The Performance Of Cryogenic Oxygen Sensor In Oxygen Saturated Lead-Bismuth Eutectic

Lead-Bismuth Eutectic（LBE）is considered as the preferred coolant material of Lead-cooled Fast Reactor（LFR）due to low melting point,high boiling point and neutrons.The oxygen concentration in LBE has an important influence on the corrosion of structural materials and the formation of Pb O impurities.Therefore,it is necessary to use reliable oxygen measurement technology to monitor LBE oxygen concentration in real time to protect structural materials from corrosion.At present,Pt/air and Bi/Bi₂O₃ are the main types of oxygen sensors studied at domestic and overseas,but there will be large errors in their measurement at low temperature.Based on this research background,the paper studied the accuracy,responsiveness and stability of the ABO₃/air oxygen sensor and the ABO₃-AX₂/air oxygen sensor in the temperature range of 200-500℃by using the static lead-bismuth alloy oxygen sensor experimental platform.The specific research content and experimental results are as follows:（1）The accuracy test and accuracy influence factor experiment of the oxygen sensor were carried out in the static oxygen saturation LBE.The results showed that the calibrated ABO₃/air type oxygen sensor and ABO₃-AX₂/air type oxygen sensor had good accuracy performance in the temperature range of 200-500℃,and the error of electromotive force（EMF）was always controlled within±1%.In the experiment of factors affecting the accuracy of oxygen sensor,it was found that the oxygen sensor activated by high temperature can excite the oxygen vacancy in the solid electrolyte,made the oxygen sensor quickly reach the thermodynamic stable state,improved the migration speed of oxygen ions,and reduced the error of electromotive force.The immersion depth of oxygen sensors in LBE had an impact on their accuracy.When the immersion depth was close to the height of the active region,the electromotive force was less affected by the oxygen partial pressure gradient in LBE.Therefore,the immersion depth of oxygen sensors in LBE should be equal to the height of the active region.At the same time,an experiment was carried out on the effect of reference electrode powder fillers of 30mm,20mm and 15mm on the accuracy and performance of the ABO₃/air type oxygen sensor.The research found that the accuracy of the oxygen sensor with 15 mm filler is better than 20mm and 30mm,and the maximum relative error between the EMF experimental value and the theoretical value was only 0.188%.When the amount of ABO₃ filler changed,it affected the porosity of ABO₃and the diffusion of oxygen to the oxygen/solid electrolyte/ABO₃ three-phase interface.（2）The research on the response of temperature change to the ABO₃/air oxygen sensor and the ABO₃-AX₂/air oxygen sensor in the step cooling stage of 500-200℃was carried out.The results showed that they can respond quickly to the temperature change.When the temperature changed suddenly within 400-500℃,the higher the temperature is,the more obvious the hysteresis effect of the electromotive force signal of the oxygen sensor is.Compared with the ABO₃/air oxygen sensor,the ABO₃-AX₂/air oxygen sensor had better response performance,mainly because of the presence of AX₂,O^2-can also be generated at the three-phase interface of the oxygen/ABO₃/AX₂.At the same time,the response performance of the two kinds of oxygen sensors varies with temperature at 200-285℃.The results showed that they had good response at low temperature.（3）The static oxygen saturation LBE stability experiment of the ABO₃/air oxygen sensor and the ABO₃-AX₂/air oxygen sensor at 450℃was carried out.The results showed that their stable working time was up to 200 h,and the difference between the mean EMF and the theoretical electromotive force was controlled within 2 m V.In the stability test at 200℃for 100h,the mean value of EMF was close to the theoretical value,and there was no large amplitude of EMF signal.The above results showed that the two oxygen sensors have good stability.To sum up,this paper has carried out the research on the performance of the low temperature oxygen sensor in the lead-bismuth alloy with saturated oxygen concentration,which provides the research basis for the practical application of the low temperature oxygen sensor in the large experimental device.