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  • 1. Ackland, G. J.
    et al.
    Hepburn, D. J.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Interatomic forces for transition metals including magnetism2010In: 139th Annual Meeting & Exhibition - Supplemental Proceedings, Vol 2: Materials Characterization, Computation And Modeling And Energy, 2010, p. 85-92Conference paper (Refereed)
    Abstract [en]

    We present a formalism for extending the second moment tight-binding model[1], incorporating ferro- and anti-ferromagnetic interaction terms which are needed for the FeCr system. For antiferromagnetic and paramagnetic materials, an explicit additional variable representing the spin is required. In a mean-field approximation this spin can be eliminated. and the potential becomes explicitly temperature dependent. For ferromagnetic interactions, this degree of freedom can be eliminated, and the formalism reduces to the embedded atom method (EAM[2]), and we show the equivalence of existing EAM potentials to "magnetic" Potentials.

  • 2.
    Bortot, Sara
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Suvdantsetseg, E.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    BELLA: a multi-point dynamics code for safety-informed design of fast reactors2015In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 85, p. 228-235Article in journal (Refereed)
    Abstract [en]

    In this paper, the multi-point dynamics code BELLA and its benchmarking with respect to SAS4A/SASSYS-1 is described for a small fast reactor cooled with natural convection of lead (ELECTRA). It is shown that BELLA is capable of reproducing the magnitude of mass-flow, reactivity, power and temperature excursions during design extension conditions with an accuracy better than 10%. Hence, the BELLA code can be used for safety-informed design and stability analyses of fast reactor systems, permitting to isolate essential phenomena and trends of significance for their safety assessment. (C) 2015 Elsevier Ltd. All rights reserved.

  • 3.
    Bortot, Sara
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Suvdantsetseg, Erdenechimeg
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    BELLA: a multi-point dynamics code for simulation of fast reactorsIn: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100Article in journal (Refereed)
    Abstract [en]

    In this paper, the multi-point dynamics code BELLA and its benchmarking with respect to SAS4A/SASSYS- 1 is described for a small fast reactor cooled with natural convection of lead (ELECTRA). It is shown that BELLA is capable of reproducing the magnitude of mass-flow, reactivity, power and temperature excursions during design extension conditions with an accuracy better than 10%. Hence, the BELLA code can be used for safety-informed design and stability analyses of fast reactor systems, permitting to isolate essential phenomena and trends of significance for their safety assessment. 

  • 4.
    Bortot, Sara
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics. Paul Scherrer Institut (PSI), Villigen, Switzerland .
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Suvdantsetseg, Erdenechimeg
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Pelloni, S.
    Modeling issues in small HLMC fast reactors: ELECTRA case study2013In: Winter Meeting 2013, American Nuclear Society, 2013, no PART 2, p. 2261-2264Conference paper (Refereed)
  • 5. Bubelis, E.
    et al.
    Tosello, A.
    Pfrang, W.
    Schikorr, M.
    Mikityuk, K.
    Panadero, A. -L
    Martorell, S.
    Ordóñez, J.
    Seubert, A.
    Lerchl, G.
    Stempniewicz, M.
    Alcaro, F.
    De Geus, E.
    Delmaere, T.
    Poumerouly, S.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    System codes benchmarking on a low sodium void effect SFR heterogeneous core under ULOF conditions2017In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 320, p. 325-345Article in journal (Refereed)
    Abstract [en]

    This paper discusses system codes benchmarking activities on an ASTRID-like heterogeneous fast core under a representative design basis accident condition: the unprotected loss of flow accident (ULOF). The paper provides evidence that all the system codes used in this exercise are capable to simulate the transient behavior of heterogeneous SFR cores up to the initiation of sodium boiling. As a proof of this, a comparison of steady-state results and dynamic simulation results for a ULOF transient (simulated using system codes in combination with neutron point kinetics) are provided and discussed in this paper. The paper contains a brief description of the system codes (TRACE, CATHARE, SIM-SFR, SAS-SFR, ATHLET, SPECTRA, SAS4A) used by the participants (PSI, CEA, EDF, KIT, GRS, UPVLC, NRG, KTH), assumptions made during the simulations, as well as results obtained.

  • 6. De Bruyn, D.
    et al.
    Alemberti, A.
    Mansani, L.
    Grasso, G.
    Bandini, G.
    Artioli, C.
    Bubelis, E.
    Mueller, G.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Orden, A.
    Main achievements of the FP7-LEADER collaborative project of the european commission regarding the design of a lead-cooled fast reactor2013In: International Congress on Advances in Nuclear Power Plants, ICAPP 2013: Nuclear Power - A Safe and Sustainable Choice for Green Future, Held with the 28th KAIF/KNS Annual Conference, 2013, p. 281-290Conference paper (Refereed)
    Abstract [en]

    Concerns over energy resource availability, climate change, air quality, and energy security suggest an important role for nuclear power in future energy supplies. While the current Generation II and III nuclear power plant designs provide an economically and publicly acceptable electricity supply in many markets, further advances in nuclear energy system design can broaden the opportunities for the use of nuclear energy. To explore these opportunities, worldwide governments, industries, and research centres started a wide-ranging discussion on the development of new systems known as "Generation IV." The European Commission has organized the Sustainable Nuclear Energy Technology Platform that through its Strategic Research Agenda promoted the development of fast reactors with closed fuel cycle. Among the promising reactor technologies, the Lead Fast Reactor (LFR) has been identified as a technology with great potential to meet needs for both remote sites and central power stations. The LFR system features a fast-neutron spectrum allowing the possibility for a closed fuel cycle for efficient conversion of fertile uranium and management of actinides. A full actinide recycle fuel cycle is therefore envisioned for the design of the reference LFR meant for deployment, while the capabilities of the system to act as a net-burner of actinides from spent fuel are object of further investigation The LEADER project deals with the development of such a technology through two main goals: the conceptual design of an industrial-size LFR (the so-called European LFRor ELFR) and the conceptual design of a scaled down facility, the demonstration reactor called ALFRED (Advanced Lead Fast Reactor European Demonstrator). The European Commission, withinits seventh framework programme, has approved the proposal submitted by 16 partners comprising research centres, industrial partners and universities. The project has started in April 2010 for a duration of three years.The focus of the first part of the LEADER project was the resolution of the key issues of the previous sixth framework programme ELSY project in order to reach a new consistent industrial-size reactor ELFR configuration.With reference to this reactor configuration the design of the ALFRED demonstrator (sized at 300 MWth, about 120 MWe) has been performed. The development of such demonstrator reactor presents obviously strong and interesting synergies with the development of MYRRHA, a material and fuel testing facility proposed by the SCK·CEN research centre in Belgium. In this paper we present a synthesis of the main results of the LEADER project.

  • 7. Delage, F.
    et al.
    Belin, R.
    Chen, X-N
    D'Agata, E.
    Klaassen, F.
    Knol, S.
    Maschek, W.
    Ottaviani, J. -P
    Rineiski, A.
    Sobolev, V.
    Somers, J.
    Staicu, D.
    Thetford, R.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wernli, B.
    ADS fuel developments in Europe: Results from the EUROTRANS integrated project2011In: Energy Procedia, 2011, p. 303-313Conference paper (Refereed)
    Abstract [en]

    Fuels to be used in Accelerator Driven Systems dedicated to Minor Actinides transmutation can be described as highly innovative in comparison with those used in critical cores. Indeed, ADS fuels are not fertile, so as to improve the transmutation performance and they contain high volumetric concentrations (∼50%) of minor actinides and plutonium compounds. This unusual fuel composition results in high gamma and neutron emissions during its fabrication, as well as degraded performances under irradiation. Ceramic-Ceramic and Ceramic Metallic composite fuels consisting of particles of (Pu, MA)O2 phases dispersed in a magnesia or molybdenum matrix were investigated within the European Research programme for Transmutation, as driver fuels for a prospective 400MWth transmuter: the European Facility for Industrial Transmutation. Fuel performances and safety of preliminary core designs were evaluated to support the project. Out -of-pile as well as in-pile experiments were carried out to gain essential knowledge on properties and behaviour under irradiation of these types of fuel. This paper gives an overview of experimental results within the project.

  • 8. Dudarev, S. L.
    et al.
    Boutard, J. -L
    Laesser, R.
    Caturla, M. J.
    Derlet, P. M.
    Fivel, M.
    Fu, C. -C
    Lavrentiev, M. Y.
    Malerba, L.
    Mrovec, M.
    Nguyen-Manh, D.
    Nordlund, K.
    Perlado, M.
    Schaeublin, R.
    Van Swygenhoven, H.
    Terentyev, D.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Weygand, D.
    Willaime, F.
    The EU programme for modelling radiation effects in fusion reactor materials: An overview of recent advances and future goals2009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 386, p. 1-7Article in journal (Refereed)
    Abstract [en]

    The EU fusion materials modelling programme was initiated in 2002 with the objective of developing a comprehensive set of computer modelling techniques and approaches, aimed at rationalising the extensive available experimental information on properties of irradiated fusion materials, developing capabilities for predicting the behaviour of materials under conditions not yet accessible to experimental tests, assessing results of tests involving high dose rates, and extrapolating these results to the fusion-relevant conditions. The programme presently gives emphasis to modelling a single class of materials, which are ferritic-martensitic EUROFER-type steels, and focuses on the investigation of key physical phenomena and interpretation of experimental observations. The objective of the programme is the development of computational capabilities for predicting changes in mechanical properties, hardening and embrittlement, as well as changes in the microstructure and phase stability of EUROFER and FeCr model alloys occurring under fusion reactor relevant irradiation conditions.

  • 9.
    Eriksson, Marcus
    et al.
    KTH, Superseded Departments, Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Cahalan, James E.
    Argonne National Laboratory.
    Tucek, Kamil
    KTH, Superseded Departments, Physics.
    Gudowski, Waclaw
    KTH, Superseded Departments, Physics.
    Safety Analysis of Na and Pb-Bi Coolants in Response to Beam Instabilities2003In: UTILISATION AND RELIABILITY OF HIGH POWER PROTON ACCELERATORS, WORKSHOP PROCEEDINGS, 2003, p. 227-236Conference paper (Refereed)
    Abstract [en]

    A comparative safety study has been performed on sodium vs. lead/bismuth as coolant for accelerator-driven systems. Transient studies are performed for a beam overpower event. We examine a fuel type of recent interest in the research on minor actinide burners, i.e. uranium-free oxide fuel. A strong positive void coefficient is calculated for both sodium and lead/bismuth. This is attributed to the high fraction of americium in the fuel. It is shown that the lead/bismuth-cooled reactor features twice the grace time with respect to fuel or cladding damage compared to the sodium-cooled reactor of comparable core size and power rating. This accounts to the difference in void reactivity contribution and to the low boiling point of sodium. For improved safety features the general objective is to reduce the coolant void reactivity effect. An important safety issue is the high void worth that could possibly drive the system to prompt criticality.

  • 10.
    Eriksson, Marcus
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Jolkkonen, Mikael
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Cahalan, James E.
    Argonne National Laboratory, Nuclear Engineering Division.
    Inherent Safety of Fuels for Accelerator-driven Systems2005In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 151, no 3, p. 314-333Article in journal (Refereed)
    Abstract [en]

    Transient safety characteristics of accelerator-driven systems using advanced minor actinide fuels have been investigated. Results for a molybdenum-based Ceramic-Metal (CerMet) fuel, a magnesia-based Ceramic-Ceramic fuel, and a zirconium-nitride-based fuel are reported. The focus is on the inherent safety aspects of core design. Accident analyses are carried out for the response to unprotected loss-of-flow and accelerator beam-overpower transients and coolant voiding scenarios. An attempt is made to establish basic design limits for the fuel and cladding. Maximum temperatures during transients are determined and compared with design limits. Reactivity effects associated with coolant void, fuel and structural expansion, and cladding relocation are investigated. Design studies encompass variations in lattice pitch and pin diameter. Critical mass studies are performed. The studies indicate favorable inherent safety features of the CerMet fuel. Major consideration is given to the potential threat of coolant voiding in accelerator-driven design proposals. Results for a transient test case study of a postulated steam generator tube rupture event leading to extensive coolant voiding are presented. The study underlines the importance of having a low coolant void reactivity value in a lead-bismuth system despite the high boiling temperature of the coolant. It was found that the power rise following a voiding transient increases dramatically near the critical state. The studies suggest that a reactivity margin of a few dollars in the voided state is sufficient to permit significant reactivity insertions.

  • 11.
    Fokau, Andrei
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Nitride fueled accelerator-driven system with high source efficiency2010In: Transactions of the American Nuclear Society, American Nuclear Society, 2010, p. 573-574Conference paper (Refereed)
  • 12.
    Fokau, Andrei
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Zhang, Youpeng
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Ishida, Shinya
    Tokyo Institute of Technology, Department of Nuclear Engineering, Sekimoto Laboratory, Japan.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    A source efficient ADS for minor actinides burning2010In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 37, no 4, p. 540-545Article in journal (Refereed)
    Abstract [en]

    Taking advantage of the good neutron economy of nitride fuel, a compact accelerator-driven system (ADS) for burning of minor actinide fuels has been designed, based on the fuel assembly geometry developed for the European Facility for Industrial Transmutation (EFIT) within the EUROTRANS project. The small core size of the new design permits reduction of the size of the spallation target region, which enhances proton source efficiency by about 80% compared to the reference oxide version of EFIT. Additionally, adoption of the austenitic steel 15/15Ti as clad material allows to safely reduce the fuel pin pitch, which leads to an increase of fuel volume fraction and therefore makes the neutron energy spectrum faster, consequently increasing minor actinides fission probabilities. Our calculations show that one can dramatically increase neutron source efficiency up to 0.95 without a significant loss of neutron source intensity, i.e. having high proton source efficiency. Consequently, the accelerator current required for operation of the ADS with a fission power of 201 MWth and a burn-up of 27 GW d/t per year (365 EFPD) is reduced by 67%.

  • 13.
    Gudowski, Waclaw
    et al.
    KTH, Superseded Departments, Physics.
    Arzhanov, Vasily
    Broeders, C.
    Broeders, I.
    Cetnar, J.
    Cummings, R.
    Ericsson, M.
    Fogelberg, B.
    Gaudard, C.
    Koning, A.
    Landeyro, P.
    Magill, J.
    Pazsit, I.
    Peerani, P.
    Phlippen, P.
    Piontek, M.
    Ramstrom, E.
    Ravetto, P.
    Ritter, G.
    Shubin, Y.
    Soubiale, S.
    Toccoli, C.
    Valade, M.
    Wallenius, Janne
    KTH, Superseded Departments, Physics.
    Youinou, G.
    Review of the European project - Impact of Accelerator-Based Technologies on Nuclear Fission Safety (IABAT)2001In: Progress in nuclear energy (New series), ISSN 0149-1970, E-ISSN 1878-4224, Vol. 38, no 1-2, p. 135-151Article in journal (Refereed)
    Abstract [en]

    The IABAT project - Impact of Accelerator Based Technologies on Nuclear Fission Safety - started in 1996 in the frame of 4(th) Framework Programme of the European Union, R&D specific programme Nuclear fission safety 1994-1998, area A.2 Exploring innovative approaches/Fuel cycle concepts, as one of the first common European activities in ADS. The project was completed October 31, 1999. The overall objective of the IABAT project has been a preliminary assessment of the potential of Accelerator-Driven Systems (ADS) for transmutation of nuclear waste and for nuclear energy production with minimum waste generation. Moreover, more specific topics related to nuclear data and code development for ADS have been studied in more detail. Four ADSs have been studied for different fuel/coolant combinations: liquid metal coolant and solid fuel, liquid metal coolant and dispersed fuel, and fast and thermal molten salt systems. Target studies comprised multiple target solutions and radiation damage problems in a target environment. In a tool development part of the project a methodology of subcriticality monitoring has been developed based on Feynman-alpha and Rossi-alpha methods. Moreover, a new Monte-Carlo burnup code taking full advantage of continuous neutron cross-section data has been developed and benchmarked. Impact on the risk from high-level waste repositories fi om radiotoxicity reduction using ADS has been assessed giving no crystal-clear benefits of ADS for repository radiotoxicity reduction but concluding some important prerequisites for effective transmutation. In proliferation studies important differences between critical reactors and ADS have been underlined and non-proliferation measures have been proposed. In assessment of accelerator technology costing models have been created that allow the circular and linear accelerator options to be compared and the effect of parameter variations examined. The calculations reported show that cyclotron systems would be more economical, due mainly to the advantage of the cost of RF power supplies. However, the accelerator community regards with skepticism the possibility of transporting and extracting more than a 10mA beam current from a 1GeV cyclotron and therefore technical factors may limit the application of cyclotrons. Finally, this review summarizes development of nuclear data in the energy region between 20 Mev and 150 MeV. Neutron and proton transport data files for Fe, Ni, Pb, Th, U-238 and Pu-239 have been created. The high-energy part of the data files consists completely of results from model calculations, which are benchmarked against the available experimental data. Although there is obviously future work left regarding fine-tuning of several parts of the data files, the representation of nuclear reaction information up to 150 MeV is already better than can be attained with intranuclear cascade codes.

  • 14. Hania, P. R.
    et al.
    Klaassen, F. C.
    Wernli, B.
    Streit, M.
    Restani, R.
    Ingold, F.
    Fedorov, A. V.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Irradiation and post-irradiation examination of uranium-free nitride fuel2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 466, p. 597-605, article id 49308Article in journal (Refereed)
    Abstract [en]

    Two identical Phénix-type 15-15Ti steel pinlets each containing a 70 mm Pu<inf>0.3</inf>Zr<inf>0.7</inf>N fuel stack in a 1-bar helium atmosphere have been irradiated in the HFR Petten at medium high linear power (46-47 kW/m at BOL) and an average cladding temperature of 505 °C. The pins were irradiated to a plutonium burn-up of 9.7% (88 MWd/kg<inf>HM</inf>) in 170 full power days. Both pins remained fully intact. Post-irradiation examination performed at NRG and PSI showed that the overall swelling rate of the fuel was 0.92 vol-%/%FIHMA. Fission gas release was 5-6%, while helium release was larger than 50%. No fuel restructuring was observed, and only mild cracking. EPMA measurements show a burn-up increase toward the pellet edge of up to 4 times. All investigated fission products except to some extent the noble metals were found to be evenly distributed over the matrix, indicating good solubility. Local formation of a secondary phase with high Pu content and hardly any Zr was observed. A general conclusion of this investigation is that ZrN is a suitable inert matrix for burning plutonium at high destruction rates.

  • 15.
    Henriksson, Krister O. E.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Sandberg, Nils
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Carbides in stainless steels: Results from ab initio investigations2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 19Article in journal (Refereed)
    Abstract [en]

    The useful properties of steels are due to a complicated microstructure containing iron and chromium carbides. Only some basic physical properties of these carbides are known with high precision, although the carbides may have a vital impact on the performance and longevity of the steel. To improve on this situation, we have performed extensive density-functional theory calculations of several carbides. The quantitative results are in perfect agreement with the relative empirical stability of the carbides. Also, in contradiction with experimental data, we find that Cr23C6 responsible for the hardness of stainless steels is not the most stable chromium-dominated carbide.

  • 16.
    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.

  • 17.
    Johnson, Kyle D.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Jolkkonen, Mikael
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Claisse, Antoine
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Spark plasma sintering and porosity studies of uranium nitride2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 473, p. 13-17Article in journal (Refereed)
    Abstract [en]

    In this study, a number of samples of UN sintered by the SPS method have been fabricated, and highly pure samples ranging in density from 68% to 99.8%TD-corresponding to an absolute density of 14.25 g/cm3 out of a theoretical density of 14.28 g/cm3-have been fabricated. By careful adjustment of the sintering parameters of temperature and applied pressure, the production of pellets of specific porosity may now be achieved between these ranges. The pore closure behaviour of the material has also been documented and compared to previous studies of similar materials, which demonstrates that full pore closure using these methods occurs near 97.5% of relative density.

  • 18.
    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.

  • 19.
    Jolkkonen, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Malkki, Pertti
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Johnson, Kyle
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Uranium nitride fuels in superheated steamIn: Journal of Nuclear Science and Technology, ISSN 0022-3131, E-ISSN 1881-1248Article in journal (Refereed)
    Abstract [en]

    Uranium mononitride (UN) pellets of different densities were subjected to a superheatedsteam/argon mixture at atmospheric pressure to evaluate their resistance to hydrolysis. Completedegradation of pure UN pellets was obtained within 1 hour in 0.50 bar steam at 500 °C. Theidentified reaction products were uranium dioxide, ammonia and hydrogen gas, with no detectableamounts of nitrogen oxides formed. However, the reaction could not be carried to completion, andthe presence of uranium sesquinitride and higher uranium oxides or uranium oxynitrides in the solidresidue is indicated. Evolution of elemental nitrogen was seen in connection with very high reactionrates. The porosity of the pellets was identified as the most important factor determining reactionrates at 400 – 425 °C, and it is suggested that in dense pellets, cracking due to internal volumeincrease initiates a transition from slow surface corrosion to pellet disintegration. The implicationsfor the use of nitride fuels in light water reactors are discussed, with some observations concerninghydrolysis as a method for 15N recovery from isotopically enriched spent nitride fuel.

  • 20.
    Jolkkonen, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Streit, M.
    Paul Scherrer Institut.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Thermo-chemical modelling of uranium-free nitride fuels2004In: Journal of Nuclear Science and Technology, ISSN 0022-3131, E-ISSN 1881-1248, Vol. 41, no 4, p. 457-465Article in journal (Refereed)
    Abstract [en]

    A production process for americium-bearing, uranium-free nitride fuels was modelled using the newly developed ALCHYMY thermochemical database. The results suggested that the practical difficulties with yield and purity are of a kinetic rather than a thermodynamical nature. We predict that the immediate product of the typical decarburisation step is not methane, but hydrogen cyanide. HCN may then undergo further reactions upon cooling, explaining the difficulty in observing any carbophoric molecules in the gaseous off stream. The thermal stability of nitride fuels in different environments was also estimated. We show that sintering of nitride compounds containing americium should be performed under nitrogen atmosphere in order to the avoid the excessive losses of americium reported from sintering under inert gas. Addition of nitrogen in small amounts to fuel pin filling gas also appears to significantly improve the in-pile stability of transuranium nitride fuels.

  • 21. Juslin, N.
    et al.
    Nordlund, K.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Malerba, L.
    Simulation of threshold displacement energies in FeCr2007In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 255, no 1, p. 75-77Article in journal (Refereed)
    Abstract [en]

    We have studied the role of chromium on threshold displacement energies in FeCr for the fusion reactor steel relevant concentration 10% Cr. We have used molecular dynamics simulations in order to determine whether the observed Cr-content dependence of macroscopic properties can be due to the defect production. We compare FeCr-alloys with pure iron and chromium, employing two different potential sets for the Fe-Cr system. We find that there are no significant differences between pure iron and FeCr with 10% Cr for the 100, 110 and 111 directions and the average threshold energy.

  • 22.
    Lagerstedt, Christina
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Terentyev, D.
    Olsson, P.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Malerba, L.
    Cluster formation mechanisms during relaxation and post-relaxation cascade stages in α-Fe:: a molecular dynamics studyArticle in journal (Other academic)
  • 23. Lambrinou, K.
    et al.
    Lapauw, T.
    Jianu, A.
    Weisenburger, A.
    Ejenstam, Jesper
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Szakálos, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Ström, E.
    Vanmeensel, K.
    Vleugels, J.
    Corrosion-resistant ternary carbides for use in heavy liquid metal coolants2016In: Ceramic Engineering and Science Proceedings, 2016, no 7, p. 19-34Conference paper (Refereed)
    Abstract [en]

    A primary concern in the development of accelerator-driven systems (ADS) with liquid leadbismuth eutectic (LBE) spallation target and Gen-IV lead-cooled fast reactors (LFRs) is the compatibility of the candidate structural steels with the heavy liquid metal (HLM) coolant In the accelerator-driven system MYRRHA, the envisaged primary coolant is liquid LBE, a potentially corrosive environment for various nuclear grade steels. The inherent LBE corrosiveness is the driving force behind diverse research incentives aiming at the development of corrosion-resistant materials for specific applications. I3ue to their superb corrosion resistance in contact with liquid LBE, MAX phases are currently being assessed as candidate materials for the construction of pump impellers suitable for MYRRHA and Gen-IV LFRs. In the case of the MYRRHA nuclear system, the pump impeller will be called to operate reliably at ∼270°C in contact with moderately-oxygenated (concentration of dissolved oxygen: [O] ≥ 7×10-7 mass%), fast-flowing LBE (LBE flow velocity: v ≈ 10-20 m/s locally on the impeller surface). Selected MAX phases are currently being screened with respect to their capability of meeting the targeted material property requirements, especially the enhanced erosion resistance requested by this particular application. This work gives a state-of-the-art overview of the processing and characterisation of selected MAX phases that are screened as candidate structural materials for the MYRRHA pump impeller. All considered MAX phases were produced via a powder metallurgical route and their performance was assessed by various mechanical tests in air/vacuum and corrosion/erosion tests in liquid LBE.

  • 24. Lindroth, E.
    et al.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Jonsell, S.
    Decay rates of excited muonic molecular ions2003In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 68, no 3Article in journal (Refereed)
    Abstract [en]

    Muonic molecular ions in excited states have been predicted to form in collisions between excited muonic atoms and hydrogen molecules. We have calculated radiative and Coulombic decay rates for ppmu(*) and ddmu(*) molecular states located below the 2s threshold, using the complex rotation method. The x-ray spectrum from the radiative decay is shown to exhibit several maxima, corresponding to the vibrational motion of the decaying molecule. The branching ratio of the radiative decay mode was calculated to be less than 15% for ppmu(*), while a radiative yield of more than 80% is predicted for the decay of ddmu(*). Our results have a significant impact on the analysis of the muon catalyzed fusion cycle as well as on the interpretation of exotic hydrogen spectroscopy.

  • 25. Malerba, L.
    et al.
    Terentyev, D. A.
    Bonny, G.
    Barashev, A. V.
    Bjorkas, C.
    Juslin, N.
    Nordlund, K.
    Domain, C.
    Olsson, P.
    Sandberg, Nils
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Modelling of radiation damage in Fe-Cr alloys2007In: Journal of ASTM International, ISSN 1546-962X, E-ISSN 1546-962X, Vol. 4, no 6Article in journal (Refereed)
    Abstract [en]

    High-Cr ferritic/martensitic steels are being considered as structural materials for a large number of future nuclear applications, from fusion to accelerator-driven systems and GenIV reactors. Fe-Cr alloys can be used as model materials to investigate some of the mechanisms governing their microstructure evolution under irradiation and its correlation to changes in their macroscopic properties. Focusing on these alloys, we show an example of how the integration of computer simulation and theoretical models can provide keys for the interpretation of a host of relevant experimental observations. In particular we show that proper accounting for two basic features of these alloys, namely, the existence of a fairly strong attractive interaction between self-interstitials and Cr atoms and of a mixing enthalpy that changes sign from negative to positive around 8 to 10% Cr, is a necessary and, to a certain extent, sufficient condition to rationalize and understand their behavior under irradiation. These features have been revealed by ab initio calculations, are supported by experimental evidence, and have been adequately transferred into advanced empirical interatomic potentials, which have been and are being used for the simulation of damage production, defect behavior, and phase transformation in these alloys. The results of the simulations have been and are being used to parameterize models capable of extending the description of radiation effects to scales beyond the reach of molecular dynamics. The present paper intends to highlight the most important achievements and results of this research activity.

  • 26. Malerba, L.
    et al.
    Terentyev, D. A.
    Bonny, G.
    Barashev, A. V.
    Bjrkas, C.
    Juslin, N.
    Nordlund, K.
    Domain, C.
    Olsson, Pär
    EDF-R and D Les Renardieres.
    Sandberg, Nils
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Modelling of Radiation Damage in Fe-Cr Alloys2008In: EFFECTS OF RADIATION ON MATERIALS: 23RD INTERNATIONAL SYMPOSIUM / [ed] Lott, RG; Busby, JT, 2008, Vol. 1492, p. 159-176Conference paper (Refereed)
    Abstract [en]

    High-Cr ferritic/martensitic steels are being considered as structural materials for a large number of future nuclear applications, from fusion to accelerator-driven systems and GenIV reactors. Fe-Cr alloys can be used as model materials to investigate some of the mechanisms governing their microstructure evolution under irradiation and its correlation to changes in their macroscopic properties. Focusing on these alloys, we show an example of how the integration of computer simulation and theoretical models can provide keys for the interpretation of a host of relevant experimental observations. In particular we show that proper accounting for two basic features of these alloys, namely, the existence of a fairly strong attractive interaction between self-interstitials and Cr atoms and of a mixing enthalpy that changes sign from negative to positive around 8 to 10 % Cr, is a necessary and, to a certain extent, sufficient condition to rationalize and understand their behavior under irradiation. These features have been revealed by ab initio calculations, are supported by experimental evidence, and have been adequately transferred into advanced empirical interatomic potentials, which have been and are being used for the simulation of damage production, defect behavior, and phase transformation in these alloys. The results of the simulations have been and are being used to parameterize models capable of extending the description of radiation effects to scales beyond the reach of molecular dynamics. The present paper intends to highlight the most important achievements and results of this research activity.

  • 27. Malerba, L.
    et al.
    Terentyev, D.
    Olsson, P.
    Chakarova, Roumiana
    KTH, Superseded Departments, Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Molecular dynamics simulation of displacement cascades in Fe-Cr alloys2004In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 329-33, 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.

  • 28. Malerba, Lorenzo
    et al.
    Caro, Alfredo
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Multiscale modelling of radiation damage and phase transformations: The challenge of FeCr alloys2008In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 382, no 2-3, p. 112-125Article in journal (Refereed)
    Abstract [en]

    We review the experimental evidence of the non-monotonic behaviour of FeCr alloys versus Cr content, particularly under irradiation (ordering versus segregation tendencies, microstructure and phase evolution, hardening and embrittlement), together with the theoretical efforts done at the electronic and atomic level to interpret them. We summarize the achievements of the two interatomic potentials developed for this system and perform a careful scrutiny of their limitations. We emphasise the difficulties related to the study, at the atomic-level, of concentrated alloys and propose routes to overcome them. Finally, we advance some opinions regarding the crucial points that deserve further investigation in order to fully understand this important binary alloy, at the basis of the steels for current and future nuclear applications.

  • 29.
    Malkki, Pertti
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Jolkkonen, Mikael
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Hollmer, T.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Manufacture of fully dense uranium nitride pellets using hydride derived powders with spark plasma sintering2014In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 452, no 1-3, p. 548-551Article in journal (Refereed)
    Abstract [en]

    Applying a combination of hydriding/nitriding of metallic uranium with the spark plasma sintering technique, we show that uranium nitride pellets with an average porosity of 0.2% may be manufactured. This is considerably smaller than the lowest porosity previously reported in the literature. The high density is attained by sintering at 1650 °C for only three minutes.

  • 30. Maschek, W.
    et al.
    Chen, X.
    Delage, F.
    Femandez-Carretero, A.
    Haas, D.
    Boccaccini, C. Matzerath
    Rineiski, A.
    Smith, P.
    Sobolev, V.
    Thetford, R.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Accelerator driven systems for transmutation: Fuel development, design and safety2008In: Progress in nuclear energy (New series), ISSN 0149-1970, E-ISSN 1878-4224, Vol. 50, no 2-6, p. 333-340Article in journal (Refereed)
    Abstract [en]

    European R&D for ADS design and fuel development is driven in the 6th FP of the EU by the EUROTRANS Programme. In EUROTRANS two ADS design routes are followed, the XT-ADS and the EFIT The XT-ADS is designed to provide the experimental demonstration of transmutation. The EFIT, the European Facility for Industrial Transmutation, aims at a conceptual design of a full transmuter. A key R&D issue is the choice of an adequate fuel. Various fuel forms have been assessed and CERCER and CERMET fuels, specifically the matrices MgO and Mo, have finally been selected. Within EUROTRANS, the domain 'AFTRA' is responsible to more deeply assess the behavior of these dedicated fuels and to provide the fuel database for the EFIT. The EFIT is optimized towards: a good transmutation efficiency, high burnup, low reactivity swing, low power peaking, adequate subcriticality, reasonable beam requirements and a high safety level. In the current paper the fuels under investigation are described, including their production route and their safety limits. First core designs of CERCER and CERMET fuelled 400 MWth EFITs have been developed within AFTRA. The trends found in the design studies and first safety analyses are presented.

  • 31. Nordlund, K.
    et al.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Malerba, L.
    Molecular dynamics simulations of threshold displacement energies in Fe2006In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 246, no 2, p. 322-332Article in journal (Refereed)
    Abstract [en]

    We compare systematically the threshold displacement energy surface of 11 interatomic potentials in Fe. We discuss in detail different possible definitions of threshold displacement energies, and how they relate to different kinds of experimental threshold displacement energies. We compare the threshold results to experiments, and find that none of the 11 tested potentials agrees fully with experiments. However, all the potentials predict some qualitative features in the same way, most importantly that the threshold energy surface close to the 100 crystal direction is flat and that the largest threshold energies occur around very roughly the 123 crystal direction.

  • 32. Olsson, Pär
    et al.
    Abrikosov, I. A.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Electronic origin of the anomalous stability of Fe-rich bcc Fe-Cr alloys2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 10, p. 104416-Article in journal (Refereed)
    Abstract [en]

    The binary Fe-Cr alloy is a system with a miscibility gap. The decomposition occurs either via the nucleation and growth mechanism or as spinodal decomposition, depending on the Cr content. However, at low chromium concentrations the alloys are anomalously stable. This is shown to be true only for the ferromagnetic body centered cubic (bcc) phase. The stability stems from the negative mixing enthalpy at low concentrations of chromium. We show that the effect has an electronic origin, that is, it is directly related to variations of the electronic structure in the alloy with concentration. We also demonstrate that the variation in the state density of the majority channel at the Fermi level in the concentration interval below 20 at. % Cr indicates increasing tendency of the system towards the spinodal decomposition in the system. Moreover, in the equimolar concentration region, significant deviations of the spin up band from its canonical shape are observed, which destabilize the bcc phase.

  • 33. Olsson, Pär
    et al.
    Abrikosov, Igor A.
    Vitos, Levente
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    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 alpha phase at Cr-concentrations above 9%, occurring at T < 900 K.

  • 34. Olsson, Pär
    et al.
    Domain, Christophe
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety. KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Ab initio study of Cr interactions with point defects in bcc Fe2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 1, p. 014110-Article in journal (Refereed)
    Abstract [en]

    The properties of Cr in alpha Fe have been investigated by ab initio calculations based on density functional theory. The intrinsic point defect formation energies were found to be larger in model bcc Cr as compared to those in ferromagnetic bcc Fe. The interactions of Cr with point defects (vacancy and self-interstitials) have been characterized. Single Cr atoms interact weakly with vacancies but significantly with self-interstitial atoms (SIA). Mixed interstitials of any interstitial symmetry are bound. Configurations where two Cr atoms are in nearest-neighbor position are generally unfavorable in bcc Fe except when they are a part of a < 111 > interstitial complex. Mixed < 110 > interstitials do not have as strong directional stability as pure Fe interstitials have. The effects on the results using the atom description scheme of either the ultrasoft pseudopotential (USPP) or the projector augmented wave (PAW) formalisms are connected to the differences in local magnetic moments that the two methods predict. As expected for the Fe-Cr system, the results obtained using the PAW method are more reliable than the ones obtained with USPP.

  • 35. Olsson, Pär
    et al.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Domain, C.
    Nordlund, K.
    Malerba, L.
    Two-band modeling of alpha-prime phase formation in Fe-Cr2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 21, p. 1-6Article in journal (Refereed)
    Abstract [en]

    We have developed a two-band model of Fe-Cr, fitted to properties of the ferromagnetic alloy. Fitting many-body functionals to the calculated mixing enthalpy of the alloy and the mixed interstitial binding energy in iron, our potential reproduces changes in sign of the formation energy as a function of Cr concentration. When applied in kinetic Monte Carlo simulations, the potential correctly predicts decomposition of initially random Fe-Cr alloys into the alpha-prime phase as function of Cr concentration.

  • 36. Pillon, Sylvie
    et al.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Oxide and nitride TRU fuels: Lessons drawn from the CONFIRM and FUTURE projects of the 5th European Framework Program2006In: Nuclear science and engineering, ISSN 0029-5639, E-ISSN 1943-748X, Vol. 153, no 3, p. 245-252Article in journal (Refereed)
    Abstract [en]

    The FUTURE and CONFIRM projects of the 5th European Framework Program address the issues of the design and fabrication of oxide and nitride fuels, respectively, for the transmutation in an accelerator-driven system (ADS). They started in December 2001 and September 2000, respectively. Advantages and drawbacks of transuranic oxides and nitrides in terms of performance and fabricability have been analyzed. Recommendations on the fuel design will be given and used for the next step of the 6th European Framework Program related to the design and the feasibility assessment of an industrial ADS prototype dedicated to transmutation.

  • 37. Pontikis, V.
    et al.
    Russier, V.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    An analytic n-body potential for bcc iron2007In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 255, no 1, p. 37-40Article in journal (Refereed)
    Abstract [en]

    We have developed an analytic n-body phenomenological potential for bcc iron made of two electron-density functionals representing repulsion via the Thomas-Fermi free-electron gas kinetic energy term and attraction via a square root functional similar to the second moment approximation of the tight-binding scheme. Electron-density is given by radial, hydrogen-like orbitals with effective charges taken as adjustable parameters fitted on experimental and ab-initio data. Although the set of adjustable parameters is small, prediction of static and dynamical properties of iron is in excellent agreement with the experiments. Advantages and shortcomings of this model are discussed with reference to published works.

  • 38.
    Pukari, Merja
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Runevall, Odd
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Sandberg, Nils
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Vacancy formation and solid solubility in the U-Zr-N system2010In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 406, no 3, p. 351-355Article in journal (Refereed)
    Abstract [en]

    For the purpose of developing a nuclear fuel with enhanced thermophysical properties and better irradiation performance density functional theory calculations are used to explore UN, ZrN and (U, Zr)N. Negative deviation of ground state energy from the ideal solution model as well as energetically favourable maximal distance between substitutional metal atoms in respective nitrides indicate mutual solubility of UN and ZrN at all temperatures. Nitrogen vacancy formation energies in UN (1.81 eV) and ZrN (1.40 eV) are considerably lower than metal vacancy formation energies. A substitutional Zr atom in UN has little effect on nitrogen vacancy formation energies (similar to 1.79 eV), while U in ZrN decreases the value by similar to 0.1 eV (similar to 1.30 eV) due to elastic stress and charge density redistribution in the material. The relative distance between a substitutional metal atom and a vacancy in UN has little influence over the radially declining displacement pattern induced by the substitutional atom, while in ZrN the relaxation of atoms is governed by the position of the vacancy. The calculated vacancy formation energies indicate a lower surface energy of ZrN in comparison with UN.

  • 39.
    Pukari, Merja
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Modeling of inert matrix nitride fuels for generation IV reactors2010In: Transactions of the American Nuclear Society, 2010, p. 838-838Conference paper (Refereed)
  • 40.
    Runevall, Odd
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Sandberg, Nils
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Helium transport in a CERMET fuel matrix2009In: Proceedings of Actinide and Fission Product Partitioning and Transmutation - Tenth Information Exchange Meeting, 2009, 2009Conference paper (Refereed)
  • 41.
    Sandberg, Nils
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Henriksson, Krister O. E.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Carbon impurity dissolution and migration in bcc Fe-Cr: First-principles calculations2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 9Article in journal (Refereed)
    Abstract [en]

    First-principles density-functional theory calculations for C solution enthalpies, H-sol, and diffusion activation enthalpies, H-diff, in body-centered-cubic Fe and Cr are presented. The results for C in Fe compare well with experiments, provided that the effect of magnetic disordering is accounted for. Likewise, in Cr, the calculated Hsol and Hdiff agree well with available experiments. In both materials, the deviation between calculated enthalpies and critically assessed experimental enthalpies are less than 0.05 eV. Further, first-principles calculations for the interaction energies between a solute (e.g., a Cr atom in bcc Fe) and an interstitial C atom are presented. The results are in conflict with those inferred from internal friction (IF) experiments in disordered Fe-Cr-C alloys. A simple model of C relaxation in disordered Fe-Cr is used to compare theoretical and experimental IF curves directly. The results suggest that a more extensive study of the energetic, thermodynamic, and kinetic aspects of C migration in Fe-Cr is needed.

  • 42.
    Seltborg, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Proton source efficiency for heterogeneous distribution of actinides in the core of an accelerator-driven system2006In: Nuclear science and engineering, ISSN 0029-5639, E-ISSN 1943-748X, Vol. 154, no 2, p. 202-214Article in journal (Refereed)
    Abstract [en]

    The distribution of actinides in the core of an accelerator-driven system loaded with plutonium, americium, and curium has been studied in order to optimize the proton source efficiency psi*. The optimization of psi* was performed by keeping some important characteristics of the system, e.g., the radial power profile and the reactivity of the core, constant. One of the basic assumptions of the study, that the magnitude of psi* is sensitive primarily to the composition of actinides in the inner part of the core, whereas only marginally to that in the outer part, has been confirmed. It has been shown that the odd-N nuclides (those nuclides with an even number of neutrons) in general and Am-241 and Cm-244 in particular have favorable properties with respect to improving psi* if they are placed in the innermost part of the core. The underlying reason for this phenomenon is that the energy spectrum of the source neutrons in the inner part of the core is harder than that of the average fission neutrons. Moreover, it has been shown that loading the inner part of the core with only curium increases psi* by similar to 7%. Plutonium, on the other hand, in particular high-quality plutonium consisting mainly of Pu-239 and Pu-241, was found to be a comparatively source inefficient element and is preferably located in the outer part of the core. The differences in psi* are due to combined effects from relative changes in the average fission and capture cross sections and in the average fission neutron yield.

  • 43.
    Seltborg, Per
    et al.
    KTH, Superseded Departments, Physics.
    Wallenius, Janne
    KTH, Superseded Departments, Physics.
    Gudowski, Waclaw
    KTH, Superseded Departments, Physics.
    Impact of heterogeneous Cm-distribution on proton source efficiency in accelerator-driven systems2004In: Proceedings of the PHYSOR 2004: The Physics of Fuel Cycles and Advanced Nuclear Systems - Global Developments, 2004, p. 489-497Conference paper (Refereed)
    Abstract [en]

    The proton source efficiency (ψ*) was studied for homogeneous and heterogeneous distributions of minor actinides in a nitride-fuelled and lead-bismuth-cooled accelerator-driven system. The findings from the MCNPX simulations indicate that, compared to a homogeneous configuration, a gain in ψ* by up to 16% can be obtained by distributing the minor actinides heterogeneously, Cm being placed in the inner zone of the active core and Am in the outer zone. The reason for this is the higher fission probability for neutrons for Cm than for Am in the energy range below 1.0 MeV. Moreover, a comparative study of two different physics packages available in MCNPX, the Bertini and the CEM models, has been performed, focusing on the production of neutrons in the spallation target and on the proton source efficiency. The Bertini model was found to produce a higher number of neutrons in the low-energy range (below ∼15 MeV) than the CEM model. Consequently, the Bertini model also over-estimates ψ* by about 10%, compared to the CEM model.

  • 44.
    Seltborg, Per
    et al.
    KTH, Superseded Departments, Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Tucek, Kamil
    KTH, Superseded Departments, Physics.
    Gudowski, Waclaw
    KTH, Superseded Departments, Physics.
    Definition and application of proton source efficiency in accelerator driven systems2003In: Nuclear science and engineering, ISSN 0029-5639, E-ISSN 1943-748X, Vol. 145, no 3, p. 390-399Article in journal (Refereed)
    Abstract [en]

    In order to study the beam power amplification of an accelerator-driven system (ADS), a new parameter, the proton source efficiency psi* is introduced. psi* represents the average importance of the external proton source, relative to the average importance of the eigenmode production, and is closely related to the neutron source efficiency rho*, which is frequently used in the ADS field. rho* is commonly used in the physics of subcritical systems driven by any external source (spallation source, (d,d), (d, t), Cf-252 spontaneous fissions, etc.). On the contrary, psi* has been defined in this paper exclusively for ADS studies where the system is driven by a spallation source. The main advantage with using psi* instead of rho* for ADS is that the way of defining the external source is unique and that it is proportional to the core power divided by the proton beam power, independent of the neutron source distribution.

    Numerical simulations have been performed with the Monte Carlo code MCNPX in order to study psi* as a function of different design parameters. It was found that, in order to maximize psi* and therefore minimize the proton current needs, a target radius as small as possible should be chosen. For target radii smaller than similar to30 cm, lead-bismuth is a better choice of coolant material than sodium, regarding the proton source efficiency, while for larger target radii the two materials are equally good. The optimal axial proton beam impact was found to be located similar to 20 cm above the core center. Varying the proton energy, psi*/E-p was found to have a maximum for proton energies between 1200 and 1400 MeV Increasing the americium content in the fuel decreases psi* considerably, in particular when the target radius is large.

  • 45.
    Suvdantsetseg, Erdenechimeg
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    An assessment of prompt neutron reproduction time in a reflector dominated fast critical system: ELECTRA2014In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 71, p. 159-165Article in journal (Refereed)
    Abstract [en]

    In this paper, an accurate method to evaluate the prompt neutron reproduction time for a reflector dominated fast critical reactor, ELECTRA, is discussed. To adequately handle the problem, explicit time dependent Monte Carlo calculations with MCNP, applying repeated time cut-off technique, is used and compared against the σ ∼ 1/v time dependent absorber method, applying artificial cross section data in the Monte Carlo code SERPENT. The results show that when a reflector plays a major role in criticality for fast neutron reactor, the two methods predict different physical parameters (Λ = 69 ± 2 ns and Λ = 83 ± 1 ns for time cut-off and the 1/v method respectively). The reason is explained by applying Avery-Cohn’s two-region prompt neutron model. 

  • 46.
    Suvdantsetseg, Erdenechimeg
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Design analysis of ELECTRA with oxide fuel2011Conference paper (Refereed)
  • 47.
    Suvdantsetseg, Erdenechimeg
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Unprotected Loss of Heat Sink Analysis for the Design of ELECTRAIn: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100Article in journal (Other academic)
    Abstract [en]

    In this paper, the transient behavior of a small fast reactor cooled by natural convection of lead (ELECTRA) is studied under unprotected loss of heat sink conditions, as a parametric function of the radiative heat loss via its outer vessel surface. The results show that when this heat loss is higher than the decay heat level, the negative reactivity feedback mechanisms of the system lead to re-criticality, bringing it into a new steady state. As a consequence, coolant freezing may be avoided during such accidents. 

  • 48.
    Suvdantsetseg, Erdenechimeg
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Bortot, Sara
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Optimization of the reactivity control drum system of ELECTRA2012In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 252, no 1, p. 209-214Article in journal (Refereed)
    Abstract [en]

    In this paper, an optimized control drum system for the European Lead Cooled Training Reactor (ELECTRA) is proposed. By changing the number of rotating drums from 6 to 12, we succeed in reducing the maximum rotational worth of a single drum from 4 $ to 1.64 $. As a consequence, the safety margin during reactivity insertions is significantly improved.

  • 49.
    Suvdantsetseg, Erdenechimeg
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Bortot, Sara
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Optimization of the reactivity control drum system of ELECTRA (vol 252C, pg 209, 2012)2013In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 255, p. 376-376Article in journal (Refereed)
  • 50. Terentyev, D. A.
    et al.
    Malerba, L.
    Chakarova, Roumiana
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Nordlund, K.
    Olsson, P.
    Rieth, M.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Displacement cascades in Fe-Cr: A molecular dynamics study2006In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 349, no 1-2, p. 119-132Article in journal (Refereed)
    Abstract [en]

    Displacement cascades up to 50 keV have been simulated in Fe-10%Cr by molecular dynamics (MD), using an embedded-atom method (EAM) interatomic potential which satisfactorily reproduces the interaction between Cr atoms and point-defects in alpha-Fe. In particular, the potential can reproduce the strong interaction with self interstitial atoms characteristic of Fe-Cr alloys. The results, when compared to the case of pure Fe, show that the presence of Cr does not significantly influence either the ballistic phase of the cascade, or the primary damage state, in terms of number of surviving defects or clustered fraction. However, the fraction of Cr atoms in interstitial position greatly exceeds the alloy concentration, in agreement with some experimental indications, and this feature is expected to influence the long-term evolution of radiation damage in the alloy. The mechanisms leading to the accumulation of Cr in interstitial positions and the expected trapping effect on interstitial clusters are analysed and discussed.

12 1 - 50 of 90
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