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

Faecal-indicator bacteria and sedimentary processes in estuarine mudflats (Seine, France)

International audienceOver a three-year period, quantification of faecal indicators and the molecular detection of Escherichia coli and Salmonella were monitored in sediments from three contrasting mudflats of the Seine estuary (France). The elevation of the mudflat surface was monitored concurrently using a high-resolution altimeter. During the period of the study, estuarine mudflats were areas of deposition for faecal-indicator bacteria and were mainly controlled by sedimentary processes. In the intertidal freshwater and subtidal mudflats, the highest abundances of faecal-indicator bacteria were counted during a depositional period. Maximum levels were observed in the freshwater mudflats during periods of high flow: thermotolerant coliforms: 3.9 × 104 cfu cm−2, enterococci: 1.2 × 104 cfu cm−2, Clostridium perfringens spores: 9.8 × 105 spores cm−2. Loss of culturability of enteric bacteria in sediment microcosms demonstrated the remediatory capacity of the mudflats, even if they might be a secondary source of bacteria-forming spores to the water column through erosion and resuspension events

Long-term hydrological changes of the Seine River flow (France) and their relation to the North Atlantic Oscillation over the period 1950-2008

International audienceThe variability of Seine River flow (France) was investigated using daily time series over the period of 1950-2008. The study aimed at characterizing the dominant modes explaining the variability of flow and at investigating their possible link with the North Atlantic Oscillation (NAO) as the dominant climate regime in the region. The Seine River flow was affected by a statistically significant increasing trend across the period. The hydrologic regime of the Seine River was found to be highly variable and seem to occur later in the year, approximately, since the end of the 1980s. Annual minimum, maximum and mean flow time series exhibited an obvious change around 1970. Continuous wavelet transform (CWT) of flow revealed energetic peaks highly localized in time, defining three time periods: before 1970, between 1970 and 1990 and after 1990. Two interannual modes (17 and 5-9 years) occur, respectively, around 1970 and in the early 1990s. The same observations on precipitation CWT ensure a climatic origin to these interannual modes. The annual oscillation was always strongly represented in flow and was affected by an increase in power from 1990 until the end of the time series. Comparison between NAO and annual flow anomalies revealed similar trend behaviour characterized by a change around 1970 towards more positive NAO indices and positive flow anomalies. In addition, CWT of NAO revealed similar modes of variability around 17 and 5-9 years as flow interannual modes. This highlighted a possible link between NAO and hydrometeorological processes in the region. The flow fluctuations (interannual modes and trend) expressing this potential link would explain approximately 23% of total variance of Seine River flow and would even reach 35% of the variance after removal of the annual cyclicity. These results would then emphasize the potential strong control of NAO on the variability of Seine River discharge. Copyright © 2009 Royal Meteorological Societ