W中嬗变元素Re/Os辐照诱导析出及对H/He行为影响机理研究

The final application of nuclear fusion energy is mainly dependent on the development of key materials in the thermonuclear fusion device, in which the choice of the plasma facing materials (PFMs) is one of the key issues. Tungsten (W) is considered as the most promising candidates for PFMs in future fusion reactor. However, as a PFM, W will be exposed to 14 MeV high energy neutrons. The burn-up reaction will take place under the irradiation of high energy fusion neutrons, and produce transmutation elements rhenium (Re) and osmium (Os), etc. Most importantly, transmutation elements will precipitate under irradiation, and precipitation of transmutation elements will have significant effect on the behavior of H and He in W. This will lead to the degradation of the service properties of W. Previous studies indicate that radiation defects play a key role in the precipitation of transmutation elements. So far the formation mechanism of irradiation-induced Re and Os precipitation and their effects on the H and He behavior in W have not been well understood. In this project, taking Re and Os as an example, we will systematically investigate the interaction between Re/Os and radiation defects via computational simulation and irradiation experiments in order to understand the formation mechanism of Re and Os precipitation. Based on these researches, we will try to explore the physical origin of effect of Re/Os on the H/He behaviors in W by investigating the dissolution, diffusion and accumulation of H/He in different Re/Os-rich phases. Our research will provide a good reference for the performance and lifetime evaluation of W in future fusion reactor.

聚变堆材料的选取是聚变能源开发面临的重大挑战之一。钨（W）被视为未来聚变堆中最有可能全面使用的面对等离子体材料。但是，在氘-氚聚变反应产生的高能（14 MeV）中子辐照下，W材料将发生嬗变反应，产生铼（Re）和锇（Os）等嬗变元素。更重要的是，嬗变元素在辐照作用下将会聚集形成析出相，并对W中氢/氦（H/He）行为产生影响，直接改变W材料的服役性能。辐照缺陷在嬗变元素聚集析出中起着关键作用。目前，嬗变元素在W中的聚集析出机制及对H/He行为的影响机理尚不清楚。本项目以W中主要嬗变元素Re和Os为例，应用计算模拟和实验验证相结合的方法，系统研究W中Re/Os与辐照缺陷的相互作用，揭示Re/Os辐照诱导聚集析出机制，并在此基础上研究H/He在不同富-Re/Os聚集析出相中的溶解、扩散和聚集行为，给出Re/Os对W中H/He行为的影响机理，以期为未来聚变堆W基材料的服役行为和寿命评估提供参考。

钨（W）是未来聚变堆中最有可能全面使用的面对等离子体材料。但在高能中子辐照下，W将发生嬗变反应，产生铼（Re）/锇（Os）等嬗变元素。更重要的是，嬗变元素在辐照作用下会聚集析出，对材料的服役性能产生严重影响。本项目以“嬗变元素团簇/析出相的形成与影响”为突破口，针对嬗变元素聚集析出的热力学与动力学行为以及辐照缺陷在嬗变元素聚集中的关键作用开展相关研究，并在此基础上探究不同分布状态下嬗变元素对W中H/He行为及力学性能的影响机理，具有重要的科学和应用价值。代表性成果如下：.1.揭示W中嬗变元素辐照诱导析出的间隙扩散聚集机制，给出辐照下嬗变元素初步成核的物理图像。研究了W中Re/Os的扩散和聚集行为及其与辐照缺陷的相互作用，发现空位/自间隙原子可以显著降低Re/Os团簇的形核自由能变，这从热力学上促进Re/Os团簇的形成。有趣的是，Re/Os与自间隙原子结合后会形成间隙Re/Os，具有极低的三维扩散能垒，这在Re/Os成团过程中起到了重要的媒介作用。.2.给出应变和晶界对W中嬗变元素Re聚集的影响机理。研究了各向同性应变下Re团簇的稳定性及其与辐照缺陷的相互作用，发现拉应变能够显著促进Re团簇的形成；研究了W晶界区域Re的聚集行为，发现Re将在晶界处偏析，形成二维片状结构，这将显著强化晶界面的结合强度。.3.发现Re对W中H/He滞留的影响与Re的分布状态密切相关。研究了不同分布状态W-Re系统中H/He的溶解、扩散和聚集行为，发现不同Re分布状态下H/He行为具有显著差异。当Re均匀分布时，其对H/He滞留的影响较弱；而Re团簇将显著抑制W中空位对H/He的捕获，降低H/He的滞留；当Re进一步聚集形成析出相时，其将显著促进W中H/He的滞留。.4.发现Re分布状态对W-Re合金机械性能的关键作用，揭示辐照下Re由韧化元素变为脆化元素的物理本质。研究了不同尺寸Re团簇与W中1/2<111>螺位错的相互作用，发现Re倾向于偏析到位错核心。其中，单个Re原子（均匀分布）能够降低位错滑移的Peierls能垒和应力，促进位错的滑移，进而提高材料韧性；而Re团簇（辐照诱导聚集）将显著钉扎位错的运动，加剧材料的辐照硬化。.本项目研究期间共发表了14篇SCI论文，国际会议邀请报告4次，建立了卓有成效的国际交流合作关系。