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11. Cs diffusion mechanisms in UO2 investigated by SIMS, TEM, and atomistic simulations.

Author

Panetier, C., Pipon, Y., Gaillard, C., Mangin, D., Amodeo, J., Morthomas, J., Wiss, T., Benedetti, A., Ducher, R., Dubourg, R., and Moncoffre, N.

Subjects
SECONDARY ion mass spectrometry, DIFFUSION, MOLECULAR dynamics, ACTIVATION energy, DEPTH profiling, DIFFUSION coefficients
Abstract

Experimental investigations and atomistic simulations are combined to study the cesium diffusion processes at high temperature in UO2. After 133Cs implantation in UO2 samples, diffusion coefficients are determined using the depth profile evolution after annealing as measured by secondary ion mass spectrometry. An activation energy of 1.8 ± 0.2 eV is subsequently deduced in the 1300–1600 °C temperature range. Experimental results are compared to nudged elastic band simulations performed for different atomic paths including several types of uranium vacancy defects. Activation energies ranging from 0.49 up to 2.34 eV are derived, showing the influence of the defect (both in terms of type and concentration) on the Cs diffusion process. Finally, molecular dynamics simulations are performed, allowing the identification of preferential Cs trajectories that corroborate experimental observations. [ABSTRACT FROM AUTHOR]

Published
2022
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25. Updates on European Americium Uranium Oxide Fuel and Clad Compatibility Tests for European Radioisotope Power Systems

Author

Watkinson, E.J., primary, Cremer, B., additional, Lajarge, P., additional, Gardeur, S., additional, Vigier, J.-F., additional, Berkmann, C., additional, Ernstberger, M., additional, Wiss, T., additional, Freis, D., additional, Crawford, T., additional, Pfirrmann, S., additional, Ambrosi, R., additional, Konings, R., additional, and Stephenson, K., additional

Published
2022
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33. Exploratory Research on Radioisotope Thermoelectric Generators for Deep Space Missions

Author

Freis D., Vigier J.F., Popa K., Wiss T., Griveau J.-C., D’Agata E., and Somers J.

Subjects
Environmental sciences, GE1-350
Abstract

To support the development of a Radioisotope Power Source (RPS) for exploration missions into deep space based on 241Am, the European Commission’s Joint Research Centre (JRC) has recently launched an exploratory research project, scheduled for a period of two years. It aims at finding innovative solutions for higher performance, safety and reliability of such a device. In addition, it will serve as a start-up platform for this field of research and enable identification of research areas, where JRC can significantly complement and support the already existing activities in Europe. The project is divided into several subtasks and will investigate –safety related properties of americium (oxide) as a heat source, – compatibility of americium compounds with cladding and structural materials, –properties of alternative americium compounds, –properties of advanced thermoelectric materials. The new exploratory research project will be introduced together with an overview on the available facilities and capabilities of JRC in this domain. Alternative americium forms with potential improved stability versus the oxides are discussed and innovative thermoelectric materials based on actinides are introduced.

Published
2017
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34. Investigation on the use of Americium Oxide for Space Power Sources: Radiation Damage Studies

Author

Wiss T., Freis D., Griveau J.-C., Popa K., Vigier J.-F., Somers J., D’Agata E., Konings R.J.M., Benes O., Colle J.-Y., and Dieste O.

Subjects
Environmental sciences, GE1-350
Abstract

Within Europe 241Am is a feasible alternative to 238Pu that can provide a heat source for radioisotope thermoelectric generators (RTGs) and radioisotope heating units (RHUs) to be used in Electrical power sources used in outer planet missions. In the EPSO-SPACE* project developed as an exploratory research at JRC, a new type of nuclear power source, to provide heat and electricity for deep space missions is considered. It will consist of a 241Am based compound with aerogel thermal insulation and thermocouples in close contact with the heat source. The assembly is inside an iridium encapsulation to withstand all relevant accident scenarios. The design will be modular and combinable for required electrical output. Several candidate Americium compounds will be investigated for chemical stability at high temperature and for self-irradiation damage. New thermo-electric converter materials containing actinides will be assessed, and a robust encapsulation designed. Safety analyses will be performed including launch explosion and re-entry accidents. The research will conclude in a conceptual design of a prototype power source. In the first part of this study, americium dioxide will be considered from the point of view of its chemical durability and of its behavior against radiation damage and helium formation, two aspects to be carefully investigated due to the high alpha-activity of the americium. Transmission electron Microscopy (TEM) and helium thermal desorption spectrometry (TDS) experiments will be described and results on aged (more than 30 years) AmO2 reported. Some comparison with 238PuO2 based RTG’s will be discussed.

Published
2017
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40. Inert Matrix Fuel

Author

Pöml, P., primary, Konings, R.J.M., additional, Somers, J., additional, Wiss, T., additional, de Haas, G.J.L.M., additional, and Klaassen, F.C., additional

Published
2012
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44. Self-irradiation effects in UO 2 and (U,Pu)O 2 accelerated by doping with 238Pu

Author

de Bona, E, Dieste, O, Benedetti, A., Wiss, T., Cologna, M, Baldinozzi, Gianguido, Konings, R, Laboratoire Structures, Propriétés et Modélisation des solides (SPMS), Institut de Chimie du CNRS (INC)-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS), European Commission - Joint Research Centre [Karlsruhe] (JRC), and Baldinozzi, Gianguido

Subjects
[CHIM.MATE] Chemical Sciences/Material chemistry, [CHIM.RADIO] Chemical Sciences/Radiochemistry, [PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], [CHIM.CRIS]Chemical Sciences/Cristallography, [CHIM.MATE]Chemical Sciences/Material chemistry, [CHIM.CRIS] Chemical Sciences/Cristallography, [CHIM.RADIO]Chemical Sciences/Radiochemistry, [PHYS.COND.CM-MS] Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci]
Abstract

International audience; In order to tackle the issue of long term sustainability and safety of nuclear waste management, the new concept of Gen IV fast reactors (FR) has been designed. These new reactor types however require the design and development of completely new materials, including new nuclear fuels (NF), which will be also the component withstanding the most severe irradiation and temperature conditions. The present work aims at improving our knowledge about the behaviour of mixed oxides (MOX) fuels, which represent a crucial step towards the licensing process of those reactors. In particular, the focus of this work is on isolating and quantifying the effect of alpha-radiation damage on the thermal and physical properties of MOX fuels.

Published
2019

45. Particle Size vs. Local Environment Relationship for ThO2 and PuO

Author

Bonato, L., Virot, M., Dalodiere, E., Dumas, T., Mesbah, A., Dieste Blanco, O., Wiss, T., Prieur, D., Rossberg, A., Venault, L., Moisy, P., Nikitenko S, I., CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), and CADARACHE, Bibliothèque

Subjects
[PHYS.NUCL] Physics [physics]/Nuclear Theory [nucl-th], actinides, plutonium, [PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th], [PHYS.NEXP] Physics [physics]/Nuclear Experiment [nucl-ex], nanoscale, [PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex], DWF, thorium, EXAFS, nanostructuration, oxides, TEM, nanoparticles
Abstract

International audience; Nanomaterials have attracted considerable interest in recent interdisciplinary research for their technological applications related to the nanometric size of the building blocks composing the solids (ex crystallite or atomic and molecular groups).[1,2] Nanostructured materials can be defined as solid samples exhibiting a microstructure the characteristic length scale of which is roughly ranging between 1 and 10 nm.[1] The controlled microstructure of materials at the atomic level offers new physical and chemical properties in comparison to similar bulk materials already applied, for instance, in catalysis, synthesis of luminescent materials, preparation of cosmetic and solar creams, preparation of solar cells, etc.[3,4] Such paradigm has been attributed to the increased surface-to-volume ratio of the shrinking particle size which increase the number of surface and interface atoms generating stress, stain, and structural perturbations.[2] In actinide chemistry, the synthesis and characterization of nanomaterials is very scarce but is of growing interest due to the contribution of actinide nanomaterials in environment (ex migration of actinides) and industry (ex high burn up structures). Recently, we observed the nanostructuration of PuO2 and noticed its outstanding reactivity under ultrasound irradiation which stirred up our curiosity concerning the local environment of this oxide at the nanoscale.[5] In this work, we investigate the synthesis and relevant characterization of nanostructured PuO2 and ThO2. Th can be considered as a good surrogate for Pu because both elements exhibit close ionic radii, their oxide crystallize in the fluorite Fm-3m structure, and they both exist at the (+IV) oxidation state. More precisely, Th only exists at the +IV oxidation state thus avoiding misinterpretations related to the potential contribution of other oxidation states in the crystalline structure. The synthesis studies allowed us to select the nanostructuration conditions for the various oxides and a careful characterization and correlation with AFM, HR-TEM, Raman spectroscopy, XRD and XAS techniques allowed us to probe the local disorder for the various oxides as a function of the particle size. Particularly, EXAFS investigations clearly show a linear decrease of the coordination number for An-O and An-An spheres with the shrinking particle sizes. The crystalline nature of the particles (HR-TEM, XRD) suggest that these observation are correlated to the increasing surface contribution of these particles. These new results raise the question of the physico-chemical properties of oxide nanomaterials crystallizing in the fluorite structure which are materials of paramount importance for engineering applications such as nuclear energy, solid oxide fuel cells, catalysis, or sensors.

Published
2019

47. Probing the Local Structure of Nanoscaled Actinide Oxides: A Comparison between PuO2 and ThO2 Nanoparticles Rules out PuO2+x Hypothesis

Author

Bonato, L., Virot, M., Dumas, T., Mesbah, A., Dalodière, E., Dieste Blanco, O., Wiss, T., Le Goff, X., Odorico, M., (0000-0001-5087-0133) Prieur, D., Roßberg, A., Venault, L., Dacheux, N., Moisy, P., Nikitenko, S. I., Bonato, L., Virot, M., Dumas, T., Mesbah, A., Dalodière, E., Dieste Blanco, O., Wiss, T., Le Goff, X., Odorico, M., (0000-0001-5087-0133) Prieur, D., Roßberg, A., Venault, L., Dacheux, N., Moisy, P., and Nikitenko, S. I.

Abstract

Actinide research at the nanoscale is gaining fundamental interest due to environmental and industrial issues. The knowledge of the local structure and speciation of actinide nanoparticles, which possibly exhibit specific physico-chemical properties in comparison to bulk materials, would help in a better and reliable description of their behavior and reactivity. Herein, the synthesis and relevant characterization of PuO2 and ThO2 nanoparticles displayed as dispersed colloids, nanopowders or nanostructured oxide powders, allow to establish a clear relationship between the size of the nanocrystals composing these oxides and their corresponding An(IV) local structure investigated by EXAFS spectroscopy. Particularly, the probed An(IV) first oxygen shell evidences an analogous behavior for both Pu and Th oxides. This observation suggests that the often observed and controversial splitting of the Pu-O shell on the Fourier transformed EXAFS signal of PuO2 samples is attributed to a local structural disorder driven by a nanoparticle surface effect rather than to the presence of PuO2+x species.

Published
2020

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