Short and Long-Term Sensitivity of Lab-Scale Thermocline Based Thermal Storage to Flow Disturbances

Molten-salt thermocline-based systems are a low-cost option for single-tank thermal energy storage in concentrated solar power plants. Due to the high variability in solar energy availability, these energy storage devices are subject to transient heat loads during charging that can affect the storage efficiency. Numerical simulations were conducted to analyze the stability characteristics of a lab-scale thermocline tank subject to a flow disturbance during charging under different operating temperatures. The charging process was first simulated at a constant Reynolds number for three different Atwood numbers; a stably stratified fluid layer develops inside the storage tank in all cases. A flow disturbance was then introduced at the inlet of the stratified thermocline tank by inserting colder fluid for a short period of time. The disturbance interacts with the thermocline and causes oscillations and mixing. The thermocline oscillations are under-damped and lead to an increase in thermocline region thickness. The transient behavior of the thermocline and the decay rate in its oscillations were analyzed; the damping time depends on the Atwood number. The persistence of flow disturbance effects during long-term cyclical operation was also investigated. Several charge/discharge cycles were simulated at constant Reynolds number to obtain a time-periodic thermal response for each Atwood number. The characteristic flow disturbance was introduced at the inlet during a single charging process, and the thermocline region was observed during several subsequent charge/discharge cycles to assess the long-term temporal attenuation of the disturbance. The thermocline almost fully recovers to the time-periodic behavior after a single cycle

Les paléoenvironnements de la fin du Pléistocène et de l'Holocène dans la réserve de Lopé (Gabon) : approche par les indicateurs géomorphologiques, sédimentologiques, phytologiques, géochimiques et anthropogènes des milieux enregistreux de la dépression de la Lopé

International audienc

C activity in dissolved mineral carbon and identified organic matter in the Loire estuary (France)

Bottom sediments, fluid mud and suspended solids and dissolved mineral carbon were sampled during 8 cruises at dates corresponding to various tidal and hydrological conditions. Evaluation of the organic matter sources in particles and surface sediments into the Loire Estuary has been performed using molecular markers. The results obtained show that the natural organic matter is an admixture of terrigenous and algal components. The terrigenous signature derived from land plants is present in the whole estuary and reflect a uniform dispersal of terrestrial inputs. The production of biogenic material by aquatic photosynthetic organisms is higher in the fluvio-estuarine zone and decreases seaward. In addition to natural organic matter, a contamination from fossil fuels and components derived from pyrolysis has been assessed. Organic carbon in suspended matter and sediments show homogenous 14C values (0.3 ± 0.2Bq/g) confirming a soil origin. At the opposite, 14C activity of dissolved mineral carbon is higher ranging between 150 to 200% of modern carbon activity and clearly indicates a noticeable contribution from reactors. Radiocarbon concentrations decrease seaward and are strongly correlated with salinity reflecting hydrodynamic and stratification processes in the marine estuary

Identification of sources and distribution of radiocarbon in the vicinity of La Hague nuclear reprocessing plant

The terrestrial environment in the vicinity of La Hague nuclear reprocessing plant (COGEMA) is potentially influenced by two sources (atmospheric and marine) and by three ways of radionuclides transfer: 1) atmospheric fallout from old nuclear bombs experiments, 2) atmospheric fallout from gaseous throwing out from the reprocessing plant 3) marine aerosol and degassing (sea to land transfer) bearing radionuclides originating from liquid waste from the plant. Institute for Protection and Nuclear Safety (IPSN) has organised since 1997, with the collaboration of the Groupe d'Etudes Atomiques (GEA) de la Marine Nationale and the Laboratoire des Sciences du Climat et de l'Environnement (LSCE/CEA-CNRS), studies to identify radionuclides sources (atmospheric and marine) and to provide an evaluation of the radiocarbon around La Hague nuclear reprocessing plant and to follow the concentration evolution versus time. A sampling strategy has been established to provide a map of the distribution of radio-elements around the reprocessing plant and to identify the mode of transfers, to determine the deposition rates on soil and vegetation in order to precise the transfer model of radio-element in plants. Three experiments in terrestrial environment with sampling of a bioindicator like furze has done in 1997, 1998 and 1999. In 2000, during TE-SEA cruise with the Research Vessel (RV) "Côtes de la Manche", the specific objective was to determine if there was 14C transfer as CO2 between sea to land