核燃料以液态形式存在的熔盐堆（热堆和快堆）是一类具有代表性的第四代核能系统，液态氟化物LiF-BeF2-ThF4-UF4熔盐是钍基熔盐堆用核燃料，燃料盐中的杂质氧会与钍和铀发生相互作用，改变核燃料的化学成分，影响其溶解性、热导率和扩散系数等宏观性能。为了使液态燃料在回路中循环时的结构稳定性长期保持在安全范围内，非常有必要研究氧对液态燃料盐中钍和铀物种微观结构的影响。本项目拟通过变温原位装置使燃料盐样品保持液态且处于目标气氛中，利用同步辐射EXAFS和HERFD-XANES技术获取液态样品中钍和铀与氧相互作用的局域结构信息，包括价态、局域对称性、非占据态5f/6d轨道、配位数和键长等，研究氧对液态燃料熔盐微观结构的影响。

Molten salt reactor with liquid nuclear fuel is one of the fourth-generation nuclear energy systems. The liquid LiF-BeF2-ThF4-UF4 molten salt was used as nuclear fuel in thorium-based molten salt reactor. The oxygen impurity in fuel salt will interact with both thorium and uranium and change the chemical constitution of fuel salt, influencing its solubility, thermal conductivity, diffusion coefficient and so on. In order to maintain the structural stability of liquid fuel within safe range when the liquid fuel is runing in salt circuit, it is necessary to study the effect of oxygen on the microstructure of both thorium and uranium in liquid fuel. The planned research work is proposed to change the fuel salt from a solid state into liquid by using an in-situ elevated temperature equipment, and to obtain the local structure on interaction between oxygen and both thorium and uranium in liquid fuel salt including valence state, local symmetry, unoccupied states of 5f-6d electron orbit, coordination number and bond length by synchrotron radiation EXAFS and HERFD-XANES techniques , and to study the effect of oxygen on microstructure of liquid fuel salt.