Combustibles nucléaires

International audienceLe combustible est l'un des éléments essentiels d'un réacteur nucléaire. En son sein ont lieu les réactions nucléaires de fission des atomes lourds, uranium et plutonium. Il est au cœur du réacteur, mais également au cœur du système nucléaire dans son ensemble. Sa conception et ses propriétés influent sur le comportement du réacteur, ses performances et sa sûreté.Même s'il rentre assez faiblement dans le coût du kilowatt-heure produit par les centrales nucléaires actuelles, sa bonne utilisation représente un enjeu économique important. De grands progrès restent à accomplir pour augmenter son temps de séjour en réacteur, lui permettre ainsi de fournir davantage d'énergie, améliorer sa robustesse.Au-delà de l'économie et de la sûreté, des questions aussi stratégiques que l'utilisation du plutonium, la préservation des ressources et la gestion des déchets nucléaires se posent, et de véritables défis technologiques surgissent.Cette monographie résume les connaissances actuelles sur le combustible nucléaire, son comportement en réacteur, ses limites d'utilisation et ses pistes de R&D. Elle illustre également les recherches en cours en présentant quelques résultats marquants obtenus récemment

Appetence behaviours of the triatomine bug Rhodnius prolixus on a servosphere in response to the host metabolites carbon dioxide and ammonia

A combination of 1,000ppm CO2 plus 30-40ppb NH3 in an air stream induced Rhodnius prolixus nymphs walking on a servosphere to perform a series of appetence behaviours. Shortly after the onset of stimulation the nymphs turned sharply upwind towards the source of the chemostimuli (within 13±9s) from mostly downwind and crosswind walks in the air stream alone. The mean vector angles of these upwind tracks were concentrated in a cone 60° either side of due upwind. The upwind walking bugs stopped more frequently but for a shorter duration and walked at a higher speed than before stimulation. During stops in the presence of the chemostimuli the bugs frequently corrected their course angles and extended their forelegs to reach higher with their antennae in the air. In the air stream alone, R. prolixus nymphs frequently sampled the sphere surface with the antennae and cleaned their antennae with the foreleg tarsi. However, the nymphs only briefly tapped the left or right antennal flagellum on the corresponding first leg tarsus and never touched the servosphere surface in the presence of the chemostimuli. After chemostimulus removal from the air stream the bugs continued to respond with the same appetence responses as during stimulation, but walked more tortuously in a crosswind direction in an effort to regain contact with the chemostimul

Genetic evolution of low pathogenecity H9N2 Avian influenza viruses in Tunisia: acquisition of new mutations

<p>Abstract</p> <p>Background</p> <p>Since the end of 2009, H9N2 has emerged in Tunisia causing several epidemics in poultry industry resulting in major economic losses. To monitor variations of Influenza viruses during the outbreaks, Tunisian H9N2 virus isolates were identified and genetically characterized.</p> <p>Methods</p> <p>The genomic RNA segments of Tunisian H9N2 strains were subjected to RT-PCR amplifications followed by sequencing analysis.</p> <p>Results</p> <p>Phylogenetic analysis demonstrated that A/Ck/TUN/12/10 and A/Migratory Bird/TUN/51/10 viruses represent multiple reassortant lineages, with genes coming from Middle East strains, and share the common ancestor Qa/HK/G1/97 isolate which has contributed internal genes of H5N1 virus circulating in Asia. Some of the internal genes seemed to have undergone broad reassortments with other influenza subtypes. Deduced amino acid sequences of the hemagglutinin (HA) gene showed the presence of additional glycosylation site and Leu at position 234 indicating to binding preference to α (2, 6) sialic acid receptors, indicating their potential to directly infect humans. The Hemagglutinin cleavage site motif sequence is <b>³³³PARSSR*GLF³⁴¹</b>which indicates the low pathogenicity nature of the Tunisian H9N2 strains and the potential to acquire the basic amino acids required for the highly pathogenic strains. Their neuraminidase protein (NA) carried substitutions in the hemadsorption (HB) site, similar to those of other avian H9N2 viruses from Asia, Middle Eastern and human pandemic H2N2 and H3N2 that bind to α -2, 6 -linked receptors. Two avian virus-like aa at positions 661 (A) and 702 (K), similar to H5N1 strains, were identified in the polymerase (PB2) protein. Likewise, matrix (M) protein carried some substitutions which are linked with increasing replication in mammals. In addition, H9N2 strain recently circulating carried new polymorphism, "GSEV" PDZ ligand (PL) C-terminal motif in its non structural (NS) protein.</p> <p>Two new aa substitutions (I) and (V), that haven't been previously reported, were identified in the polymerase and matrix proteins, respectively. Nucleoprotein and non-structural protein carried some substitutions similar to H5N1 strains.</p> <p>Conclusion</p> <p>Considering these new mutations, the molecular basis of tropism, host responses and enhanced virulence will be defined and studied. Otherwise, Continuous monitoring of viral genetic changes throughout the year is warranted to monitor variations of Influenza viruses in the field.</p

A new polyomavirus isolated in goose: from the identification of the virus toward the development of a vaccine

Hemorrhagic nephritis enteritis of geese (HNEG) is a major disease affecting goose. We have isolated its agent and shown that it is a novel member of Polyomavirus genus. The biology of this viral infection has been studied, at the level of both animal and flocks, on breeders and fattening goslings. An inactivated and adjuvanted vaccine has also been prepared and assayed on breeders and goslings. This program should result in the control of the disease on the field. It also addresses the question of the impact of polyomaviruses in animal and public health.La Néphrite hémorragique entérite de l'oie (NHEO) constitue une maladie majeure de l'oie. Nous avons récemment isolé son agent et montré qu'il s'agit d'une nouvelle espèce virale du genre Polyomavirus. La biologie de cette infection virale a été étudiée, à l'échelle de l'animal infecté et des populations d'oies, chez les reproducteurs et les oisons destinés au gavage. Un candidat vaccin, inactivé et adjuvé, a été préparé et testé chez les oies reproductrices et les oisons en croissance. Ce programme de recherche devrait permettre à terme le contrôle de l'affection sur le terrain. Il pose aussi la question de l'impact en santé animale, voire en santé publique, des polyomavirus

Episode H5N8 d'influenza aviaire en France en 2016-2017 : quel rôle pour la faune sauvage ?

L'influenza aviaire (IA) est une menace permanente, qui arrive parfois en Europe par le biais des oiseaux migrateurs. Un dispositif de surveillance est en place en permanence pour surveiller les mortalités dans l'avifaune, et particulièrement celles des oiseaux d'eau migrateurs. En octobre 2016, un épisode d'IA H5N8 qui était surveillé depuis sa survenue en République de Touva (Fédération de Russie, avril 2016) s'est déclaré en Europe. Il a entraîné des pertes conséquentes dans certaines populations d'oiseaux sauvages en Europe, ainsi que dans des filières avicoles. La situation en France s'est révélée paradoxale : l'atteinte a été majeure dans la filière avicole de canards gras du Sud- Ouest, mais les cas dans la faune sauvage sont restés peu nombreux et circonscrits. Ce n'est pas faute d'avoir renforcé la surveillance, soit événementielle (analyse des oiseaux trouvés morts) soit active autour des foyers domestiques. Plus de 800 cadavres d'oiseaux sauvages ont été analysés, dont beaucoup d'anatidés, 90 ont été détectés infectés regroupés en 55 cas dans l'avifaune libre et captive, et dix sites stratégiques ont fait l'objet d'une recherche intensifiée des cadavres et n'ont permis de trouver aucun cas positif supplémentaire. Plus de 300 oiseaux commensaux des élevages domestiques foyers ont été analysés et se sont tous révélés négatifs. Les performances du système de surveillance ne semblent pas pouvoir être mises en cause, et il apparaît donc qu'il y a bien eu des différences de circulation du virus par rapport à nos voisins d'outre-Rhin, mal expliquées à ce stade mais la situation en France est similaire à celle observée en Italie et en Espagne cet hiver, et correspond assez bien à l'épisode H5N8 qui avait circulé en Europe fin 2014/début 2015, sans toucher la France. (Résumé d'auteur

Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion