熔融物材料扩散系数的从头算分子动力学计算

Ab Initio Molecular Dynamics Calculation of Diffusion Coefficients of Molten Materials

为获得核反应堆严重事故后期反应堆压力容器(RPV)下腔室内熔融物微观组织的演化规律,需要对熔融物的材料物理性质进行研究。以熔融池中发生熔化过程的实际材料,包括燃料芯块UO_(2)、包壳管熔融后的U-Zr-O材料以及不锈钢构件熔融后的U-Fe-O材料为研究对象,采用基于第一性原理的从头算分子动力学模拟了熔融物材料高温液态下的原子扩散行为。研究结果表明,在高温液相中的U、Zr、Fe、O的原子扩散系数与原子质量呈负相关,且在相同温度下受组分的影响较小,仍保持相对稳定的比例关系。不同原子扩散系数的差异理论上会导致熔融池形成分层结构,因此,可对比上述3种材料在高温液态下各种原子的扩散系数,确定直接的量化关系,为在大尺度下进一步研究熔融物微观组织的演化奠定基础。

In order to understand the evolution of the microstructure of the molten materials in the lower chamber of the reactor pressure vessel(RPV)of the nuclear reactor at the later stage of a severe accident,it is necessary to investigate the physical properties of the molten material.The atomic diffusion behavior of molten materials in high temperature liquid is simulated by ab initio molecular dynamics based on the first principles,with the actual materials in the melting process in the melting pool,including fuel pellet UO_(2),U-Zr-O materials after melting cladding tubes and U-Fe-O materials after melting stainless steel components as the research objects.The results show that the atomic diffusion coefficients of U,Zr,Fe,O in the high temperature liquid phase are negatively related to the atomic mass,and are less affected by the components at the same temperature,maintaining a relatively stable proportional relationship.The difference of different atomic diffusion coefficients will theoretically lead to the formation of layered structure in the melting pool.Therefore,the diffusion coefficients of various atoms in the above three materials at high temperature can be compared,and the direct quantitative relationship can be determined,which lays a foundation for the further study of the microstructure evolution of molten materials at large scale.