[论文解读] Object Kinetic Monte Carlo Simulations of Radiation Damage in Neutron-Irradiated Tungsten Part-I: Neutron Flux with a PKA Spectrum Corresponding to the High-flux Isotope Reactor

Giridhar Nandipati, Wahyu Setyawana+4 more|arXiv (Cornell University)|Oct 9, 2015

Nuclear Materials and Properties参考文献 2被引用 4

一句话总结

本研究采用对象动力学蒙特卡罗（OKMC）模拟，研究在高通量同位素反应堆（HFIR）中子辐照下多晶钨的辐射损伤。结果表明，较高剂量率会增加空位团簇密度，但降低平均团簇尺寸和团簇中空位的比例；而更大的晶粒尺寸则通过类熟化效应增强空位团簇的形成，且无论晶粒尺寸或剂量率如何，均观察到{110}面有序排列。

ABSTRACT

Object kinetic Monte Carlo simulations were performed to study the impact of varying dose rate and grain size up to a dose of 1.0 dpa in pure, polycrystalline tungsten, subjected to a neutron irradiation having a PKA spectrum corresponding to the High Flux Isotope Reactor. The present study models defect cluster accumulation in tungsten, but does not consider the impact of transmutation or pre-existing defects beyond the grain boundary sinks, with varying grain size. With increasing dose rate, the vacancy cluster density increases, while the number density of vacancies decreases. Accordingly, the average vacancy cluster size and the fraction of vacancies that are part of visible clusters decreases with increasing dose rate. With increasing grain size, both the number densities of vacancies and vacancy clusters decrease, while both the fraction of vacancies in visible clusters and the average vacancy cluster size increase. This is caused by the pseudo-ripening of the vacancy clusters due to the longer-lived self-interstitial clusters in larger grains. The spatial ordering of vacancy clusters along {110} planes was observed for both grain sizes and all dose rates studied. Interplanar spacing increases with grain size; however, no clear dependence on dose or dose rate was observed. The results of this study show that 1D diffusion of self-interstitial clusters, while necessary, is not sufficient to form a void lattice, and that the diffusion of vacancies is also required. A methodology is suggested for choosing the simulation box dimensions so as to represent more faithfully the effects of one-dimensional migrating self-interstitial-atom clusters.

研究动机与目标

• 研究剂量率与晶粒尺寸对多晶钨中缺陷团簇累积的影响。
• 利用代表高通量同位素反应堆（HFIR）的PKA谱模拟辐射损伤。
• 考察晶界作为点缺陷汇区的作用及其对团簇演化的影响。
• 评估在何种条件下空位团簇沿{110}面有序排列会形成。

提出的方法

• 采用对象动力学蒙特卡罗（OKMC）模拟方法，研究纯多晶钨中的缺陷动力学。
• 模拟采用对应于高通量同位素反应堆（HFIR）的中子通量，模拟初级反冲原子（PKA）事件。
• 缺陷演化追踪至1.0 dpa，重点关注空位与自间隙原子（SIA）团簇的形成与迁移。
• 通过改变晶粒尺寸，研究其对缺陷汇效率与团簇分布的影响。
• 对自间隙原子团簇的一维扩散进行建模，以评估其在空位晶格形成中的作用。
• 开发了一种用于选择模拟盒尺寸的方法，以更准确地表征一维迁移SIA团簇的影响。

实验结果

研究问题

• RQ1 在HFIR中子辐照下，剂量率如何影响钨中空位团簇密度、平均团簇尺寸及团簇中空位比例？
• RQ2 晶粒尺寸如何影响多晶钨中空位与SIA团簇的数量密度与尺寸分布？
• RQ3 自间隙原子团簇的一维扩散在有序缺陷结构（如空位晶格）形成中起何种作用？
• RQ4 在给定辐照条件下，空位团簇沿{110}面的空间有序排列是否依赖于剂量率或晶粒尺寸？
• RQ5 晶界在多大程度上作为空位与SIA团簇的有效汇区，其作用如何影响整体缺陷演化？

主要发现

• 随着剂量率增加，空位团簇密度上升，而孤立空位数量密度下降，表明高剂量率下团簇化增强。
• 由于复合速率加快且团簇生长时间受限，平均空位团簇尺寸及可见团簇中空位比例随剂量率增加而降低。
• 较大的晶粒尺寸降低了空位与空位团簇的数量密度，但通过延长SIA团簇寿命和类熟化效应，提高了平均团簇尺寸与团簇中空位比例。
• 在小晶粒与大晶粒中，空位团簇均沿{110}面呈现空间有序排列，且晶粒尺寸越大，面间距越大。
• 仅靠自间隙原子团簇的一维扩散不足以形成空位晶格；空位扩散亦为稳定与有序化缺陷结构所必需。
• 本研究提出了一种更优的模拟盒尺寸选择方法，可更准确地捕捉多晶钨中一维迁移SIA团簇的影响。