Status of the Sodium Gas Heat Exchanger (SGHE) development for the Nitrogen Power Conversion System planned for the ASTRID SFR prototype

International audienceIn the framework of the CEA RandD program developing the Advanced Sodium Technological Reactor for Industrial Demonstration (ASTRID), the present work describes the current status of an innovative compact heat exchanger and highlights the industrial challenges this technology raises. One of the main innovative options under investigation for ASTRID is the use of a Brayton cycle gas-power conversion system. This system permits to avoid the energetic sodium-water interaction, which can occur in steam generators in case of tube failure if a traditional Rankine cycle is used. In this novel concept, steam generators would be replaced by the Sodium Gas Heat Exchanger (SGHE). The first part of this paper presents the details of the original design of this heat exchanger which allows a high thermal compactness. The main studies supporting this development are described in the second part of the paper. The thermal hydraulic program demonstrates the potential of the technology used. An innovative geometry is also studied on the gas side improving the thermal compactness. Thermomechanical analyses show the good behavior of this exchanger under the ASTRID operating conditions. The manufacturing / welding process optimization is ongoing in order to produce a component with nuclear specifications. Specific sensors and control techniques are also being developed in order to assess the manufacturing process quality and to allow future in-service inspections. At last, the qualification program is presented and the first results obtained on an operating small scale SGHE mock up working under ASTRID conditions are described

Global genetic capacity for mixotrophy in marine picocyanobacteria

12 pages, 6 figures, 2 tablesThe assimilation of organic nutrients by autotrophs, a form of mixotrophy, has been demonstrated in the globally abundant marine picocyanobacterial genera Prochlorococcus and Synechococcus. However, the range of compounds used and the distribution of organic compound uptake genes within picocyanobacteria are unknown. Here we analyze genomic and metagenomic data from around the world to determine the extent and distribution of mixotrophy in these phototrophs. Analysis of 49 Prochlorococcus and 18 Synechococcus isolate genomes reveals that all have the transporters necessary to take up amino acids, peptides and sugars. However, the number and type of transporters and associated catabolic genes differ between different phylogenetic groups, with low-light IV Prochlorococcus, and 5.1B, 5.2 and 5.3 Synechococcus strains having the largest number. Metagenomic data from 68 stations from the Tara Oceans expedition indicate that the genetic potential for mixotrophy in picocyanobacteria is globally distributed and differs between clades. Phylogenetic analyses indicate gradual organic nutrient transporter gene loss from the low-light IV to the high-light II Prochlorococcus. The phylogenetic differences in genetic capacity for mixotrophy, combined with the ubiquity of picocyanobacterial organic compound uptake genes suggests that mixotrophy has a more central role in picocyanobacterial ecology than was previously thought.We thank the US National Science Foundation OCE postdoctoral research fellowship program and the Fulbright Commission, Spain for supporting APY. The work was also supported in part by the European Molecular Biology Laboratory, grants to SWC from the Gordon and Betty Moore Foundation (grant GBMF495) the National Science Foundation (grants OCE-1356460 and DBI-0424599), grants from the Simons Foundation (grant 337262), the Spanish Ministry of Science and Innovation grant to SGA, CGL2011-26848/BOS MicroOcean PANGENOMICS and U FP7-OCEAN.2011-2. Micro3B Marine Microbial Biodiversity, the Bioinformatics and Biotechnology Large Collaborative grant 287589 and is a contribution of the Simons Collaboration on Ocean Processes and Ecology (SCOPE)Peer Reviewe