Oxygen control in lead-bismuth eutectic: First validation of electrochemical oxygen sensors in static conditions

The control of the impurities, and of oxygen in particular, is of major interest for ensuring adequate and safe operation of lead alloys facilities from the viewpoint of the corrosion phenomenon : spallation targets or coolants for hybrid or fast reactors, currently under studies within the transmutation topic of the 1991 law on nuclear waste disposal. In addition, because of the very low oxygen solubility in lead alloys, it is compulsory to avoid saturation in any part of a defined system and in any operating condition so as to avoid any plugging by lead oxide built-up (fuel assembly feet, ...). For the oxygen control, the on-line monitoring of the dissolved oxygen content is required. Electrochemical sensors built with yttria stabilized zirconia were developed and tested in various static facilities : BIP, JACOMEX glove box, COLIMESTA. The experimental results were compared to the theoretical formulation, and a calibration method was applied (search for the singular point defining the saturation temperature). The operating range is as follows: 280°C-550°C, $10^{-10}$ - 10 ppm (1 ppm = l0$^{-4}$ weight%), for a 40% estimated accuracy. Service life is more than 1000 hours up to now. Reproducibility, time drift, time to response, and mechanical resistance are satisfactory. Based upon these results a first validation of these oxygen sensors is obtained in static conditions

The effect of wave-induced turbulence on intertidal mudflats: Impact of boat traffic and wind

Semi-diurnal and fortnightly surveys were carried out to quantify the effects of wind- and navigation-induced highenergy events on bed sediments above intertidal mudflats. The mudflats are located in the upper fluvial part (Oissel mudflat) and at the mouth (Vasiere Nord mudflat) of the macrotidal Seine estuary. Instantaneous flow velocities and mudflat bed elevation were measured at a high frequency and high resolution with an acoustic doppler velocimeter (ADV) and an ALTUS altimeter, respectively. Suspended particulate matter concentrations were estimated by calibrating the ADV acoustic backscattered intensity with bed sediments collected at the study sites. Turbulent bed shear stress values were estimated by the turbulent kinetic energy method, using velocity variances filtered from the wave contribution. Wave shear stress and maximum wave–current shear stress values were calculated with the wave–current interaction (WCI) model, which is based on the bed roughness length, wave orbital velocities and the wave period (TS). In the fluvial part of the estuary, boat passages occurred unevenly during the surveys and were characterized by long waves (TS450 s) induced by the drawdown effect and by short boat-waves (TSo10 s). Boat waves generated large bottom shear stress values of 0.5Nm-2 for 2–5 min periods and, in burst of several seconds, larger bottom shear stress values up to 1Nm-2. At the mouth of the estuary, west south-west wind events generated short waves (TSo10 s) of HS values ranging from 0.1 to 0.3 m. In shallow-water environment (water depth o1.5 m), these waves produced bottom shear stress values between 1 and 2Nm-2. Wave–current shear stress values are one order of magnitude larger than the current-induced shear stress and indicate that navigation and wind are the dominant hydrodynamic forcing parameters above the two mudflats. Bed elevation and SPM concentration time series showed that these high energy events induced erosion processes of up to several centimetres. Critical erosion shear stress (tce) values were determined from the SPM concentration and bed elevation measurements. Rough tce values were found above 0.2Nm-2 for the Oissel mudflat and about 1Nm-2 for the Vasiere Nord mudflat. These results demonstrate the advantages of combining the measurement of instantaneous velocity and bed elevation to determine in situ the erosion and deposition processes as a function of bottom shear stress variations

Morphological responses of an estuarine intertidal mudflat to constructions since 1978 to 2005: The Seine estuary (France)

International audienceSince 1834 the Seine estuary (France) has been the site of numerous construction projects with the aim to accommodate and secure boat traffic. Since 1978, the increasing of the activities of Le Havre port, located at the mouth of the estuary, has accelerated the construction work rate. Several dykes, a bridge, and new port facilities have been constructed in rapid succession, modifying considerably the hydrodynamic conditions which sustain a partially vegetated sandy–muddy tidal flat located in the North bank of the estuary between the new port of Le Havre and the Normandy bridge achieved in 1995. The present study deals with the morphological evolution of this zone from 1978 to 2005. The use of a low altitude remote sensing technique combined with traditional methods of ground survey and probes allow to demonstrate the impact of human activities on sedimentary and vegetation dynamics. The Northern mudflat of the estuary is the most affected by these human activities, which surface have reduced of 62% during the last 27 years with an intensified local erosion during the last 27 months corresponding to a loss 1250 000 m3 of fine-grained sediment. At the same time, the general sanding up in the channel of the zone has caused a loss of more than 31% of the tidal prism, more than three quarters of which occurred during the last three years. Results also establish that the response times of the sedimentary or topographic readjustment to an installation depend on the extent and the nature of the construction. In fact, the sedimentary readjustments to an installation can be delayed by up to 10 years in the case of the Seine estuary. This delay is explained by a rapid succession of construction works which may occult the effect of a single installation. Except in the case of a dyke built perpendicular to ebb and flood currents, the impacts of these installations reach a hydrosedimentary equilibrium on the level between 1 and 7 years after their completion

Glacial, fluvial, coastal and offshore cascading-system to assess deglaciation in a polar environment, a case study in the Kongsffjorden area, Svalbard

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