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

Abstract
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.