European DEMO divertor target: Operational requirements and material-design interface

Recently, an integrated program of conceptual design activities for the European DEMO reactor was launched in the framework of the EUROfusion Consortium, where reliable power handling capability was identified as one of the most critical scientific as well as technological challenges for a DEMO reactor. The divertor is the key in-vessel plasma-facing component being in charge of power exhaust and removal of impurity particles. The DEMO divertor target will have to withstand extreme thermal loads where the local peak heat flux is expected to reach up to 20 MW/m2 during slow transient events in DEMO. To assure sufficient heat removal capability of the divertor target against normal and transient operational scenarios under expected cumulative neutron dose of up to 13 dpa is one of the fundamental engineering challenges imposed on target design. To develop the design of the DEMO divertor and related technologies, an R&D work package 'Divertor' has been set up in this consortium. The subproject 'Target Development' is devoted to the development of the conceptual design and the core technologies of the plasma-facing target. Devising and implementing novel structural heat sink materials (e.g. W/Cu composites) to advanced target design concepts is one of the major objectives of this subproject. In this paper, the underlying design requirements imposed by the envisaged power exhaust goal and the prominent material-design interface issues are discussed. In addition, the candidate design concepts being currently considered are presented together with the related material issues. Finally, the first results achieved so far are presented

Validity and limitations of simple reaction kinetics to calculate concentrations of organic compounds from ion counts in PTR-MS

In September 2017, we conducted a proton-transfer-reaction mass-spectrometry (PTR-MS) intercomparison campaign at the CESAR observatory, a rural site in the central Netherlands near the village of Cabauw. Nine research groups deployed a total of 11 instruments covering a wide range of instrument types and performance. We applied a new calibration method based on fast injection of a gas standard through a sample loop. This approach allows calibrations on timescales of seconds, and within a few minutes an automated sequence can be run allowing one to retrieve diagnostic parameters that indicate the performance status. We developed a method to retrieve the mass-dependent transmission from the fast calibrations, which is an essential characteristic of PTR-MS instruments, limiting the potential to calculate concentrations based on counting statistics and simple reaction kinetics in the reactor/drift tube. Our measurements show that PTR-MS instruments follow the simple reaction kinetics if operated in the standard range for pressures and temperature of the reaction chamber (i.e. 1-4 mbar, 30-120 degrees, respectively), as well as a reduced field strength E/N in the range of 100-160 Td. If artefacts can be ruled out, it becomes possible to quantify the signals of uncalibrated organics with accuracies better than +/- 30 %. The simple reaction kinetics approach produces less accurate results at E/N levels below 100 Td, because significant fractions of primary ions form water hydronium clusters. Deprotonation through reactive collisions of protonated organics with water molecules needs to be considered when the collision energy is a substantial fraction of the exoergicity of the proton transfer reaction and/or if protonated organics undergo many collisions with water molecules.Peer reviewe

Deficits of psychomotor and mnesic functions across aging in mouse lemur primates.

Owing to a similar cerebral neuro-anatomy, non-human primates are viewed as the most valid models for understanding cognitive deficits. This study evaluated psychomotor and mnesic functions of 41 young to old mouse lemurs (Microcebus murinus). Psychomotor capacities and anxiety-related behaviors decreased abruptly from middle to late adulthood. However, mnesic functions were not affected in the same way with increasing age. While results of the spontaneous alternation task point to a progressive and widespread age-related decline of spatial working memory, both spatial reference and novel object recognition (NOR) memory tasks did not reveal any tendency due to large inter-individual variability in the middle-aged and old animals. Indeed, some of the aged animals performed as well as younger ones, whereas some others had bad performances in the Barnes maze and in the object recognition test. Hierarchical cluster analysis revealed that declarative-like memory was strongly impaired only in 7 out of 25 middle-aged/old animals. These results suggest that this analysis allows to distinguish elder populations of good and bad performers in this non-human primate model and to closely compare this to human aging.journal article20142015 01 09importe

β-Adrenoreceptor Stimulation Mediates Reconsolidation of Social Reward-Related Memories

In recent years, the notion that consolidated memories become transiently unstable after retrieval and require reconsolidation to persist for later use has received strong experimental support. To date, the majority of studies on reconsolidation have focused on memories of negative emotions, while the dynamics of positive memories have been less well studied. Social play, the most characteristic social behavior displayed by young mammals, is important for social and cognitive development. It has strong rewarding properties, illustrated by the fact that it can induce conditioned place preference (CPP). In order to understand the dynamics of positive social memories, we evaluated the effect of propranolol, a β-adrenoreceptor antagonist known to influence a variety of memory processes, on acquisition, consolidation, retrieval and reconsolidation of social play-induced CPP in adolescent rats.Systemic treatment with propranolol, immediately before or after a CPP test (i.e. retrieval session), attenuated CPP 24 h later. Following extinction, CPP could be reinstated in saline--but not in propranolol-treated rats, indicating that propranolol treatment had persistently disrupted the CPP memory trace. Propranolol did not affect social play-induced CPP in the absence of memory retrieval or when administered 1 h or 6 h after retrieval. Furthermore, propranolol did not affect acquisition, consolidation or retrieval of social play-induced CPP.We conclude that β-adrenergic neurotransmission selectively mediates the reconsolidation, but not other processes involved in the storage and stability of social reward-related memories in adolescent rats. These data support the notion that consolidation and reconsolidation of social reward-related memories in adolescent rats rely on distinct neural mechanisms

Les nouveaux combustibles pour réacteurs à neutrons rapides

Les études sur le combustible des Réacteurs à Neutrons Rapides (RNR) explorent, depuis 1990, différentes options destinées à la gestion du plutonium et des actinides mineurs principalement dans le cadre des programmes CAPRA et SPIN. De nouveaux types de combustibles sont ainsi considérés et les solutions prises en compte pour ces applications concernent le choix du matériau combustible lui-même mais aussi la conception de l'aiguille et de l'assemblage combustible (notion d'hétérogénéité faisant appel à l'introduction de matériaux nouveaux inertes ou modérateurs). Néanmoins, les objectifs filière comme la possibilité d'atteindre de forts taux de combustion (économie) et la nécessité de travailler avec des matériaux de structure capables de supporter de très fortes doses restent d'actualité. Aujourd'hui, un important programme d'irradiation avec toutes ses activités connexes (fabrications, caractérisations, examens et études de retraitement) est en place. Il est traité dans le cadre de nombreuses collaborations internationales et se déroule dans différents réacteurs français et étrangers. On attend un retour significatif de ce programme vers 2003-2005

Origine et développement du combustible Uranium-Molybdène (U-Mo)

Historiquement, la plupart des réacteurs expérimentaux, en particulier les Réacteurs de Test et de Recherche, producteurs de hauts flux neutroniques, ont utilisé du combustible métallique à haut enrichissement en U235 (>90%). La politique actuelle est de plafonner l'enrichissement en U235 à 20% (objectif de non-prolifération). Après une première génération de combustible enrichi à 19.75% en U235 de type siliciure non retraitable, un consensus s'est dégagé au niveau international autour d'une nouvelle génération de combustible enrichi à 19.75% en U235, le combustible U-Mo (uranium - molybdène). Ce combustible permet de maintenir, voire d'améliorer, les performances actuelles des réacteurs tout en garantissant une fin de cycle acceptable (combustible retraitable). CEA, COGEMA, CERCA, FRAMATOME et TECHNICATOME ont regroupé leurs moyens techniques, financiers et leur savoir-faire pour développer en commun ce nouveau combustible U-Mo. Il est destiné aux réacteurs existants déjà convertis ou devant se convertir à l'uranium faiblement enrichi (en France, en Allemagne, au Japon, en Suède, ...) ainsi qu'aux nouveaux réacteurs tels que le RJH en France ou RRR en Australie. Ce programme de R& D démarré en 1999 est conduit en cohérence avec les travaux réalisés aux USA par l'Argonne National Laboratory. Compte tenu de la nécessité impérieuse pour les réacteurs de disposer en 2006 de ce nouveau combustible, seul à offrir une véritable solution de fin de cycle, l'objectif du groupe U-Mo français est de terminer la R& D et la qualification du combustible en 2005

Relationship between the herbaceous and woody vegetation caracteristics and biological soil crusts distribution in fallow and rangeland across a latitudinal gradient in Sahelian Western Niger [abstract]

EGU.European Geosciences Union General Assembly, Vienne, AUT, 22-/04/2012 - 27/04/201

Circulation du virus West Nile dans l’avifaune française. Bilan de sept années de surveillance

International audienc