Arche de Tchernobyl

L’arche de Tchernobyl est un dispositif de confinement du réacteur accidenté de la centrale nucléaire de Tchernobyl, en Ukraine, et de son sarcophage endommagé construit en 1986. Il s'agit d'une structure métallique en forme d'arche de de haut et de large pour une portée de . Elle est conçue pour une durée de service de cent ans. Sa construction doit permettre le futur démantèlement du réacteur endommagé. Le dispositif a trois fonctions :

le confinement des matières radioactives ;

la protection du premier sarcophage dégradé, contre les agressions climatiques ;

la protection des travailleurs sur site ; ce second sarcophage abrite des ateliers destinés à décontaminer, démanteler et conditionner les matériaux radioactifs en vue de leur évacuation vers un futur lieu de stockage.

L’arche a été construite en retrait du réacteur, sur des longrines traitées au téflon, qui ont permis ensuite son déplacement jusqu'à son emplacement final en . Après des travaux de t

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Enhancing the Reliability and Throughput of Neurosphere Culture on Hydrogel Microwell Arrays

Stefan Kobel, Monika Limacher, Matthias Lütolf

The neurosphere assay is the standard retrospective assay to test the self-renewal capability and multipotency of neural stem cells (NSC) in vitro. However, it has recently become clear that not all neurospheres are derived from a NSC and that on conventional cell culture substrates, neurosphere motility may cause frequent neurosphere 'merging' (Singec et al., Nature Methods, 2006; Jessberger et al., Stem Cells, 2007). Combining biomimetic hydrogel matrix technology with microengineering, we developed a microwell array platform on which NSC fate and neurosphere formation can be unequivocally attributed to a single founding cell. Using time-lapse microscopy and retrospective immunostaining, the fate of several hundred single NSCs was quantified. Compared to conventional neurosphere culture methods on plastic dishes, we detected a more than 100% increase in single NSC viability on soft hydrogels. Effective confinement of single proliferating cells to microwells led to neurosphere formation of vastly different sizes, a high percentage of which showed stem cell phenotypes after one week in culture. The reliability and increased throughput of this platform should help to elucidate better the function of sphere-forming stem/progenitor cells independent of their proliferation dynamics.

2008

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Modelling of sawtooth-induced fast ion transport in positive and negative triangularity in TCV

Marcelo Baquero Ruiz, Basil Duval, Alexander Karpushov, Antoine Pierre Emmanuel Alexis Merle, Dmytry Mykytchuk, Mario Podesta, Olivier Sauter, Lorenzo Stipani, Duccio Testa, Matteo Vallar

Internal kinks are a common magneto hydro-dynamic (MHD) instability observed in tokamak operation when the q profile in the plasma core is close to unity. This MHD instability impacts both the transport of the bulk plasma (current, particle and energy transport) and minority species, such as fast ions. In tokamak a configuration variable (TCV) (R (0)/a = 0.88 m/0.25 m) the fast ion population is generated in the plasma by neutral beam tangential injection of energies up to 28 keV. TCV features 16 active shaping coils permitting a great flexibility in plasma shape, including negative triangularity (delta) configurations that show surprisingly high confinement. This study focuses on the transport of fast ions induced by sawteeth, by comparing two triangularity cases and simulation results with experimental data. Comparison of two equilibria with opposite delta shows that the fast ion drifts are larger for delta < 0. Furthermore, the sawtooth-induced transport in this case is larger than delta > 0 in similar conditions. Comparison with experimental data confirms the dominance of the modification of thermal kinetic profiles following the sawtooth crash in explaining drops in the neutron rates and fast ion D-alpha signals. Additional fast ion diffusion, however, improves the interpretation of the experimental data. For delta < 0, the amplitude of the perturbation better representing the experimental data is larger. Finally, an exploratory study for 50 keV particles (soon available in TCV) shows that the situation does not worsen for such particles.

IOP Publishing Ltd2022

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Does the Surface Matter? Hydrogen-Bonded Chain Formation of an Oxalic Amide Derivative in a Two- and Three-Dimensional Environment

Harald Brune, Marta Canas Ventura, Sylvain Clair, Klaus Kern, Uta Schlickum

We report on a multi-technique investigation of the supramolecular organisation of N,N-diphenyl oxalic amide under differently dimensioned environments, namely three-dimensional (3D) in the bulk crystal, and in two dimensions on the Ag(111) surface as well as on the reconstructed Au(111) surface. With the help of Xray structure analysis and scanning tunneling microscopy (STM) we find that the molecules organize in hydrogen-bonded chains with the bonding motif qualitatively changed by the surface confinement. In two dimensions, the chains exhibit enantiomorphic order even though they consist of a racemic mixture of chiral entities. By a combination of the STM data with near-edge X-ray absorption fine-structure spectroscopy, we show that the conformation of the molecule adapts such that the local registry of the functional group with the substrate is optimized while avoiding steric hindrance of the phenyl groups. In the low coverage case, the length of the chains is limited by the Au(111) reconstruction lines restricting the molecules into fcc stacked areas. A kinetic Monte Carlo simulated annealing is used to explain the selective assembly in the fcc stacked regions.

2008

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Catastrophe nucléaire de Tchernobyl

La catastrophe nucléaire de Tchernobyl () est un accident nucléaire majeur survenu le à dans le réacteur de la centrale nucléaire V.I. Lénine de Tchernobyl, située à de la ville de Prypiat et à

Centrale nucléaire de Tchernobyl

La centrale nucléaire de Tchernobyl (en « Черно́быльская атомная электростанция »), aussi désignée sous le nom officiel de « centrale nucléaire V. I. Lénine », est une centrale nucléaire à l'arrêt d

Énergie nucléaire

Selon le contexte d'usage, le terme d’énergie nucléaire recouvre plusieurs acceptions, toutes liées à la physique et aux réactions de noyaux atomiques.

Dans le langage courant, l’énergie nucléair