Study On Phase Diagram And Volatilization Characteristics Of Pb-Bi-Te Alloy

Lead-bismuth eutectic（LBE）has excellent physical and chemical properties.It is considered as the primary candidate material for accelerator driven nuclear system（ADS）spallation target and coolant in the new generation of lead-based reactors.However,a concern with the use of lead-bismuth eutectic is the production of radioactive nuclide polonium.²¹⁰Po as the main safety-relevant nuclide,is formed by neutron capture bismuth in the LBE and subsequentβdecay of ²¹⁰Bi.From safety view,understanding of the physiochemistry properties and behaves of polonium in evaporation from LBE is crucial for the development of LBE purify technique.However,it is difficult to perform an experiment using Po directly,due to its radiotoxicity.The chemical properties of tellurium and polonium are highly similar.It is regarded as a chemical substitute for polonium.The volatilization characteristics of lead-bismuth eutectic alloy containing tellurium（LBE+xTe）at high temperature were studied based on chemical substitution of polonium for tellurium.On the other hand,the phase relationship of Pb-Bi-Te system is not perfect reported.The existence form and mechanism of tellurium in the system are not clear.The phase relationship of Pb-Bi-Te ternary system and the mechanism of tellurium were investigated.It is very important to solve the problem of ²¹⁰Po produced by liquid lead-bismuth eutectic.The main work and research results of this subject are as follows:The equilibrium vapor pressures of bismuth and lead-bismuth eutectic at800℃,850℃ and 900℃ were measured by self-built vapor pressure research platform.The equilibrium vapor pressure equation of bismuth and lead-bismuth eutectic was obtained by extrapolation experimental data.The uncertainty was analyzed by the Guide to Measurement Uncertainty（GUM）,which verified the accuracy of the self-built equilibrium vapor pressure research equipment.The liquidus surface projection,phase relationship,solid solubility,ternary compound type and the existence form of Te in Pb-Bi-Te system were studied by SEM-EDS,EPMA-WDS and XRD.The liquidus projection of Pb-Bi-Te system was measured.It was found that Pb Te phase filled most of the liquidus projection.The existence of Pb Bi₂Te₄,Pb Bi₄Te₇ and Pb Bi₆Te₁₀ was confirmed at 400 ℃ and 520 ℃ by measuring the vertical section phase diagram of Pb Te-Bi₂Te₃ pseudobinary system.The solid solubility of Bi in Pb Te phase was 3.6at.%,3.8 at.%and 10.8 at.%at 360℃,400℃ and 520℃.The vertical section phase diagram of LBE-Te（0-35 at.%）pseudobinary system was determined.It is confirmed that Pb Te phase leads to the change of liquid phase properties of LBE+xTe alloy.The LBE+xTe（x=1.6 at.%,4.6 at.%and 7.5 at.%）alloy samples were prepared by alloy quenching method.At 700℃～1100℃,the vapor pressure experiments were carried out.The equilibrium vapor pressure equation of LBE+xTe alloy was obtained by extrapolation experimental data.When the carrier gas flow rate is 100 ml·min^-1,the experimental results show that the vapor pressure of LBE+xTe alloy sample is in equilibrium.The residual tellurium content of the experimental samples was obtained by ICP test method.Henry’s constant and Te release rate of LBE+xTe alloy were calculated.The experimental results show that the tellurium element is basically evaporated at1100 ℃.