| Lead-bismuth eutectic alloy（LBE）is considered as an important cooling liquid for lead-based fast reactor of Generation IV reactor and that is also a good candidate material for the spallation target or a coolant of the subcritical reactor in an Accelerator-Driven Sub-critical Systems（ADS）because it has some advantages of neutron performances and physical chemistry properties.However,the oxidation of LBE and the corrosion of the structural materials will usually occur in the loop with LBE which are seriously impact on the safe and stable operation of the system.So these issues are critical to the advanced nuclear energy systems for their negative effects and are interested in solving the problems world widely.In order to make clear the oxidation behaviors of LBE and the corrosion mechanisms of structural materials,a set of experimental device equipping with oxygen control system in LBE has been designed and developed in this thesis.Moreover,the performance testing of the facility and some related experiments have been carried out.The main R&D and results are shown as follows.According to the requirements of the LBE experimental device,most of the structures and the major parameters have been analyzed and optimized to be better by CFD computing method.Finally,the designs and constructions of the experimental device for controlling oxygen concentration in LBE have completed.The device is mainly consists of a high-temperature shielding pump,the flow meters,a storage tank,a box for controlling oxygen,a material corrosion room and the main lines.In addition,it also composed of the vacuuming systems,the feeding systems,the temperature control systems,the gas phase oxygen control systems and the oxygen sensors.The primary technical parameters of the device are presented as follows:（a）The capacity of containing LBE is about 500 kg.（b）The operating temperature is up to 600℃.（c）LBE flow rate in the loop is 03 m3/h.（d）The oxygen contents range from 10-6 wt-ppm to the saturation.（e）The vacuum degree of the systems is better than 5×10-4 Pa.（f）.The leakage rate is less than 5×10-7 Pa·L/s.（g）The maximum of pressure is 0.6 MPa.The high-temperature type shielding pump with a single-stage and single-suction centrifugal form for application to LBE loop at 600℃has been designed and investigated.Based on the hydraulic analysis of the impeller and the chamber of the shielding pump by CFD numerical simulation method,the special optimized structure that the motor chamber is completely independent of the pump chamber was determined in the agreement.In this case,the pump may be work normally at the higher temperatures in LBE loop with no leakage.It is indicated that the pump has some excellent performance,such as a high head of 10 m,a large flow rate at 3 m3/h and a lower power with 3 k W.Many different kinds of oxygen control systems based on gas phase control have been produced for application to control the oxygen concentration in LBE.These devices can provide the gas mixture of Ar-H2/Ar-O2 and Ar-H2-H2O with different elements,proportions and flow rates.When the gaseous mixtures are introduced to LBE tank as covering gas and directly bubbled into LBE,the oxygen concentration will increase on account of the existing oxygen in the atmosphere or decrease according to the recovering from oxides by hydrogen gas diluted with argon.All the chemical reactions occur at the interface between the gas and the liquid bulk.The gas phase control systems have been successfully used to controlling oxygen content in LBE and obtained some expected results.The two types of Pt-air oxygen sensor and Bi-Bi2O3 probe assembly have been made in the laboratory.In fact the sensors are work at Nernst’law and on the basis of a electrochemical galvanic cell with a solid electrolyte of ZrO2-Y2O3（YSZ）and a reference electrode as well as metal wire.The solid electrolyte material is critical for the most consisting components which determine the performances of the probes on available temperature,reliability,accuracy and so on.The calibration of the oxygen sensors have been carried out in the LBE with saturated oxygen and the testing have already completed under various experimental conditions such as different temperatures and unsaturated oxygen.It was found that the Pt-air type sensors can be available to measure the oxygen content in LBE at temperatures above 450℃,while the Bi-Bi2O3 type sensors are above 400℃.Both the two kinds of oxygen sensors have the maximum deviations of 4%between the measuring EMFs and the theoretical values in the range of reliable working temperatures.However,the relative error of Co in the former reached 20%and that of the latter was less than 8%.The compositions,proportions and flows of the gas mixture are highly significant factors in the operating specifications for oxygen.The influences of them on the oxygen content in LBE have been investigated systematically.In addition,the expected oxygen concentrations of ranging from 1×10-4 to 1 wt-ppm were obtained successfully by different methods.Furthermore,the minimum of oxygen content have been reached 1×10-8 wt-ppm.In short,this device has been built and there have a lot of great achievements and valuable results in many experiments at present.It would provide some useful data and experiments in study of controlling oxygen content and corrosion of steel in LBE.Furthermore,it is helpful for the design of the subcritical reactors requiring oxygen management in ADS project in future. |
PDF Full Text Request