preview all symposia



Nuclear materials under extreme conditions

The Symposium focuses on new results about fabrication and performance of nuclear materials exposed to extreme conditions and radiation. This includes structural and fuel materials and their waste forms. A great emphasis is put on advanced approaches, such as experimental and computational multi-scale plus new fabrication techniques.


The science and engineering of nuclear materials, and especially radiation induced effects, is an active field of research. Many workshops and conference on the subject are therefore application-oriented with a certain lack in addressing basic principles. The scope of our symposium is to highlight basic theoretical and experimental principles, focusing on the fabrication of nuclear materials and to describe key mechanisms responsible for their aging and degradation under the given exposure. The main goal of the symposium is to review the latest progress and chart future advances in experimental and modelling multi scale approaches to describe the synthetization and the behavior of these solids under extreme environments like irradiation, mechanical/thermomechanical stress, high temperature and/or chemically reactive environment.


The symposium will address topics pertaining to nuclear structural materials and fuels, their fabrication and performance under nuclear reactor conditions, especially advanced systems with more demanding parameters in temperature, radiation dose and corrosion. Moreover, the behavior of the waste forms in the repository or alternatively the reprocessing of fuel will be treated. The addressed theoretical methods span many orders of magnitude from ab-initio up to the mesoscale size. The experimental approaches emphasize the role of advanced techniques, which will allow the understanding of basic processes in synthesis of materials or their degradation mechanisms contributing to the validation of modelling results. As a special form of the connection between experimental and computations methods, machine learning will also be addressed in the symposium.

Hot topics to be covered by the symposium

Targeted materials/components

  • Nuclear structural materials
  • Nuclear fuels
  • Nuclear waste forms

Scientific questions

  • Synthesis of materials
  • Multi scale modelling
  • New experimental device
  • New simulation tools


  • Modelling from Ab-Initio to Mesoscale
  • Advanced characterization techniques
  • New fabrication techniques

Machine learning

Start atSubject View AllNum.Add
Authors : Piotr. M. Kowalski1,2, Steve Lange1,2, Guido Deissmann1,2, Victor. L. Vinograd1,2, Andreas Wilden1,2, Giuseppe Modolo1,2, Mengli Sun1,2, Robert Baker3, Dirk Bosbach1,2
Affiliations : 1Institute of Energy and Climate Research (IEK-6), Forschungszentrum Jülich, Wilhelm-Johnen-Straβe, 52425 Jülich, Germany; 2JARA High-Performance Computing, Schinkelstraβe 2, 52062 Aachen, Germany; 3 School of Chemistry, University of Dublin, Trinity College, College Green, Dublin 2, Ireland;

Resume : A worldwide accepted solution to the HLW (High Level Nuclear Waste) problem is a permanent deep geological disposal of the wastes. We will discuss how the complementary to the experimental effort, atomistic simulations contribute to the scientific basis of safety case of nuclear waste repositories. We will present a few cases of successful synergy of atomistic simulations and experiments applied in order to understand: the uptake/retention of radionuclides by secondary phases and materials present in the engineered barriers of the repository, the separation of radionuclides from HLW streams and the properties of vitrified nuclear wastes. In particular we will discuss: (1) the ability of C-S-H phases in cementitious barrier materials and of studtite/metastudtite secondary phases to uptake radionuclides such as Ra, Sr, Np and Am, obtained through a combination of ab initio calculations and thermodynamic considerations [1,2], (2) the highly selective extraction of Am and Cm by diastereomers of Me-TODGA organic extractant [3] and (3) the potential of atomisitc simulations to investigate the properties of vitrified HLW from spent nuclear fuel reprocessing [4]. [1] Lange, S. et al. Applied Geochemistry, 96, 204 (2018). [2] Biswas et al. In preparation (2019); Vitova, T., et al. Inorg. Chem. 57, 1735 (2018). [3] Wilden, A., Kowalski, P. M. et al. Chemistry- a European Journal 25, 5507 (2019). [4] Zhao et al., Int. J. Appl. Glass Sci. doi:10.1111/ijag.13043 (2018).

Authors : Gabriel L. Murphy1, Evgeny V. Alekseev1, Piotr Kowalski1, Philip Kegler1, Brendan J. Kennedy2, Zhaoming Zhang3, and Helen Maynard-Casely3.
Affiliations : 1 Institute of Energy and Climate Research, Forschungszentrum Jülich GmbH, 52428 Jülich, Germany 2 School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia 3 Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia

Resume : In situ neutron and synchrotron X-ray powder diffraction measurements demonstrate when polymorphs of SrUO4 are exposed to pressures above 500 MPa they undergo anomalous bond expansion of all uranium-oxygen bonds caused by pressure induced electron delocalization associated with charge transfer of U6+ uranyl cation. Supported by ab initio calculations, measurements indicate that the onset of this bond expansion process coincides with a reversible insulator-metallic electronic transition that is without an associated structural transition. This demonstrates, for the first time, the inapplicability of Badgers rule to uranyl bearing nuclear materials and waste forms. Additionally it shows pressure acts towards increasing the reactivity and instability of uranium materials. This has profound consequences for the interpretation and validity of spectroscopic data arising from high pressure studies of uranium materials in addition to predicting and simulating the behavior of uranium materials under pressure. Consequently this new insight allows an improved understanding into the chemical reactivity and structure property relationships that can occur between uranium materials exposed to high pressure environments. Examples of this will be discussed for our ex situ high pressure studies of the Ni-U-O system of oxides, the hexavalent uranium ionic conductor K2UO11-x and the aliovalent substituted (Cr3+,Fe3+,Pt4+)U2O6 solid solution and also other relevant nuclear materials under pressure.

Authors : Martin LEBLANC, Gilles LETURCQ, Eléonore WELCOMME, Xavier DESCHANELS, Thibaud DELAHAYE
Affiliations : CEA, DEN, MAR, DMRC, SFMA, LPCA, F-30207 Bagnols-sur-Cèze Cedex, France; CEA, DEN, MAR, DMRC, SFMA, LPCA, F-30207 Bagnols-sur-Cèze Cedex, France;CEA, DEN, MAR, DMRC, SFMA, LPCA, F-30207 Bagnols-sur-Cèze Cedex, France; Institut de Chimie Séparative de Marcoule, ICSM UMR5257, Centre de Marcoule, F-30207 Bagnols/Cèze, France; CEA, DEN, MAR, DIR, F-30207 Bagnols-sur-Cèze Cedex, France

Resume : Within the U and Pu recycling process from nuclear spent fuels, the conversion of purified U and Pu solution into oxide powder is a key step at the interface between the separation / purification processes and the fabrication of uranium-plutonium oxide fuels called MOx ("Mixed Oxides"). This study deals with the development of a new "direct" conversion route based on advanced thermal denitration to synthetize mixed actinide oxide (U1-xPuxO2±δ). This new synthetize method consists in the gelation of an actinide nitrate solution within a crosslinked polymer, followed by dehydration and calcination under controlled conditions to obtain the targeted mixed actinide oxide. On the basis of 0.5 g batch productions, the feasibility of the synthesis of all the solid solution U1-xPuxO2±δ with x ranging from 0 to 1 was demonstrated without any redox adjustment of the actinide feeding solutions and whatever nitric acidity (up to 7 M) or total actinide concentrations. Moreover, a first scale up was operated on the basis of a 15 g U0.80Pu0.20O2±δ batch, also dedicated to study the pellet fabrication using the powder as synthetized (i.e. without any grinding step). 94% of the theoretical density pellet was obtained with oxygen to metal ratio of 2.00. Therefore, such a conversion route allows fabrication of any kind of MOx fuels (PWR or SFR) offering several advantages: no redox adjustments, no solid/liquid partitioning required and reduction of actinide dissemination risks.

Authors : Evgeny V. Alekseev, Piotr Kowalski, Philip Kegler, Mike Cooper, Thomas E. Albrecht-Schmitt
Affiliations : Institute of Energy and Climate Research (IEK-6) Forschungszentrum Jülich;Institute of Energy and Climate Research (IEK-6) Forschungszentrum Jülich;Institute of Energy and Climate Research (IEK-6) Forschungszentrum Jülich; Los Alamos National Lab; Florida State University

Resume : Uranium is one of the most complex chemical elements showing five oxidation states and very diverse coordination environment in solid state materials. Herein we performed a series of studies of U(VI) reactivity under high-temperature/high-pressure conditions in supercritical water (400-600MPa/650C) and in solid state systems (2-15GPa/800-1500C). This study reveals a significant difference in chemical behavior of uranium(VI) under extreme conditions compared to its properties at standard pressure. We found that under extreme conditions uranium(VI) can be easily reduced to U(V) and stabilized in this, usually unstable, form. The experiments were performed in presence of boron oxide which reacted with uranium in supercritical water but in certain cases was not involved into reactions with uranium (plays a role of flux) in solid state systems. UO3 was directly reduced to a high pressure modification of U2O5 under 10GPa and 1000C. Structure of HP-U2O5 is strongly related to the fluorite–type UO2. Using crystallographic data for HP-U2O5 modification as a reference, we performed a DFT study of phase transition in pentavalent uranium oxide. These data were used for delivery of accurate force field parameters for U(V) in oxygen systems.

Authors : Gordon Thorogood1, Christoph Lenz 1,2, Robert Aughterson1, Daniel Gregg1, Joel Davis1, Greg Lumpkin1 and Mihail Ionescu1
Affiliations : 1 Australian Nuclear Science and Technology Organisation, Sydney, NSW, Australia 2 Institut für Mineralogie und Kristallographie, Universität Wien, Vienna, Austria

Resume : In the case of radiation damage of nuclear materials it can at times be difficult to determine the degree to which and what type of damage has occurred. Part of the reason for this is that the damage event depending on the radiation can be very localised, however the sum of these localised events has a net effect on the bulk properties of the material. The term radiation tolerant is very common in the literature but in fact it’s the materials ability to recover from these events that determines its “tolerance”. In an attempt to determine the amorphous fraction in monazite and xenotime on a micrometer scale we have combined laser-induced photoluminescence (PL) of Nd3+ with surface-sensitive grazing-incidence X-ray diffraction (GIXRD). Poly-crystalline, cold-pressed, sintered LaPO4, and YPO4 ceramics were exposed to quadruple Au-ion irradiation with ion energies 35 MeV (50% of the respective total fluence), 22 MeV (21%), 14 MeV (16%), and 7 MeV (13%). Ion-irradiation resulted in amorphization and damage accumulation to a depth of ∼5μm below the irradiated surfaces. The amorphous fraction was quantified by GIXRD and PL using confocal spectrometers with spatial resolution in the μm range. Transmission electron microscopy of lamella cut from irradiated surfaces with the focused-ion beam technique confirmed damage depth-profiles with those obtained from PL hyperspectral mapping. The degree to which we have been successful will be given in this presentation.

Authors : Karin Popa, Olaf Walter
Affiliations : European Commission, Joint Research Centre, P.O. Box 2340, D-76125 Karlsruhe, Germany

Resume : In 2016, we have proposed for the first time the hydrothermal decomposition of tetravalent actinides oxalates as a straightforward method to produce reactive actinide oxide nanocrystals [1]. The method could be easily applied at very low temperature (95-250 °C) in order to generate nanocrystalline AnO2 (An= Th, U, Np and Pu) or different solid solutions. With respect to other thermal methods employing organic solvents, the hydrothermal decomposition of oxalates presents the advantage that the material obtained is free of any residual carbon impurities possibly blocking the nanocrystals surface [2]. Reproducible synthesis of a full series of (U,Th)O2 solid solutions and extended mechanical characterization of spark plasma sintered pellets have been also reported [3]. We present here the first results on the production of several nano-sized (U,Pu)O2 and we discuss the oxidation state of the actinides. [1] O. Walter, K. Popa, O. Dieste Blanco, "Hydrothermal decomposition of the actinide(IV) oxalates: a new aqueous route towards reactive actinide oxides nanocrystals", Open Chem. 14 (2016) 170-174 [2] K. Popa, O. Walter, O. Dieste Blanco, A. Guiot, D. Bouëxière, J.-Y. Colle, L. Martel, M. Naji, D. Manara, "A low-temperature synthesis method for AnO2 nanocrystals (An = Th, U, Np, and Pu) and associate solid solutions", CrystEngComm. 20 (2018) 6414-6422 [3] L. Balice, D. Bouëxière, M. Cologna, A. Cambriani, J.-F. Vigier, E. De Bona, D.G. Sorarù, C. Kübel, O. Walter, K. Popa, "Nano and micro U1-xThxO2 solid solutions: from powders to pellets", J. Nucl. Mater. 498 (2018) 307-313

Authors : P. Warnicke1, A. Cavaliere1, A. De Luca2, C. Leinenbach2, and M. Pouchon1
Affiliations : 1. Paul Scherrer Institut, 5232 Villigen, Switzerland 2. EMPA, Swiss Federal Laboratories for Materials Science and Technology, 8600 Duebendorf, Switzerland

Resume : Oxide dispersion strengthened (ODS) steels are considered promising materials for high-temperature applications (e.g. jet turbines and advanced nuclear reactors) owing to their ability to withstand degradation caused by irradiation, corrosion, or high-temperature creep. Although the production of ODS steel is well established through conventional powder metallurgy route, the difficulty of (i) maintaining uniform properties throughout the material combined with the (ii) complexity and (iii) the high cost of fabrication are major known problems. Additive manufacturing offers a way to resolve the problems mentioned above. Here, powder specimens were produced by mechanically alloying base powder consisting of Fe-9Cr steel with 0.5% yttrium oxide. The physical properties of the powder such as particle morphology, size distribution, and spreading performance were pre-characterized followed by fabrication of 5 mm thick ODS steel specimens in a layer-by-layer growth using selective laser melting (SLM). By varying the laser power and scanning speed, we obtained specimens that exhibit densities close to nominal values (i.e. densities differ less than 0.1% from the theoretical density). Thin film specimens for synchrotron X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) measurements have been prepared using electro-polishing. Electron microscopy observations of the specimens reveal oxide dispersoids formed in the steel matrix with sizes down to sub-10 nm range. Understanding the influence of processing parameters on final dispersoid size and shape in ODS steel produced via additive manufacturing is essential for further development of this material class.

Authors : Manuel A. Pouchon
Affiliations : Laboratory for Nuclear Materials, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland

Resume : In the past internal gelation has proven to be one of the most promising production methods for the production of transmutation targets, containing an important fraction of minor actinides. Compared to the classical powder base pellet production, the aqueous gelation can efficiently be integrated into a shielded, remotely handled environment, where the generation and accumulation of dust has to be strictly limited, and where the maintenance of mechanical equipment would be more challenging. The gelation based production of particle fuel was subject of numerous programs internationally, including irradiation programs and post irradiation experiments of such fuels. At PSI a new program has been launched to extend the gelation technique to additive manufacturing. The idea is to use the gelation technique to produce the printing material online with a variable composition, allowing not only the production of 3D shaped bodies, but also the introduction of regions with tailored properties or content. This way complex fuel bodies can be produced, allowing enhanced safety features and bearing other advantages. In the present paper some concepts will be introduced, demonstrating some of these advantages using fem based simulation methods.

Start atSubject View AllNum.Add
Authors : Laurent Marot, Lucas Moser, Kunal Soni, Roland Steiner, Ernst Meyer
Affiliations : Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland

Resume : First Mirrors (FMs) will play a crucial role in optical diagnostic systems of future fusion devices like the International Thermonuclear Experimental Reactor (ITER). Unlike to- day’s tokamaks, forthcoming reactors are expected to produce a high level of radiations and neutrons, preventing the use of common optical components (windows, fibers). Instead, an alternative solution based on an optical labyrinth embedded in the neutron shielding and employing metallic mirrors was proposed. Being the first element of the optical path which allows light to cross the neutron shielding, FMs will be placed close to the thermonuclear plasma and will, therefore, be subject to intense thermal and radiations loads, bombardment by plasma particles (mainly charge-exchange neutrals, CXNs) and deposition of material eroded from the plasma-facing components. The choice of the FM materials and the physical structure will be developed in details including several tests under plasma exposure and tokamaks. Net deposition of particles eroded from the First Wall (FW), i.e. mainly beryllium (Be) and tungsten (W), can degrade the reflectivity of FMs severely compromising the reliability of the optical diagnostics. Although passive mitigation techniques are predicted to reduce the amount of Be and W on FMs, optical degradation cannot be fully suppressed; in situ mirror cleaning techniques are indispensable and proposed techniques will be presented.

Authors : X. Deschanels, Y. Lou, S. Dourdain, C. Rey
Affiliations : Institut de Chimie Séparative de Marcoule, CEA/CNRS/UM/ENSCM, 30207 Bagnols-sur–Cèze (France)

Resume : Because of their high surface/volume ratio which may allowed self-healing processes, mesoporous materials could be tolerant materials to radiation damage defects [1]. To investigate this topic, mesoporous and nonporous sol-gel silica thin films (e~100 nm) deposited on Si substrates [2] were irradiated with gold ions of medium energies from 0.5 MeV to 12 MeV. X-ray reflectivity measurement and SEM observations were used to monitor the porous network of the thin films. Infrared measurement was used to characterize the silica network. These characterizations show an evolution of the porous network of the materials depending on the irradiation conditions (fluence, energy of ions) and the initial parameters of the porous network (pore size, porous volume). A total compaction is achieved for a fluence of about 2×1014 cm-2 (~5×1021 (figure 1)[3]. The process of mesoporosity collapse seems different according to the irradiation regime (nuclear versus electronic). The sol-gel mesoporous and nonporous samples exhibit a delayed radiation damage compared to material elaborate by classical route, which indicates that sol-gel materials are more radiation tolerant from this point of view. The presentation aims to discuss these different observations, and clarified the role of the interfacial surface on the healing of the defects created by irradiation. From another point of view, the sensitivity of these mesoporous structures to the radiation damage opens interesting prospects for obtaining self-conditioning materials.

Authors : Yong Dai
Affiliations : Paul Scherrer Institute, 5232 Villigen PSI, Switzerland

Resume : Helium (He) and hydrogen (H) are two most important transmutation products in structural materials applied in fusion and accelerator driven systems. In a fusion reactor, the first wall blankets are exposed to 14 MeV neutron irradiation, which produces He and H at about 11 appm He/dpa and 40 appm H/dpa. In accelerator driven systems (ADS) the high energy protons produce He and H at much higher rates, up to about 200 appm He/dpa and 1000 appm H/dpa in components like proton beam windows. Since it is known that He or H may induce strong embrittlement effect in many structural materials, the He and H effects are of great concern for the safe operation of fusion and ADS facilities. In the last two decades, various structural materials were irradiated in the targets of the Swiss spallation source (SINQ) within the STIP irradiation program. Of the particular interest to developing high power spallation sources for both neutron science and ADS applications, austenitic steels, tempered martensitic steels, Ni- and Al-based alloys have been extensively investigated. Post-irradiation examinations (PIE) include mechanical testing using tensile, bend, impact etc techniques and microstructural analysis employing transmission electron microscopy (TEM), positron annihilation spectroscopy (PAS) and atom probe tomography (ATP). The specimens used for the PIE are with irradiation dose up to about 20 dpa and helium concentration of about 1800 appm, irradiated in a temperature range of 60 – 500°C. The hydrogen content is hardly to determine, due to its high mobility in materials, especially at relatively higher temperatures. The results of mechanical tests demonstrate pronounced embrittlement effect when the He concentration is above about 500 appm. Meanwhile, additional hardening effect is also observed, which can be attributed to high-density He bubbles of 1-2 nm in diameter. In this presentation, the STIP irradiation program will be briefly introduced. The results of austenitic steels, tempered martensitic steels and ODS steels irradiated in SINQ targets will be shown and compared with those obtained from irradiations in fission reactors. The He and H effects on these materials will be discussed.

Authors : A. M. Rostas (1), D. Craciun (2), S. Irimiciuc (2), B. Hodoroaba(2, 3), G. Dorcioman (2), I. Anghel (2), P. Garoi (2), O. Uteza (4) and V. Craciun (2, 5)
Affiliations : 2 National Institute for Laser, Plasma, and Radiation Physics, Bucharest-Magurele, Romania 1 National Institute for Materials Physics, Magurele, Romania 3 Physics Faculty, University of Bucharest, Magurele, Romania 4 Laboratoire LP3, Universite de Marseille, Campus de Luminy, Marseille, France 5 Extreme Light Infrastructure for Nuclear Physics, Bucharest-Magurele, Romania

Resume : Ultra-high power fs-laser opened new areas of physics and technology of laser-matter interaction under extreme conditions. There are already several operational 1 to 10 PW-level laser installations in Europe and worldwide, while even higher power installations, up to 100 PW are being planned. Experiments with these high power fs-laser beams require high-quality mirrors, which are using either dielectric layers/multilayers or metallic layers that have single pulse laser-induced damage thresholds from 0.1 up to 2 J/cm2 for 25 fs long laser pulses. However, multiple pulse laser-induced damage thresholds are getting lower with the increase of the number of pulses due to a process known as laser incubation. The actual physics of this incubation process is still a matter of investigation. We used the EPR technique to investigate the changes induced by fs-laser irradiation on HfO2 thin films at fluences below the laser-induced damage threshold. The HfO2 films were deposited by the pulsed laser deposition technique (PLD) using an ArF excimer laser. The fs-laser irradiations were performed with the aid of two laser installations. One installation emits 400 fs pulses at kHz repetition rates, while the other one emits 25 fs pulses at a repetition rate of 100 Hz. The EPR investigations showed that after fs-laser irradiation an increase of the signal with respect to the as-deposited value was observed, indicating a higher concentration of defects in the substrate. The increase of the signal was correlated with a similar increase in the leakage current values measured through these films.

Authors : C. Martin, I. Sydoryk, K.H. Miller, R.M. Martin
Affiliations : Ramapo College of New Jersey, Mahwah, New Jersey 07430, USA; Ramapo College of New Jersey, Mahwah, New Jersey 07430, USA; NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA; Montclair State University, Montclair, NJ 07043

Resume : Ceramic Compounds such as nitrides and carbides of transition metals (ZrN, ZrC, TiC, or TiN) are of increasing interest nowadays for various technological applications, aiming to their high hardness, high wear resistance, high melting temperature, and high electrical and thermal conductivities. The latest potential applications include space technology, nuclear barrier coatings in nuclear reactors, and materials for plasmonic devices. In this talk, we present measurements of broadband optical reflectance (20 meV to 6 eV) on argon and gold-ion irradiated ceramic thin films, obtained by Pulsed Laser Deposition. We show that at fluences in the range of 1E14 - 2E15 cmE-2, both Ar and Au-ion irradiations have a significant effect on far and mid-infrared reflectance, which is dominated by the free (Drude) carriers response. Low fluence irradiation enhances the Drude conductivity by reducing the scattering rate. Additionally, Au-ion irradiation increases the carrier concentration, therefore acting as a charge dopant. We further show that the effect of irradiation is to enhance the plasmonic performances of these ceramics, especially in the visible and near-infrared ranges.

Authors : P. Garcia,D Simeone
Affiliations : CEA, DEN, DEC, Centre de Cadarache, 13108, Saint-Paul-Lez-Durance Cedex CEA/DEN/DMN/SRMA/LA2M-LRC CARMEN, CEA, Universit\'e Paris-Saclay, F-91191, Gif-sur-Yvette, France \& CNRS/CentraleSupelec/UMR 8085, Grande voie des vignes, Chatenay Malabry France

Resume : The phase separation observed at low temperature (below \textit{circa} 600~K) in the U_{1-y}Ce_{y}O_{2-x} system and for values of y between roughly 0.34 an 0.5, purportedly involves fluorite structures only. However, for y values above 0.5, an oxygen deficient C-type bixbyite is also reported. In this work, the phase separation in U_{0.54}Ce_{0.46}O_{2-x} has been reexamined using x-ray and neutron diffraction. Below a critical temperature, the existence of two fluorite related structures in the miscibility gap is confirmed: a stoichiometric U_{0.54}Ce_{0.46}O_{2} phase and an oxygen-deficient U_{0.54}Ce_{0.46}O_{2-x} phase. Although the former is indeed a fluorite, we show that the other end-member phase has a C-type bixbyite structure. This would suggest that the oxygen deficient phase can be described as a bixbyite over the entire cerium composition range.

Authors : G. Kuri, M. Martin, J. Bertsch
Affiliations : Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland

Resume : Measurement of structural properties of UO2 fuels is a key component in understanding and for the modeling of the performance and safety of nuclear fuels in the reactor. The steep temperature distribution and the concomitant intense radiation field during fuel burnup affect and alter the crystallographic UO2 lattice structure in the irradiated matrix. This study examines the effect of neutron irradiation on the distortion of UO2 crystal lattice structure in high burnup spent fuel material having an average burnup of 62 MWd/kgU in the pellet. Experiments have been carried out using synchrotron radiation microbeam X-ray diffraction (XRD) technique at the Swiss Light Source, Paul Scherrer Institute, Switzerland. Microbeam XRD data of Bragg peaks originating from different (hkl) planes have been analyzed. Structural analysis with XRD indicates that the lattice constant and unit cell volume of UO2 in spent fuel have increased, and the measured lattice strain in the irradiated matrix is considerably higher when compared to the predictive critical strain value of UO2 ploygonization. These results can reasonably be ascribed to the fission products dissolution and accumulated radiation-induced defects, which modify the UO2 crystallites in the irradiated matrix. The experimental method adopted here also allows investigation of UO2 crystal properties and possible dimensional changes within a single grain in the irradiated matrix, necessary to understand better the initiation of UO2 grains (sub)division, origin of high burnup structure and fuel restructuring at extended burnup. All these results will be presented and discussed.

Authors : Rajchawit Sarochawikasit1, Rachanon Thongprong2, and Sutatch Ratanaphan2,3*
Affiliations : 1Department of Computer Engineering, King Mongkut’s University of Technology Thonburi, 126 Pracha Uthit Rd, Thung Khru, Bangkok 10140, Thailand. 2Nanoscience and Nanotechnology Graduate Research Program, King Mongkut’s University of Technology Thonburi, 126 Pracha Uthit Rd, Thung Khru, Bangkok 10140, Thailand. 3Department of Tool and Materials Engineering, King Mongkut’s University of Technology Thonburi, 126 Pracha Uthit Rd, Thung Khru, Bangkok 10140, Thailand

Resume : Grain boundary energies in austenitic twinning-induced plasticity (TWIP) steel, computed using the meta-atom embedded atom method (EAM) potential, are compared with experimental boundary energies in a high-manganese TWIP steel [H. Beladi, N. T. Nuhfer, and G. S. Rohrer, Acta Materialia (2014) 70: 281–289]. We found that there is a strong correlation between the experimental and simulated boundary energies for the most frequently observed boundaries, while the experimental energies of less observed boundaries are not correlated with the simulated energies [S. Ratanaphan, R. Sarochawikasit, N. Kumanuvong, S. Hayakawa, H. Beladi, G. S. Rohrer, and Taira Okita, J Mater Sci (2019) 54:5570–5583]. We also observed that the simulated grain boundary energies and the measured grain boundary population in the high-manganese TWIP steel are inversely correlated when groups of boundaries with fixed misorientations are compared. Because, these inverse relationships are consistent with our recent study in the high purity polycrystalline copper [S. Ratanaphan, D. Raabe, R. Sarochawikasit, D. L. Olmsted, G. S. Rohrer, and K. N. Tu, J Mater Sci (2017) 52:4070–4085], it might be possible to obtain a larger set of grain boundary energies in the TWIP steel by using the Bulatov-Reed-Kumar (BRK) grain boundary energy function for face-centered cubic (fcc) metals [V.V. Bulatov et al. Acta Materialia (2014) 65:161–175]. It should be noted that these interpolated grain boundary energies were consistent with the simulated energies and also inversely correlated to the measured grain boundary populations. Regardless of compositional complexity in the TWIP steel composed of multiple elements, this work shows that the shapes of the grain boundary energy distributions in the austenitic alloy and pure fcc metals are similar. The results in the current study could impact to the field of Grain Boundary Engineering (GBE) in the complex alloys and the application of GBE to the high entropy alloys.

Authors : Mark Fedorov, Jan Wróbel, Antonio Fernández-Caballero, Kamil Czelej, Krzysztof Kurzydłowski, Duc Nguyen-Manh
Affiliations : Faculty of Materials Science and Engineering, Warsaw University of Technology, ul. Woloska 141, 02-507 Warsaw, Poland; Faculty of Materials Science and Engineering, Warsaw University of Technology, ul. Woloska 141, 02-507 Warsaw, Poland; EPSRC Centre for Doctoral Training in Materials for Demanding Environments, Faculty of Science and Engineering, University of Manchester, M13 9PL Manchester, United Kingdom; Faculty of Materials Science and Engineering, Warsaw University of Technology, ul. Woloska 141, 02-507 Warsaw, Poland; Faculty of Mechanical Engineering, Bialystok University of Technology, ul. Wiejska 45C, 15-351 Bialystok, Poland; CCFE, United Kingdom Atomic Energy Authority, Abingdon, OX14~3DB, United Kingdom

Resume : Understanding the phase stability of alloys with multiple principal elements under irradiation is one of the great challenges in the developing of materials for engineering components such as the plasma-facing materials for fusion reactors. Recently, it was shown that high entropy alloys (HEAs) based on Fe-Cr-Ni-Mn have better radiation resistance in a comparison with austenitic steels. The investigation of phase stability and magnetic properties of quaternary Fe-Cr-Mn-Ni alloys using a combination of density functional theory (DFT), cluster expansion method and Monte Carlo (MC) simulations has shown that the addition of Mn to Fe-Cr-Ni alloys decreases the effect of magnetic moment changing with the volume. This fact supports the experimental results of reduced swelling. The point defect properties of Fe-Cr-Mn-Ni were studied as a function of local environment of a defect and chemical short-range ordering of alloy. The representative structures of HEA have been obtained using DFT-based MC simulations. Vacancy formation energies and migration barriers have been calculated for each element, including varying next-nearest neighborhood in the disordered alloys. The dependence of migration properties on the chemical composition and short-range ordering is analyzed and presented.

Authors : D. Sobieraj, O. El-Atwani, N. Li, M. Li, A. Devaraj, J. K. S. Baldwin, M. M. Schneider, S. A. Maloy, E. Martinez, J.S. Wróbel, T. Rygier, G. Cieślak, K.J. Kurzydłowski, D. Nguyen-Manh
Affiliations : Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warsaw, Poland CCFE, United Kingdom Atomic Energy Authority, Abingdon OX14 3DB, UK; Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, USA. ; Center for Integrated Nanotechnologies, MPA-CINT, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.; Division of Nuclear Engineering, Argonne National Laboratory, Argonne, IL, USA. ; Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, USA. ; Center for Integrated Nanotechnologies, MPA-CINT, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.; Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, USA. ; Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, USA. ; Theoretical Division, T-1, Los Alamos National Laboratory, Los Alamos, NM, USA.; Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warsaw, Poland; Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warsaw, Poland; Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warsaw, Poland; Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warsaw, Poland; 2CCFE, United Kingdom Atomic Energy Authority, Abingdon OX14 3DB, UK;

Resume : Recently, multi-component alloys containing four or more elements in equal or near-equal atomic compositions or so-called High-Entropy Alloys (HEAs) have attracted great interest in high-temperature materials applications due to the presence of significantly larger configurational entropy contributions to alloy free energies. Understanding the phase stability under irradiation of alloys with multiple principal elements is one of the great challenges in developing materials components for nuclear reactors. A body-centered cubic (bcc) quaternary W-Ta-Cr-V refractory high entropy alloy with outstanding radiation resistance has been developed as a thin film using magnetron sputtering deposition and no sign of irradiation-created dislocation loops, even after 8 dpa, was observed. The ab-initio based Cluster Expansion (CE) model developed for quinary Cr-Ta-Ti-V-W system in combination with Monte Carlo (MC) simulations has been used to explain the formation of Cr- and V-rich second-phase particles observed using TEM, APT and XRD in the irradiated W38Ta36Cr15V11 alloy. Moreover, the Density-Functional Theory (DFT)-based MC simulations enabled to investigate systematically the dependence of phase stability and short-range order of HEAs as a function of composition. Experimental characterization using light microscopy, SEM, EDS and XRD on arc-melted and annealed samples has been performed to validate the modelling results from the DFT-based MC simulations.

Authors : Bianca Cristiana Hodoroaba (1,2), Stefan Andrei Irimiciuc (1), Andrei Stancalie (1), Emanuel Axente (1), Doina Craciun (1), Petronela Garoi (1), Dan Cristea (3), Victor Geanta (4), Ionelia Voiculescu (4), Valentin Craciun (1)
Affiliations : 1National Institute for Laser, Plasma and Radiation Physics – NILPRP, 409 Atomistilor Street, Bucharest, Romania 2University of Bucharest, Faculty of Physics, Bucharest-Magurele, Romania 3Materials Science Department Transilvania University, Brasov, Romania 4Polytechnic University of Bucharest, Bucharest, Romania

Resume : Laser induced breakdown spectroscopy (LIBS) technique has got a lot of attention in the last years as a useful tool for elemental analysis of various compounds. The flexibility of the technique makes it perfect for the analysis of multi-element compounds like high entropy alloys (HEAs). HEAs are defined as metallic alloys containing 4 or 5 elements which lead to physical properties superior to classical alloys, such as higher degree of fracture resistance, tensile strength, as well as corrosion and oxidation resistance, which are essential for applications in nuclear industry. In this study we investigated the elemental composition of a series of 6 HEAs using advanced surface investigations techniques like SEM, EDS and LIBS in order to understand the elemental distribution in both surface and volume of targets and deposited thin films. The surface mapping was performed by implementing LIBS technique (10Hz, 10ns, 5J/cm2, 1024 nm) on a relative wide area (20 mm x 20 mm) with the subsequent EDS and SEM analysis performed in the ablated crater area for an accurate comparison and a better elemental identification. Quantitative investigations were performed regarding the plasma excitation temperature and electron density. The local heterogeneity of the irradiated spot was corelated with the values of these plasma parameters. Finally, thin films were deposited using pulsed laser deposition technique on a wide range of experimental conditions (various fluences, background pressures, repetition rates). Correct stoichiometry transfer was attempted as well as tailored changes in stoichiometry for the improvement of the thin film physical properties.

Authors : Lijuan Cui1*, Yong Dai1, Stephan Gerstl2, Manuel Pouchon1, Xing Huang2, Willinger M. Georg2, Robin Schäublin2,
Affiliations : 1 Laboratory for Nuclear Materials, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland 2 Scientific Center for Optical and Electron Microscopy, ETH Zurich, 8093 Zurich, Switzerland

Resume : Reduced activation ferritic/martensitic (RAFM) steels are key materials studied in the fusion and Generation-IV reactor materials programs. In the last two decades, extensive mechanical testing and electron microscopy investigation were carried out to reveal the changes in mechanical properties and microstructure of these steels. In order to get a better understanding of the irradiation-induced microstructural and chemical evolutions, a comprehensive study has been performed on F82H, Eurofer 97 irradiated at doses up to 20 dpa by combining Atom Probe Tomography (APT) and Transmission Electron Microscopy (TEM) techniques. The main subjects include: 1) radiation-induced segregation (RIS) at grain-boundaries (GBs) and interfaces of large carbides, 2) radiation-induced precipitate formation and evolution. The segregation behaviors of all the detectable solute elements of the steels (Cr, W, Mn, C, V, Si, Ni, Ta, P, B) and the transmutants of spallation reaction (Ti, Sc, Ca, K) at both GBs and precipitate-matrix interfaces have been studied. It was observed that some elements (e.g. Cr, Si) enriched, while some other elements (e.g. V, W) depleted at GBs after irradiation. Some differences between low-angle and high-angle GBs could be figured out. For most of solute elements, RIS is more evident at high-angle GBs. Irradiation induced precipitate evolution includes the formation of new precipitates and the dissolution of pre-exist precipitates. It was found that the irradiation changed the composition of the outer edge of pre-exist carbides (M23C6 and MX), e.g. C, Cr, W and V diffused from the M23C6 precipitate into matrix, W, V and Ta depleted in the phase boundaries. Although ’ phase was not detected, Cr-rich clusters, together with enrichment of some other elements (e.g. Si, Mn), were observed after irradiation.

Authors : Darío Fernández-Pello, María Ángeles Cerdeira, Roberto Iglesias
Affiliations : Department of Physics, University of Oviedo, Federico García Lorca 18, Oviedo, E-33007, Spain

Resume : The passage of ionising radiation through structural materials, depositing energies in the keV to MeV regime, has been under scrutiny for decades [1, 2]. Specifically, the characterisation by means of multiscale modelling techniques of the Nuclear and Electronic Stopping Powers in response to irradiation of advanced nuclear materials [3] traditionally described via Monte Carlo [4] methods, not designed to deal with electron dynamics, has become a hot research topic. A multiscale modelling methodology based on state-of-the art DFT simulations (hybrid formalisms, perturbation theory, time-dependent DFT) in combination with Ab Initio MD and Ehrenfest dynamics techniques to tackle intense electronic excitation effects in nuclear materials is presented. An operational interconnection among these modelling strategies relies undisputedly on the development of transferable interatomic potentials. Machine learning approaches as GAP [5], SNAP [6] or Atomicrex [7], among others, may be used for that purpose. The main advantages lie on DFT-like accuracy of MD results at a low computational cost. The present approach has been checked against the behavior of light H and He impurities following the passage of an ionising particle through the archetypical plasma facing material W metallic matrix. [1] P. Sigmund, Particle penetration and radiation effects, Springer, Volumes I (2006) and II (2014). [2] K. Nordlund et al., J. Nucl. Mater. 512 (2018) 450. [3] A. Correa, Comp. Mater. Sci. 150 (2018) 291. [4] J. F. Ziegler, M. D. Ziegler, J. P. Biersack, Nucl. Instr. Meth. Phys. Res. B 268 (2010) 1818. [5] W. J. Szlachta, A. P. Bartók, G. Csányi, Phys. Rev. B 90 (2014) 104108. [6] A. P. Thompson, L. P. Swiler, C. R. Trott, S. M. Foiles, G. J. Tucker, J. Comp. Phys. 285 (2015) 316. [7] A. Stukowski, E. Fransson, M. Mock, P. Erhart, Modelling Simul. Mater. Sci. Eng. 25 (2017) 055003.

Authors : A. Platonenko, D. Gryaznov, A. I. Popov, E. K. Kotomin
Affiliations : Institute of Solid State Physics, University of Latvia, Kengaraga st. 8, LV1063, Riga, Latvia

Resume : Spinel-structured magnesium aluminate (MgAl2O4) possesses high transparency from visible to infrared wavelength range, enhanced strength and melting temperature, as well as excellent chemical and radiation resistance. Combination of these properties makes magnesium aluminate suitable for a number of technological applications, including involvement in construction of fusion and fission reactors inert matrices for nuclear fuels, radiofrequency windows for fusion reactors, where spinel exhibits a very high tolerance to irradiation with fast neutrons due to efficient recombination of primary Frenkel defects – vacancies and interstitials (i–V pairs). Here we analyze by means of ab initio calculations stability and properties of all types vacancies and antisite defects in various charge states for better understanding of annealing processes. Using LCAO approach and hybrid B3LYP functional as implemented in the CRYSTAL17 [1] computer code structural and optical properties are evaluated for each defect, suggesting possible defect-specific "fingerprints" for EPR and vibrational spectroscopy. For example, we calculated the Al or Mg vacancy and Mg antisite with simultaneous hole defect localization on oxygen in accordance with the EPR measurements [2]. Analysis of structural changes and calculated density of states revealed a correspondence between our calculation results and EPR results. In addition, we were able to compare model Hamiltonian parameters found in present ab initio calculations and experiments model. [1] [2] Lushchik, A., S. Dolgov, E. Feldbach, R. Pareja, A. I. Popov, E. Shablonin, and V. Seeman. Nucl. Instrum. Methods Phys. Res 435 (2018) 31-37

Authors : Marcin Roland Zemła(1), Jan S. Wróbel(1), Duc Nguyen-Manh(2), Chu-Chun Fu(3), Frederic Soisson(3), Tomasz Wejrzawnoski(1)
Affiliations : (1)Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warsaw, Poland; (2)CCFE, United Kingdom Atomic Energy Authority, Abingdon OX14 3DB, UK; (3)DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France

Resume : Fe-Cr based alloys are promising structural materials for components in fusion power plants. One of the main issues of using these alloys is related to the embrittlement by He produced under neutron irradiation. He atoms have low solubility in metals and tend to segregate in defects such as vacancies or grain boundaries (GBs) where He can form bubbles. Cr atoms may also segregate to GBs. Moreover, GBs have considerable influence on mechanical properties. Therefore, the segregation of Cr and He to GBs is an important effect for understanding properly the performance of ferritic steels based on the Fe-Cr alloys. Currently we investigated the segregation of Cr and He atoms at Fe-Cr tilt GBs, namely Σ3 and Σ5. Density functional theory (DFT) calculations of systems with GBs were performed to study Cr and He segregation energies and their impact onto GBs cohesion. Moreover, the formation energies of point defects were studied as a function of distance from the GB’s plane. The NEB method was applied to determine the migration barriers of Fe, Cr, He. The established database was used to parameterize the Atomistic Kinetic Monte Carlo (AKMC) model that allowed to obtain Langmuir-McLean segregation isotherms. Those simulations enabled to analyse the relations between global chemical composition and temperature with segregation processes (depletion or enrichment of element at GBs) for different types of GBs. DFT calculations of bulk systems combined with the Cluster Expansion method were applied to study the interactions between atoms and vacancies. The obtained effective cluster interaction will be used in the future in the AKMC model to investigate the segregation to different GBs in Fe-Cr-He alloys as a function of temperature and Cr, He concentrations

Affiliations : Max Planck Institute for Solid State Research, Stuttgart, Germany; Institute of Solid State Physics, University of Latvia, Riga, Latvia

Resume : The color F centers (electron trapped in the halide vacancy) are very common defects in alkali halides, identified by means of the ESR and optical absorption/luminescence. In particular, their properties in fluorites (CaF2, SrF2 and BaF2) are very well studied and understood in detail. However, the manifestation of similar defects in binary oxides with fluorite structure (CeO2 or UO2) is debated for a long time. Recently, we successfully applied the Mollwo-Ivey rule (correlation between lattice constant and optical absorption energy) to explain similarity of optical properties of the F-type centers in alkali halides, alkaline earth oxides and sulfides with NaCl lattice structure [1]. In this study, we have performed a similar comparative analysis of the F-type centers in alkaline earth halides and oxides with fluorite structure supported by detailed analysis of the literature. Special attention is paid to oxygen vacancies in partly covalent CeO2. Obtained results and conclusions are supported by the first principles calculations of the atomic and electronic structure of defective ceria [2]. [1]. A.I. Popov, E.A. Kotomin, J. Maier, Nucl.Inst.Meth. B 268 (2010) 3084-3089. [2] R.A. Evarestov, E.A. Kotomin, J.Maier et al, Phys Chem Chem Phys 19 (2017) 8340

Authors : Jung-Hwan Park, Yang-Il Jung, Dong-Jung Park, Hyun-Gil Kim, Byoung-kwon Choi, Young-Ho Lee
Affiliations : Korea Atomic Energy Research Institute

Resume : In the past decades, zirconium alloys have been widely used as fuel cladding materials because of their low thermal neutron absorption cross-section, excellent mechanical properties, and good corrosion resistance under normal pressure water reactor (PWR) operating condition. However, zirconium alloys have weak oxidation resistance especially at elevated temperature, because they react with water, releasing a large amount of hydrogen gas and heat above 1473 K. After the Fukushima Daiichi nuclear accident, the major issue of nuclear researchers has been an improvement in the oxidation resistance under beyond-design accident conditions. Therefore, accident tolerant fuel (ATF) has been widely studied, which has high-temperature oxidation resistance. Coating technology is an effective way to protect fuel claddings from steam oxidation. Several surface coating technologies have been applied to deposit coatings on zirconium alloys, including physical vapor deposition, chemical vapor deposition, and spray coatings. Among coating methods, PVD is one of the promising coating methods, and it is widely used in the fields of oxidation protection. Moreover, Preparation of chromium alloy coatings, known for their high hardness, excellent corrosion, and wear resistance, by PVD is well established for corrosion resistance. In this work, we deposited chromium alloy coatings on Zircaloy-4 tubes by cathodic arc ion plating, and r.f. sputtering to study the effect of PVD deposition technologies on corrosion, adhesion, and residual stress.

Authors : Kyuhong Lee, Sunghwan Kim, Wonjae So, Ki Nam Kim, Yong Jin Jeong, Jong Man Park
Affiliations : Korea Atomic Energy Research Institute

Resume : Research reactor fuels are fabricated as rod-type or plate-type dispersed fuels by mixing the uranium powder into the metallic matrix powder which has high thermal conductivity for the efficient discharge of heat by fission. The dispersion fuel fabrication processes are carried out in the order of powder preparation, powder mixing, compaction, extrusion or rolling. Due to the nature of powder mixing process, partial heterogeneous mixing such as segregation is likely to occur. As a result, the homogeneity of uranium in the dispersion fuel is lowered and the irradiation stability of the fuel can be impaired. In this study, aluminum matrix was coated on the each fuel powder instead of powder mixing to improve the uranium homogeneity in the fuel. The aluminum coating was deposited to uniform thickness throughout the powder surface, and the coating thickness was controlled according to the PVD process parameters. Because the uranium loading in the fuel is determined by the thickness of the matrix coating and the size distribution of the fuel powder, correlation equation was derived.

Authors : Mihail LUNGU 1, Cosmin DOBREA 1, 2 and Ion TISEANU 1.
Affiliations : 1. National Institute for Laser, Plasma and Radiation Physics, Bucharest, Romania; 2. Technical University of Cluj-Napoca, Faculty of Science and Material Engineering, Cluj-Napoca, Romania;

Resume : Development of erosion-resistant functional materials applicable as plasma facing first wall components is crucial to guarantee a reasonable lifetime for future fusion reactors. In the frame of the qualification activities on the ITER like divertor plasma-facing components [1], X-ray imaging (microtomography / laminography – μXCT/L) and microbeam fluorescence (μXRF) were developed for microstructural analysis of tungsten coated carbon substrate materials and of smart marker lamellae that are fabricated in multilayer configuration of high Z materials. Appling μXCL, planar objects were visualized by increasing the quality of the grey level histogram based on the X-ray interaction with the W coating [2]. Thus, high resolution (~2 μm in lateral and ~5 μm in depth) stack of images of W coated CFC samples were collected. As expected, the W layers spatially correlate with the 3D morphology of the carbon-based composite substrate, which is isotropically resolved by μXCT at maximum space resolution of the W coated layer. The μXCL analysis is reinforced with additional information on W layer thickness as determined via an ad-hoc K-line XRF method intended to overcome the thickness saturation threshold. Smart marker lamellae that are fabricated in multilayer configuration of high Z materials (W and Mo layers on bulk W) are good functional simulator of the current ITER full-tungsten divertor design. Our solution for erosion analysis consists of high-resolution thickness and composition mapping by μXRF. Customized μXRF calibration protocols were based on a combination of standard samples, Monte Carlo simulations and Fundamental Parameter theoretical approach. X-ray imaging methods of plasma exposed samples could provide a useful reference overview of the coating structural integrity including those with opaque deposits or contaminants. [1] Rubel, Marek et al. Journal of Nuclear Materials, vol. 438, pp. S1204-S1207, 2013; [2] Misawa M. and Tiseanu I., 2006 Oblique-view cone-beam CT, US Patent 7139363.

Authors : K. Tomić(1), R. Heller(2), S. Akhmadaliev(2), H. Lebius(3), A. Benyagoub(3), C. Ghica(4), F. Scholz(5), O. Rettig(5), B. Šantić(1), S. Fazinić(1) and M. Karlušić*(1)
Affiliations : (1) Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia (2) Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrase 400, 01328 Dresden, Germany (3) CIMAP, CEA-CNRS-ENSICAEN-UCN, BP 5133, 14070 Caen Cedex 5, France (4) National Institute of Materials Physics, Str. Atomistilor 105 bis, 077125 Magurele, Romania (5) Institute of Functional Nanosystems, Universität Ulm, Albert-Einstein-Allee 45, 89081 Ulm, Germany

Resume : Behavior of materials in radiation harsh environment is an important issue and damage build-up within the material in such environment can exhibit complex behavior. Therefore, as one of the most prominent candidate materials that can be used in radiation harsh environments, response of GaN to ion irradiation should be studied in detail. Dense electronic excitation in the wake of the swift heavy ion passage through a material (mass > 20 amu, kinetic energy > 1 MeV/amu) can lead to nanoscale material damage along ion trajectory called ion track [1], [2]. Irradiation with heavy ions in the keV energy range can also produce defects but via different energy dissipation channel. In this case, it is well known that direct ion-atom collision (i.e. nuclear energy loss) can produce defects in GaN [3]. In our previous study [1], we found no evidence of ion track formation in the bulk after swift heavy ion irradiation using 23 MeV I and 90 MeV Xe beams. Recently, synergistic effects of nuclear and electronic energy loss came into research focus. After introducing additional disorder into moderately damaged GaN crystals via pre-irradiating them either with 2 MeV Au or with 900 MeV Xe ion beams, we were able to introduce additional damage using the same (as in our previous study [1]) 23 MeV I and 90 MeV Xe ion beams. Here, we report the results of sequential ion irradiation of GaN based on the RBS/c, TEM and AFM measurements. [1] M. Karlušić et al., Response of GaN to energetic ion irradiation - conditions for ion track formation, J. Phys. D: Appl. Phys. 48 (2015) 325304 [2] M. Sall et al., Track formation in III-N semiconductors irradiated by swift heavy ions and fullerene and re-evaluation of the inelastic thermal spike model, J. Mater. Sci. (2015) 50:5214–5227 [3] S. O. Kucheyev et al., Ion implantation into GaN, Mater. Sci. Eng., R , 33 (2001) 51-107 *Corresponding author:

Authors : Mengli Sun1,2,3,4, Victor. L. Vinograd2,3, Evgeny V. Alekseev2,3, Philip Kegler2,3, Gabriel Murphy2,3, Tieshan Wang4, Brendan Kenedy5, Zhaoming Zhang6, Kristina Kvashnina7, Dirk Bosbach2,3, Sandro Jahn1, Piotr. M. Kowalski2,3
Affiliations : 1. University of Cologne, Institute of Geology and Mineralogy, Zülpicher Strasse 49b, 50674 Köln, Germany; 2. Institute of Energy and Climate Research (IEK-6), Forschungszentrum Jülich, Wilhelm-Johnen-Straβe, 52425 Jülich, Germany, email:; 3. JARA High-Performance Computing, Schinkelstraβe 2, 52062 Aachen, Germany; 4. School of Nuclear Science and Technology, Lanzhou University, Tianshui South Road 222, Lanzhou 730000, China; 5. School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia; 6. Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia; 7. Rossendorf Beamline at ESRF – The European Synchrotron, CS40220 38043 Grenoble Cedex 9, France;

Resume : HLW(High Level Nuclear Waste) is usually stored as spent nuclear fuel or vitrified glass. In order to provide a solid scientific basis of waste disposal we try to understand the properties of various relevant materials, including waste and waste forms, and their long-term performance. In this contribution, we report the results of joint atomistic modeling and experimental efforts of spent nuclear fuel/HLW related materials such as nuclear glass and UO2-based model systems. Vitrification into borosilicate glass is a widely used process for long-term storage of the spent nuclear fuel. In order to understand the physical and chemical properties of glass waste forms and their changes under irradiation conditions we have performed a series of measurements and simulations of elastic moduli, hardness and internal energies of a series of irradiated borosilicate glasses. Both experimental and simulation results show significant change (decrease) of Young’s modulus and hardness of borosilicate glasses and amorphization at ~0.1 dpa (displacements per atom). The molecular dynamics simulations of the irradiation process indicate significant changes in volume and stored energy, which are B/Si content dependent. We also applied atomistic simulations to investigate the behavior of Cr (fission product) in the UO2 matrix and the properties of uranium-based secondary phases. We will discuss the simulated doping geometry and oxidation state of Cr, the limit of the Cr solubility in the host matrix, electronic states of the mixed U-oxides as well as the properties of the O-depleted MUO4-x (M=Ca,Sr) phases.

Authors : Marko Karlušić, Kristina Tomić, Stjepko Fazinić
Affiliations : Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia

Resume : Rutherford backscattering spectroscopy in channeling mode (RBS/c) is an excellent tool to study ion tracks, i.e. permanent damage in the material after swift heavy ion impact. Especially close to the ion track formation threshold, when ion tracks have discontinuous morphology, measuring their effective cross section by RBS/c yields important information needed to understand physical processes relevant in this energy range [1,2]. At the RBI accelerator facility in Zagreb, recently developed RBS/c setup offers possibilities for in situ measurements. These facilitate ion track measurement, but also enable precise measurements of ion track formation in channeling and near channeling conditions [3,4]. We demonstrate possibilities of this approach by reporting here results of our investigations on ion tracks in quartz SiO2 [3]. In case of crystalline silicon, it is known this material to be extremely resistant to any damage formation by means of electronic stopping. Only cluster ion irradiations with extreme values of electronic stopping were able to induce damage [5]. Amorphous silicon is known to be more sensitive to ion beam damage, yielding ion tracks at lower electronic stopping values [6]. Here we report results of electronic stopping on defects recovery in silicon. As shown by our RBS/c study, defects in silicon introduced by nuclear stopping can be effectively erased by swift heavy ion beams of only moderate electronic stopping values. [1] A. Rivera et al., Kinetics of amorphization induced by swift heavy ions in alpha-quartz, J. Nucl. Mater. 430 (2012) 125. [2] M. Karlušić et al., Infrared spectroscopy of ion tracks in amorphous SiO2 and comparison to gamma irradiation induced changes, J. Nucl. Mater. 514 (2019) 74. [3] M. Karlušić et al., Monitoring ion track formation using in situ RBSc, ToF-ERDA, and HR-PIXE, Materials 10 (2017) 1041. [4] M. Karlušić et al., Swift heavy ion track formation in SrTiO3 and TiO2 under random, channeling and near-channeling conditions, J. Phys. D: Appl. Phys. 50 (2017) 205302. [5] A. Dunlop et al., Latent track formation in silicon irradiated by 30 MeV fullerenes, Nucl. Instr. Meth. B 146 (1998) 302. [6] M. Toulemonde et al., Transient thermal process after a high-energy heavy-ion irradiation of amorphous metals and semiconductors, Phys. Rev. B 46 (1992) 14362.

Authors : A. I. Popov (1), E. Elsts (1), V. Grāveris(1), V.Kuzovkov (1), E. Shablonin (2) , E. Vasil'chenko (2), G. Prieditis (2), A. Ch.Lushchik (2)
Affiliations : (1) Institute of Solid State Physics, University of Latvia, Latvia (2) Institute of Physics, University of Tartu, W.Ostwald Str. 1, 50411 Tartu, Estonia

Resume : Y3Al5O12 (YAG), single crystals are known for their interesting properties such as high radiation-resistance, high melting point and high thermal conductivity. Consequently, YAG is among candidates to several technological applications such as fusion energy devices and nuclear applications. Irradiation of single crystal Y3Al5O12 in the reactor (i.e. fast and thermal neutrons and gamma radiation) produces many color centers (such as F-type center, interstitials [1-5] and many others) in the material. Similar defects are also formed by heavy ion irradiation or by fast electrons, while only electronic processes are important in the case of UV, X-ray and low energetic electron irradiation.. In this presentation we report the results of the thermostimulated luminescence measurements, performed between 300 and 720°K of the stored energy in Y3Al5O12 single crystals, irradiated by fast neutrons with fluences of 2.1 x 1017 or 2.18 x 1019 n/cm2, or also by 1.8 MeV electrons, or thermochemically reduced. A clear pronounced dose effect was found and analyzed. In particular, four TSL peaks were observed in Y3Al5O12 samples subjected 2.18 x 1019 n/cm2, while in sample subjected 2.16 x 1017 n/cm2, only three TSL peaks were detected. A comprehensive kinetic analysis of the glow peaks in Y3Al5O12 is performed. As usual, each TSL peak is characterized by the appropriate activation energies, which both crystals are 0.8 – 1.3 eV. The obtained values are compared with the appropriate activation energies for F-type center annealing in neutron- and heavy-ion irradiated Y3Al5O12 as well as also with similar TSL data for Al2O3 and Y3Al5O12.

Authors : J.J. Terblans1, H.C. Swart1, E Coetsee1, M.M. Duvenhage1, D. Craciun2, G. Dorcioman2, V. Craciun2, 3
Affiliations : 1 Department of Physics, University of the Free State, Bloemfontein, South Africa 2 National Institute for Lasers, Plasma and Radiation Physics, Măgurele, Romania 3 Extreme Light Infrastructure-Nuclear Physics, Magurele, Romania

Resume : Thin films used for nuclear fuel encapsulation applications in advanced nuclear reactors should exhibit many excellent characteristics such as high temperature stability, a good radiation tolerance and retention of fission products. ZrC is a potential material for such applications since it possesses a high melting temperature, a single crystalline phase up to the melting point and good thermochemical stability. Many investigations showed that ZrC has a high irradiation tolerance when irradiated with high energy ions. We investigated Pd diffusion, one of the most radioactive fission products, through thin films of ZrC. First, a thin film of Pd was deposited using magnetron rf sputtering at room temperature on a Si wafer. Then, without breaking the vacuum, a thin ZrC film was then deposited using pulsed laser deposition on top of the Pd film. The structure, surface, interface morphology and density of the deposited films were investigated using X-ray reflectivity and grazing incidence X-ray diffraction. After deposition, the sample was transferred to a Time of Flight Secondary Ion Mass Spectroscopy (ToF SIMS) system. The sample was mounted on the heating stage of the ToF SIMS. A depth profile was obtained at room temperature, where after the sample was heated to 400 °C at a rate of 1 K/s. The temperature was maintained at 400 °C for 10, 20, 40, 80 and 160 minutes, respectively. In between each heating cycle, a depth profile was obtained. From the depth profiles, it was clear that the ZrC formed a diffusion barrier that prevented the Pd to diffuse towards surface. The Si diffused up to the ZrC diffusion barrier and was blocked by the ZrC layer.

Authors : E. Akshaya Devi, Ravi Chinnappan
Affiliations : Materials Science Group, Indira Gandhi Centre for Atomic Research, HBNI, Kalpakkam 603102, Tamilnadu, India

Resume : In nuclear power plants, stainless steels are the predominant structural material. Ferritic and ferritic-martensitic steels are known to offer better dimensional stability than austenitic steels under neutron irradiation. The operating temperatures of these steels are however limited to about 600◦C. In order to achieve higher operating temperatures, oxide dispersion strengthened (ODS) steels have been developed. These modern steels are multicomponent alloys (with about 20 components: Fe,C,Mn,P,Si,Ni,Cr,Mo,V, Ti, Co, Cu, Al, B, W, Zr, N, O, Y) made up of Fe-Cr ferrite matrix in which a homogeneous distribution of small precipitate particles is created by ball milling and subsequent consolidation process involving either hot extrusion or hot isostatic pressing. These ODS steels have superior creep resistance and stability under irradiation, attributed to the finest oxide particles densely dispersed in the ferrite matrix with high dislocation density. The dissolution energy of the oxide particles in an iron matrix and bulk modulus of the oxide embedded iron are important thermophysical parameters of the ODS iron. At the high-temperature environment, there will be a thermal expansion so high bulk modulus is required to resist it. And the knowledge of the dissolution energy of oxides in iron is used to stop the movement of dislocation in the alloy. Several types of oxide particles are found in the ODS steel such as Y2Ti2O7, Y2TiO5, and a defective NaCl-type TiO. We, in this work, compute the dissolution energy and bulk modulus of NaCl-type oxide particles AO embedded iron, where A is transition metal, using density functional theory calculation. Our model of oxide-embedded iron is made by removing 4 Fe atoms at the centre of 128-atoms 4x4x4 bcc supercell and placing a NaCl-type A4O4 cluster such that the A’s substitute for the removed Fe atoms and O’s placed at the appropriate octahedral interstitial sites. The physical origin behind the endothermic/exothermic dissolution energy will be analyzed through the projected density of state. Analysis of the dissolution energies together with bulk moduli would improve our understanding of these oxides as precipitate particles in ODS steel.

Authors : Cristian Mihailescu1, Gabriela Dorcioman1, Doina Craciun, and Petronela Garoi1
Affiliations : 1National Institute for Laser, Plasma, and Radiation Physics, Magurele, Romania

Resume : Amorphous Indium Zinc Oxide (IZO) is a transparent conductive oxide (TCO), which could be synthesized at low temperatures for applications on optoelectronic devices fabricated on plastic or paper substrates. Since IZO films are amorphous, devices incorporating them are rather insensitive to radiation and could be used in outer space. IZO electrical and optical properties strongly depend on both In/(In+Zn) value and oxygen content. In this study, thermal conductivity of high and low electrical conductivity IZO thin films (In/(In+Zn) = 0.40 and 0.70) before and after gamma irradiation was investigated using the laser flash method (TF-LFA). IZO films were grown on Si substrate at room temperature using pulsed laser deposition technique (PLD) with an ArF laser under various oxygen pressures. The IZO films electrical properties were measured using a 4-point probe system, the stoichiometry was investigated using energy dispersive X-rax spectroscopy and X-ray photoelectron spectroscopy, while the thickness was obtained from cross-section scanning electron microscopy images. For thermal conductivity measurements, a ~200 nm thick film of Au was deposited using thermal evaporation. The thermal conductivity of IZO films ranged from 0.7 W/m/K to 1.95 W/m/K. The phonon contribution to the total thermal conductivity was constant. The electric conductance of the IZO films varied inversely to the O2 pressure during deposition. No major change after gamma irradiation was observed in these IZO films.

Authors : L.S. Alekseeva, E.A. Potanina
Affiliations : Lobachevsky state university of Nizhny Novgorod

Resume : The processing of plutonium and minor actinides (MA) waste, which have accumulated over the years, is an important problem in nuclear power. Creating inert matrix fuels (IMFs) for post-burning Pu and transmutation MA would be the best solution to this problem. Potential IMF are CeO2, PuO2, LnPO4, Y3Al5O12, etc. One of the main disadvantages of such materials is their low thermal conductivity, which can lead to uneven heating of the fuel pellet and, as a result, to its mechanical damage and decrease in the degree of the fuel burn time-up The solution to this problem can be the introduction of additional components, for example, metals, their oxides, nitrides, carbides, etc. In the present work, studies aimed at increasing the thermal conductivity of ceramics are performed. The object of this study are composites CeO2–SiC (0, 10, 20 vol.%). They were prepared using the SPS method (T=1025 °С, sintering time did not exceed 10 min). The microstructure of ceramics, their microhardness, fracture toughness and thermal conductivity (in the temperature range 25–1100 °C) were studied. It was established that an increase in the concentration of SiC leads to a significant increase in the thermal conductivity of composites at room temperature: by 49% (10% SiC) and 79% (20% SiC). In the high-temperature region, a significant increase in the thermal conductivity is not observed. This study has been carried out with the support of the Russian Science Foundation (Grant No. 16-13-10464).

Authors : W.Chrominski, L. Ciupinski, P. Bazarnik, S. Markelj, T.Schwarz-Selinger
Affiliations : Faculty of Materials Science and Engineering, Warsaw University of Technology, Poland; Faculty of Materials Science and Engineering, Warsaw University of Technology, Poland; Faculty of Materials Science and Engineering, Warsaw University of Technology, Poland; Jožef Stefan Institute, Slovenia; 3Max-Planck-Institut für Plasmaphysik, Germany

Resume : Tungsten is chosen as a primary candidate to serve as a plasma facing component (PFC) in future fusion reactors. Demanding fusion environment features frequent thermal shocks, neutron bombardment and exposure to hydrogen isotopes. PFCneed to maintain mechanical properties during the lifetime as well as they should not store radioactive hydrogen isotopes both during reactor operation and after its decommissioning. Laboratory equipment is constantly developing in order to faithfully reproduce fusion reactor environment and study plasma facing materials behavior during their service. This study focuses on comparison of material damaged in two-step procedure of firstly ion bombardment and then deuterium exposure and single-step damaging by simultaneous W ion irradiation and D exposure. The latter seems to be closer to real fusion environment that the former, since in real conditions PFC are subjected to mutual actions of multiple particles. TEM investigation revealed that dislocation structures in the studied samples vary. Differences include both morphology of defects as well as their density. This result indicates that future experiments concerning D retention in irradiated tungsten targets need to be designed with more caution.

Authors : Doina Craciun, Gabriela Dorcioman and Valentin Craciun
Affiliations : National Institute for Lasers, Plasma and Radiation Physics, Magurele, Romania

Resume : Amorphous indium zinc oxide (IZO) films have good electronic and optical properties, which are used in transparent thin film transistors and display devices. These films maintain their properties when grown at room temperature, which allows for the use of inexpensive substrates such as paper or plastic. We used the pulsed laser deposition technique to grow thin films of IZO with In/(In+Zn) values from 0.1 to 0.9 on Si and glass substrates at room temperature. The films were irradiated by Co gamma radiation up to a dose of 30 kGy to investigate the effects of radiation on their structure and properties. The films surface morphology was smooth, with rms values below 1 nm. Spectroscopic ellipsometry was used to observe the effect of gamma irradiation on the optical properties. The results showed that after gamma irradiation the films density, extracted from simulations of the acquired X-ray reflectivity curves, decreased by a 1-2 %, which resulted in a small thickness increase, while spectroscopic ellipsometry measurements indicated that the refractive index values also decreased by 1-2 percent, consistent with the observed changes in density. Similar small changes were also observed in films electrical conductivity. These results showed that amorphous IZO is a material that could withstand a high level of gamma radiation without adverse effects on its structure or properties.

Authors : D. Craciun1, G. Dorcioman1, M. D. Dracea2, D. Pantelica2, B. S. Vasile3, V. Craciun1, 4
Affiliations : 1National Institute for Lasers, Plasma and Radiation Physics, Magurele, Romania; 2Horia Hulubei National Institute for Physics and Nuclear Engineering, Magurele, Romania; 3Faculty of Applied Chemistry and Material Science, Polytechnic University of Bucharest, Bucharest, Romania; 4Extreme Light Infrastructure-Nuclear Physics, HH-IFIN Magurele, Romania

Resume : Thin films and devices used in advanced nuclear reactors, fusion installations or space exploration are exposed to high level of various type of radiation. It has been recently observed that nanostructured thin films, which possess very small crystal grains exhibited better radiation resistance than polycrystalline or single crystal films. Therefore, the structure, composition and properties of these films will be less affected by exposure to radiation. Dislocations cannot form in such small crystalline grains and the increase of mechanical hardness after irradiation, observed for single crystals or large grain films is not observed in these nanostructured films. To investigate the radiation effects on properties, chemical composition and structure we used the Pulsed Laser Deposition (PLD) technique to grow ZrC and ZrN nanocrystalline thin films. The effects of 800 keV Ar and 1.0 MeV Au ions on the properties of nanocrystalline ZrC and ZrN thin films were investigated using high resolution transmission electron microscopy, nanoindentation, X-ray specular and diffuse reflectivity, and X-ray diffraction investigations. The results confirmed that nanocrystalline films could withstand high irradiation fluences without degrading their crystalline structure, while the Si substrate was completely amorphized. Grazing incidence XRD investigations found that there is grain growth in ZrC films as an effect of ion irradiation, while a decrease of the grain size was observed under similar irradiation conditions for ZrN.

Authors : Dhriti Bhattacharyya, Alan Xu, Michael Saleh, Tao Wei, Mihail Ionescu
Affiliations : Australian Nuclear Science and Technology Organisation

Resume : The characterization and testing of neutron irradiated materials for understanding the changes in microstructure and mechanical properties is time consuming and hazardous. Ion irradiation is an attractive alternative as it is relatively quick (~ hours/days) and does not render the sample radioactive in general. However, ion irradiation forms an extremely thin damaged layer (~ 100s of nm to a few m). Secondly, the damaged layer has a large gradient in the dose through the thickness, which makes the microstructural and mechanical changes vary appreciably through depth, making it difficult to characterize these aspects of the material after irradiation. Recent advances in technology have made the study of the mechanical properties of these thin layers easier. Nanoindentation has been used successfully to study the hardness change in the irradiated layers for some years. However, the three-dimensional stress state in nanoindented samples and the interaction of such a stress field with irradiated layers having a strong gradient makes it difficult to interpret the results. Finite element modelling at ANSTO has shown a pathway to analyse and interpret these results. As a further step towards an easier and improved methodology to study the mechanical properties of ion irradiated layers, in situ micromechanical testing including tension and compression tests have become more widespread in recent years. This progress has been facilitated by the advances in focused ion beam (FIB) technology allowing the fabrication of micro-sized samples. Here, the authors present some of the recent experimental and modelling results of such tests performed on ion irradiated materials, and discuss their pros and cons vis-à-vis nanoindentation methods.

Authors : Bianca Cristiana Hodoroaba (1, 2), Raluca Ivan (1,2), Stefan Andrei Irimiciuc (1), Doina Craciun (1), Petronela Garoi (1), Eniko Gyorgy (1,3), Valentin Craciun (1, 4)
Affiliations : (1) National Institute for Laser, Plasma and Radiation Physics – NILPRP, 409 Atomistilor Street, Bucharest, Romania (2) University of Bucharest, Faculty of Physics, Bucharest-Magurele, Romania (3) Consejo Superior de Investigaciones Científicas, Instituto de Ciencia de Materiales de Barcelona (CSIC-ICMAB), Campus UAB, 08193 Bellaterra, Spain (4) Extreme Light Infrastructure-Nuclear Physics, Magurele, Romania

Resume : Low-density materials are of great interest both for fundamental material science and high-tech applications. They belong to the class of nano-porous materials characterized by unconventional physical properties: nanometer-size pores, densities lower than water, within the 100 mg/cm3 regime, high specific surface areas, and high porosity. They have been used for microsensor pre-concentrators, bone implantation, scaffold for tissue regeneration, electrochemical supercapacitors, and lightweight microwave shielding structures. Foams show unique properties, as for example an almost perfect black-body-like absorption, an anomalous ferromagnetic behavior, additionally an increased gas and liquid adsorption and storage capability. The absorption of high-power fs-laser pulses by matter is observed to significantly increase in such density range. We report here on the generation of low density carbon foams by pulsed laser deposition through the irradiation of graphite targets in controlled environment. Different deposition geometries were attempted in order to take into account the flip-over effect and the strong asymmetries from the carbon generated plasma. The deposition process was calibrated by adjusting the laser beam energy, frequency, and deposition time on a wide range of values. Various background gasses (Ar, CH4) and pressures were used to find the best media that could aid the generation of complex carbon structures and the subsequent formation of foam-like films. The obtained films were investigated by means of complimentary surface analysis methods like ATR-FTIR spectroscopy, XRD, XRR, XPS, SEM, and EDS in order to accurately describe their structure, chemical bonds between the elements, and morphology.

Authors : Laurence Luneville David Simeone
Affiliations : CEA/DEN/DM2S/SERMA/LLPR-LRC CARMEN, CEA, Universit\'e Paris-Saclay, F-91191, Gif-sur-Yvette, France,CNRS/ECP/UMR 8085, Grande voie des vignes, Chatenay Malabry, France CEA/DEN/DMN/SRMA/LA2M-LRC CARMEN, CEA, Universit\'e Paris-Saclay, F-91191, Gif-sur-Yvette, France, CNRS/ECP/UMR 8085, Grande voie des vignes, Chatenay Malabry, Franc

Resume : We demonstrate that the Swift-Hohenberg functional as used to describe patterning observed in out of equilibrium systems such as diblock copolymers, Rayleigh-Benard convection and thin film magnetic garnets, can be applied to radiation-induced patterns that occur in non-miscible alloys. By comparing ground states obtained from the minimization of this functional and a 2D numerical simulation performed on an irradiated AgCu material which is the archetype of a non-miscible alloy we show that the Swift-Hohenberg functional provides all possible patterns generated under irradiation and the solubility limits of radiation-induced precipitates in these patterns. To rationalize the formation of these radiation-induced patterns, we propose a generic "pseudo phase diagram" that relies not only on the irradiation flux and temperature but also the overall composition of the alloy. Tuning this overall composition offers the opportunity to tailor new materials with various micro-structures overcoming the limitation of the equilibrium phase diagram.

Start atSubject View AllNum.Add
Affiliations : Institute of Solid State Physics, University of Latvia, Riga, Latvia; Max Planck Institute for Solid State Research, Stuttgart, Germany; Nuclear Research Center of Draria, Algiers; CIEMAT, Madrid, Spain

Resume : The radiation-resistant oxide insulators (Al2O3, Y3Al5O12, MgAl2O4 etc) are important materials for applications in fusion reactors, e.g. in optical windows. It is very important to predict/simulate a long-time defect structure evolution including thermal defect annealing after irradiation. For further prediction of the radiation stability of materials is necessary extract main kinetic parameters - interstitial migration energy Ea and diffusion pre-exponent D0. Primary radiation defects in ionic solids consist of Frenkel defects—pairs of anion vacancies with trapped electrons (F-type centers) and interstitial ions. The thermal annealing is controlled by the interstitial ion migration, whose mobility is much higher than that of the F centers. The theory (how to extract from experimental data the migration energy of interstitials and pre-exponential factor of diffusion) was developed and applied to irradiated insulators in our recent study [1,2]. It was showed that the correlation of these two parameters satisfies the so-called Meyer–Neldel rule (MNR) [2] observed more than once earlier in glasses, liquids, and disordered materials, but not in the irradiated materials. We analyzed here the available experimental kinetics of the F-type center annealing for two different ionic solids: neutron/ion-irradiated Al2O3 (sapphire) [1,2] and ion-irradiated Y3Al5O12 (YAG) [3]-- both wide gap insulating materials but with different crystalline structures. We demonstrated that in sapphire upon an increase of radiation fluence, both the migration energy and pre-exponent are decreasing, irrespective of the type of irradiation. This is MNR with normal dose dependence. For YAG we have confirmed MNR, but the dose dependence is inverse. We discuss the cause of this phenomenon. Thus, in this study, we demonstrated that the dependence of defect migration parameters on the radiation fluence plays an important role in the quantitative analysis of the radiation damage of real materials and cannot be neglected. [1] V.Kuzovkov, E.Kotomin, A.Popov, R.Villa, Nucl. Inst. Meth. B 374, 107 (2016). [2] E.Kotomin, V.Kuzovkov, A.Popov, J.Maier, R.Vila, J.Phys.Chem.A,22,28 (2018). [3] M. Izerrouken, A. Meftah, M. Nekkab, Nucl. Instr. Meth. B 258, 395 (2007).

Authors : N. Cautaerts, R. Delville, E. Stergar, M. Verwerft, D. Schryvers, J. Pakarinen, Y. Yang, P. Hosemann, S. Vachhani, C. Hoffer, R. Schnitzer, P. Felfer, S. Lamm
Affiliations : SCK-CEN, Mol, Belgium: N. Cautaerts, R. Delville, E. Stergar, M. Verwerft; University of Antwerp, Antwerp, Belgium: N. Cautaerts, D. Schryvers; Studsvik Nuclear AB, Nyköping, Sweden: J. Pakarinen; University of Florida, Gainesville, FL, USA: Y. Yang; University of California, Berkeley, CA, USA: P. Hosemann, S. Vachhani; University of Leoben, Leoben, Austria: C. Hoffer, R. Schnitzer; FAU, Erlangen, Germany: P. Felfer, S. Lamm;

Resume : In this work, advanced characterization techniques such as APT and TEM were combined to investigate how ion irradiation conditions and prior heat treatment influence the evolution of the microstructure of a new heat of the DIN 1.4970 alloy (a 15-15Ti austenitic stainless steel). First, different ageing heat treatments were explored, with a particular focus on precipitation and minor element partitioning. Heat treatment conditions had only a modest influence on the TiC precipitate population; the most important considerations were avoiding recrystallization at high temperature and minimizing intergranular M23C6 formation at low temperature. Second, Fe ion irradiations were performed on heat treated and non-heat-treated material up to 40 dpa for 3 different temperatures. The resulting materials were studied by various TEM techniques, APT and nanoindentation, with a focus on Frank loop populations, precipitates and radiation induced segregation (RIS). Small TiC clusters were stable down to at least 450 °C under ion irradiation, regardless of prior heat treatment. Heat treated material showed a lower TiC number density and coarser particles, but an increased volume fraction of RIS induced phases compared to non-heat treated material. This may be correlated with reduced swelling resistance. Overall, an improved understanding of the role of Ti and MC precipitates in the microstructure during irradiation was established, which may lead to more targeted neutron irradiation experiments as well as general alloy improvement strategies in the 15-15Ti alloys.

Authors : A. Lushchik1, E.A. Kotomin2, V.N. Kuzovkov2, A.I. Popov2, V. Seeman1, E. Shablonin1, E. Vasilchenko1
Affiliations : 1Institute of Physics, University of Tartu, Estonia 2Institute of Solid State Physics, University of Latvia

Resume : Magnesium aluminate spinel single crystals and optical ceramics are important optical materials for the use in harsh radiation environment and many other applications. The kinetics of thermal annealing of the basic radiation-induced electron centers (F and F+ - two or one electron in the field of an oxygen vacancy) as well as complementary hole-containing ones (a set of the so-called paramagnetic V-centers) in Mg-Al spinel with different ratio of stoichiometry irradiated by ~1-MeV fast fission neutrons, 100-keV protons, and 0.23 GeV Xe ions is analyzed in terms of diffusion-controlled bimolecular reactions. Properties of single crystals and optical ceramics with different grain sizes exposed to irradiation of different type/fluence are compared. The EPR spectra recorded by an X-band spectrometer Bruker ELEXYS-II E500 and the optical absorption bands were taken as the measure of the radiation-induced V- and F-type centers, respectively [1]. The annealing of radiation damage was performed in a stepwise regime. It is demonstrated that both ceramics and single crystals, as well as heavy ion irradiation show qualitatively similar kinetics but the major impact on the effective migration energy Ea and pre-exponent D0 is caused by the radiation fluencies. These two parameters are strongly correlated and their values increase considerably with radiation fluence. This effect is discussed in terms of the Meyer-Neldel rule known in chemical kinetics of condensed matter [2]. Recommendations on the enhancement of spinel radiation tolerance are suggested. The results for irradiated spinel samples are compared with those for sapphire, MgO and other radiation-resistant materials. [1] A. Lushchik et al., Nucl. Instrum. Meth. B 435 (2018) 31-37. [2] E.A. Kotomin, V.N. Kuzovkov, A.I. Popov, R.Villa, Nucl. Instum. Meth. B 374 (2016) 107-110.

Authors : Lionel Desgranges
Affiliations : CEA DEN-DEC, C.E. Cadarache 13108 Saint-Paul les Durance

Resume : The most used nuclear fuel in the world is a UO2 based ceramic. During operation, fissions generate fission products creating heat that is removed through the pellet surface towards the primary circuit water. This heat flow creates a thermal gradient inside the pellet. Because UO2 is a non-stoichiometric compound, this thermal gradient induces the redistribution of oxygen along the pellet radius. We will explain how this oxygen redistribution can induce the formation of a hypo-stoichiometric area in the pellet centre and a hyper-stoichiometric area outside this centre. We will then discuss our current knowledge about the structural transformations that are induced in UO2 crystalline structure by both hypo and hyper-stoichiometry. In hyper-stoichiometric UO2, the formation of clusters made of interstitial oxygen accommodates the excess in oxygen. These clusters named cuboctahedra are associated to new cationic crystalline sites, which could be preferential incorporation sites for some fission products. In hypo-stoichiometric UO2, stacking faults were evidenced but their exact crystallographic nature is not known. The incorporation of Lanthanide fission products in hypo-stoichiometric UO2 can lead to formation of a so called “miscibility gap”, which will also be discussed. These crystallographic statements are a driving force for more investigations on the behaviour of non-stoichiometric

Authors : Cheol Min Lee(a), Gwan Yoon Jeong(b), Young-Soo Han(a), Dong-Seong Sohn(b)
Affiliations : a: Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong-gu, Daejeon 34057, Republic of Korea b: Ulsan National Institute of Science and Technology, 50 UNIST-gil, Eonyang-eup, Uljoo-gun, Ulsan 689-798 Republic of Korea

Resume : Zirconium alloys have been used as fuel cladding materials in light water reactors (LWR) since the 1960s due to their low neutron absorption cross section. However, it has been reported that zirconium alloys have some disadvantages in accident conditions such as loss of coolant accident (LOCA). As a LOCA occurs, cladding temperature increases rapidly, which causes abrupt increase of oxidation rate. One of the most critical oxidation behaviors that can occur is breakaway oxidation. It is known that zirconium alloys are vulnerable to breakaway oxidation during oxidation at 800 and 1000 ºC. So far, many researches have been carried out to analyze the breakaway oxidation that occurs at 1000 ºC. However, a few studies have been performed to characterize the breakaway oxidation that occurs at 800 ºC. Hence, in this study, aspect of breakaway oxidation that occurs on a zirconium alloy cladding tube was analyzed after high-temperature steam oxidation tests at 800 ºC. It was found that breakaway oxidation at 800 ºC proceeds as radial cracks are formed in the oxides, and these radial cracks caused local excessive oxidation. Comparing to the breakaway oxidation that occurs at 1000 ºC, at which breakaway oxidation proceeds as circumferential cracks are formed in the oxides, the microstructural aspect during breakaway oxidation at 800 ºC is clearly different. Analyzing the reason of this phenomenon will enhance our understanding of breakaway oxidation, and a new method improving accident resistance of zirconium alloy cladding can be developed in the future.

Authors : E.A. Potanina, M.G. Tokarev
Affiliations : Lobachevsky state university of Nizhny Novgorod

Resume : One of the promising technologies for recycling spent nuclear fuel is dissolution it in chloride melts, which are resistant to extreme conditions, with including of radwaste into insoluble mineral-like compounds. For example in molybdates and tungstates with the structure of mineral scheelite (CaWO4), which are studied as forms of binding such fission products as alkaline earth and rare earth elements. In the present work was developed technology concentration of Sr, Ba and Nd from the molten LiCl-KCl in mineral form; stability of such phases in the melt and kinetics of dissolving the formed precipitates at T = 450, 500, 600 °C were studied. Samples were obtained by us using the precipitating processes in aqueous systems or in melts and characterized by X-ray diffraction (XRD). The alkaline earth and rare earth element transition into the solid phase from both of liquid mediums is ~ 98 - 99 %. Mineral phase remain stable in contact with melt LiCl-KCl to T = 600 °C, t = 10 h. An increase in temperature increases the solubility of obtained compounds in 1.5 - 2 times. This study has been carried out with the support of the Russian Science Foundation (Grant No. 16-13-10464).

Authors : Orlova A.I., Nokhrin A.V., Chuvildeev V.N., Boldin M. S.
Affiliations : National Research Lobachevsky State University of Nizhny Novgorod

Resume : The increasing safety of radwaste is a key element in the development of atomic energy. The basic factors: a scientifically-based choice of the structure of compounds and the technology of forming of ceramics. We obtained and characterized ceramics with the structures: fluorite, garnet, pollucite, monazite, kosnarite, langbeinite, scheelite. The achieved under extreme conditions: do not decompose at T 1300-1400 °C, to thermal stress, to radiation (γ-radiation, accelerated xenon ions and alpha particles), in water systems: minimum leaching rates 10^(-6) g/(cm^2·Day). To improve these service characteristics, we used the method of sintering ceramics SPS. The SPS has important advantages for nuclear materials compared to traditional methods: production of ceramics with a relative density of more than 99.9 % in very short times (3-10 min). They contribute to increasing chemical stability and lowering release of radionuclides into the gas phase. Such tests of above mentioned ones confirmed the correctness and feasibility of such concept. It can be concluded that this new method will be used in technology centers in the world for the production of ceramic materials for nuclear energy. The work was financially supported by RSF. №16-13-10464.

Authors : Jiachao Chen1, Sylvain Jacques2, Jean-Paul Tarsbot3, MF Barthe3, Chonghong Zhang4, M. Pouchon1
Affiliations : 1 Department of Nuclear Energy and Safety, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland; 2 Laboratoire des Composites Thermostructuraux, University of Bordeaux/CNRS, 33600 Pessac, France; 3 CEMHTI/CNRS, Université d’Orléans, 3A rue de la Férollerie, 45071 Orléans CEDEX 2, France CEA/DEN, SRMA, F-91191 Gif-sur-Yvette CEDEX, France; 4 Institute of Modern Physics, Chinese Academy of China, Lanzhou, China;

Resume : A newly developed clamping system for ceramic specimen is described in the present report. By using this system, the uniaxial tensile loading was first successfully applied up to fracture (950 MPa) on a SiCf/SiC minicomposite. A minicomposite is a 1D model composite. It consists of a SiC-based fiber tow embedded in a SiC matrix, which has a diameter of about 0.5 mm. Afterwards, the irradiation creep properties of SiCf/SiC minicomposite were studied. In-situ creep was performed in an in-beam creep device under uniaxial tensile stresses from 50 to 400 MPa during homogeneous helium irradiation. Homogenous irradiation was carried out by helium implantation with energies varying from 0 to 45 MeV. The displacement dose rate was 1.25e-6 dpa/s. The average temperature was controlled to 700 and 900°C within ±10°C. Irradiation creep compliance of minicomposite was measured to be 2.6e-5 and 4.32e-5 1/(dpa*MPa) at 700°C and 900°C, respectively. 

Authors : Young-Ho Lee, Hyung-Kyu Kim, Jung-Hwan Park, Hyun-Gil Kim
Affiliations : Korea Atomic Energy Research Institute

Resume : A grid-to-rod fretting (GTRF) is well known as one of the most frequent failure mechanisms of nuclear fuel rod in operating PWRs. GTRF damages could be accelerated when the contact force is loosened during operations. In this case, both fuel rod and grid are gradually oxidized in reactor condition, and Zr oxides are formed on their contact surfaces. In this study, effect of the surface oxide of both rod and grid on the fretting wear behaviors was evaluated. Zr-based rod and grid samples were exposed to high-temperature water (360°C) up to 360 days for preparing pre-oxidized samples with different oxide thickness. Both oxide thickness of the rod and grid samples gradually increased with the exposed time. It was found that the oxidation rate of the grid was faster than that of the rod due to the difference in the microstructure and manufacturing process. In the results of fretting wear tests, the wear volume and maximum wear depth of the pre-oxidized rod were dramatically decreased with the increase of the oxide thickness. It was concluded that the oxide thickness is one of the important factors for determining the fretting wear resistance of fuel rod.


No abstract for this day

Symposium organizers
Christian EKBERGChalmers

Kemivägen 4, SE 41296 Göteborg, Sweden

DEN/DANS/DMN/SRMA/LA2M, 91191 Gif sur Yvette, France
Manuel A. POUCHONPaul Scherrer Institut

OHLD / 102, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland

National Institute for Laser, Plasma and Radiation Physics and Extreme Light Infrastructure-Nuclear Physics, Magurele, Romania