| 1. |
- Rieth, M., et al.
(författare)
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A brief summary of the progress on the EFDA tungsten materials program
- 2013
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 442:1-3, s. S173-S180
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Tidskriftsartikel (refereegranskat)abstract
- The long-term objective of the European Fusion Development Agreement (EFDA) fusion materials programme is to develop structural and armor materials in combination with the necessary production and fabrication technologies for reactor concepts beyond the International Thermonuclear Experimental Reactor. The programmatic roadmap is structured into four engineering research lines which comprise fabrication process development, structural material development, armor material optimization, and irradiation performance testing, which are complemented by a fundamental research programme on "Materials Science and Modeling." This paper presents the current research status of the EFDA experimental and testing investigations, and gives a detailed overview of the latest results on materials research, fabrication, joining, high heat flux testing, plasticity studies, modeling, and validation experiments.
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| 2. |
- Rieth, M., et al.
(författare)
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Recent progress in research on tungsten materials for nuclear fusion applications in Europe
- 2013
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 432:1-3, s. 482-500
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Forskningsöversikt (refereegranskat)abstract
- The current magnetic confinement nuclear fusion power reactor concepts going beyond ITER are based on assumptions about the availability of materials with extreme mechanical, heat, and neutron load capacity. In Europe, the development of such structural and armour materials together with the necessary production, machining, and fabrication technologies is pursued within the EFDA long-term fusion materials programme. This paper reviews the progress of work within the programme in the area of tungsten and tungsten alloys. Results, conclusions, and future projections are summarized for each of the programme's main subtopics, which are: (1) fabrication, (2) structural W materials, (3) W armour materials, and (4) materials science and modelling. It gives a detailed overview of the latest results on materials research, fabrication processes, joining options, high heat flux testing, plasticity studies, modelling, and validation experiments.
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| 3. |
- Rieth, M., et al.
(författare)
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Review on the EFDA programme on tungsten materials technology and science
- 2011
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 417:1-3, s. 463-467
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Tidskriftsartikel (refereegranskat)abstract
- All the recent DEMO design studies for helium cooled divertors utilize tungsten materials and alloys, mainly due to their high temperature strength, good thermal conductivity, low erosion, and comparably low activation under neutron irradiation. The long-term objective of the EFDA fusion materials programme is to develop structural as well as armor materials in combination with the necessary production and fabrication technologies for future divertor concepts. The programmatic roadmap is structured into four engineering research lines which comprise fabrication process development, structural material development, armor material optimization, and irradiation performance testing, which are complemented by a fundamental research programme on "Materials Science and Modeling". This paper presents the current research status of the EFDA experimental and testing investigations, and gives a detailed overview of the latest results on fabrication, joining, high heat flux testing, plasticity, modeling, and validation experiments.
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| 4. |
- Malerba, L., et al.
(författare)
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Ab initio calculations and interatomic potentials for iron and iron alloys : Achievements within the Perfect Project
- 2010
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 406:1, s. 7-18
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Tidskriftsartikel (refereegranskat)abstract
- The objective of the FP6 Perfect Project was to develop a first example of integrated multiscale computational models, capable of describing the effects of irradiation in nuclear reactor components, namely vessel and internals. The use of ab initio techniques to study, in the most reliable way currently possible, atomic-level interactions between species and defects, and the transfer of this knowledge to interatomic potentials, of use for large scale dynamic simulations, lie at the core of this effort. The target materials of the Project were bainitic steels (vessel) and austenitic steels (internals), i.e. iron alloys. In this article, the advances made within the Project in the understanding of defect properties in Fe alloys, by means of ab initio calculations, and in the development of interatomic potentials for Fe and Fe alloys are overviewed, thereby providing a reference basis for further progress in the field. Emphasis is put in showing how the produced data have enhanced our level of understanding of microstructural processes occurring under irradiation in model alloys and steels used in existing nuclear power plants.
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| 5. |
- Malerba, L., et al.
(författare)
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Comparison of empirical interatomic potentials for iron applied to radiation damage studies
- 2010
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 406:1, s. 19-38
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Tidskriftsartikel (refereegranskat)abstract
- The performance of four recent semi-empirical interatomic potentials for iron, developed or used within the FP6 Perfect Project, is evaluated by comparing them between themselves and with available experimental or, more often, density functional theory data. The quantities chosen for the comparison are of specific interest for radiation damage studies, i.e. they concern mainly properties of point-defects and their clusters, as well as dislocations. For completeness, an earlier, widely used (also within the Project) iron potential is included in the comparison exercise as well. This exercise allows conclusions to be drawn about the reliability of the available potentials, while providing a snapshot of the state-of-the-art concerning fundamental properties of iron, thereby being also useful as a kind of handbook and as a framework for the validation of future semi-empirical interatomic potentials for iron. It is found that Mendelev-type potentials are currently the best choice in order to "extend density functional theory" to larger scales and this justifies their widespread use, also for the development of iron alloy potentials. However, a fully reliable description of self-interstitial atom clusters and dislocations with interatomic potentials remains largely an elusive objective, that calls for further effort within the concerned scientific community.
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| 6. |
- De Backer, A., et al.
(författare)
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Primary damage in tungsten using the binary collision approximation, molecular dynamic simulations and the density functional theory
- 2016
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Ingår i: Physica Scripta. - : Institute of Physics Publishing (IOPP). - 0031-8949 .- 1402-4896. ; T167
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Tidskriftsartikel (refereegranskat)abstract
- The damage produced by primary knock-on atoms (PKA) in W has been investigated from the threshold displacement energy (TDE) where it produces one self interstitial atom-vacancy pair to larger energies, up to 100 keV, where a large molten volume is formed. The TDE has been determined in different crystal directions using the Born-Oppenheimer density functional molecular dynamics (DFT-MD). A significant difference has been observed without and with the semi-core electrons. Classical MD has been used with two different empirical potentials characterized as 'soft' and 'hard' to obtain statistics on TDEs. Cascades of larger energy have been calculated, with these potentials, using a model that accounts for electronic losses (Sand et al 2013 Europhys. Lett. 103 46003). Two other sets of cascades have been produced using the binary collision approximation (BCA): a Monte Carlo BCA using SDTrimSP (Eckstein et al 2011 SDTrimSP: Version 5.00. Report IPP 12/8) (similar to SRIM www.srim.org) and MARLOWE (RSICC Home Page. (https://rsicc.ornl.gov/codes/psr/psr1/psr-137.html) (accessed May, 2014)). The comparison of these sets of cascades gave a recombination distance equal to 12 angstrom which is significantly larger from the one we reported in Hou et al (2010 J. Nucl. Mater. 403 89) because, here, we used bulk cascades rather than surface cascades which produce more defects (Stoller 2002 J. Nucl. Mater. 307 935, Nordlund et al 1999 Nature 398 49). Investigations on the defect clustering aspect showed that the difference between BCA and MD cascades is considerably reduced after the annealing of the cascade debris at 473 K using our Object Kinetic Monte Carlo model, LAKIMOCA.
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| 7. |
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| 8. |
- Piochaud, J. B., et al.
(författare)
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First-principles study of point defects in an fcc Fe-10Ni-20Cr model alloy
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:2, s. 024101-
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the local environment on vacancy and self-interstitial formation energies has been investigated in a face-centered-cubic (fcc) Fe-10Ni-20Cr model alloy by analyzing an extensive set of first-principle calculations based on density functional theory. Chemical disorder has been considered by designing special quasirandom structures and four different collinear magnetic structures have been investigated in order to determine a relevant reference state to perform point defect calculations at 0 K. Two different convergence methods have also been used to characterize the importance of the method on the results. Although our fcc Fe-10Ni-20Cr would be better represented in terms of applications by the paramagnetic state, we found that the antiferromagnetic single-layer magnetic structure was the most stable at 0 K and we chose it as a reference state to determine the point defect properties. Point defects have been introduced in this reference state, i.e., vacancies and Fe-Fe, Fe-Ni, Fe-Cr, Cr-Cr, Ni-Ni, and Ni-Cr dumbbell interstitials oriented either parallel or perpendicular to the single layer antiferromagnetic planes. Each point defect studied was introduced at different lattice sites to consider a sufficient variety of local environments and analyze its influence on the formation energy values. We have estimated the point defect formation energies with linear regressions using variables which describe the local environment surrounding the point defects. The number and the position of Ni and Cr first nearest neighbors to the point defects were found to drive the evolution of the formation energies. In particular, Ni is found to decrease and Cr to increase the vacancy formation energy of the model alloy, while the opposite trends are found for the dumbbell interstitials. This study suggested that, to a first approximation, the first nearest atoms to point defects can provide reliable estimates of point defect formation energies.
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| 9. |
- Becquart, C. S., et al.
(författare)
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A DFT study of the stability of SIAs and small SIA clusters in the vicinity of solute atoms in Fe
- 2018
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Ingår i: Journal of Nuclear Materials. - : Elsevier B.V.. - 0022-3115 .- 1873-4820. ; 500, s. 92-109
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Tidskriftsartikel (refereegranskat)abstract
- The energetics, defect volume and magnetic properties of single SIAs and small SIA clusters up to size 6 have been calculated by DFT for different configurations like the parallel 〈110〉 dumbbell, the non parallel 〈110〉 dumbbell and the C15 structure. The most stable configurations of each type have been further analyzed to determine the influence on their stability of various solute atoms (Ti, V, Cr, Mn, Co, Ni, Cu, Mo, W, Pd, Al, Si, P), relevant for steels used under irradiation. The results show that the presence of solute atoms does not change the relative stability order among SIA clusters. The small SIA clusters investigated can bind to both undersized and oversized solutes. Several descriptors have been considered to derive interesting trends from results. It appears that the local atomic volume available for the solute is the main physical quantity governing the binding energy evolution, whatever the solute type (undersized or oversized) and the cluster configuration (size and type).
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| 10. |
- Costa, D., et al.
(författare)
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Vacancy migration energy dependence on local chemical environment in Fe-Cr alloys : A Density Functional Theory study
- 2014
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 452:1-3, s. 425-433
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Tidskriftsartikel (refereegranskat)abstract
- The first step towards the understanding and the modelling of the Fe-Cr alloy kinetic properties consists in estimating the migration energies related to the processes that drive the microstructure evolution. The vacancy's migration barrier is expected to depend on the vacancy-migrating atom pair atomic environment as pointed out by Nguyen-Manh et al. or Bonny et al. In this paper, we address the issue of the dependence on the vacancy's local atomic environment of both the vacancy migration energy and the configurational energy change Delta E that occurs when the vacancy jumps towards one of its nearest neighbour sites. A DFT approach is used to determine the ground state energy associated to a given configuration of the system. The results are interpreted in the light of the chromium-chromium and chromium-vacancy binding energies as well as the substitutional chromium atoms magnetic properties.
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| 11. |
- De Backer, A., et al.
(författare)
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Modelling the primary damage in Fe and W : influence of the short-range interactions on the cascade properties: Part 2 – multivariate multiple linear regression analysis of displacement cascades
- 2021
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 549
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Tidskriftsartikel (refereegranskat)abstract
- Neutrons and high energy ions create displacement cascades in materials, which have been simulated using Molecular Dynamics, for many decades now. The breakthrough of this work is to explore in a large statistics of more than 7000 cascades the relation between early cascade morphology and the final primary damage using a multivariate multiple regression analysis. For two energies in Fe and W, the total number of defects, the number of SIA and vacancy clusters and their full size distributions have been characterized using a multivariate multiple linear regression analysis based on 7 descriptors of the primary damage and 3 morphology descriptors. We find that the combination of the volume and the sphericity is significant. This analysis highlights several cascade properties, among them, that the large and spherical cascades create less defects and in particular, less mono defects than small and fragmented ones. 13 interatomic potentials differing either by their equilibrium part or the way they were hardened have been included in this study and the multivariate analysis shows that the choice of potential has a limited influence on the total number of defects but a large one on the number of mono vacancies. On average, soft potentials create cascades of larger volume, smaller sphericity and producing more defects than hard potentials. Finally, the formation of vacancy clusters is different in Fe than in W. In Fe, the fraction of vacancies in clusters is larger than that of SIAs and larger vacancy clusters are created than SIA clusters. In W, it is the opposite. The reasons are the differences of stopping power and threshold displacement energies, which result in different spatial distributions of open volumes that form during the expansion stage of the cascade.
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| 12. |
- Kay, E., et al.
(författare)
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NanoSIMS Imaging Reveals the Impact of Ligand-ASO Conjugate Stability on ASO Subcellular Distribution
- 2022
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Ingår i: Pharmaceutics. - : MDPI AG. - 1999-4923. ; 14:2
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Tidskriftsartikel (refereegranskat)abstract
- The delivery of antisense oligonucleotides (ASOs) to specific cell types via targeted en-docytosis is challenging due to the low cell surface expression of target receptors and inefficient escape of ASOs from the endosomal pathway. Conjugating ASOs to glucagon-like peptide 1 (GLP1) leads to efficient target knockdown, specifically in pancreatic β-cells. It is presumed that ASOs dissociate from GLP1 intracellularly to enable an ASO interaction with its target RNA. It is unknown where or when this happens following GLP1-ASO binding to GLP1R and endocytosis. Here, we use correlative nanoscale secondary ion mass spectroscopy (NanoSIMS) and transmission electron microscopy to explore GLP1-ASO subcellular trafficking in GLP1R overexpressing HEK293 cells. We isotopically label both eGLP1 and ASO, which do not affect the eGLP1-ASO conjugate function. We found that the eGLP1 peptide and ASO are not detected at the same level in the same endosomes, within 30 min of GLP1R-HEK293 cell exposure to eGLP1-ASO. When we utilized different linker chemistry to stabilize the GLP1-ASO conjugate, we observed more ASO located with GLP1 compared to cell incubation with the less stable conjugate. Overall, our work suggests that the ASO separates from GLP1 relatively early in the endocytic pathway, and that linker chemistry might impact the GLP1-ASO function. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
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| 13. |
- Ngayam-Happy, R., et al.
(författare)
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Isochronal annealing of electron-irradiated dilute Fe alloys modelled by an ab initio based AKMC method Influence of solute-interstitial cluster properties
- 2010
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 407:1, s. 16-28
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of the microstructure of dilute Fe alloys under irradiation has been modelled using a multiscale approach based on ab initio and atomistic kinetic Monte Carlo simulations In these simulations both self interstitials and vacancies isolated or in clusters are considered Isochronal annealing after electron irradiation experiments have been simulated in pure Fe Fe-Cu and Fe-Mn dilute alloys focusing on recovery stages I and II The parameters regarding the self interstitial - solute atom interactions are based on ab initio predictions and some of these interactions have been slightly adjusted without modifying the interaction character on isochronal annealing experimental data The different recovery peaks are globally well reproduced These simulations allow interpreting the different recovery peaks as well as the effect of varying solute concentration For some peaks these simulations have allowed to revisit and re-interpret the experimental data In Fe-Cu the trapping of self interstitials by Cu atoms allows experimental results to be reproduced although no mixed dumbbells are formed contrary to the former inter pretations Whereas in Fe-Mn the favorable formation of mixed dumbbell plays an important role in the Mn effect.
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| 14. |
- Olsson, Pär, et al.
(författare)
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Ab initio threshold displacement energies in iron
- 2016
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Ingår i: Materials Research Letters. - : Taylor & Francis. - 2166-3831. ; 4:4, s. 219-225
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Tidskriftsartikel (refereegranskat)abstract
- The threshold displacement energy in iron is determined using ab initio molecular dynamics. This is the most fundamental input parameter for radiation damage assessments. The predictions agree well with the available experiments and provide a significantly lower average value for iron than the standard one. This result impacts radiation damage assessments in iron alloys and steels and especially so for dose estimations and conditions close to the threshold. The importance of using an appropriate description of the core and valence electrons is highlighted. Energy loss simulations provide important fitting parameters for improved interatomic potentials. IMPACT STATEMENT Ground-breaking ab initio calculations of the threshold displacement energies in iron show significant differences in the angular anisotropy and predicted average value with respect to previous literature.
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| 15. |
- Toijer, Elin, et al.
(författare)
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Solute-point defect interactions, coupled diffusion, and radiation-induced segregation in fcc nickel
- 2021
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Ingår i: Physical Review Materials. - : American Physical Society (APS). - 2475-9953. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- Radiation-induced segregation (RIS) of solutes in materials exposed to irradiation is a well-known problem. It affects the lifetime of nuclear reactor core components by favoring radiation-induced degradation phenomena such as hardening and embrittlement. In this work, RIS tendencies in face centered cubic (fcc) Ni-X (X = Cr, Fe, Ti, Mn, Si, P) dilute binary alloys are examined. The goal is to investigate the driving forces and kinetic mechanisms behind the experimentally observed segregation. By means of ab initio calculations, point-defect stabilities and interactions with solutes are determined, together with migration energies and attempt frequencies. Transport and diffusion coefficients are then calculated in a mean-field framework, to get a full picture of solute-defect kinetic coupling in the alloys. Results show that all solutes considered, with the exception of Cr, prefer vacancy-mediated over interstitial-mediated diffusion during both thermal and radiation-induced migration. Cr, on the other hand, preferentially migrates in a mixed-dumbbell configuration. P and Si are here shown to be enriched, and Fe and Mn to be depleted at sinks during irradiation of the material. Ti and Cr, on the other hand, display a crossover between enrichment at lower temperatures, and depletion in the higher temperature range. Results in this work are compared with previous studies in body centered cubic (bcc) Fe, and discussed in the context of RIS in austenitic alloys.
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| 16. |
- Terentyev, D., et al.
(författare)
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Effect of the interatomic potential on the features of displacement cascades in alpha-Fe : A molecular dynamics study
- 2006
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 351:03-jan, s. 65-77
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Tidskriftsartikel (refereegranskat)abstract
- The primary state of damage obtained in molecular dynamics (MD) simulations of displacement cascades in alpha-Fe, particularly the fraction of point-defects in clusters, depends on the interatomic potential used to describe the atomic interactions. The differences may influence the microstructural evolution predicted in damage accumulation models which use results from MD cascade simulations as input. In this work, a number of displacement cascades of energy ranging from 5 to 40 keV have been simulated using the same procedure with four different interatomic potentials for alpha-Fe, each of them providing, among other things, varying descriptions of self-interstitial atoms (SIA) in this metal. The behaviour of the cascades at their different phases and the final surviving defect population have been studied and compared applying the same cascade analysis criteria for all potentials. The outcome is discussed trying to identify the characteristics of the potential that have the largest influence on the predicted primary state of damage.
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