ZrC中辐照缺陷行为的模拟研究

Due to the high temperature capabilities, good mechanical strength and low neutron absorption cross-section, zirconium carbide (ZrC) has been considered as a potential material for use in nuclear applications. One application is the substitution of ZrC for silicon carbide (SiC) as the coating material for nuclear fuel used in the high temperature gas-cooled reactor. In this project, the behavior of radiation defects in ZrC will be investigated by molecular dynamics simulations. These studies are important in clarifying the evolution mechanisms of defects in ZrC, as well as their influence on the mechanical properties. A comparative study of the properties of defective ZrC and SiC will be carried out, which provides application guide for ZrC. Three aspects of work will be carried out in this project: (1) The dynamics evolution of defects (vacancy, void, self-interstitial atom and its cluster, dislocation loop and grain boundary) in ZrC will be studied, as well as their influence on the mechanical properties. (2) The diffusion of He atoms in bulk and grain boundary of ZrC, and the thermal release of near-surface He bubbles will be investigated. (3) A comparative study of the properties of radiation defects in ZrC and SiC will be carried out.

ZrC因其高温稳定性好、机械强度高、中子吸收截面小等优点，在核能领域有重要的应用前景，被认为是高温气冷堆中传统包覆燃料颗粒SiC涂层的一种较好的替代材料。本项目拟通过分子动力学方法，模拟辐照缺陷在ZrC中的行为，逐步阐明缺陷在ZrC中的演化机理及其对力学性能的影响。并与传统涂层SiC进行对比，为ZrC的应用提供一些依据和指导。拟开展以下三方面的工作：（1）ZrC中空位及其团簇、自间隙原子及其团簇、位错环和晶界等缺陷的动力学演化，以及它们对材料力学性能的影响。（2）He与ZrC的相互作用，包括He在块体和晶界的扩散、近表面He泡的热释放等行为。（3）对比ZrC和SiC中辐照缺陷行为的异同。

ZrC由于具有良好的高温和抗辐照性能，被认为是现有高温气冷堆中TRISO燃料颗粒的包覆材料SiC涂层的替代材料。ZrC和SiC涂层的主要作用之一是防止燃料颗粒的压力壳式破损，因此辐照缺陷对它们力学性能的影响值得关注。分子动力学方法作为原子级的模拟手段，原子间作用势的有效描述是关键要素之一，但目前ZrC体系的势函数较少，因此在本项目中：1）用修正嵌入原子法MEAM构造了ZrC体系的势函数，它能较好描述B1-ZrC的点缺陷性质和力学性质。2）基于新建立的势函数，计算了化学计量比、温度对ZrCx（x=0.7−1.0）拉伸力学性能的影响，杨氏模量随碳含量的降低而降低。3）计算了He在ZrC和SiC中的形成能、扩散激活能，发现He团簇在ZrC中形核和扩散有一定难度。4）研究了SiC双晶的力学响应，发现其力学性能与界面能、晶界夹角密切相关；通过级联碰撞模拟了纳米晶SiC的辐照过程，提出缺陷演化存在三种机制，纳米晶SiC在辐照后拉伸强度变化不大，说明晶界结构对材料力学性能的影响远大于辐照缺陷的影响。以上结果可为ZrC和SiC材料在核能领域的应用提供一些依据和指导。