Change search
Refine search result
1 - 11 of 11
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Adorno Lopes, Denise
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Wilson, T. L.
    Univ South Carolina, Columbia, SC 29208 USA..
    Kocevski, V.
    Univ South Carolina, Columbia, SC 29208 USA..
    Moore, E. E.
    Univ South Carolina, Columbia, SC 29208 USA..
    Besmann, T. M.
    Univ South Carolina, Columbia, SC 29208 USA..
    Wood, E. Sooby
    Univ Texas San Antonio, San Antonio, TX USA..
    White, J. T.
    Los Alamos Natl Lab, Los Alamos, NM USA..
    Nelson, A. T.
    Los Alamos Natl Lab, Los Alamos, NM USA..
    Middleburgh, S. C.
    Westinghouse Elect Sweden AB, Vasteras, Sweden.;Bangor Univ, Nucl Futures Inst, Bangor LL57 1UT, Gwynedd, Wales..
    Claisse, Antoine
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Experimental and computational assessment of U-Si-N ternary phases2019In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 516, p. 194-201Article in journal (Refereed)
    Abstract [en]

    Uranium nitride-silicide composites are being considered as a high-density and high thermal conductivity fuel option for light water reactors. During development, chemical interactions were observed near the silicide melting point which resulted in formation of an unknown U-Si-N ternary phase. In the present work, U-Si-N composite samples were produced by arc-melting U3Si2 under an argon-nitrogen atmosphere to form the ternary phase. The resulting samples were characterized by SEM/EDS-EPMA and XRD, and demonstrated an equilibrium between U3Si2, UN, USi and a U-Si-N phase with a distinct crystallographic structure. Rietveld refinement of the ternary structure was performed, considering the ternary structures existent in the analogue U-Si-C system, and a good fit was obtained for the hexagonal U(20)Si(16)N(3 )phase. DFT + U calculations were performed in parallel to evaluate the thermodynamic and dynamic stability of the ternaries U20Si16N3 and U3Si2N2. The calculated enthalpy of formation and phonon dispersion support the existence of stable U20Si16N3 and U3Si2N2, although some soft modes in the U(20)Si(16)N(3)( )phase phonons are observed. The results presented here thus demonstrate the occurrence of at least one ternary phase in the U-Si-N system.

  • 2.
    Claisse, Antoine
    et al.
    KTH.
    Adorno Lopes, Denise
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Investigation of the ground- and metastable states of AnN (An=Th..Pu)Manuscript (preprint) (Other academic)
  • 3.
    Claisse, Antoine
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Schuler, Thomas
    Lopes, Denise Adorno
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Transport properties in dilute UN(X) solid solutions (X = Xe, Kr)2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 17, article id 174302Article in journal (Refereed)
    Abstract [en]

    Uranium nitride (UN) is a candidate fuel for current GEN III fission reactors, for which it is investigated as an accident-tolerant fuel, as well as for future GEN IV reactors. In this study, we investigate the kinetic properties of gas fission products (Xe and Kr) in UN. Binding and migration energies are obtained using density functional theory, with an added Hubbard correlation to model f electrons, and the occupation matrix control scheme to avoid metastable states. These energies are then used as input for the self-consistent mean field method which enables to determine transport coefficients for vacancy-mediated diffusion of Xe and Kr on the U sublattice. The magnetic ordering of the UN structure is explicitly taken into account, for both energetic and transport properties. Solute diffusivities are compared with experimental measurements and the effect of various parameters on the theoretical model is carefully investigated. We find that kinetic correlations are very strong in this system, and that despite atomic migration anisotropy, macroscopic solute diffusivities show limited anisotropy. Our model indicates that the discrepancy between experimental measurements probably results from different irradiation conditions, and hence different defect concentrations.

  • 4.
    Johnson, Kyle D.
    et al.
    Studsvik Nucl AB, SE-61182 Nykoping, Sweden..
    Lopes, Denise Adorno
    KTH.
    Grain growth in uranium nitride prepared by spark plasma sintering2018In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 503, p. 75-80Article in journal (Refereed)
    Abstract [en]

    Uranium mononitride (UN) has long been considered a potential high density, high performance fuel candidate for light water reactor (LWR) and fast reactor (FR) applications. However, deployability of this fuel has been limited by the notable resistance to sintering and subsequent difficulty in producing a desirable microstructure, the high costs associated with N-15 enrichment, as well as the known proclivity to oxidation and interaction with steam. In this study, the stimulation of grain growth in UN pellets sintered using SPS has been investigated. The results reveal that by using SPS and controlling temperature, time, and holding pressure, grain growth can be stimulated and controlled to produce a material featuring both a desired porosity and grain size, at least within the range of interest for nuclear fuel candidates. Grain sizes up to 31 mm were obtained using temperatures of 1650 degrees C and hold times of 15 min. Evaluation by EBSD reveal grain rotation and coalescence as the dominant mechanism in grain growth, which is suppressed by the application of higher external pressure. Moreover, complete closure of the porosity of the material was observed at relative densities of 96% TD, resulting in a material with sufficient porosity to accommodate LWR burnup. These results indicate that a method exists for the economic fabrication of an N-15-bearing uranium mononitride fuel with favorable microstructural characteristics compatible with use in a light water-cooled nuclear reactor.

  • 5.
    Johnson, Kyle D.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Raftery, Alicia M.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Lopes, Denise Adorno
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Fabrication and microstructural analysis of UN-U3Si2 composites for accident tolerant fuel applications2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 477, p. 18-23Article in journal (Refereed)
    Abstract [en]

    In this study, U3Si2 was synthesized via the use of arc-melting and mixed with UN powders, which together were sintered using the SPS method. The study revealed a number of interesting conclusions regarding the stability of the system - namely the formation of a probable but as yet unidentified ternary phase coupled with the reduction of the stoichiometry in the nitride phase - as well as some insights into the mechanics of the sintering process itself. By milling the silicide powders and reducing its particle size ratio compared to UN, it was possible to form a high density UN-U3Si2 composite, with desirable microstructural characteristics for accident tolerant fuel applications.

  • 6.
    Johnson, Kyle
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Adorno Lopes, Denise
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Oxidation of accident tolerant fuel candidates2017In: Journal of Nuclear Science and Technology, ISSN 0022-3131, E-ISSN 1881-1248, Vol. 54, no 3, p. 280-286Article in journal (Refereed)
    Abstract [en]

    In this study, the oxidation of various accident tolerant fuel candidates produced under different conditions have been evaluated and compared relative to the reference standard–UO2. The candidates considered in this study were UN, U3Si2, U3Si5, and a composite material composed of UN–U3Si2. With the spark plasma sintering (SPS) method, it was possible to fabricate samples of UN with varying porosity, as well as a high-density composite of UN–U3Si2 (10%). Using thermogravimetry in air, the oxidation behaviors of each material and the various microstructures of UN were assessed. These results reveal that it is possible to fabricate UN to very high densities using the SPS method, such that its resistance to oxidation can be improved compared to U3Si5 and UO2, and compete favorably with the principal ATF candidates, U3Si2, which shows a particularly violent reaction under the conditions of this study, and the UN–U3Si2 (10%) composite.

  • 7.
    Lopes, Denise Adorno
    et al.
    KTH. AlbaNova University Center.
    Benarosch, Anna
    KTH. AlbaNova University Center.
    Middleburgh, Simon
    Johnson, Kyle D.
    Spark plasma sintering and microstructural analysis of pure and Mo doped U3Si2 pellets2017In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 496, p. 234-241Article in journal (Refereed)
    Abstract [en]

    U3Si2 has been considered as an alternative fuel for Light Water Reactors (LWRs) within the Accident Tolerant Fuels (ATF) initiative, begun after the Fukushima-Daiichi Nuclear accidents. Its main advantages are high thermal conductivity and high heavy metal density. Despite these benefits, U3Si2 presents an anisotropic crystallographic structure and low solubility of fission products, which can result in undesirable effects under irradiation conditions. In this paper, spark plasma sintering (SPS) of U3Si2 pellets is studied, with evaluation of the resulting microstructure. Additionally, exploiting the short sintering time in SPS, a molybdenum doped pellet was produced to investigate the early stages of the Mo-U3Si2 interaction, and analyze how this fission product is accommodated in the fuel matrix. The results show that pellets of U3Si2 with high density (>95% TD) can be obtained with SPS in the temperature range of 1200 degrees C-1300 degrees C. Moreover, the short time employed in this technique was found to generate a unique microstructure for this fuel, composed mainly of closed nano-pores (<1 mu m) and small average grain size (similar to 4.5 mu m). The addition of Mo (1.5 at%) demonstrated no solubility of Mo in the U3Si2 matrix. The interaction of this fission product with the fuel matrix at 1200 degrees C formed, in the early stages, the stoichiometric U2Mo3Si4 ternary as well as precipitates of free uranium with small quantities of dissolved Si and Mo at the front of the reaction.

  • 8.
    Lopes, Denise Adorno
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Claisse, Antoine
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Ab-initio study of C and O impurities in uranium nitride2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 478, p. 112-118Article in journal (Refereed)
    Abstract [en]

    Uranium nitride (UN) has been considered a potential fuel for Generation IV (GEN-IV) nuclear reactors as well as a possible new fuel for Light Water Reactors (LWR), which would permit an extension of the fuel residence time in the reactor. Carbon and oxygen impurities play a key role in the UN microstructure, influencing important parameters such as creep, swelling, gas release under irradiation, compatibility with structural steel and coolants, and thermal stability. In this work, a systematic study of the electronic structure of UN containing C and O impurities using first-principles calculations by the Density Functional Theory (DFT) method is presented. In order to describe accurately the localized U 5f electrons, the DFT + U formalism was adopted. Moreover, to avoid convergence toward metastable states, the Occupation Matrix Control (OMC) methodology was applied. The incorporation of C and O in the N-vacancy is found to be energetically favorable. In addition, only for O, the incorporation in the interstitial position is energetically possible, showing some degree of solubility for this element in this site. The binding energies show that the pairs (C-N-vac) and (O-N-vac) interact much further than the other defects, which indicate the possible occurrence of vacancy drag phenomena and clustering of these impurities in grain boundaries, dislocations and free surfaces. The migration energy of an impurity by single N-vacancy show that C and O employ different paths during diffusion. Oxygen migration requires significantly lower energy than carbon. This fact is due to flexibility in the U-O chemical bonds, which bend during the diffusion forming a pseudo UO2 coordination. On the other hand, C and N have a directional and inflexible chemical bond with uranium; always requiring the octahedral coordination. These findings provide detailed insight into how these impurities behave in the UN matrix, and can be of great interest for assisting the development of this new nuclear fuel for next-generation reactors.

  • 9.
    Lopes, Denise Adorno
    et al.
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Uygur, Selim
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Johnson, Kyle
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Degradation of UN and UN-U3Si2 pellets in steam environment2017In: Journal of Nuclear Science and Technology, ISSN 0022-3131, E-ISSN 1881-1248, Vol. 54, no 4, p. 405-413Article in journal (Refereed)
    Abstract [en]

    In this work, a systematic study of the degradation of UN pellets (density range 96%-99.9% and grain size of 6-24 mu m) and UN-10%U3Si2 (wt%) composite in a steam environment is presented. Static steam autoclave tests were performed at 300 degrees C and 9 MPa for period of 0.5-1.5 hours. Microstructural analyses of UN pellets show that, in a high-pressure atmosphere, the fuel collapses principally by intergranular cracking generated by the precipitation of an oxide phase in the grain boundaries. This mechanism leads to a premature mechanical collapse of the fuel pellet, exposing fresh surfaces to steam, and ultimately accelerating the oxidation process. Increasing density (specifically eliminating open porosity) was found to delay the oxidation process, while increasing grain size was found to accelerate the degradation process due to a greater susceptibility to mechanical fracture by way of intergranular oxidation. The performance of the UN-10%U3Si2 composite proved to be better when compared to UN. The U3Si2 phase served to stabilize the UN grain boundary interface and reacted preferentially with the steam, thereby altering the failure mechanism. In this composite material, the cracking was predominantly intra-granular and the exposure of fresh surfaces was limited, resulting in a slower degradation process.

  • 10. Schuler, Thomas
    et al.
    Adorno Lopes, Denise
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Claisse, Antoine
    KTH.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Transport properties of C and O in UN fuelsManuscript (preprint) (Other academic)
  • 11. Schuler, Thomas
    et al.
    Lopes, Denise Adorno
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Claisse, Antoine
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Transport properties of C and O in UN fuels2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 9, article id 094117Article in journal (Refereed)
    Abstract [en]

    Uranium nitride fuel is considered for fast reactors (GEN-IV generation and space reactors) and for light water reactors as a high-density fuel option. Despite this large interest, there is a lack of information about its behavior for in-pile and out-of-pile conditions. From the present literature, it is known that C and O impurities have significant influence on the fuel performance. Here we perform a systematic study of these impurities in the UN matrix using electronic-structure calculations of solute-defect interactions and microscopic jump frequencies. These quantities were calculated in the DFT+U approximation combined with the occupation matrix control scheme, to avoid convergence to metastable states for the 5f levels. The transport coefficients of the system were evaluated with the self-consistent mean-field theory. It is demonstrated that carbon and oxygen impurities have different diffusion properties in the UN matrix, with O atoms having a higher mobility, and C atoms showing a strong flux coupling anisotropy. The kinetic interplay between solutes and vacancies is expected to be the main cause for surface segregation, as incorporation energies show no strong thermodynamic segregation preference for (001) surfaces compared with the bulk.

1 - 11 of 11
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf