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  • 1. Bakaev, A.
    et al.
    Terentyev, D.
    Bonny, G.
    Klaver, T. P. C.
    Olsson, P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Neutron Research.
    Van Neck, D.
    Interaction of minor alloying elements of high-Cr ferritic steels with lattice defects: An ab initio study2014In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 444, no 1-3, p. 237-246Article in journal (Refereed)
    Abstract [en]

    Basic properties of minor alloying elements, namely Mo, W, Nb, Ta, V, Mn, Si entering the conventional and reduced-activation structural Fe-(9-12)Cr steels have been analyzed using ab initio calculations. The electronic structure calculations were applied to study the interaction of minor alloying elements with a number of important and well defined lattice structures, such as point defects, the 1/2 < 111 > screw dislocation core, high angle symmetric grain boundaries and free surfaces. The studied elements were classified according to their similarities and discrepancies regarding the interaction with the above mentioned defects. The refractory alloying elements are found to follow the same trend whereas Mn and Si exhibit peculiar behavior with respect to the interaction with both point and extended lattice defects. The obtained results are discussed and compared with previously published ab initio and available experimental data.

  • 2. Bergsaker, H.
    et al.
    Bykov, I.
    Petersson, P.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Tandem Laboratory.
    Likonen, J.
    Koivuranta, S.
    Coad, J. P.
    Van Renterghem, W.
    Uytdenhouwen, I.
    Widdowson, A. M.
    Microscopically nonuniform deposition and deuterium retention in the divertor in JET with ITER-like wall2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, p. 956-960Article in journal (Refereed)
    Abstract [en]

    The divertor surfaces in JET with ITER-like wall (ILW) have been studied using micro ion beam analysis (mu-IBA) methods and scanning electron microscopy (SEM). Deposited layers with beryllium as main constituent had been formed during plasma operations through 2011-2012. The deuterium trapping and impurity deposition were non-uniform, frequently enhanced within pits, cracks and valleys, regions reaching in size from 10 mu m to 200 mu m. The impurity deposition and fuel retention were correlated with the surface slope with respect to the direction of ion incidence. Typically more than 70% of the total measured areal density of trapped D was found in less than 30% of the surface area. This is of consequence for the interpretation of other surface analyses and in extrapolation from fuel retention in JET with ITER-like wall and rough divertor surfaces to ITER with smoother surfaces.

  • 3. Bergsaker, H.
    et al.
    Petersson, P.
    Bykov, I.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Likonen, J.
    Koivuranta, S.
    Coad, J. P.
    Widdowson, A. M.
    Microanalysis of deposited layers in the divertor of JET following operations with carbon wall2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, p. S668-S672Article in journal (Refereed)
    Abstract [en]

    Elemental mapping of cross sections of deposited layers on inboard tiles in the JET divertor after exposure to plasma operations with carbon wall are presented. The study was made using microbeam ion beam analysis methods in combination with optical microscopy and SEM. The surfaces had been exposed to plasma through different periods of operation (1998-2007, 2007-2009 and 1998-2009). The texture and composition of the layers are non-uniform. The physical structures include columnar, lamellar and disordered globular appearances. The distribution of trapped deuterium was frequently found to be lamellar, with well-defined sub layers with higher deuterium concentration. However, 3D regions with dimensions of about 100 mu m with enhanced deuterium content were also found, both at the layer surfaces and in the layer cross sections. The distributions of beryllium and Inconel components were lamellar but did not otherwise show large non-uniformity on the same scale length as the deuterium. (C) 2013 Euratom. Published by Elsevier B. V. All rights reserved.

  • 4.
    Bergsåker, H.
    et al.
    Kungliga Tekniska Högskolan.
    Emmoth, B.
    Petersson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Ion Physics.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Ion Physics.
    Coad, J.P.
    Likonen, J.
    Nuclear reaction analysis with ion microbeam of cross sections of surface layers deposited in tokamak divertor2007In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 362, no 2-3, p. 215-221Article in journal (Refereed)
    Abstract [en]

    Ion micro beam analysis has been applied to the investigation of plasma deposited layers covering the divertor tiles in the JET tokamak. Since the layers are about 100 μm thick they are too thick to be completely investigated by ordinary ion beam analysis. Cross sections of the layers were prepared by cutting and polishing. Elemental depth profiles were determined from the two dimensional images that could be derived by nuclear reaction analysis and resonant backscattering spectrometry, using ion beams focused to a few μm spot size. A combination of analysis methods are shown, which allow measurements of the concentration profiles of carbon, beryllium, deuterium, oxygen and stainless steel components at levels of a few percent, with an accuracy better than 10%.

  • 5.
    Bes, R.
    et al.
    Aalto Univ, Dept Appl Phys, POB 14100, FI-00076 Aalto, Finland.
    Kvashnina, K.
    ESRF European Synchrotron, Rossendorf Beamline, CS40220, F-38043 Grenoble 9, France;Helmholtz Zentrum Dresden Rossendorf HZDR, Inst Resource Ecol, POB 510119, D-01314 Dresden, Germany.
    Rossberg, A.
    ESRF European Synchrotron, Rossendorf Beamline, CS40220, F-38043 Grenoble 9, France;Helmholtz Zentrum Dresden Rossendorf HZDR, Inst Resource Ecol, POB 510119, D-01314 Dresden, Germany.
    Dottavio, G.
    CEA, DEN, DEC, F-13108 St Paul Les Durance, France.
    Desgranges, L.
    CEA, DEN, DEC, F-13108 St Paul Les Durance, France.
    Pontillon, Y.
    CEA, DEN, CAD, DEC,SA3C,LAMIR, St Paul Les Durance, France.
    Solari, P. L.
    Synchrotron SOLEIL, Ligne Lumiere MARS, BP 48, F-91192 Gif Sur Yvette, France.
    Butorin, Sergei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Martin, P.
    CEA, Res Dept Min & Fuel Recycling Proc, Nucl Energy Div, SFMA,LCC, Bagnols Sur Ceze, France.
    New insight in the uranium valence state determination in UyNd1-yO2 +/- x2018In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 507, p. 145-150Article in journal (Refereed)
    Abstract [en]

    The charge compensation mechanisms in UyNd1-yO2 +/- x, and its consequence on the overall O stoichiometry (or O/M ratio where M = Nd + U) have been studied through the uranium valence state mixture evolution as a function of Nd content up to y = 0.62 by means of high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD-XAS) at the U M-4-edge. Our results clearly demonstrate the formation of U5+ at low Nd content (y < 0.15). Upon increasing the Nd content, oxygen vacancies and the formation of U6+ appear as competing mechanisms for intermediate Nd concentrations, leading to the co-existence of U4+/U5+/U6+ mixed valence and an overall hypostoichiometry (O/M < 2.00). Finally, the formation of U6+ associated with strongly distorted U local environment is observed for high Nd concentrations (y = 0.62), leading to an overall hyperstoichiometry (O/M < 2.00).

  • 6. Bykov, I.
    et al.
    Bergsaker, H.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Tandem Laboratory.
    Heinola, K.
    Miettunen, J.
    Groth, M.
    Petersson, P.
    Widdowson, A.
    Likonen, J.
    Materials migration in JET with ITER-like wall traced with a Be-10 isotopic marker2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, p. 773-776Article in journal (Refereed)
    Abstract [en]

    The current configuration of JET with ITER-like Wall (ILW) is the best available proxy for the ITER first wall. Beryllium redistribution in JET-ILW can be used for estimates of its migration in ITER. To trace it, a localized isotopic Be marker has been implemented. A bulk Be-9 tile has been enriched with Be-10 up to atomic concentrations of 1.7 x 10(-9) and installed at the inner midplane of JET before the campaign. During the 2012 shutdown over 100 surface samples were taken non destructively from surfaces of two toroidally opposite limiter beams. The absolute areal densities of the marker were inferred from Be-15 atomic concentration in each sample, measured with Accelerator Mass Spectrometry with sensitivity <10(-14). The results of marker mapping are compared with predictions made with the ASCOT orbit following code.

  • 7. Bykov, I.
    et al.
    Bergsaker, H.
    Ratynskaia, S.
    Litnovsky, A.
    Petersson, P.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Time resolved collection and characterization of dust particles moving in the TEXTOR scrape-off layer2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, p. S681-S685Article in journal (Refereed)
    Abstract [en]

    Moving dust has been collected in the SOL of TEXTOR in a time-resolved way with silica aerogel collectors [1-3]. The collectors were exposed to the toroidal particle flux in NBI heated discharges during the start-up and flat top phase. Intrinsic dust was collected in several discharges. Other discharges were accompanied with injection of known amounts of pre-characterized dust (W, C flakes and C microspheres) from a position toroidally 120 degrees away from the collector. Particle flux, composition and dust size distribution have been determined with SEM and EDX. Calibration allowed particle velocity estimates to be made. Upper limits for the deuterium content of individual dust grains have been determined by NRA. (C) 2013 Elsevier B. V. All rights reserved.

  • 8. Eckle, M.
    et al.
    Eloirdi, R.
    Gouder, T.
    Colarieti-Tosti, Massimiliano
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Wastin, F.
    Rebizant, J.
    Electronic Structure of UCx Films Prepared by Sputter Co-Deposition2004In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 334, no 1, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Thin layers of UCx (x=0–12) have been prepared by sputter co-deposition of uranium and carbon in an Ar atmosphere. The films were investigated in-situ by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively). Special interest was put on the evolution of the electronic structure with the composition of the films, as deduced from the U-4f, C-1s and valence region spectra. With increasing carbon content, three types of carbon species were detected according to C-1s core level line, at 282, 282.6 and 284.5 eV binding energy (BE). They are attributed to the UC, UC2 and graphite phases, respectively. The U-4f core levels do not change strongly with increasing carbon content, showing well-itinerant U-5f electrons. Similarly, valence region spectra show three types of carbon species for different UCx films, which are differentiated by their C-2p signals. A strong hybridisation between C-2p and U-5f states is detected in UC, while the C-2p signal in UC2 appears only weakly hybridised, and for higher carbon contents a π band characteristic of graphite appears.

  • 9. Emmoth, B.
    et al.
    Kreter, A.
    Hallén, A.
    Jakubowski, M.
    Lehnen, M.
    Litnovsky, A.
    Petersson, Patrick
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Tandem Laboratory.
    Philipps, V.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Tandem Laboratory.
    Rubel, M.
    Schweer, B.
    Sundelin, P.
    Unterberg, B.
    Wienhold, P.
    In-situ measurements of carbon and deuterium deposition using the fast reciprocating probe in TEXTOR2009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 390-91, no 1, p. 179-182Article in journal (Refereed)
    Abstract [en]

    Silicon samples were exposed in the scrape-off layer of the TEXTOR plasma using a fast reciprocating probe, with the aim of studying carbon deposition and deuterium retention during Dynamic Ergodic Divertor (DED) operation. Separate samples were exposed for 300 ms at the flat-top phase of neutral beam heated discharges. The exposure conditions were varied on a shot-to-shot basis by external magnetic perturbations generated by the DED in the m/n = 3/1, DC regime, base configuration. Nuclear Reaction Analysis (NRA) was used to characterise collector sample surfaces after their exposure. Enhanced concentrations of both carbon and deuterium (C 3-10 x 10(16) at./cm(2), D 8-60 x 10(15) at./cm(2)) were found. The D/C ratio was less than unity which indicates that most of the carbon and deuterium were co-deposited. Carbon e-folding lengths of about 2 cm were found on both toroidal sides of the probe independent of DED perturbations.

  • 10.
    Frazer, D.
    et al.
    Univ Calif Berkeley, Dept Nucl Engn, Berkeley, CA 94720 USA..
    Qvist, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. Univ Calif Berkeley, Dept Nucl Engn, Berkeley, CA 94720 USA..
    Parker, S.
    Univ Calif Berkeley, Dept Nucl Engn, Berkeley, CA 94720 USA..
    Krumwiede, D. L.
    Univ Calif Berkeley, Dept Nucl Engn, Berkeley, CA 94720 USA..
    Caro, M.
    Los Alamos Natl Lab, Mat Sci & Technol Div, Los Alamos, NM USA..
    Tesmer, J.
    Los Alamos Natl Lab, Mat Sci & Technol Div, Los Alamos, NM USA..
    Maloy, S. A.
    Los Alamos Natl Lab, Mat Sci & Technol Div, Los Alamos, NM USA..
    Wang, Y. Q.
    Los Alamos Natl Lab, Mat Sci & Technol Div, Los Alamos, NM USA..
    Hosemann, P.
    Univ Calif Berkeley, Dept Nucl Engn, Berkeley, CA 94720 USA..
    Degradation of HT9 under simultaneous ion beam irradiation and liquid metal corrosion2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 479, p. 382-389Article in journal (Refereed)
    Abstract [en]

    A potentially promising coolant/structural material pair for a liquid-metal-cooled fast reactors is lead bismuth eutectic (LBE) coolant with the ferritic/martensitic steel HT9. The challenge of deploying LBE, however, is the corrosive environment it creates for structural materials. This corrosion can be mitigated with precise oxygen content control in the LBE to allow for the growth of passive protective oxide layers on the surface of the steel. In this paper, results are reported from the Irradiation Corrosion Experiment II (ICE-II), which allowed the simultaneous irradiation of a sample while in contact with LBE. It was found that a characteristic multilayer structure with an outer Fe3O4 oxide and inner FeCr2O4 spinel was grown and the oxidation was significantly larger in the irradiated region when compared to the region that was only exposed to LBE corrosion. Possible mechanisms are discussed to help understand this irradiation enhanced corrosion behavior.

  • 11. Gasior, P.
    et al.
    Irrek, F.
    Petersson, Patrick
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Tandem Laboratory.
    Penkalla, Hj.
    Rubel, M.
    Schweer, B.
    Sundelin, P.
    Wessel, E.
    Linke, J.
    Philipps, V.
    Emmoth, B.
    Wolowski, J.
    Hirai, T.
    Laser-induced removal of co-deposits from graphitic plasma-facing components: Characterization of irradiated surfaces and dust particles2009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 390-91, no 1, p. 585-588Article in journal (Refereed)
    Abstract [en]

    Laser-induced fuel desorption and ablation of co-deposited layers on limiter plates from the TEXTOR tokamak have been studied. Gas phase composition was monitored in situ, whereas the ex situ studies have been focused on the examination of irradiated surfaces and broad analysis of dust generated by ablation of co-deposits. The size of the dust grains is in the range of few nanometers to hundreds of micrometers. These are fuel-rich dust particles, as determined by nuclear reaction analysis. The presence of deuterium in dust indicates that not all fuel species are transferred to the gas phase during irradiation. This also suggests that photonic removal of fuel and the ablation of co-deposit from plasma-facing components may lead to the redistribution of fuel-containing dust to surrounding areas.

  • 12.
    Gyoeroek, Michael
    et al.
    Univ Innsbruck, Inst Ion Phys & Appl Phys, Technikerstr 25, A-6020 Innsbruck, Austria.
    Kaiser, Alexander
    Univ Innsbruck, Inst Ion Phys & Appl Phys, Technikerstr 25, A-6020 Innsbruck, Austria.
    Sukuba, Ivan
    Comenius Univ, Dept Nucl Phys & Biophys, Fac Math Phys & Informat, SK-84248 Bratislava, Slovakia.
    Urban, Jan
    Comenius Univ, Dept Nucl Phys & Biophys, Fac Math Phys & Informat, SK-84248 Bratislava, Slovakia.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Probst, Michael
    Univ Innsbruck, Inst Ion Phys & Appl Phys, Technikerstr 25, A-6020 Innsbruck, Austria. ; VISTEC, Wangchan 20210, Rayong, Thailand.
    Surface binding energies of beryllium/tungsten alloys2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 472, p. 76-81Article in journal (Refereed)
    Abstract [en]

    Binding energies of beryllium and tungsten atoms on surfaces of the alloys Be2W and Be12W were obtained from density functional theory calculations. Values of 4.08–5.63 eV for beryllium and 6.81–10.04 eV for tungsten were obtained. An analytical force field agrees for beryllium, but its tungsten surface atoms are too strongly bound. The surface binding energies of Be and W on Be12W surfaces is slightly smaller than on the pure Be and W surfaces, respectively. For higher tungsten content, i.e. for Be2W, the situation is more complicated. For some surfaces of this alloy the surface binding energies are enhanced while for others they are diminished, compared to the pure metal surfaces. The dependency of the cohesive energy on the mole fraction follows a linear relationship.

  • 13. Ivanova, D.
    et al.
    Rubel, M.
    Philipps, V.
    Schweer, B.
    Freisinger, M.
    Huber, A.
    Gierse, N.
    Penkalla, H.
    Petersson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Dittmar, T.
    Laser-based and thermal methods for fuel removal and cleaning of plasma-facing components2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 415, no 1, p. S801-S804Article in journal (Refereed)
    Abstract [en]

    The efficiency of two methods for in situ fuel removal has been tested on carbon and tungsten limiters retrieved from the TEXTOR and Tore Supra tokamaks: laser-induced ablation of co-deposits and annealing in vacuum at elevated temperature. The analyses of gas phase and surfaces performed with thermal desorption spectrometry, optical spectroscopy, ion beam analysis, surface profilometry and microscopy methods have shown: (i) the ablation leads to the generation of dust particles of 50 nm - 2 mu m; (ii) volatile products of ablation undergo condensation on surrounding surfaces; (iii) D/C ratio in such condensate is in the range 0.02-0.03; (iv) long-term annealing of 623 K for 70 h results in release of not more than 10% of deuterium accumulated in plasma-facing components; (v) effective removal is reached by heating to 900-1300 K.

  • 14. Landa, A.
    et al.
    Söderlind, P.
    Turchi, P. E. A.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Peil, O. E.
    Ruban, A. V.
    Density-functional study of bcc Pu-U, Pu-Np, Pu-Am, and Pu-Cm alloys2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 408, no 1, p. 61-66Article in journal (Refereed)
    Abstract [en]

    Density-functional theory previously used to describe phase equilibria in the gamma-Pu-U-Zr alloys [A. Landa, P. Soderlind, PEA. Turchi, L. Vitos, A. Ruban, J. Nucl. Mater. 385 (2009) 68; A. Landa, P. Soderlind, PEA. Turchi, L. Vitos, A. Ruban, J. Nucl. Mater. 393 (2009) 141], is extended to study ground-state properties of the gamma-Pu-Np, gamma-Pu-Am, and gamma-Pu-Cm solid solutions. Calculated heats of formation are compared with CALPHAD assessments where possible. We discuss how the heat of formation correlates with the charge transfer between the alloy components.

  • 15. Malerba, L.
    et al.
    Terentyev, D.
    Olsson, Pär
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Neutron Research.
    Chakarova, R.
    Wallenius, J.
    Molecular dynamics simulation of displacement cascades in Fe-Cr alloys2004In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 329-333, no PartB, p. 1156-1160Article in journal (Refereed)
    Abstract [en]

    An embedded atom method (EAM) empirical potential recently fitted and validated for Fe–Cr systems is used to simulate displacement cascades up to 15 keV in Fe and Fe–10%Cr. The evolution of these cascades up to thermalisation of the primary damage state is followed and quantitatively analysed. Particular attention is devoted to assessing the effect of Cr atoms on the defect distribution versus pure Fe. Using the Wigner–Seitz cell criterion to identify point defects, first results show that the main effect of the presence of Cr in the system is the preferential formation of mixed Fe–Cr dumbbells and mixed interstitial clusters, with expected lower mobility than in pure Fe.

  • 16.
    Olsson, Pär
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Neutron Research.
    Abrikosov, Igor A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Wallenius, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Neutron Research.
    Ab initio formation energies of Fe–Cr alloys2003In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 321, no 1, p. 84-90Article in journal (Refereed)
    Abstract [en]

    We have calculated ab initio lattice parameters, formation energies, bulk moduli and magnetic moments of Fe–Cr alloys. The results agree well with available experimental data. In addition to body centered cubic (bcc) alloys, which are representative of ferritic steels used in fast neutron reactors, face centered cubic (fcc) and hexagonal close packed (hcp) phases were considered in order to complete a theoretical database of thermodynamic properties. Calculations were done for the ferromagnetic phase, as well as for a phase with local moment disorder, simulating the magnetic structure at high temperatures. For the latter case, the formation energy of the alloy is strictly positive smooth function of chromium concentration, in agreement with experiments performed at high temperature. In the ferromagnetic case, a negative mixing enthalpy is found for chromium concentrations below 6%. Our observation is consistent with the experimentally observed inversion of the ordering trend, as well as with formation of the chromium rich α phase at Cr-concentrations above 9%, occurring at T<900 K.

  • 17. Pegourie, B.
    et al.
    Panayotis, S.
    Languille, P.
    Martin, C.
    Dittmar, T.
    Gauthier, E.
    Hatchressian, J. -C
    Pascal, J. -Y
    Roubin, P.
    Ruffe, R.
    Tsitrone, E.
    Vartanian, S.
    Wang, H.
    Beaute, A.
    Bouvet, J.
    Brosset, C.
    Bucalossi, J.
    Cabie, M.
    Caprin, E.
    Courtois, X.
    Dachicourt, R.
    Delchambre, E.
    Dominici, C.
    Douai, D.
    Ekedahl, A.
    Gunn, J. P.
    Hakola, A.
    Jacob, W.
    Khodja, H.
    Likonen, J.
    Linez, F.
    Litnovsky, A.
    Marandet, Y.
    Markelj, S.
    Martinez, A.
    Mayer, M.
    Meyer, O.
    Monier-Garbet, P.
    Moreau, P.
    Negrier, V.
    Oddon, P.
    Pardanaud, C.
    Pasquet, B.
    Pelicon, P.
    Petersson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Philipps, V.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Reiter, D.
    Roth, J.
    Roure, I.
    Rubel, M.
    St-Laurent, F.
    Samaille, F.
    Vavpetic, P.
    Deuterium inventory in Tore Supra: Coupled carbon-deuterium balance2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, p. S120-S125Article in journal (Refereed)
    Abstract [en]

    This paper presents an analysis of the carbon-deuterium circulation and the resulting balance in Tore Supra over the period 2002-2007. Carbon balance combines the estimation of carbon gross erosion from spectroscopy, net erosion and deposition using confocal microscopy, lock-in thermography and SEM, and a measure of the amount of deposits collected in the vacuum chamber. Fuel retention is determined from post-mortem (PM) analyses and gas balance (GB) measurements. Special attention was paid to the deuterium outgassed during the nights and weekends of the experimental campaign (vessel under vacuum, Plasma Facing Components at 120 degrees C) and during vents (vessel at atmospheric pressure, PFCs at room temperature). It is shown that this outgassing is the main process reconciling the PM and GB estimations of fuel retention, closing the coupled carbon-deuterium balance. In particular, it explains why the deuterium concentration in deposits decreases with increasing depth. (C) 2013 Elsevier B.V. All rights reserved.

  • 18.
    Petersson, Per
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Bergsåker, H.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Tandem Laboratory.
    Coad, J. P.
    Likonen, J.
    Koivuranta, S.
    Hakola, A.
    Cross sections of deposited layers investigated by micronuclear reaction analysis2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 415, no 1, p. S262-S265Article in journal (Refereed)
    Abstract [en]

    Cross sections of deposited layers from the divertor of the Joint European Torus (JET) have been investigated, microscopically and by ion microbeam analysis. The thickness of these layers on the studied samples varies between about 50 mu m and 800 mu m depending on the exposure time and poloidal location of the sample. For most of the thicker layers a laminar structure is observed. In some locations changes, such as gaps, are also observed along the laminar structure as well as more complex structures. The possibility to use the layers as historical reference was also investigated.

  • 19.
    Petersson, Per
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Rubel, M
    Dittmar, T
    Pégouiré, B
    Tsitrone, E
    Wessel, E
    An Overview of Nuclear Micro beam Analysis of Surface and Bulk Fuel Retention in Carbon-Fibre Composites from Tore Supra2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 451, no 1, p. s764-s764Article in journal (Refereed)
    Abstract [en]

    Surface and bulk retention of deuterium in tiles of the pump limiter from Tore Supra was examined with nuclear reaction analysis using both standard and micro-beam techniques. The aim was to determine the variations in the content and distribution of fuel species in carbon-fibre composites. On plasma-facing surfaces from the deposition zone, the D content reaches 2.5 × 1019 cm−2 in about 8 μm thick top layer, but lateral differences reach even more than one order of magnitude. This is also measured in the erosion zone: 6.6 × 1017 cm−2 to 7.7 × 1018 cm−2 D atoms. Bulk content was examined on cross-sections opened by fracturing the tiles. Fuel is detected up to the depth of 1–1.5 mm beneath the plasma-facing surface in tiles from both the erosion and deposition zones. It occurs in bands, about 100 μm wide and several mm long, roughly parallel to the original plasma-facing surface.

  • 20. Porro, S.
    et al.
    De Temmerman, G.
    Lisgo, S.
    Rudakov, D. L.
    Litnovsky, A.
    Petersson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    John, P.
    Wilson, J. I. B.
    Diamond coatings exposure to fusion-relevant plasma conditions2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 415, no 1, p. S161-S164Article in journal (Refereed)
    Abstract [en]

    Several types of diamond layers have been deposited on molybdenum tiles by chemical vapour deposition techniques, and exposed under erosion-dominated conditions in the SOL of TEXTOR in order to assess them as a suitable candidate for plasma-facing material. Post-exposure characterisation of physical properties and surface modification induced by the plasma was performed by SEM imaging, investigation of diamond surface by micro-Raman spectroscopy and deuterium retention measurements by NRA. The analyses evidenced that lightly boron-doped micro-crystalline diamond is performing better than undoped and heavily doped samples, and nano-crystalline diamond and diamond-like carbon, as it showed lower surface modification, lower presence of arcing traces at the surface and lower deuterium retention. High concentration of boron in the layers led to higher retention of deuterium, whereas undoped (insulating) diamond showed increased arcing activity. Nano-crystalline diamond and diamond-like carbon layers generally showed poorer mechanical properties.

  • 21.
    Qvist, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    An approach to quantifying the chemical conditions necessary to form a magnetite layer on steels in lead and lead-bismuth eutectic2014In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 454, no 1-3, p. 105-113Article in journal (Refereed)
    Abstract [en]

    In this study, the parameter space where a magnetite (Fe3O4) film forms on the surfaces of steels exposed to non-isothermal oxygen-controlled Pb and LBE coolant loops while avoiding PbO contamination has been quantified by a consistent set of 6 equations. These equations provide both the allowable temper- ature range of operation as well as the range of oxygen concentrations that must be maintained within the loop. The equations allow for a set of margins on the oxygen and iron concentrations in the system. Given a value for the maximum temperature within the loop, the minimum allowable temperature can be calculated and vice versa. The ‘‘protective triangle’’ concept was introduced to visualize the principles of the conditions promoting corrosion protection, and how these are affected by changing temperatures, concentrations and applied margins.

  • 22. Rubel, M.
    et al.
    Philipps, V.
    Marot, L.
    Petersson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Pospieszczyk, A.
    Schweer, B.
    Nitrogen and neon retention in plasma-facing materials2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 415, no 1, p. S223-S226Article in journal (Refereed)
    Abstract [en]

    Tungsten plate was exposed in the TEXTOR tokamak during nitrogen-assisted discharges. In order to determine material mixing on tungsten, the plate was examined ex situ with ion beam analysis techniques including time-of-flight heavy ion elastic recoil detection analysis and also with X-ray photoelectron spectroscopy. Nitrogen content in the range from 1.3 x 10(15) to 3.4 x 10(15) cm(-2) is measured in the outermost surface layer (20 nm) of the W plate. Photoelectron spectroscopy detects nitrogen both in the elemental and compound form, i.e. tungsten nitride (WN/W2N). Nitrogen is measured even in hot areas free from deuterium. Also neon co-implantation into the plasma-facing components has been identified following Ne-cooled pulses.

  • 23.
    Rubel, Marek
    et al.
    KTH, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Fusionsplasmafysik.
    Ström, Petter
    KTH, Fusionsplasmafysik.
    Petersson, Per
    KTH, Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Fusionsplasmafysik.
    Brezinsek, S.
    Coenen, J.
    Kreter, A.
    Moeller, S.
    Wienhold, P.
    Wauters, T.
    Fortuna-Zalesna, E.
    Tracer techniques for the assessment of material migration and surface modification of plasma-facing components2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, p. 280-284Article in journal (Refereed)
    Abstract [en]

    Tracer techniques were used in the TEXTOR tokamak to determine high-Z metal migration and the deposition of species used for plasma edge cooling or wall conditioning under different types of operation conditions. Volatile molybdenum hexa-fluoride, nitrogen-15 and oxygen-18 were used as markers in tokamak or ion cyclotron wall conditioning discharges (ICWC). The objective was to obtain qualitative and quantitative of a global and local deposition pattern and material mixing effects. The deposition and retention was studied on plasma-facing components, collector probes and test limiters. Optical spectroscopy and ex-situ analysis techniques were used to determine the plasma response to tracer injection and the modification of surface composition. Molybdenum and light isotopes were detected on all types of limiters and short-term probes retrieved from the vessel showing that both helium and nitrogen are trapped following wall conditioning and edge cooling. Only small amounts below 1 x 10(19) m(-2) of O-18 were detected on surfaces treated by oxygen-assisted ICWC.

  • 24.
    Soroka, Inna L.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Vegelius, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Korelis, Panagiotis T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Fallberg, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Butorin, Sergei M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Structural stability and oxidation resistance of amorphous Zr-Al alloys2010In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 401, no 1-3, p. 38-45Article in journal (Refereed)
    Abstract [en]

    We investigated the structural stability and oxidation resistance of Zr-Al films upon annealing in air. The concentration of Zr was varied from 0 to 100 at.%, with a step of 10 at.%. The films were fabricated using ultra-high vacuum based magnetron sputtering. The as-deposited films with Zr content from 17.3 at.% to 70.7 at.% were found to be X-ray amorphous at room temperature. When exposed to air a thin oxide layer, typically less than 6 nm, is formed. The thickness of the oxide layers increases when the samples are annealed in air and most of these are found to be fully oxidized at 700 degrees C with the formation of crystalline and amorphous oxides on the top of crystalline and amorphous metal films, respectively. The amorphous oxide layers are found to be dense, with well defined thicknesses. An experimental non-equilibrium phase diagram is provided, covering the whole concentration range of the Zr-Al system. (C) 2010 Elsevier B.V. All rights reserved.

  • 25.
    Ström, Petter
    et al.
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Dept Fus Plasma Phys, SE-10044 Stockholm, Sweden.
    Petersson, Per
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Dept Fus Plasma Phys, SE-10044 Stockholm, Sweden.
    Parra, Rodrigo Arredondo
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany.
    Oberkofler, Martin
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany.
    Schwarz-Selinger, Thomas
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany.
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Sputtering of polished EUROFER97 steel: Surface structure modification and enrichment with tungsten and tantalum2018In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 508, p. 139-146Article in journal (Refereed)
    Abstract [en]

    Surface structure modification and enrichment with tungsten and tantalum were measured for polished EUROFER97 samples after exposure to a deuterium ion beam. Time-of-flight medium energy ion scattering and time-of-flight elastic recoil detection analysis were implemented for measuring atomic composition profiles. Atomic force microscopy and optical microscopy were used to investigate surface morphology. The deuterium particle fluence was varied between 10(21) D/m(2) and 10(24) D/m(2), projectile energy was 200 eV/D and exposure temperatures up to 1050 K were applied. The average fraction of tungsten plus tantalum to total metal content in the 2 nm closest to the sample surface was increased from an initial 0.0046 to 0.12 for the sample exposed to the highest fluence at room temperature. The enrichment was accompanied by an increase in surface roughness of one order of magnitude and grain dependent erosion of the material. The appearance of protrusions with heights up to approximately 40 nm after ion beam exposure at room temperature was observed on individual grains. Samples exposed to 10(23) D/m(2) at temperatures of 900 K and 1050 K displayed recrystallization and cracking while changes to the total surface fraction of tungsten and tantalum were limited to less than a factor of two compared to the sample exposed to the same fluence at room temperature.

  • 26.
    Ström, Petter
    et al.
    Department of Fusion Plasma Physics, Royal Institute of Technology (KTH).
    Petersson, Per
    Department of Fusion Plasma Physics, Royal Institute of Technology (KTH).
    Rubel, Marek J.
    Department of Fusion Plasma Physics, Royal Institute of Technology (KTH).
    Fortuna-Zaleśna, Elzbieta
    Warsaw University of Technology.
    Widdowson, Anna
    Culham Centre for Fusion Energy, Culham Science Centre.
    Sergienko, Gennady
    Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik.
    Binda, Federico (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Cecconello, Marco (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Conroy, Sean (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Dzysiuk, Nataliia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Ericsson, Göran (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Eriksson, Jacob (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Hellesen, Carl (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Hjalmarsson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Possnert, Göran (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Sjöstrand, Henrik (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Skiba, Mateusz (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Weiszflog, Matthias (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Zychor, Izabella (Contributor)
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall2019In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 516, p. 202-213Article in journal (Refereed)
    Abstract [en]

    Inconel-600 blocks and stainless steel covers for quartz microbalance crystals from remote corners in the JET-ILW divertor were studied with time-of-flight elastic recoil detection analysis and nuclear reaction analysis to obtain information about the areal densities and depth profiles of elements present in deposited material layers. Surface morphology and the composition of dust particles were examined with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The analysed components were present in JET during three ITER-like wall campaigns between 2010 and 2017. Deposited layers had a stratified structure, primarily made up of beryllium, carbon and oxygen with varying atomic fractions of deuterium, up to more than 20%. The range of carbon transport from the ribs of the divertor carrier was limited to a few centimeters, and carbon/deuterium co-deposition was indicated on the Inconel blocks. High atomic fractions of deuterium were also found in almost carbon-free layers on the quartz microbalance covers. Layer thicknesses up to more than 1 mu m were indicated, but typical values were on the order of a few hundred nm. Chromium, iron and nickel fractions were less than or around 1% at layer surfaces while increasing close to the layer-substrate interface. The tungsten fraction depended on the proximity of the plasma strike point to the divertor corners. Particles of tungsten, molybdenum and copper with sizes less than or around 1 mu m were found. Nitrogen, argon and neon were present after plasma edge cooling and disruption mitigation. Oxygen-18 was found on component surfaces after injection, indicating in-vessel oxidation. Compensation of elastic recoil detection data for detection efficiency and ion-induced release of deuterium during the measurement gave quantitative agreement with nuclear reaction analysis, which strengthens the validity of the results.

  • 27.
    Yun, Younsuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    First-principles modeling of He-clusters in UO22009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 385, no 1, p. 72-74Article in journal (Refereed)
    Abstract [en]

    We have investigated the behavior of He in UO2, Using the projector-augmented-wave (PAW) method and the generalized gradient approximation (GGA) based on the density functional theory. Total energy calculations with atomic relaxation included have been performed in a 96-atom large supercell. We have found that He has a strong tendency to form a cluster in vicinity of an octahedral interstitial site (OIS) in the UO2 matrix. In addition, the strain energy produced by a He-cluster was found to be sufficient to create point defects of the host atoms in UO2. Our study suggests that He-clusters and He-induced point defects play an important role for the local mechanical properties Of UO2 (C) 2008 Elsevier B.V. All rights reserved.

  • 28.
    Yun, Younsuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Theory of He trapping, diffusion, and clustering in UO22009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 385, no 3, p. 510-516Article in journal (Refereed)
    Abstract [en]

    We have performed ab initio total energy calculations to investigate the behavior of helium and its diffusion properties in uranium dioxide MOD. Our investigations are based on the density functional theory within the generalized gradient approximation (GGA). The trapping behavior of He in UO2 has been modeled with a supercell containing 96-atoms as well as uranium and oxygen vacancy trapping sites. The calculated incorporation energies show that for He a uranium vacancy is more stable than an oxygen vacancy or an octahedral interstitial site (OIS). Interstitial site hopping is found to be the rate-determining mechanism of the He diffusion process and the corresponding migration energy is computed as 2.79 eV at 0 K (with the spin-orbit coupling (SOC) included), and as 2.09 eV by using the thermally expanded lattice parameter of UO2 at 1200 K, which is relatively close to the experimental value of 2.0 eV. The lattice expansion coefficient of He-induced swelling of UO2 is calculated as 9 x 10(-2). For two He atoms, we have found that they form a dumbbell configuration if they are close enough to each other, and that the lattice expansion induced by a dumbbell is larger than by two distant interstitial He atoms. The clustering tendency of He has been studied for small clusters of up to six He atoms. We find that He strongly tends to cluster in the vicinity of an OIS, and that the collective action of the He atoms is sufficient to spontaneously create additional point defects around the He cluster in the UO2 lattice. (C) 2008 Elsevier B.V. All rights reserved.

  • 29.
    Yun, Younsuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Kim, Hanchul
    Park, Kwangheon
    First-principles theory for helium and xenon diffusion in uranium dioxide2009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 385, no 2, p. 364-367Article in journal (Refereed)
    Abstract [en]

    The diffusion properties of He and Xe in UO2 have been investigated, using density-functional calculations employing the projector-augmented-wave (PAW) method and the generalized gradient approximation (GGA). The migration energies corresponding to both interstitial and vacancy-assisted mechanisms have been calculated and the results for the two noble gas atoms are compared with each other. We suggest that He likely diffuses by hopping through a single vacancy with computed low migration energies smaller than 0.79 eV and its diffusivity is much higher than that of Xe. Xe has a quite large migration energy compared to He; the strain energy plays a key role in Xe diffusion in UO2.

  • 30.
    Yun, Younsuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Kim, Hanchul
    Kim, Heemoon
    Park, Kwangheon
    Atomic diffusion mechanism of Xe in UO22008In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 378, no 1, p. 40-44Article in journal (Refereed)
    Abstract [en]

    We have investigated vacancy-assisted diffusion of Xe in uranium dioxide MOO calculating incorporation, binding, and migration energies. All the energy values have been obtained using the density functional theory (DFT) within the generalized gradient approximation (GGA) and the projector-augmented-wave (PAW) method. Considering spin-polarization effect, we find that the computed migration energy is reduced by and agrees well with experimental data compared to those obtained from nonmagnetic calculations. We also find that an oxygen vacancy lowers the migration energy of a uranium vacancy by about 1 eV, enhancing an effective movement of vacancy clusters consisting of both uranium and oxygen vacancies. Furthermore, the strain energy of Xe is large enough to contribute to the clustering of vacancies making it the driving force for the vacancy-assisted diffusion of Xe in UO2. In summary all the calculated results suggest that the trivacancy is a major diffusion pathway of Xe in UO2.

  • 31.
    Yun, Younsuk
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Legut, Dominik
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Phonon spectrum, thermal expansion and heat capacity of UO2 from first-principles2012In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 426, no 1-3, p. 109-114Article in journal (Refereed)
    Abstract [en]

    We report first-principles calculations of the phonon dispersion spectrum, thermal expansion, and heat capacity of uranium dioxide. 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 (DOSs) 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 from first-principles. Both quantities are in good agreement with available experimental data for temperatures up to about 500 K. 

1 - 31 of 31
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