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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. Andersson, P.
    et al.
    Gustavsson, C.
    Bevilacqua, R.
    Blomgren, J.
    Hjalmarsson, A.
    Kolozhvari, A.
    LeColley, F. -R
    Marie, N.
    Osterlund, M.
    Pomp, S.
    Prokofiev, A.
    Simutkin, V.
    Tesinsky, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Tippawan, U.
    An upgrade of the SCANDAL setup for measurements of elastic neutron scattering at 175 MeV2010In: RADIATION MEASUREMENTS, 2010, Vol. 45, no 10, p. 1142-1144Conference paper (Refereed)
    Abstract [en]

    The experimental setup SCANDAL used for measurements of the differential cross section for elastic and inelastic neutron scattering, has recently been upgraded with larger CsI scintillating detectors to enable measurements at energies up to 175 MeV. Measurements on Fe. Bi and Si have been carried out using the quasi mono-energetic neutron beam at the The Svedberg Laboratory, and data is under analysis. The experimental setup can be used for measurements on a wide range of target nuclei, including C and O, which are important for dosimetry applications. SCANDAL can also run in proton mode, for measurements of the (n,p) reaction. This paper describes the new experimental setup, and reports on its properties, such as energy resolution.

  • 3.
    Anglart, Henryk
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Anghel, Ionut
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    On post-dryout heat transfer in channels with flow obstacles2014In: International Congress on Advances in Nuclear Power Plants, ICAPP 2014, 2014, Vol. 2, p. 1518-1523Conference paper (Refereed)
    Abstract [en]

    In this paper a new approach to predict wall temperature during post-dryout heat transfer in channels with flow obstacles is presented. The proposed approach takes into account the obstacle specifics and location in the channel to determine the post-dryout patch onset. The wall temperature in the dry patch area is predicted from Anghel and Anglart correlation to account for developing post-dryout conditions. The method is applied to post-dryout conditions in annulus with pin-spacers and a significant improvement of prediction accuracy in comparison to other reference methods is demonstrated.

  • 4.
    Anglart, Henryk
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Caraghiaur, Diana
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    CFD modeling of boiling annular-mist flow for dryout investigations2011In: Multiphase Science and Technology, ISSN 0276-1459, E-ISSN 1943-6181, Vol. 23, p. 223-251Article in journal (Refereed)
    Abstract [en]

    This paper presents applications of computational fluid dynamics (CFD) to modeling of two-phase annular-mist flows with evaporating liquid films. This type of two-phase flow exists in boiling channels prior to the onset of dryout. Annular-mist flows have a very complex structure since they contain liquid and vapor, both as the continuous and the dispersed phase. Due to this feature, both the Eulerian-Eulerian as well as the Eulerian-Lagrangian approaches are often used to model such flows. The two approaches, with pertinent conservation equations and closure relationships, are reviewed in this paper.

  • 5.
    Arnesson, Jennifer
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Numerical Modeling of Radioactive Release Implemented for Loss of Coolant Accident, Evaluated using Latin Hypercube Sampling2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 6. Bakaev, A.
    et al.
    Terentyev, D.
    Chang, Z.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Posselt, M.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Zhurkin, E. E.
    Effect of isotropic stress on dislocation bias factor in bcc iron: an atomistic study2018In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 98, no 1, p. 54-74Article in journal (Refereed)
    Abstract [en]

    The effect of externally applied stress on the dislocation bias factor (BF) in bcc iron has been studied using a combination of atomistic static calculations and finite element integration. Three kinds of dislocations were considered, namely, a0/2〈1 1 1〉{1 1 0} screw, a0/2〈1 1 1〉{1 1 0} edge and a0〈1 0 0〉{0 0 1} edge dislocations. The computations reveal that the isotropic crystal expansion leads to an increasing or constant dislocation bias, depending on the Burgers vector and type of dislocation. On the other hand, compressive stress reduces the dislocation bias for all the dislocations studied. Variation of the dislocation BF depending on dislocation type and Burgers vector is discussed by analysing the modification of the interaction energy landscape and the capture efficiency values for the vacancy and self-interstitial atom. 

  • 7. Becares, V.
    et al.
    Villamarin, D.
    Fernandez-Ordonez, M.
    Gonzalez-Romero, E. M.
    Berglöf, Carl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Bournos, V.
    Fokov, Y.
    Mazanik, S.
    Serafimovich, I.
    Evaluation of the criticality constant from Pulsed Neutron Source measurements in the Yalina-Booster subcritical assembly2013In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 53, p. 40-49Article in journal (Refereed)
    Abstract [en]

    The prompt decay constant method and the area-ratio (Sjostrand) method constitute the reference techniques for measuring the reactivity of a subcritical system using Pulsed Neutron Source experiments (PNS). However, different experiments have shown that in many cases it is necessary to apply corrections to the experimental results in order to take into account spectral and spatial effects. In these cases, the approach usually followed is to develop different specific correction procedures for each method. In this work we discuss the validity of prompt decay constant method and the area-ratio method in the Yalina-Booster subcritical assembly and propose a general correction procedure based on Monte Carlo simulations.

  • 8. Becares, V.
    et al.
    Villamarin, D.
    Fernandez-Ordonez, M.
    Gonzalez-Romero, E. M.
    Berglöf, Carl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Bournos, V.
    Fokov, Y.
    Mazanik, S.
    Serafimovich, I.
    Validation of ADS reactivity monitoring techniques in the Yalina-Booster subcritical assembly2013In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 53, p. 331-341Article in journal (Refereed)
    Abstract [en]

    The development of a reactivity monitoring system for subcritical reactors is a major task prior to industrial scale accelerator driven system (ADS) construction. Within the 6th European Framework Program, the IP-EUROTRANS project has performed a series of experiments at the Yalina-Booster subcritical assembly located at the Joint Institute for Power and Nuclear Research (JIPNR) of the National Academy of Sciences of Belarus, using a continuous (D, T) (fusion) neutron source in pulsed and continuous mode with short interruptions (beam trips). In this paper, the implementation and results of three different monitoring techniques intended to operate with continuous neutron sources will be presented, namely the source-jerk technique, the prompt decay constant technique and the current-to-flux technique. The results will be compared with the values of the reactivity obtained using the pulsed source in PNS experiments, discussed in detail in another paper.

  • 9. Becquart, C. S.
    et al.
    Ngayam Happy, R.
    Olsson, P.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Domain, C.
    A DFT study of the stability of SIAs and small SIA clusters in the vicinity of solute atoms in Fe2018In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 500, p. 92-109Article in journal (Refereed)
    Abstract [en]

    The energetics, defect volume and magnetic properties of single SIAs and small SIA clusters up to size 6 have been calculated by DFT for different configurations like the parallel 〈110〉 dumbbell, the non parallel 〈110〉 dumbbell and the C15 structure. The most stable configurations of each type have been further analyzed to determine the influence on their stability of various solute atoms (Ti, V, Cr, Mn, Co, Ni, Cu, Mo, W, Pd, Al, Si, P), relevant for steels used under irradiation. The results show that the presence of solute atoms does not change the relative stability order among SIA clusters. The small SIA clusters investigated can bind to both undersized and oversized solutes. Several descriptors have been considered to derive interesting trends from results. It appears that the local atomic volume available for the solute is the main physical quantity governing the binding energy evolution, whatever the solute type (undersized or oversized) and the cluster configuration (size and type).

  • 10.
    Berglöf, Carl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    On measurement and monitoring of reactivity in subcritical reactor systems2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Accelerator-driven systems have been proposed for incineration of transuranic elements from spent nuclear fuel. For safe operation of such facilities, a robust method for reactivity monitoring is required. Experience has shown that the performance of reactivity measurement methods in terms of accuracy and applicability is highly system dependent. Further investigations are needed to increase the knowledge data bank before applying the methods to an industrial facility and to achieve license to operate such a facility. In this thesis, two systems have been subject to investigation of various reactivity measurement methods. Conditions for successful utilization of the methods are presented, based on the experimental experience. In contrast to previous studies in this field, the reactivity has not only been determined, but also monitored based on the so called beam trip methodology which is applicable also to non-zero power systems. The results of this work constitute a part of the knowledge base for the definition of a validated online reactivity monitoring methodology for facilities currently being under development in Europe (XT-ADS and EFIT).

  • 11.
    Berglöf, Carl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Fernández-Ordóñez, M.
    Villamarín, D.
    Bécares, V.
    González-Romero, E.
    Bournos, V.
    Serafimovich, I.
    Mazanik, S.
    Fokov, Y.
    Muñoz-Cobo, J. -L
    Summary of conclusions from the EUROTRANS reactivity monitoring experiments at YALINA-booster2010In: Transactions of the American Nuclear Society: Volume 102, 2010, p. 11-12Conference paper (Refereed)
  • 12.
    Berglöf, Carl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Fernández-Ordóñez, M.
    Villamarín, D.
    Bécares, V.
    González-Romero, E. M.
    Bournos, V.
    Serafimovich, I.
    Mazanik, S.
    Fokov, Y.
    Kiyavitskaya, H.
    Pulsed neutron source reference measurements in the subcritical experiment YALINA-Booster2009In: Proceedings of International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators: 4-8 May 2009, Vienna, International Atomic Energy Agency, 2009Conference paper (Refereed)
    Abstract [en]

    In support of an online reactivity monitoring experiment, also presented in this conference, this work presents the reactivity calibration measurements performed with a pulsed neutron source in the coupled fast-thermal subcritical facility YALINA-Booster. These experiments reveal the complexity of experimentally obtaining a global reactivity from a highly heterogeneous core. Moreover, the effect of varying the source multiplication at constant reactivity on the area ratio technique is explored. It is found that the reactivity obtained with the area ratio technique carry strong spatial dependence, but it can be handled by calculated correction factors. On the other hand the method is showed not to be sensitive to changes in the source multiplication. It is also shown that the prompt neutron decay constant does not vary strongly over the core except at deep subcritical states.

  • 13.
    Berglöf, Carl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Fernández-Ordóñez, M.
    Villamarín, D.
    Bécares, V.
    González-Romero, E. M.
    Bournos, V.
    Serafimovich, I.
    Mazanik, S.
    Kiyavitskaya, H.
    Neutron noise measurements in the YALINA-Booster experiments2009In: Proceedings of International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators: 4-8 May 2009, Vienna, International Atomic Energy Agency, 2009Conference paper (Refereed)
    Abstract [en]

    In addition to the pulsed neutron source measurements and the continuous source beam-trip and current-to-flux measurements performed in the YALINA-Booster facility, also presented in this conference, a set of neutron noise measurements has been performed to achieve a complete characterization of the core. The neutron noise measurements have been performed in three different configurations covering a subcriticality range from 0.85 to 0.977. The Rossi-α neutron noise technique has been applied to detector counts from two channels in the thermal part of the core. The Rossi-α results are compared to the experimental prompt neutron decay constants obtained from the pulsed neutron source measurements. A first approach fitting procedure reveals a need of three exponentials to describe the Rossi-α histograms. It has been found that at deep subcriticality, the fundamental mode decay may coincide with or be close to a higher eigenmode, thus making it difficult to determine the prompt neutron decay constant correctly.

  • 14.
    Berglöf, Carl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Fernández-Ordóñez, M.
    Villamarín, D.
    Bécares, V.
    González-Romero, E. M.
    Bournos, Victor
    Muñoz-Cobo, José-Luis
    Auto-correlation and variance-to-mean measurements in a subcritical core obeying multiple alpha-modes2011In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 38, no 2-3, p. 194-202Article in journal (Refereed)
    Abstract [en]

    Neutron noise measurements based on the Rossi-alpha and Feynman-alpha methodologies have been performed in a heterogeneous subcritical system. It is shown that the traditional single alpha-mode formulations of the Rossi-alpha and Feynman-alpha methods are not applicable due to the presence of higher alpha-modes. Formalisms taking into account multiple alpha-modes are applied resulting in satisfactory results. Three alpha-modes could be identified using the Rossi-alpha method, whereas only two could be obtained using the Feynman-alpha method. In the Feynman-alpha case, the possibility to obtain the fastest decaying alpha-mode was diminished due to detector dead time effects. It was found that the slowest decaying alpha-mode does not exactly correspond to the prompt decay found in pulsed neutron source measurements, which confirms the results of previous studies. Strengths and weaknesses of the multiple alpha-mode Rossi-alpha and Feynman-alpha methods observed in this study are pointed out.

  • 15.
    Berglöf, Carl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Fernández-Ordóñez, M.
    Villamarín, D.
    Bécares, V.
    González-Romero, E. M.
    Bournos, Victor
    Serafimovich, Ivan
    Mazanik, Sergei
    Fokov, Yurii
    Spatial and Source Multiplication Effects on the Area Ratio Reactivity Determination Method in a Strongly Heterogeneous Subcritical System2010In: Nuclear science and engineering, ISSN 0029-5639, E-ISSN 1943-748X, Vol. 166, no 2, p. 134-144Article in journal (Refereed)
    Abstract [en]

    The area ratio method of Sjostrand is generally considered one of the most reliable reactivity determination methods and thus is a major candidate for off-line calibration purposes in future accelerator-driven systems for high-level waste incineration. In this work, the Sjostrand area ratio method has been evaluated experimentally under thorough conditions in the strongly heterogeneous subcritical facility YALINA-Booster. Both strengths and weaknesses of the method have been identified. Most surprisingly, it has been found that the area ratio reactivity estimates may differ a factor of 2 depending on detector position. It is also shown that this strong spatial dependence can be explained based on a simple two-region point-kinetics model and corrected by means of correction factors obtained through Monte Carlo simulations. A new Monte Carlo correction method is proposed that includes, at the same time, the spatial disturbance and the effective delayed neutron fraction. In that way, the value of the effective multiplication factor is obtained from the measured dollar reactivity without the need of calculating the effective delayed neutron fraction explicitly, and thereby, the delayed neutron transport is performed only once. Further, it has been found that the Sjostrand area ratio method is not sensitive to perturbations of the source multiplication factor.

  • 16. Bevilacqua, R.
    et al.
    Pomp, S.
    Hayashi, M.
    Hirayama, S.
    Naito, Y.
    Watanabe, Y.
    Tippawan, U.
    Simutkin, V.
    Andersson, P.
    Blomgren, J.
    Österlund, M.
    Tesinsky, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Lecolley, F. -R
    Marie, N.
    Hjalmarsson, A.
    Prokofiev, A.
    Kolozhvari, A.
    Study of pre-equilibrium emission of light complex particles from Fe and Bi induced by intermediate energy neutrons2011In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 312, no SECTION 8, p. 082013-Article in journal (Refereed)
    Abstract [en]

    We have measured double differential cross sections (DDX) for emission of hydrogen- and helium-isotopes in the interaction of 175 MeV quasi-monoenergetic neutrons with Fe and Bi using the Medley setup at the The Svedberg Laboratory (Uppsala, Sweden). We compared experimental DDX with calculations with the TALYS code, which includes exciton model and Kalbach systematics; the code fails to reproduce the emission of complex light ions, generally overestimating it. We propose an correction for the application of the Kalbach phenomenological model in the TALYS code by introducing a new energy dependence for the nucleon transfer mechanism in the pre-equilibrium emission region. Our results suggest also evidence for multiple pre-equilibrium emission of composite particles at 175 MeV.

  • 17. Bevilacqua, R.
    et al.
    Pomp, S.
    Simutkin, V. D.
    Tippawan, U.
    Andersson, P.
    Blomgren, J.
    Osterlund, M.
    Hayashi, M.
    Hirayama, S.
    Naito, Y.
    Watanabe, Y.
    Tesinsky, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    LeColley, F. -R
    Marie, N.
    Hjalmarsson, A.
    Prokofiev, A. V.
    Kolozhvari, A.
    Neutron induced light-ion production from iron and bismuth at 175 MeV2010In: RADIATION MEASUREMENTS, 2010, Vol. 45, no 10, p. 1145-1150Conference paper (Refereed)
    Abstract [en]

    We have measured light-ion (p, d, t, He-3 and alpha) production in the interaction of 175 MeV neutrons with iron and bismuth with low-energy thresholds and for a wide angular range (from 20 degrees to 160 degrees, in steps of 20 degrees). Measurements have been performed with the Medley setup, semi-permanently installed at the The Svedberg Laboratory, Uppsala (Sweden), where a quasi-monoenergetic neutron beam is available and well characterized. Medley is a conventional spectrometer system and consists of eight telescopes, each of them composed of two silicon surface barrier detectors, to perform particle identification, and a CsI(Tl) scintillator to fully measure the kinetic energy of the produced light-ions. We report preliminary double-differential cross sections for production of protons, deuterons and tritons in comparison with model calculations using TALYS-1.0 code. These show better agreement for the production of protons, while the theoretical calculations seem to overestimate the experimental production of deuterons and tritons.

  • 18. Bevilacqua, R.
    et al.
    Pomp, S.
    Simutkin, V. D.
    Tippawan, U.
    Hayashi, M.
    Hirayama, S.
    Naitou, Y.
    Watanabe, Y.
    Prokofiev, A. V.
    Hjalmarsson, A.
    Andersson, P.
    Blomgren, J.
    Osterlund, M.
    Tesinsky, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Lecolley, F. -R
    Marie, N.
    Kolozhvari, A.
    Light-Ion Production in the Interaction of 175 MeV Neutrons with Iron and Bismuth2011In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 59, no 2, p. 1701-1704Article in journal (Refereed)
    Abstract [en]

    We have measured double-differential (angle and energy) cross sections for light-ion (p, d, t, (3)He, and a) production in the interaction of quasi-monoenergetic 175 MeV neutrons with iron and bismuth. Measurements have been performed at the The Svedberg Laboratory, Uppsala (Sweden), using the Medley setup which allows low-energy thresholds and wide energy and angular ranges. Medley is a spectrometer system consisting of eight three-element telescopes placed at angles from 20 degrees to 160 degrees, in steps of 20 degrees. Each telescope is composed of two silicon surface barrier detectors and a CsI(Tl) scintillator, to perform particle identification, fully stop the produced light-ions and measure their kinetic energy. The time-of-flight was used to reduce the contribution from the low energy tail in the accepted incident neutron spectrum. We report double-differential production cross sections for protons, deuterons, tritons, (3)He and alpha particles and compare them with model calculations with TALYS-1.2.

  • 19. Bevilacqua, R.
    et al.
    Pomp, S.
    Simutkin, V.
    Tippawan, U.
    Andersson, P.
    Blomgren, J.
    Österlund, M.
    Hayashi, M.
    Hirayama, S.
    Naito, Y.
    Watanabe, Y.
    Tesinsky, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    LeColley, F. -R
    Marie, N.
    Hjalmarsson, A.
    Prokofiev, A.
    Kolozhvari, A.
    Neutron induced light-ion production from Iron and Bismuth at 175 MeV2010In: CNR*09 - Second International Workshop on Compound Nuclear Reactions and Related Topics, EDP Sciences, 2010, Vol. 2, p. 05005-Conference paper (Refereed)
    Abstract [en]

    We have measured light-ion (p, d, t, 3He and α) production in the interaction of 175 MeV neutrons with iron and bismuth, using the MEDLEY setup. A large set of measurements at 96 MeV has been recently completed and published, and now higher energy region is under investigation. MEDLEY is a conventional spectrometer system that allows low-energy thresholds and offers measurements over a wide angular range. The system consists of eight telescopes, each of them composed of two silicon surface barrier detectors, to perform particle identification, and a CsI(Tl) scintillator to fully measure the kinetic energy of the produced light-ions. The telescopes are placed at angles from 20° to 160°, in steps of 20°. Measurements have been performed at The Svedberg Laboratory, Uppsala (Sweden), where a quasi mono-energetic neutron beam is available and well characterized. Time of flight techniques are used to select light-ion events induced by neutrons in the main peak of the source neutron spectrum. We report preliminary double differential cross sections for production of protons, deuterons and tritons in comparison with model calculations using TALYS-1.0 code.

  • 20. Bevilacqua, Riccardo
    et al.
    Pomp, Stephan
    Simutkin, Vasily
    Hayashi, Masateru
    Hirayama, Shusuke
    Naitou, Yuuki
    Watanabe, Yukinobu
    Tippawan, Udomrat
    Tesinsky, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Ban, Gilles
    Lecouey, Jean-Luc
    Lecolley, Francois-Rene
    Marie, Nathalie
    Hamel, Quentin
    Medley spectrometer for light ions in neutron-induced reactions at 175 MeV2011In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 646, no 1, p. 100-107Article in journal (Refereed)
    Abstract [en]

    We have upgraded the Medley spectrometer to measure neutron-induced double differential cross-sections for light-ion production, with neutron energies up to 175 MeV. Measurements were performed at the quasi-monoenergetic neutron beam line at the The Svedberg Laboratory, in Uppsala (Sweden). Medley is a spectrometer system composed of eight three-element telescope detectors; Delta E-E technique is used for particle identification and total kinetic energy measurement. We have improved particle separation and installed new detectors that fully stop ions with kinetic energy up to 170 MeV. To reduce the contribution of the low energy tail in the quasi-monoenergetic neutron spectrum, we have applied time-of-flight techniques and investigated the results for measurements with 175 MeV neutrons. We have investigated the response function of the CsI(Tl) scintillators and describe a method for efficiency correction. We have studied the signal-to-background ratio of the new configuration of the spectrometer and of the collimation system. A method to obtain absolute cross-section normalization, separating the peak neutrons from the low-energy tail, is proposed. Finally we have characterized the 175 MeV quasi-monoenergetic neutron spectrum with the Medley spectrometer. This upgraded configuration has been used in 2007 and 2009 for light-ion production measurements at 175 MeV from C, Si, O, Fe, Bi and U.

  • 21. Bonny, G.
    et al.
    Bakaev, A.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Domain, C.
    Zhurkin, E. E.
    Posselt, M.
    Interatomic potential to study the formation of NiCr clusters in high Cr ferritic steels2017In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 484, p. 42-50Article in journal (Refereed)
    Abstract [en]

    Under irradiation NiSiPCr clusters are formed in high-Cr ferritic martensitic steels as well as in FeCr model alloys. In the literature little is known about the origin and contribution to the hardening of these clusters. In this work we performed density functional theory (DFT) calculations to study the stability of small substitutional NiCr-vacancy clusters and interstitial configurations in bcc Fe. Based on DFT data and experimental considerations a ternary potential for the ferritic FeNiCr system was developed. The potential was applied to study the thermodynamic stability of NiCr clusters by means of Metropolis Monte Carlo (MMC) simulations. The results of our simulations show that Cr and Ni precipitate as separate fractions and suggest only a limited synergetic effect between Ni and Cr. Therefore our results suggest that the NiCrSiP clusters observed in experiments must be the result of other mechanisms than the synergy of Cr and Ni at thermal equilibrium.

  • 22. Bonny, G.
    et al.
    Castin, N.
    Domain, C.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Verreyken, B.
    Pascuet, M. I.
    Terentyev, D.
    Density functional theory-based cluster expansion to simulate thermal annealing in FeCrW alloys2017In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 97, no 5, p. 299-317Article in journal (Refereed)
    Abstract [en]

    In this work, we develop a rigid lattice cluster expansion as an ultimate goal to track the micro-structural evolution of Eurofer steel under neutron irradiation. The fact that all (defect) structures are mapped upon a rigid lattice allows a simplified computation and fitting procedure, thus enabling alloys of large chemical complexity to be modelled. As a first step towards the chemical complexity of Eurofer steels, we develop a cluster expansion (CE) for the FeCrW-vacancy system based on density functional theory (DFT) calculations in the dilute alloy limit. The DFT calculations suggest that only CrW clusters containing vacancies are stabilised. The cluster expansion was used to simulate thermal annealing in Fe–20Cr–xW alloys at 773 K. It is found that the addition of W to the alloy results in a non-linear decrease in the precipitation kinetics. The CE was found suitable to describe the energetics of the FeCrW-vacancy system in the Fe-rich limit.

  • 23.
    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.

  • 24.
    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. 

  • 25.
    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)
  • 26. 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.

  • 27. Bécares, V.
    et al.
    Villamarín, D.
    Fernández-Ordóñez, M.
    González-Romero, E. M.
    Berglöf, Carl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Fokov, Y.
    Bournos, V.
    Mazanik, S.
    Serafimovich, I.
    Reactivity deter-mination of the Yalina-Booster subcritical assembly using the prompt decay constant methodArticle in journal (Refereed)
  • 28. Bécares, V.
    et al.
    Villamarín, D.
    González-Romero, E. M.
    Berglöf, Carl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Fokov, Y.
    Bournos, V.
    Mazanik, S.
    Serafimovich, I.
    Validation of ADS reactivity monitoring techniques in a strongly heterogeneous subcritical systemArticle in journal (Refereed)
  • 29. Bécares-Palacios, V.
    et al.
    Fernández-Ordóñez, M.
    Villamarín, D.
    González-Romero, E. M.
    Berglöf, Carl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Bournos, V.
    Mazanik, S.
    Reactivity monitoring with imposed beam trips and pulsed mode detectors in the subcritical experiment YALINA-Booster2009In: Proceedings of International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators: 4-8 May 2009, Vienna, International Atomic Energy Agency, 2009Conference paper (Refereed)
    Abstract [en]

    Reactivity monitoring is one of the urgent problems that require a solution in order to achieve a license for a future full-scale ADS. As a part of the EUROTRANS experiments at the YALINA-Booster facility, presented in this conference, a set of measurements with imposed beam-trips has been performed. Traditionally, the source jerk method has been used in subcritical systems to obtain the reactivity by comparing the total neutron flux before the neutron source removal to the semi-stable delayed neutron flux after the source removal. The deuterium-tritium neutron source of the YALINA-Booster facility can, in addition to pulsed mode operation, operate with continuous beam with short imposed millisecond-scale interruptions, thus providing the possibility to monitor the reactivity at each beam trip in the source jerk manner. In order to test the validity of the beam-trip reactivity values determined by using detectors operating in current-mode (also presented in this conference), the reactivity values of the YALINA-Booster assembly obtained through the beam-trip technique using pulsed-mode detectors is presented in this work. In these experiments, a beam-trip frequency of 1 Hz and an interruption time of ∼20 ms have been chosen and two different core loadings with effective multiplication factor around 0.95 have been investigated. These two different loadings with close to equal reactivity but different source multiplication characteristics make it possible to explore the effect of the different source multiplications. In addition, the response of the imposed beam-trip reactivity monitoring technique to reactivity insertions and removals has been studied through control rod movements. Experimental data from fission chambers have been acquired from all three zones of the core: the fast booster zone, the thermal zone and the reflector.

  • 30. Castin, N.
    et al.
    Messina, L.
    Domain, C.
    Pasianot, R. C.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Improved atomistic Monte Carlo models based on ab-initio -trained neural networks: Application to FeCu and FeCr alloys2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 21, article id 214117Article in journal (Refereed)
    Abstract [en]

    We significantly improve the physical models underlying atomistic Monte Carlo (MC) simulations, through the use of ab initio fitted high-dimensional neural network potentials (NNPs). In this way, we can incorporate energetics derived from density functional theory (DFT) in MC, and avoid using empirical potentials that are very challenging to design for complex alloys. We take significant steps forward from a recent work where artificial neural networks (ANNs), exclusively trained on DFT vacancy migration energies, were used to perform kinetic MC simulations of Cu precipitation in Fe. Here, a more extensive transfer of knowledge from DFT to our cohesive model is achieved via the fitting of NNPs, aimed at accurately mimicking the most important aspects of the ab initio predictions. Rigid-lattice potentials are designed to monitor the evolution during the simulation of the system energy, thus taking care of the thermodynamic aspects of the model. In addition, other ANNs are designed to evaluate the activation energies associated with the MC events (migration towards first-nearest-neighbor positions of single point defects), thereby providing an accurate kinetic modeling. Because our methodology inherently requires the calculation of a substantial amount of reference data, we design as well lattice-free potentials, aimed at replacing the very costly DFT method with an approximate, yet accurate and considerably more computationally efficient, potential. The binary FeCu and FeCr alloys are taken as sample applications considering the extensive literature covering these systems.

  • 31.
    Castin, N.
    et al.
    Studie Ctr Kerneenergie, Ctr Etud Energie Nucl SCK CEN, NMS Unit, Boeretang 200, B-2400 Mol, Belgium..
    Pascuet, M. I.
    Consejo Nacl Invest Cient & Tecn CONICET, Godoy Cruz 2290 C1425FQB CABA, Buenos Aires, DF, Argentina..
    Messina, Luca
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Domain, C.
    EDF R&D, Dept Mat & Mecan Composants, F-77250 Moret Sur Loing, France..
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Pasianot, R. C.
    Consejo Nacl Invest Cient & Tecn CONICET, Godoy Cruz 2290 C1425FQB CABA, Buenos Aires, DF, Argentina.;Comis Nacl Energia Atom CNEA, Gcia Mat, Av Gral Paz 1499, RA-1650 San Martin, Argentina..
    Malerba, L.
    Studie Ctr Kerneenergie, Ctr Etud Energie Nucl SCK CEN, NMS Unit, Boeretang 200, B-2400 Mol, Belgium..
    Advanced atomistic models for radiation damage in Fe-based alloys: Contributions and future perspectives from artificial neural networks2018In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 148, p. 116-130Article in journal (Refereed)
    Abstract [en]

    Machine learning, and more specifically artificial neural networks (ANN), are powerful and flexible numerical tools that can lead to significant improvements in many materials modelling techniques. This paper provides a review of the efforts made so far to describe the effects of irradiation in Fe-based and W-based alloys, in a multiscale modelling framework. ANN were successfully used as innovative parametrization tools in these models, thereby greatly enhancing their physical accuracy and capability to accomplish increasingly challenging goals. In the provided examples, the main goal of ANN is to predict how the chemical complexity of local atomic configurations, and/or specific strain fields, influence the activation energy of selected thermally-activated events. This is most often a more efficient approach with respect to previous computationally heavy methods. In a future perspective, similar schemes can be potentially used to calculate other quantities than activation energies. They can thus transfer atomic-scale properties to higher-scale simulations, providing a proper bridging across scales, and hence contributing to the achievement of accurate and reliable multiscale models.

  • 32.
    Chang, Zhongwen
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Modelling of Dislocation Bias in FCC Materials2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Irradiation induced void swelling is problematic for the application of austenitic steels under high dose irradiation. In this thesis, the swelling is characterized by dislocation bias. The dislocation bias is obtained using the finite element method, accounting for fcc copper and nickel under electron irradiation. The methodology is implemented with the interaction energies between an edge dislocation and point defects. Analytically derived interaction energies, which are based on elasticity theory, are compared with interaction energies obtained from atomistic model using semi-empirical atomic potentials as physics basis. The comparison shows that the description of analytical interaction energies is inaccurate in the dislocation core regions. The bias factor dependence on dislocation density and temperature is presented and discussed. At high temperatures or low dislocation densities, the two approaches tend to converge. However, the dislocation bias based on the interaction energies from the two approaches, reveals larger discrepancy for nickel than for copper. The impact on dislocation bias from the different stacking fault energies of copper and nickel is elaborated. Nickel, which has a larger stacking fault energy, is predicted to have larger swelling rate than copper under the same irradiation conditions.

  • 33.
    Chang, Zhongwen
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Multiscale modelling of radiation-enhanced diffusion phenomena in metals2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A multiscale modelling framework and an experiment campaign are used to study void swelling and Cu precipitation under irradiation. Several aspects regarding defect and solute diffusion under irradiation have been studied in this thesis.

    First, a self-diffusion model in bcc Fe has been constructed in order to describe the non-linear effects, especially the magnetic transition, around the Curie temperature. First principles calculations are applied to obtain the parameters in the model. The paramagnetic state is simulated by statistical sampling of randomly arranged spin states on each atom. The model fits well with the experimental observations.

    Then, a combination of atomistic calculations and the finite element method (FEM) is developed in order to solve the diffusion equations of point defects, which are under the influence of a dislocation strain field. The dislocation bias, a key parameter in void swelling models, is hence obtained numerically. The method has been applied in different structural lattices. In the bcc materials, anomalous bias factors have been found for both edge- and screw dislocations. For the edge dislocations, the traditional assumption that the dislocation bias value is proportional to the Burgers vector has been proven not appropriate. For the screw dislocation, a negative bias value is obtained. This implies that vacancies, instead of self-interstitials, are preferentially absorbed into the screw dislocations. Thus a possible complementary mechanism is here introduced for explaining the long swelling incubation time before the steady swelling in bcc materials compared to that in fcc materials.

    Edge dislocations in fcc materials split into partial dislocations due to their  relatively low stacking fault energy. This feature complicates the analytical derivation of the dislocation bias. However, by transforming the analytical dislocation-point defect interaction energies to discrete interaction maps numerically applied in the FEM method, it is possible to perform a systematic study on typical fcc materials, i.e. Cu, Ni and Al. The impacts on the dislocation bias from elastic constants and stacking fault energy have been studied. It is found that the partial splitting distance is the dominating factor that determines the dislocation bias. A prediction method has been hence developed to obtain the dislocation bias of the austenitic alloys, for which it is difficult to use an atomistic description of the interaction maps. A prediction of about 8% dislocation bias of a typical austenitic 316 alloy has been made without performing specific atomistic calculations in the austenitic alloys.

    Finally, Cu precipitation under irradiation has been studied using both experiment and simulations. Cast iron and FeCu alloy samples were irradiated for a week with 2 MeV electrons. The resistivity of the samples was measured in situ. The microstructure of the samples was then examined by atom probe tomography. No Cu precipitation was found in the cast iron sample while small Cu clusters are observed in the FeCu model alloy. To simulate the clustering process, Kinetic Monte Carlo (KMC) and rate theory methods are used. Both the KMC and rate theory simulations show clearly the Cu clustering process in the FeCu alloy but not in cast iron within the irradiation dose.

  • 34.
    Chang, Zhongwen
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Messina, Luca
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Sandberg, Nils
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Yousfi, Amine
    Toijer, Elin
    Thuvander, Mattias
    Boizot, Bruno
    Brysbaert, Gauthier
    Metayer, Vincent
    Gorse-Pomonti, Dominique
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Electron irradiation accelerated Cu precipitation in cast iron and an FeCu model alloyManuscript (preprint) (Other academic)
  • 35.
    Chang, Zhongwen
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Sandberg, Nils
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Terentyev, Dmitry
    Interaction Energy Calculations of Edge Dislocation with Point Defects in FCC Cu2013Conference paper (Refereed)
    Abstract [en]

    In order to improve the dislocation bias (DB) model of swelling under irradiation, a large scale of atomistic simulation of the interaction in face centered cubic (FCC) Cu model lattice between an edge dislocation (ED) and point defects such as a vacancy, a self-interstital atom (SIA) have been performed for various configurations. It is found dislocation core splits into partial cores after energy relaxation. Interactions with any SIA conficurations is one order of magnitute larger than with a vacancy. The reason that SIA creats a larger dilatation volumn than the vacancy is directly observed from calculation. Furthurmore, within the interaction range, an octahedron position rather than dumbbell in <100> direction is observed in the stable state after relaxation in interactions between a edge dislocation and a dumbbell SIA. Comparision of interaction energy in analytical and atomistic calculation shows that analytical one has a stronger interaction in vacancy-ED systems, suggesting that the bias factor (BF) from analytical calculation is larger than from atomistic calculation.

  • 36.
    Chang, Zhongwen
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Terentyev, D
    Nuclear Materials Science Institute, Belgium.
    Sandberg, N
    Swedish Radiation Safety Authority, Sweden.
    Multiscale calculation of dislocation bias in fcc Ni and bcc Fe model lattices2014In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584Article in journal (Refereed)
    Abstract [en]

    In order to gain more insights on void swelling, dislocation bias is studied in this work. Molecular staticsimulations with empirical potentials are applied to map the dislocation–point defects interactionenergies in both fcc Ni and bcc Fe model lattices. The interaction energies are then used to numericallysolve the diffusion equation and obtain the dislocation bias. The importance of the dislocation core regionis studied under a the temperature range 573–1173 K and the dislocation densities 1012—1015 m-2. Theresults show that larger dislocation bias is found in the fcc Ni than in the bcc Fe under differenttemperatures and dislocation densities. The anisotropic interaction energy model is used to obtain thedislocation bias and the result is compared to that obtained using the atomistic interaction model, thecontribution from the core structure is then shown in both the Ni lattice and the Fe lattice.

  • 37.
    Chang, Zhongwen
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Terentyev, Dmitry
    Sandberg, Nils
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Dislocation bias factors in fcc copper derived from atomistic calculations2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 441, no 1-3, p. 357-363Article in journal (Refereed)
    Abstract [en]

    Atomistic calculations were employed in order to calculate the interaction energy of an edge dislocation with different point defects. The bias factor was calculated by applying a finite element method on the interaction energy landscapes obtained from the atomistic calculations. A comparison of the calculated bias factor with a model based on elasticity theory reveals around 30% discrepancy under conditions representative for electron irradiation at 600 degrees C. Possible reasons are discussed. The bias factor dependence on dislocation density and ambient temperature is presented and discussed.

  • 38.
    Chang, Zhongwen
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Sandberg, Nils
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics. Swedish Radiation Safety Authority, Sweden.
    Dmitry, Terentyev
    Samuelsson, Karl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Bonny, Giovanni
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Assessment of the dislocation bias in fcc metals and extrapolation to austenitic steels2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 465Article in journal (Refereed)
    Abstract [en]

    A systematic study of dislocation bias has been performed using a method that combines atomistic and elastic dislocation-point defect interaction models with a numerical solution of the diffusion equation with a drift term. Copper, nickel and aluminium model lattices are used in this study, covering a wide range of shear moduli and stacking fault energies. It is found that the dominant parameter for the dislocation bias in fcc metals is the width of the stacking fault ribbon. The variation in elastic constants does not strongly impact the dislocation bias value. As a result of this analysis and its extrapolation, the dislocation bias of the widely applied austenitic stainless steels of 316 type is predicted to be about 0.1 at temperature close to the swelling peak (815 K) and typical dislocation density of 1014 m-2. This is in line with the bias calculated using the elastic interaction model, which implies that the prediction method can be used readily in other fcc systems even without EAM potentials. By comparing the bias values obtained using atomistic- and elastic interaction energies, about 20% discrepancy is found, therefore a more realistic bias value for the 316 type alloy is 0.08 in these conditions.

  • 39.
    Chang, Zhongwen
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Terentyev, Dmitry
    Nuclear Materials Science Institute, Belgium.
    Samuelsson, Karl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Dislocation bias calculations in fcc materialsManuscript (preprint) (Other academic)
  • 40.
    Chang, Zhongwen
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Terentyev, Dmitry
    Nuclear Materials Science Institute, Belgium.
    Sandberg, Nils
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics. Swedish Radiation Safety Authority, Sweden.
    Samuelsson, Karl
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Anomalous bias factors of dislocations in bcc iron2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 461, p. 221-229Article in journal (Refereed)
    Abstract [en]

    Dislocation bias factors in bcc Fe have been calculated based on atomistic interaction energy maps on three kinds of dislocations, namely the a0/2〈1 1 1〉{1 1 0} screw, a0/2〈1 1 1〉{1 1 0} and a0〈1 0 0〉{0 0 1} edge dislocations. The results show that the dislocation bias is higher for the a0/2〈1 1 1〉 edge dislocation than for the a0〈1 0 0〉 edge dislocation, even though the latter possesses a larger Burgers vector. This indicates the importance of the dislocation core contribution. For the a0/2〈1 1 1〉{1 1 0} screw dislocation, a negative dislocation bias has been obtained, which implies a more efficient absorption of vacancies than of SIAs. The effect of coexistence of both edge- and screw dislocations are assessed by a total bias. A possible complementary mechanism for explaining the long swelling incubation time in bcc metals is suggested and discussed.

  • 41. Chiapetto, Monica
    et al.
    Messina, Luca
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics. Université Paris-Saclay, Gif-sur-Yvette, France.
    Becquart, Charlotte S.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Malerba, Lorenzo
    Nanostructure evolution of neutron-irradiated reactor pressure vessel steels: Revised Object kinetic Monte Carlo model2017In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 393, p. 105-109Article in journal (Refereed)
    Abstract [en]

    This work presents a revised set of parameters to be used in an Object kinetic Monte Carlo model to simulate the microstructure evolution under neutron irradiation of reactor pressure vessel steels at the operational temperature of light water reactors (∼300 °C). Within a “grey-alloy” approach, a more physical description than in a previous work is used to translate the effect of Mn and Ni solute atoms on the defect cluster diffusivity reduction. The slowing down of self-interstitial clusters, due to the interaction between solutes and crowdions in Fe is now parameterized using binding energies from the latest DFT calculations and the solute concentration in the matrix from atom-probe experiments. The mobility of vacancy clusters in the presence of Mn and Ni solute atoms was also modified on the basis of recent DFT results, thereby removing some previous approximations. The same set of parameters was seen to predict the correct microstructure evolution for two different types of alloys, under very different irradiation conditions: an Fe-C-MnNi model alloy, neutron irradiated at a relatively high flux, and a high-Mn, high-Ni RPV steel from the Swedish Ringhals reactor surveillance program. In both cases, the predicted self-interstitial loop density matches the experimental solute cluster density, further corroborating the surmise that the MnNi-rich nanofeatures form by solute enrichment of immobilized small interstitial loops, which are invisible to the electron microscope.

  • 42.
    Claisse, Antoine
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Multiscale modeling of nitride fuels2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nitride fuels have always been considered a good candidate for GENIV reactors, as well as space reactors, due to their high fissile density, highthermal conductivity and high melting point. In these concepts, not beingcompatible with water is not a significant problem. However, in recent years,nitride fuels started to raise an interest for application in thermal reactors,as accident tolerant or high performance fuels. However, oxide fuels havebenefited from decades of intensive research, and thousands of reactor-years.As such, a large effort has to be made on qualifying the fuel and developingtools to help assess their performances.In this thesis, the modeling side of this task is chosen. The effort istwo-fold: determining fundamental properties using atomistic models andputting together all the properties to predict the performances under irradi-ation using a fuel performance code. The first part is done combining manyframeworks. The density functional theory is the basis to compute the elec-tronic structure of the materials, to which a Hubbard correction is added tohandle the strong correlation effects. Negative side effects of the Hubbardcorrection are tackled using the so-called occupation matrix control method.This combined framework is first tested, and then used to find electronic andmechanic properties of the bulk material as well as the thermomechanicalbehavior of foreign atoms. Then, another method, the self-consistent meanfield (SCMF) one, is used to reach the dynamics properties of these foreignatoms. In the SCMF theory, the data that were obtained performing the abinitio simulations are treated to provide diffusion and kinetic flux couplingproperties.In the second step of the work, the fuel performance code TRANSURA-NUS is used to model complete fuel pins. An athermal fission gas releasemodel based on the open porosity is developed and tested on oxide fuels.A model for nitride fuels is introduced, and some correlations are bench-marked. Major issues remaining are pointed out and recommendations asto how to solve them are made.

  • 43.
    Claisse, Antoine
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Open porosity fission gas release model applied to nuclear fuels2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nitride fuels have gained a new interest in the last few years as both a candidate for GEN IV reactors and as accident tolerant fuels for current light water reactors. They however are decades behind oxide fuels when it comes to qualication and development of tools to assess their performances. In this thesis, such a tool is developed. The fuel performance codeTRANSURANUS, which has very good results with oxide fuels, is extended to handle nitride fuels. The relevant thermo-mechanical properties are implemented and fuel type dependent modules are updated. Their limitations and discrepancies are discussed. A particular attention is brought to the athermal ssion gas release, and a new model based on the open fabrication porosity is developed and added to the code, as a starting point toward a mechanistic model. It works well on oxide fuels, but its eciency is harder to evaluate for nitride fuels, due to large uncertainties on many key correlations such as the thermal conductivity and the eective diusion coecient of gas atoms. Recommendations are made to solve the most important problems.

  • 44.
    Claisse, Antoine
    et al.
    KTH.
    Adorno Lopes, Denise
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Investigation of the ground- and metastable states of AnN (An=Th..Pu)Manuscript (preprint) (Other academic)
  • 45.
    Claisse, Antoine
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Klipfel, Marco
    Lindbom, Niclas
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Freyss, Michel
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    GGA plus U study of uranium mononitride: A comparison of the U-ramping and occupation matrix schemes and incorporation energies of fission products2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 478, p. 119-124Article in journal (Refereed)
    Abstract [en]

    Uranium mononitride is studied in the DFT + U framework. Its ground state is investigated and a study of the incorporation of diverse fission products in the crystal is conducted. The U-ramping and occupation matrix control (OMC) schemes are used to eliminate metastable states. Beyond a certain amount of introduced correlation, the OMC scheme starts to find a lower total energy. The OMC scheme is chosen for the second part of this study. Furthermore, the influence of the magnetic ordering is studied using the U-ramping method, showing that antiferromagnetic order is the most stable one when the U parameter is larger than 1.75 eV. The effect on the density of states is investigated and elastic constants are provided for comparison with other methods and experiments. The incorporation energies of fission products in different defect configurations are calculated and these energies are corrected to take into account the limited size of the supercell.

  • 46.
    Claisse, Antoine
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    First-principles calculations of (Y, Ti, O) cluster formation in body centred cubic iron-chromium2013In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 303, p. 18-22Article in journal (Refereed)
    Abstract [en]

    In the present work, the ab initio parametrization necessary for a Monte Carlo study of the (Y, Ti, O) clusters in a FeCr matrix is done. The cohesive, binding and migration energies of all the solutes have been calculated in the dilute limit in the framework of density functional theory. The special case of the strong interaction between an Y atom and a vacancy has been considered. In the dilute limit, Cr is transparent with respect to Y, Ti, O or vacancies. On the contrary, Y binds O strongly in 2NN configuration while not in 1NN. Ti binds O in 1NN and 2NN configurations. A vacancy binds strongly with Y and O in 1NN position which is resulting in a low diffusion coefficient for Y. The peculiar case of the binding attraction between two interstitial oxygen atoms has been studied and is believed to be the main reason for the planar (2D) symmetry of the cluster nuclei. A preferential cluster shape is determined for the early nucleation stage, up to 12 atoms.

  • 47.
    Claisse, Antoine
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Schuler, Thomas
    Lopes, Denise Adorno
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Transport properties in dilute UN(X) solid solutions (X = Xe, Kr)2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 17, article id 174302Article in journal (Refereed)
    Abstract [en]

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

  • 48.
    Claisse, Antoine
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Van Uffelen, P.
    Towards the inclusion of open fabrication porosity in a fission gas release model2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 466, p. 351-356Article in journal (Refereed)
    Abstract [en]

    A model is proposed for fission product release in oxide fuels that takes into account the open porosity in a mechanistic manner. Its mathematical framework, assumptions and limitations are presented. It is based on the model for open porosity in the sintering process of crystalline solids. More precisely, a grain is represented by a tetrakaidecahedron and the open porosity is represented by a continuous cylinder along the grain edges. It has been integrated in the TRANSURANUS fuel performance code and applied to the first case of the first FUMEX project as well as to neptunium and americium containing pins irradiated during the SUPERFACT experiment and in the JOYO reactor. The results for LWR and FBR fuels are consistent with the experimental data and the predictions of previous empirical models when the thermal mechanisms are the main drivers of the release, even without using a fitting parameter. They also show a different but somewhat expected behaviour when very high porosity fuels are irradiated at a very low burn-up and at low temperature.

  • 49.
    Claisse, Antoine
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Van-Uffelen, Paul
    Towards the inclusion of open fabrication prosity in a fission gas release modelManuscript (preprint) (Other academic)
  • 50. Costa, D.
    et al.
    Adjanor, G.
    Becquart, C. S.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics. Etude et Modelisation des Microstructures Pour le Vieillissement des Materiaux, France .
    Domain, C.
    Vacancy migration energy dependence on local chemical environment in Fe-Cr alloys: A Density Functional Theory study2014In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 452, no 1-3, p. 425-433Article in journal (Refereed)
    Abstract [en]

    The first step towards the understanding and the modelling of the Fe-Cr alloy kinetic properties consists in estimating the migration energies related to the processes that drive the microstructure evolution. The vacancy's migration barrier is expected to depend on the vacancy-migrating atom pair atomic environment as pointed out by Nguyen-Manh et al. or Bonny et al. In this paper, we address the issue of the dependence on the vacancy's local atomic environment of both the vacancy migration energy and the configurational energy change Delta E that occurs when the vacancy jumps towards one of its nearest neighbour sites. A DFT approach is used to determine the ground state energy associated to a given configuration of the system. The results are interpreted in the light of the chromium-chromium and chromium-vacancy binding energies as well as the substitutional chromium atoms magnetic properties.

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