Pb-Bi-(Po/Te)-O体系相图及含氧气氛下放射性Po（Te）挥发行为的研究

One of the main challenges with the use of liquid lead-bismuth eutectic (LBE) alloy as the spallation target and primary coolant of future Accelerator Driven System (ADS) concepts is the generation, accumulation and evaporation of the high-level radioactive Polonium (210 Po). Improving the safety of using LBE, it is essential to understand the existing form and volatilization behavior of Po-polluted LBE under normal and accident conditions. However, the high-budget experiment and technical challenges restrict the acquisition of relevant basic data such as phase diagram. Through a scientific method integrated the CALPHAD approach, ab-initio calculations and key experiments, the present research project focuses on the following aspects in molten lead-bismuth eutectic alloys contaminated by Po or Te (Po's homologous substitutes) under oxygen atmosphere: (1) Establish a thermodynamic database of Pb-Bi-Te-O system to provide important data for the Po alloy research as a reference; (2) Establish a thermodynamic database of Pb-Bi-Po-O system to predict the effect on the phase equilibria by Polonium and Oxygen contents; (3) Describe Quantitatively the volatilization behavior of Po alloy in oxygen atmosphere on the basis of Te alloy experiment. The completion of this project will provide reliable basic data for understanding the characteristics of Po in LBE, and provide an important theoretical direction for the development of a Po decontamination technology.

液态铅铋共晶（LBE）合金作为加速器驱动系统（ADS）散裂靶材和主冷却剂应用的主要挑战之一是高放射性钋（210Po）的生成、累积和挥发。掌握Po污染的LBE合金在正常运行和事故工况下的存在形式和挥发行为对提高LBE使用安全性至关重要。然而实验的高成本性和高技术挑战性限制了相关基础数据如相图的获取。本项目以含氧气氛下被Po或Te（Po的同族替代物）污染的熔融铅铋共晶合金为对象，集成相图计算、第一性原理和关键实验开展以下工作：（1）建立Pb-Bi-Te-O体系热力学数据库，为Po的相关研究提供重要参考数据;（2）建立Pb-Bi-Po-O体系热力学数据库，预测LBE受Po、O含量影响的物相变化;（3）在Te合金实验的基础上，实现Po合金在含氧气氛下挥发行为的定量描述。本项目的完成将为深入了解Po在LBE中的特性提供可靠的基础数据，并为Po去污技术的研发提供重要的理论指导。

中子辐照后产生并累积的210Po是铅铋共晶应用于加速器驱动次临界系统（ADS）面临一个不可忽视的问题。提纯净化铅铋共晶中钋可以使210Po的含量降低，进而降低堆外的放射性水平。但由于钋的危险性，缺乏相关热力学实验数据，无法对钋的净化准确预测。本项目采用化学性质相近且无放射性的同族替代物碲Te，对Te在液态Bi-Pb-Te体系中的存在形式及其对物性的影响进行了研究，获得具有参考价值的高Te含量成分区域相平衡及凝固信息。在含Te的液态LBE中，极易形成PbTe化合物，且随Te含量的增加，LBE的熔点迅速升高。Bi-Pb-Te体系中确定存在三个三元化合物，但是不会在Te含量小于50%的液态LBE凝固后生成。搭建了用于研究挥发行为的实验平台，并通过传输法对纯Bi、纯LBE、LBE-xTe(x=0.01,0.03,0.05)在高温下的饱和蒸汽压展开了研究，实现了Te挥发行为的定量描述。