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  • 1.
    Cui, D.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Low, J.
    Rondinella, V. V.
    Spahiu, K.
    Hydrogen catalytic effects of nanostructured alloy particles in spent fuel on radionuclide immobilization2010In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 94, no 02-jan, p. 173-178Article in journal (Refereed)
    Abstract [en]

    For the first time, hydrogen catalytic effects of fission product alloy particles nondestructively extracted from spent nuclear fuel were demonstrated. The redox sensitive radionuclides at oxidized forms Se(IV), Tc(VII), U(VI), Np(V) and Pu(VI) were found to be stable in a solution saturated with a gas mixture (Ar + 10% H-2 + 0.03% CO2) but rapidly immobilized in the same solution when contacted with the particles. In comparison, a synthetic alloy sample with similar elemental composition as the alloy particles generated in nuclear fuel displayed a smaller, but unequivocal catalytic effect. The smaller catalytic effect of synthetic alloy was apparently enhanced by a P-radiation source. The information obtained in this work contributes to improved understanding of the redox chemistry of radionuclides in nuclear waste geologic repository environments and, in particular, of the catalytic properties of these unique alloy particles.

  • 2.
    Cui, Daqing
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Environmental Chemistry.
    A Review of Beneficial Effects of Reducing Environment at the Near-Field of KBS-3 Repository2011In: Huaxue jinzhan, ISSN 1005-281X, Vol. 23, no 7, p. 1411-1428Article, review/survey (Refereed)
    Abstract [en]

    The recent research activities, i.e. relevant publications and the author's experiments on chemical behaviors of spent nuclear fuel (SNF) and canister materials at near-field of KBS-3 deep geological repository were reviewed. The advantages of reductive substances at KBS-3 repository to the spent fuel disposal safety were discussed. Using data from literatures and experiments, the author demonstrated the blocking effect of hydrogen generated for iron canister corrosion on SNF dissolution, and discussed the reaction mechanism. It is also proved that the gamma radiation expected at the early stage of disposal and micro mole level oxidative species in water solution can only slightly enhance the corrosion rate of copper canister to mu m/y level, still 10(3) times slower than that at air saturated conditions. During a long period of time after copper canister leaks, under combined effects of iron canister material, hydrogen and fission product alloy particle catalysts, SNF dissolution can be depressed or blocked, and Most radiotoxic multivalent radionuclides U, Np, Tc and Se released from SNF can be reduced and precipitated. This paper supplies scientific bases for the sitting of a SNF repository at a stable reducing area, and designing of canisters with massive iron material.

  • 3.
    Cui, Daqing
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Low, Jeanett
    Spahiu, Kastriot
    Environmental behaviors of spent nuclear fuel and canister materials2011In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 4, no 7, p. 2537-2545Article in journal (Refereed)
    Abstract [en]

    The world's first spent nuclear fuel repository concept (Swedish KBS-3) is illustrated and the results of experiments on environmental behaviors of spent fuel and canister materials under a potential canister breaching at early stage of disposal are reported. In a deoxygenated synthetic groundwater (2 mM NaHCO(3)) under radiation (gamma 0.9 Gy h(-1)), inventory fraction leaching rates of fission-products ((137)Cs, (90)Sr and (99)Tc) and actinides ((238)U, (237)Np) from a spent fuel segment were found to be around 10(-6) and 10(-7) per day, respectively. A cast-iron canister surface was found to be able to immobilize (238)U, (90)Sr, (99)Tc and (237)Np dissolved from spent fuel, but a copper surface could not. In the presence of the oxidative species generated from water radiolysis, the corrosion rates of waste canister materials, copper and cast-iron were found to be 1 and 30 mm per year, respectively. The observation of insignificant dissolution of spent fuel in the leaching solution equilibrated with 0.1 atm H(2) is explained by the reducing effects of H(2) in the presence of fission-product alloy particles (Mo-Tc-Ru-Rh-Pd) as catalysts and dissolved Fe(II) in groundwater. The coating effect of ferric precipitates on spent nuclear fuel dissolution is also discussed.

  • 4.
    Cui, Daqing
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Environmental Chemistry.
    Puranen, A.
    Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Department of Physical, Inorganic and Structural Chemistry.
    Devoy, J.
    Scheidegger, A.
    Leupin, O. X.
    Wersin, P.
    Gens, R.
    Spahiu, K.
    Reductive immobilization of Se-79 by iron canister under simulated repository environment2009In: Journal of Radioanalytical and Nuclear Chemistry, ISSN 0236-5731, E-ISSN 1588-2780, Vol. 282, no 2, p. 349-354Article in journal (Refereed)
    Abstract [en]

    To understand the fate of Se-79 in a repository-like environment, the interactions between iron canister surface with dissolved selenite (SeO3 (2-)) and selenate (SeO4 (2-)) in anaerobic solutions have been investigated. Se(IV) immobilization on iron surface was observed to be about 100 times faster than that of Se(VI) at same conditions. An iron surface coated with a FeCO3 layer corrosion product is more reactive than a polished iron to immobilize Se(IV) and Se(VI). The reacted iron surfaces were analysed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Raman spectrometry and micro-X-ray Absorption Spectroscopy (XAS). The result show that Se(IV) and Se(VI) were reduced and precipitated. The dominating phase was found to be FeSe2..

  • 5.
    Cui, Daqing
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Chemistry.
    Ranebo, Ylva
    Low, Jeanette
    Rondinella, V.V
    Pan, J
    Spahiu, K
    Immobilization of Radionuclides on Iron Canister Material at Simulated Near-field Conditions2009In: Scientific basis for nuclear waste management XXXII / [ed] Neil C. Hyatt, David A. Pickett, Raul B. Rebak, Warrendale, Pa: Materials Research Society , 2009, Vol. 1124, p. 111-116Conference paper (Refereed)
    Abstract [en]

    This work is a continuation of a long-term spent fuel leaching and radionuclides immobilization (by iron canister) experiment under simulated near-field conditions, in deoxygenated 2 mM NaHCO3 solution with 1 Gy/h g irradiation. The corrosion of iron canister material was investigated by electrochemical and microanalytical methods. Significant amounts of radionuclides (U, Np, Tc, Sr) were found to be immobilized on the corrosion layer of iron canister material by using SEM_WDS and SIMS methods. The observation is useful for bettering our understanding of near-field chemical processes at earlier canister failure conditions.

  • 6.
    Cui, Daqing
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Environmental Chemistry.
    Rondinella, V. V.
    Fortner, J. A.
    Kropf, A. J.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wronkiewicz, D. J.
    Spahiu, K.
    Characterization of alloy particles extracted from spent nuclear fuel2012In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 420, no 1-3, p. 328-333Article in journal (Refereed)
    Abstract [en]

    We characterized, for the first time, submicro- and nanosized fission product-alloy particles that were extracted nondestructively from spent nuclear fuel, in terms of noble metal (Mo-Ru-Tc-Rh-Pd-Te) composition, atomic level homogeneity and lattice parameters. The evidences obtained in this work contribute to an improved understanding of the redox chemistry of radionuclides in nuclear waste repository environments and, in particular, of the catalytic properties of these unique metal alloy particles.

  • 7. Kvashnina, K.
    et al.
    Butorin, S
    Cui, Daging
    Stockholm University, Faculty of Science, Department of Environmental Chemistry.
    Vegelius, J.
    Puranen, A
    Gens, R
    Glatzel, P.
    Electron transfer during selenium reduction by iron surfaces in aqueous solution: high resolution X-ray absorption study2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 190, no 012191, p. 1-4Article in journal (Refereed)
    Abstract [en]

    In several designs proposed by different countries, high-level radioactive waste will be disposed in a canister with a copper outer container and a cast iron or carbon steel insert. If the iron insert comes into contact with anoxic geological water, anaerobic corrosion could take place and release fission products such as 79Se to the biosphere. This paper present studies of  the long-term kinetics of selenate (SeO42-) in the presence of iron surface under anaerobic conditions  by Near Edge X-ray Absorption Spectroscopy (XANES). Substantial changes in the selenium oxidation state is found and discussed in details. We assume that such behaviour corresponds  to the electron transfer from iron to selenium, which couldn't take place on oxidized iron surface. When selenate was in contact with polish steel foil in groundwater solution, reduction of Se and formation of Se(II-)was found.  These findings suggest that depending of corroded or oxidised iron surface, the selenium mobility in nuclear waste disposal systems will be different.

  • 8.
    Olsén, Jon
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhou, Xin
    Zhong, Yuan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wang, Dianzheng
    Yu, Chenfan
    Wang, Yafei
    Li, Kailun
    Xing, Leilei
    Ma, Jing
    Cui, Daqing
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Wei
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    Tailoring hierarchical structures in selective laser melted materials2017In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 219, article id 012036Article in journal (Refereed)
    Abstract [en]

    With selective laser melting the potential to manufacture a wide variety of geometries from different materials has presented itself. Interest in this technology keeps growing every year, and with that growth a deeper understanding of the process and resulting materials is urgently needed. In this paper we present a short overview of the structural elements that appear during selective laser melting, and explain how to tailor them to achieve specific structures and material properties. Melt-pools, texture and grains, subgrain cells, and inclusions are the elements discussed herein, and tailoring of these elements can have effects on density, and corrosion resistance, as well as mechanical properties in general.

  • 9. Yang, H.
    et al.
    Cui, Daqing
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Studsvik Nuclear AB, Sweden; China Institute of Atomic Energy, China.
    Grolimund, D.
    Rondinella, V. V.
    Brutsch, R.
    Amme, M.
    Kutahyali, C.
    Wiss, A. T.
    Puranen, A.
    Spahiu, K.
    Reductive precipitation of neptunium on iron surfaces under anaerobic conditions2017In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 496, p. 109-116Article in journal (Refereed)
    Abstract [en]

    Reductive precipitation of the radiotoxic nuclide Np-237 from nuclear waste on the surface of iron canister material at simulated deep repository conditions was investigated. Pristine polished as well as pre corroded iron specimens were interacted in a deoxygenated solution containing 10-100 mu M Np(V), with 10 mM NaCl and 2 mM NaHCO3 as background electrolytes. The reactivity of each of the two different systems was investigated by analyzing the temporal evolution of the Np concentration in the reservoir. It was observed that pre-oxidized iron specimen with a 40 tm Fe3O4 corrosion layer are considerably more reactive regarding the reduction and immobilization of aqueous Np(V) as compared to pristine polished FeM surfaces. Np-237 immobilized by the reactive iron surfaces was characterized by scanning electron microscopy as well as synchrotron-based micro-X-ray fluorescence and X-ray absorption spectroscopy. At the end of experiments, a 5-8 tm thick Np-rich layer was observed to be formed ontop of the Fe3O4 corrosion layer on the iron specimen. The findings from this work are significant in the context of performance assessments of deep geologic repositories using iron as high level radioactive waste (HLW) canister material and are of relevance regarding removing pollutants from contaminated soil or groundwater aquifer systems.

  • 10.
    Zhong, Yuan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wikman, Stefan
    Cui, Daqing
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Intragranular cellular segregation network structure strengthening 316L stainless steel prepared by selective laser melting2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 470, p. 170-178Article in journal (Refereed)
    Abstract [en]

    A feasibility study was performed to fabricate ITER In-Vessel components by Selective Laser Melting (SLM) supported by Fusion for Energy (F4E). Almost fully dense 316L stainless steel (SS316L) components were prepared from gas-atomized powder and with optimized SLM processing parameters. Tensile tests and Charpy-V tests were carried out at 22 degrees C and 250 degrees C and the results showed that SLM SS316L fulfill the RCC-MR code. Microstructure characterization reveals the presence of hierarchical macro-, micro- and nano-structures in as-built samples that were very different from SS316L microstructures prepared by other established methods. The formation of a characteristic intragranular cellular segregation network microstructure appears to contribute to the increase of yield strength without losing ductility. Silicon oxide nano-inclusions were formed during the SLM process that generated a micro-hardness fluctuation in the building direction. The combined influence of a cellular microstructure and the nano-inclusions constraints the size of ductile dimples to nano-scale. The crack propagation is hindered by a pinning effect that improves the defect-tolerance of the SLM SS316L. This work proves that it was possible to manufacture SS316L with properties suitable for ITER First Wall panels. Further studies on irradiation properties of SLM SS316L and manufacturing of larger real-size components are needed.

  • 11.
    Zhong, Yuan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zou, Ji
    Li, Xiaodong
    Olsén, Jon
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cui, Daqing
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Oxide dispersion strengthened austenitic steel prepared by selective laser melting with superior strength and ductilityManuscript (preprint) (Other academic)
  • 12.
    Zhong, Yuan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Rännar, Lars-Erik
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Koptyug, Andrey
    Wikman, Stefan
    Olsén, Jon
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cui, Daqing
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Additive manufacturing of 316L stainless steel by electron beam melting for nuclear fusion applications2017In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 486, p. 234-245Article in journal (Refereed)
    Abstract [en]

    A feasibility study was performed to fabricate ITER In-Vessel components by one of the metal additivemanufacturing methods, Electron Beam Melting®(EBM®). Solid specimens of SS316L with 99.8% relativedensity were prepared from gas atomized precursor powder granules. After the EBM®process the phaseremains as austenite and the composition has practically not been changed. The RCC-MR code used fornuclear pressure vessels provides guidelines for this study and tensile tests and Charpy-V tests werecarried out at 22C (RT) and 250C (ET). This work provides thefirst set of mechanical and micro-structure data of EBM®SS316L for nuclear fusion applications. The mechanical testing shows that theyield strength, ductility and toughness are well above the acceptance criteria and only the ultimatetensile strength of EBM®SS316L is below the RCC-MR code. Microstructure characterizations reveal thepresence of hierarchical structures consisting of solidified melt pools, columnar grains and irregularshaped sub-grains. Lots of precipitates enriched in Cr and Mo are observed at columnar grain boundarieswhile no sign of element segregation is shown at the sub-grain boundaries. Such a unique microstructureforms during a non-equilibrium process, comprising rapid solidification and a gradient‘annealing’process due to anisotropic thermalflow of accumulated heat inside the powder granule matrix. Relationsbetween process parameters, specimen geometry (total building time) and sub-grain structure are dis-cussed. Defects are formed mainly due to the large layer thickness (100mmÞwhich generates insufficientbonding between a few of the adjacently formed melt pools during the process. Further studies shouldfocus on adjusting layer thickness to improve the strength of EBM®SS316L and optimizing total buildingtime.

  • 13.
    Zhong, Yuan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Rännar, Lars-Erik
    Wikman, Stefan
    Koptyug, Andrey
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cui, Daqing
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Additive manufacturing of ITER first wall panel parts by two approaches: Selective laser melting and electron beam melting2017In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 116, p. 24-33Article in journal (Refereed)
    Abstract [en]

    Fabrication of ITER First Wall (FW) Panel parts by two additive manufacturing (AM) technologies, selective laser melting (SEM) and electron beam melting (EBM), was supported by Fusion for Energy (F4E). For the first time, AM is applied to manufacture ITER In-Vessel parts with complex design. Fully dense SS316L was prepared by both SLM and EBM after developing optimized laser/electron beam parameters. Characterizations on the density, magnetic permeability, microstructure, defects and inclusions were carried out. Tensile properties, Charpy-impact properties and fatigue properties of SLM and EBM SS316L were also compared. ITER FW Panel parts were successfully fabricated by both SLM and EBM in a onestep building process. The SLM part has smoother surface, better size accuracy while the EBM part takes much less time to build. Issues with removing support structures might be solved by slightly changing the design of the internal cooling system. Further investigation of the influence of neutron irradiation on materials properties between the two AM technologies is needed.

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