钨辐照后氢滞留机理及合金元素对其影响的模拟研究

The plasma facing material should retain as little hydrogen as possible. The primary candidate material is tungsten, which features a very low solubility for hydrogen among other favorable properties such as a low physical sputtering yield and a high melting temperature. In fusion reactors, the high energy neutron irradiation and high flux plasma particle bombardment produce lots of defects, acting as trapping sites for hydrogen atoms, which greatly enhances the potential for hydrogen retention in tungsten and poses critical safety hazard. Recent experiments show that the concentration of deuterium significantly increased by irradiation, which is related to the irradiation damage level, temperature and the alloying elements. However, the mechanisms of the hydrogen retention in irradiated tungsten and the influence mechanisms of the temperature and alloying elements on them. Therefore, in the present proposal, we will investigate the long (in hour) co-evolution behavior of irradiation defects (vacancies and vacancy clusters, interstitial defects and their clusters), alloying elements (Re, Ta, Ti and V) and hydrogen in large tungsten system (in micron) by the combination of first-principles calculation and object kinetic Monte Carlo. The role of the interaction between them and their evolution mechanisms will be obtained, which can reveal the influence mechanism of irradiation defects and alloying elements on the hydrogen retention in irradiated tungsten and its dependency relationship with the temperature. It is expected to provide theoretical guidance for the tungsten alloy design and the assessment and inhibition of the hydrogen retention in tungsten in the actual service environment of the fusion reactor.

低氢滞留是面向等离子体材料（PFM）的必要条件。钨因具有低氢滞留及低物理溅射率、高熔点等优点而成为最有前景的PFM。在苛刻的聚变堆服役环境下（高能中子辐照和高通量等离子体轰击），辐照产生的大量缺陷可作为氢的捕获点，致使钨中氢滞留量升高，威胁聚变堆的安全运行。近期实验表明钨辐照后氢滞留量显著升高，且与辐照剂量、温度和合金元素密切相关。然而，钨辐照后氢滞留机制及温度和合金对其影响的机理仍不清楚。因此，本项目拟采用基于第一性原理的实体动力学蒙特卡洛方法，模拟钨中辐照缺陷（空位及其团簇、间隙及其团簇等）、合金元素（Re、Ta、Ti和V）与氢在大体系中（微米）长时间（小时）协同演化行为，获得三者作用规律和演化机制，揭示辐照缺陷和合金元素对氢滞留的影响机理及其对温度的依赖关系，期望为钨合金成分的优化设计及评估和抑制实际聚变堆服役环境下钨中氢滞留量提供指导。

低氢滞留是面向等离子体材料（PFM）的必要条件。在苛刻的聚变堆服役环境下（高能中子辐照和高通量等离子体轰击），辐照产生的大量缺陷可作为氢的捕获点，致使钨中氢滞留量升高，威胁聚变堆的安全运行。近期实验表明钨辐照后氢滞留量显著升高，且与辐照剂量、温度和合金元素密切相关。因此，本项目采用基于第一性原理的实体动力学蒙特卡洛方法研究辐照缺陷和合金元素对氢滞留的影响，所取得的主要结果如下：（1）建立了氢、空位（团簇）以及合金元素缺陷间相互作用参数库（结合强度、作用范围、扩散机制和激活能等），基于该数据库对缺陷间作用机制进行分析，发现了：①合金元素金属半径和电负性可作为相关缺陷间作用强弱的标度量。合金元素一方面能通过促进辐照缺陷复合降低钨辐照后氢滞留量，另一方面通过自身捕获氢提高钨中氢滞留，定性解释了钨-铼、钨-钽合金中不同辐照条件下氢滞留实验结果间的差异。并从氢滞留、合金元素相析出以及嬗变效应的角度考虑，我们认为钽是综合性能较好的合金元素。②提出了间隙氢自团簇机制，并基于该机制预测了钨中氢泡成核的临界氢浓度，为近十年来长期困惑的低能氢轰击下钨中氢泡形成现象提供了定量解释。③建立了一个通用的物理模型来预测纳米孔洞中氢的能量、结构、以及氢压。以该模型为基础的多尺度模拟结果与近年来的热脱附实验结果高度吻合。阐明了主导纳米孔洞对氢俘获行为的本质物理规律，给出了氢在纳米孔洞中俘获的多尺度预测模型，为理解氢致金属材料损伤提供了寻求已久的关键性信息。（2）开发了一套适用于模拟钨中氢滞留行为的动力学蒙特卡洛程序，目前该程序软件著作权正在申请中。该模拟程序通过多种加速算法实现了在微米级空间尺度和小时级时间尺度上对材料中缺陷演化的模拟，并利用该软件对缺陷的俘获强度和氢离子辐照后钨中氢脱附行为，有助于对氢在缺陷处俘获、聚集，成泡、长大等现象的定量理解。