Development And Experiment Of Oxygen Sensors In High Temperature Liquid LBE

Due to its good thermal-physical and chemical properties etc., lead-bismuth eutectic (LBE) is promising candidate materials for spallation target and coolant of accelerator driven subcritical systems. However, critical issues, such as the compatibility of LBE with structural material, plugging of tubes due to oxide impurities formation, and so on, restrict the application of LBE in nuclear systems. Studies have shown that oxygen concentrations in LBE should be kept among certain margin between Fe3O4and PbO formation. The accurate measurement of oxygen concentration is a prerequisite for the precise control of it, so oxygen sensor became one of research hotspots in LBE related fields in recent years. Based on this background, the development of oxygen sensors were done in this paper, following with the experimental studies on signal accuracy, responsiveness, stability and other performances of oxygen sensors, the main contents and results are listed as follows:1. Based on the principle of galvanic cell, learnt from the research experiences of similar sensors, two schemes of oxygen sensor structural design, flange interface type and ferrule interface type, were proposed, and assembled serials of Bi/Bi2O3and Pt/air reference electrodes oxygen sensors with yttria-stabilized zirconia (YSZ) as solid electrolyte, these sensors were subjects of later study. With improved design, the ferrule type scheme has features of simple assembly process, compact, large adjustable range and so on.2. The calibration experiments of oxygen sensors were carried out in stagnant oxygen saturated LBE, and the electromotive force (EMF) outputs of oxygen sensors showed consistent with theoretical values above400℃, the absolute errors were within±5mV; as to the cross-calibration experiments, the values of oxygen concentrations, which calculated from the EMFs of two oxygen sensors in test, showed consistent with each other in the process of temperature changing; the calibration and cross-calibration results illustrated the good signal accuracy of oxygen sensors. In the analyzed of factors that affect the signal accuracy of oxygen sensor, models about oxygen migration in LBE caused by circulating currents were first proposed to interpret the measurement results of different immersion depth experiments with different reference electrodes oxygen sensors in liquid LBE; within the specific range of gas flow used in this experiment, the gas disturbance caused little effect to the accuracy of oxygen sensors.3. The signal responsiveness tests of oxygen sensors with LBE temperature variations, and the change of injection gas compositions were carried out, respectively, and oxygen sensors exhibited quick response to each time a change in the conditions. In the analyzed of factors that affect the signal responsiveness of oxygen sensor, phenomenon of the higher the LBE temperature begins to change, the faster the response of sensor was observed; and the experiment of different wall thicknesses of YSZ tubes was firstly carried out in this paper, within the present experimental parameters, the results showed that the response time extended with increasing of YSZ tube wall thickness in the heating process, in the cooling process, for compared with the rapid temperature drop rate to the influence of response, effect of oxygen migration time in different wall thicknesses of YSZ tube to response was not obvious.4. Both Bi/Bi2O3and Pt/air oxygen sensors were in good performances during the signal stability test in stagnant oxygen saturated LBE; and with an oxygen sensor from Karlsruhe Institute of Technology as reference, the self-developed Pt/air sensor given stable and reliable outputs longer than100hours in the flowing LBE loop. In addition, the insufficient sealing between coexistence phase reference electrode and outside will affect the chemical equilibrium of the reference system, and then affecting the normal and stable work of oxygen sensor. The SEM and EDX results showed good stability of YSZ in LBE with conditions of temperature at480℃and oxygen concentration at10-6wt%in600hours.In summary, the development and experiment of oxygen sensors in high temperature LBE were carried out in this paper, related performance data of oxygen sensor and then some laws were obtained, the above results offered some theoretical basis and data support both to the in-depth study of oxygen sensor, and to the development of oxygen measurement and control technologies for future lead alloy cooled reactor.