calculations of heat conduction in actinide oxides under thermal gradient Authors : Taku Matsumoto, Tatsumi Arima, Yaohiro Inagaki, Kazuya Idemitsu, Masato Kato, Teppei Uchida Affiliations : Kyushu University; Kyushu University; Kyushu University; Kyushu University; Japan Atomic Energy Agency; Japan Atomic Energy Agency Resume : Under the reactor operating conditions, nuclear oxide fuel behaviors such as oxygen and actinide redistributions and fuel restructuring that caused by a large temperature gradient to a radial direction of fuel pellet affect the thermophysical properties, e.g. thermal conductivity and melting point. In this study, thermal conductivities of UO2, PuO2 and (U0.8,Pu0.2)O2-x (x=0.02-0.1) under the temperature gradient were evaluated at the atomic level by means of non-equilibrium molecular dynamics (NEMD) simulations. To provide the temperature gradient to the system, the momentum exchange algorithm was implemented in NEMD scheme [1]. Thus, the thermal conductivity was calculated by Fourier’s law. The results from NEMD calculations of small UO2 system are in good agreement with the empirical formula proposed by Fink [2]. However, it was found in the NEMD scheme that the thermal conductivity decreases with a decrease of supercell size. Then, reproducibility of the thermal conductivity values seems to be somewhat low. Meanwhile, the present NEMD method, as well as previous EMD method [3], shows that Umklapp process causes the decrease of thermal conductivity at high temperatures.
[1] C. N. Draghi, J. B. Avalos, Mol. Phys. 101 (2003) 2302.
[2] J. K. Fink, J. Nucl. Mater. 279 (2000) 1.
[3] T. Arima, S. Yamasaki, Y. Inagaki, K. Idemitsu, J. Alloys and Compd. 415 (2006) 43. | 4 1 |
| 17:00 | Thermal conductivities of ThO2, NpO2 and their related oxides: Molecular dynamics study Authors : Keita Yoshida, Tatsumi Arima, Yaohiro Inagaki, Kazuya Idemitsu Affiliations : Kyushu university; Kyushu university; Kyushu university; Kyushu university Resume : Thorium-232 is an abundant fertile material, and has been also produced as a by-product from mining rare metals. On the other hand, neptunium has been produced mainly in reactors, and in particular, Np-237 (half-life of 2.14 million years) is an important nuclide for geological disposal. Burning their related oxides in reactors is, therefore, expected to be an efficient use of resources and to be reducing the environmental impact.
To achieve the above fuel cycle systems, various thermo-physical properties, e.g., thermal conductivity and melting point, of ThO2, NpO2 and the related oxides should be assessed from the experimental and theoretical point of view. Thus, we evaluated their thermal conductivities using the molecular dynamics technique, the MXDORTO program.
In the present study, the inter-atomic potential parameters of Busing-Ida potential function were determined for ThO2 and NpO2 based on their experimental thermal expansions and compressibilities. The thermal conductivity was evaluated by the equilibrium method (the Green-Kubo formula) and the homogeneous non-equilibrium method developed by Evans.
Thermal conductivities of ThO2 and NpO2 given by equilibrium and non-equilibrium methods were almost comparable up to 2000 K and deceased with an increase with temperature. In addition, these were also comparable with those of UO2 and PuO2. At relatively low temperatures, thermal conductivities of (Th,U)O2 and (U,Np)O2 decreased with an increase of UO2 and NpO2 contents (up to 30 mol%), respectively. Such temperature and composition dependences of the thermal conductivity were interpreted as a decrease in it due to phonon-phonon interaction and phonon scattering by impurities. | 4 2 |
| 17:00 | Characterization of Sm- & Tb-Orthophosphates used for Nuclear Waste Management Authors : J. Heuser, H. Schlenz, D. Bosbach Affiliations : Institute of Energy- and Climate Research, Department of Nuclear Waste Management and Reactor Safety, Forschungszentrum Juelich GmbH, D-52425 Juelich (Germany); E-mail: j.heuser@fz-juelich.de Resume : The goal to find an appropriate answer to the question of a safe disposal of nuclear waste is of great public interest. REE-phosphate- and -phosphosilicate-ceramics represent a promising material for the immobilization of radionuclides like U, Pu and/or minor actinides resulting from the reprocessing of spent fuel of nuclear power plants. For the conditioning of radioactive waste, ceramics are a good alternative to the widely used borosilicate-glasses. In terms of their crystal structures, e. g. monazite-type ceramics offer outstanding properties concerning chemical durability and radiation resistance [1, 2] which can also be confirmed by their natural analogues.
Therefore we synthesized and characterized monazite-type solid solutions of sixteen different chemical compositions Sm1-xCexPO4 in the range 0 ≤ x ≤ 1.
Besides we investigated metastable orthophosphates with monoclinic crystal structure.
Different synthesis-routes were examined, the products were thermally analysed by coupled TG-DSC, chemically by EDX and structurally by XRD and Raman spectroscopy.
Due to our results we assume a minimum of melting point in the solid solution near the chemical composition Sm0.7Ce0.3PO4 which could improve the conditions for future industrial synthesis. So far not yet available Raman data for metastable monazite-type TbPO4 will be presented.
[1] G. R. Lumpkin, Elements 2, 365 (2006)
[2] A. Meldrum, L. A. Boatner, R. C. Ewing, Physical Review B 56, 13805 (1997) | 4 3 |
| 17:00 | Structural and thermal analysis of Nd-Monazite-type ceramics used for Nuclear Waste Management Authors : S. SCHMITZ, H. SCHLENZ, D. BOSBACH Affiliations : Institute of Energy- and Climate Research, Department of Nuclear Waste Management and Reactor Safety, Forschungszentrum Juelich GmbH, D-52425 Juelich (Germany). ste.schmitz@fz-juelich.de Resume : Monazit-type ceramics (LnPO4, Ln = La, Ce, Nd, Sm, Eu, Gd) could be a alternative to borosilicate glasses as matrices used for nuclear waste disposal. Monazite is a natural thorium ore, chemically variable and highly radiation resistant. The oldest known monazites including thorium are determined up to 3.2 Ga in age [1]. Our starting phase is NdPO4 with a melting temperature of 1975±20 °C [2]. Our intention is to reduce the melting and sintering temperature of this particular monazite phase, but maintaining the positive properties of monazite simultaneously. In order to include tetravalent actinides (e.g. Th, U, Pu) instead of Nd, a second phase is used for charge balance. We used cheralite (CaTh(PO4)2) and huttonite (ThSiO4) as solid solution end members. Two solid solution series NdPO4-CaTh(PO4)2 and NdPO4-ThSiO4 were pressed to pellets and synthesized by solid state reactions. The sample properties were analyzed by EDX, XRD, Raman spectroscopy, and TG-DSC. The analysis by SEM e.g. shows compact conglomerates of crystallites with diameters of 1 4 µm at Th-amounts up to 20%. The differences in the Raman spectra hint at changes in the structures of our phases at Th-phase amounts of 20% in both systems. Furthermore cell parameters show a significant linear shift as a function of chemical composition in both systems.
[1] B. Rassmussen, I.R. Fletcher, J.R. Muhling, Geochim. Cosmochim Acta 71, 670-690 (2007); [2] Y. Hikichi, T. Nomura, J. Am. Ceram. Soc. 70, C-252-C-253 (1987) | 4 4 |
| 17:00 | First-principles investigations of surface defect formation energies and adsorption reactions Authors : P. Maldonado, P. M. Oppeneer Affiliations : Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden Resume : The long-term storage of spent nuclear fuel materials has still a large num-
ber of uncertainties. Particularly the reaction processes at the surface of the
spent-fuel material are not well understood. To examine these uncertainties we
study computationally processes at the UO2 surfaces, aiming at clarifying the
occurring oxidation/reduction mechanisms.
We present a study of the CaF2, CeO2 and UO2 bulk and surface electronic
structure based on density functional theory calculations using two different
codes (Vasp and Abinit). The fluorite structure is the common point among
these systems. Initially we have studied the CaF2 and CeO2 systems, which
have been used as a model for UO2, since for these model systems experiments
can be readily done, giving us a good possibility to test the model.
We focus on the high index surfaces energies -(111),(110),(100),(211),(221),
(311),(331)- for CaF2, CeO2 and UO2 and the defect formation energies on
these surfaces, analyzing as well the position of the vacancy formation on the
surface. We find that the work to create an oxygen vacancy at such surfaces is
not directly related with the relative ordering of the surface stabilities. We also
give an explanation for the cluster of oxygen vacancies formation on the (110)
surface, including the vacancy monomer, dimer, and trimer, showing that the
linear vacancy formation is the most stable vacancy formation.
Furthermore, we have studied the adsorption of H2O and H2 on different
sites of the (110) surface, computing the dissociation energy of these molecules.
The research leading to these results has received funding from the European
Atomic Energy Community’s Seventh Framework Programme (FP7/2007-2011)
under grant agreement No. 269903. | 4 5 |
| 17:00 | Phonon spectrum, thermal expansion and heat capacity of UO2 from first-principles Authors : Y. Yun, D. Legut, P. M. Oppeneer Affiliations : Laboratory of Reactor Physics and Systems Behaviour, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland; Nanotechnology Centre, VSB-Technical University of Ostrava, CZ-708 33 Ostrava, Czech Republic; Dept. of Physics and Astronomy, Uppsala University, SE-751 20 Uppsala, Sweden Resume : With the aim to study thermal properties of the nuclear fuel material uranium dioxide, we have performed ab-initio calculations of its phonon dispersion spectrum, thermal
expansion, and heat capacity. The so-called direct method, based on the quasiharmonic approximation, is used to calculate the phonon frequencies within a density functional framework for the electronic structure. The phonon dispersions calculated at the theoretical equilibrium volume agree well with experimental dispersions. The computed phonon density of states compare reasonably well with measured data, as do also the calculated frequencies of the Raman and infrared active modes including the LO/TO splitting. To study the pressure dependence of the phonon frequencies we calculate phonon dispersions for several lattice constants. Our computed phonon spectra demonstrate the opening of a gap between the optical and acoustic modes induced by pressure. Taking into account the phonon contribution to the total free energy of UO2, its thermal expansion coefficient and heat capacity have been computed, and are found to be in good agreement with available experimental data for temperatures up to about 500K.
Our results exemplify the feasibility of performing first-principles modeling of the thermal properties of this important nuclear fuel material. | 4 6 |
| 17:00 | EURATOM FP7 Collaborative Project FIRST-Nuclides Authors : Volker Metz (1), Bernhard Kienzler (1), Vanessa Montoya (2) Affiliations : (1) Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (KIT-INE), Karlsruhe, Germany (2) AMPHOS21, Barcelona, Spain Resume : With respect to the fast/instant release of radionuclides from spent nuclear fuel under deep underground repository conditions, a series of questions are still open. These questions concern key input data to safety analysis, such as “instant release fraction (IRF)” values of various radionuclides.
In the present communication we report on the EURATOM FP7 Collaborative Project “Fast/Instant Release of Safety Relevant Radionuclides from Spent Nuclear Fuel (CP FIRST-Nuclides)”, which started in January 2012 and has a duration of three years. The project is established with the overall objective to provide for improved understanding of the fast / instantly released radionuclides from disposed high burn-up UO2 spent nuclear fuel. The dependence of the IRF on critical characteristics of the spent nuclear fuel (e.g. manufacturing process, burn-up history and fuel temperature history, ramping processes and storage time) are studied in detail. The project provides for experiments combined with modeling studies on integration of the different results as well as for up-scaling from experimental conditions to entire LWR fuel rods.
Experimental facilities with specialized equipment for work with highly radioactive materials collaborate for improving the knowledge relevant for the period after losing of the disposed canister integrity. The project is implemented by a consortium with ten beneficiaries (AEKI/MTA, AMPHOS21, CNRS, CTM, FZ Juelich, JRC-ITU, KIT, PSI, SCK/CEN and STUDSVIK). | 4 7 |
| 17:00 | Characterisation of Depleted Uranium Particles from a Test-Firing Range Using Secondary Ion Mass Spectrometry Authors : Mustafa Sajih(a), Torsten Henkel(b), Ian C. Lyon(b) and Francis R. Livens(a) Affiliations : (a) The University of Manchester, Centre for Radiochemistry Research, School of Chemistry, Manchester, M13 9PL, UK. (b) The University of Manchester, School of Earth, Atmospheric and Environmental Sciences, Manchester, M13 9PL, UK. Resume : Following the use of depleted uranium (DU) anti-armour munitions, the environmental impact of depleted uranium and its behaviour in the environment have become a topic of considerable interest. When a DU round hits a hard target such as amour plate, some DU aerosolizes and ignites during the impact, because uranium metal is pyrophoric. Heating and aerosol formation from the target material will also create small, reactive particles and fragments, which will be dispersed in the vicinity of the target. It is necessary to characterise these particles in order to assess their fate and environmental impact. In this study, time of flight secondary ion mass spectrometry (TOF-SIMS) was used to examine depleted uranium (DU) particles derived from test-firing of DU penetrators against hard targets. Imaging thin sectioned particles with TOF-SIMS revealed the internal chemistry, and showed the distribution of both major elements (Fe, U, Cr), and a wide range of trace elements (e.g. Ti, K, Ca, Al, Mg). Quantitative analysis showed correlation between the following groups of elements: Fe, Cr, Mn, Ni derived from target material; trace elements derived from soil, and U and Ti, derived from DU (0.75% Ti) alloy. The isotopic composition of U was consistent with DU. | 4 8 |
| 17:00 | Americium coprecipitation with and adsorption on hectorite Authors : N. Finck*, K. Dardenne Affiliations : Institute for Nuclear Waste Disposal (INE), Karlsruhe Institute of Technology (KIT), P.O. Box 3640, D-76021 Karlsruhe, Germany. (*nicolas.finck@kit.edu) Resume : Over geological time scales, the nuclear waste glass may corrode in the presence of ground water. The neoformation of alteration phases, such as the smectite hectorite [1], represents a significant retention potential for radionuclides, including actinides (An) [2]. Recent investigations [3] showed the possibility to incorporate Lu(III) at octahedral sites of hectorite.
Hectorite was crystallized from an Am(III)-containing brucite precursor phase. All samples associated with the synthesis protocol [3] were characterized by XRD and the Am(III) local chemical environment was probed by X-ray absorption spectroscopy. The EXAFS data point to Am(III) located in an octahedral environment in the brucite precursor phase. Oxygen atoms were detected as first neighbors and the two next nearest Mg subshells suggest a splitting in octahedral Mg neighbors. In the doped hectorite, EXAFS data indicate that Am(III) is 6-fold coordinated by O atoms and the detection of next nearest Mg/Si backscatterers strongly corroborate with a clay-related environment. In contrast, higher number of O backscatterers were detected for surface adsorbed Am(III), as well as lower number of Mg/Si neighbors at larger distances.
[1] H.U. Zwicky, et al., Mater. Res. Soc. Symp. Proc. 127, 129-136 (1989).
[2] J.I. Kim, et al., Engineer. Geol. 52, 221-230 (1999).
[3] N. Finck, et al., Environ. Sci. Technol. 43, 8807-8812 (2009). | 4 9 |
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