核聚变堆包层结构材料研究进展及展望

A Review on the Development of the Structural Materials of the Fusion Blanket

随着人类对能源需求的增加,核聚变能的发展越来越受到人们的关注。材料问题是目前限制聚变能发展的一个重要因素。包层是实现能量转换、氚自持及辐照屏蔽的主要部件,满足包层结构材料苛刻环境要求的结构材料的开发及性能检测成为目前研究的热点。以低活化铁素体马氏体(RAFM)钢为代表的包层结构材料已发展多年,然而依据中国聚变能发展路线图,CFETR一期包层结构材料的中子辐照水平可达到约10dpa,在二期达到约50dpa,目前没有材料能满足包括抗辐照损伤在内的苛刻环境要求并能满足工程建设需求。低活化铁素体马氏体钢是目前包层结构材料的首选候选结构材料,国内外已开发了多个牌号的低活化品种并具备了丰富的材料基础数据库,然而低活化钢的工作温度区间严重受限,高温蠕变及抗辐照能力无法满足CFETR二期及未来聚变堆的要求。为解决传统RAFM钢的不足,提出了两条思路:一种是添加氧化物弥散相以有效提高高温蠕变强度,其中又以制备过程中是否涉及机械合金化可进行进一步的区分;另一种思路是基于热力学模拟计算,优化RAFM钢化学成分并进行多轮热机械处理以增加MX相密度。其中,机械合金化制作的氧化物弥散强化钢(ODS钢)的性能最佳,但受限于机械合金化法,成本高且效率低。非机械合金化ODS钢与优化的RAFM钢的性能接近机械合金化ODS钢,成本远远低于机械合金化ODS钢且制备效率高,大批量制备技术相对容易。除了铁基材料外,钒合金及碳化硅复合材料在多方面展现了优势,长期以来都是研究人员关注的热点。钒合金的热蠕变和氦脆导致温度上限低并且与氢同位素兼容性不好,碳化硅复合材料的规模化生产及连接技术仍存在困难,这些缺陷限制了钒合金与碳化硅复合材料的发展,使之在现阶段无法满足应用需求。面向更高辐照水平的示范堆及商用堆,目前已有的包层结构材料可能无法满足需求。根据目前很有限的研究数据,非晶材料及高熵合金的工程应用还非常遥远:一方面需要借助材料设计和制备的新理念、新方法不断挖掘现有材料的性能潜力,另一方面应重视具有潜在优势的复合块状非晶材料及低活化高熵合金等新型材料的研发。本文依据中国磁约束聚变材料路线图草稿,对RAFM钢、机械合金化制备的ODS钢,钒合金以及碳化硅复合材料的发展进行了综述,对最近几年兴起的改良RAFM钢、非机械合金化制备的ODS钢等新型候选结构材料进行了介绍,并对具有更佳性能的先进结构材料种类进行了展望。

With the advance of ITER and CFETR,issues concerning materials become a serious problem which limits the development of fusion energy.Blanket is an important components for energy transform,tritium sustain and radiation shielding.The development of structural materials which fit the requirement of the harsh service environment has become a research focus worldwide.Various blanket structural materials such as reduced activation ferritic/martensitic steels(RAFMs)have been developed for decades.Based on the Roadmap of Fusion Energy of China,the neutron irradiation dose in the structural materials can reach 10 dpa in Phase 1,and 50 dpa in Phase 2.Until now,there are no materials that can satisfy both the harsh working environment requirement and engineering building requirement.RAFM steels are the main candidate for the blanket structural materials.Several specification of RAFM steels have been deve-loped worldwide,and the database has been established.However,limited by the narrow working temperature range and the low creep strength at high temperature,RAFM steels cannot reach the requirement of the CFETR Phase 2 and future fusion reactor.Two method have been proposed,one is adding oxide dispersion phase into the steel to promote the high creep performance,the steels obtained by this method is called oxide dispersion strengthened steels(ODSs).This method can be further classified into two kinds depending on if the mechanical alloyed(MA)is needed in the manufacture process.The other method is based on computational thermodynamics modelling.The density of MX phase can be increased by modifying chemical composition and thermomechanical treatments.The ODSs obtained by MA have the best performance at high temperature and under irradiation,but it should be noted that the MA process is of high cost and low efficiency.The none-MA ODSs and modified RAFM steels have the properties close to those of the MA ODSs,and they are much cheaper than the MA ODSs with potential for large-scale manufacture.Except for structural materials based on iron,vanadium alloys and SiC composite materials are all candidates for blanket structural materials with some good properties over the steels.For vanadium alloys,their working upper temperature is low and they are not compatible with hydrogen isotopes,which limits the application of vanadium in fusion reactor.For SiC composite materials,the joint technology and large-scale manufacture remain as problems.For future fusion reactor,the irradiation dose of the structural materials is larger,thus the current candidate materials may not fully satisfy the requirement.In the future,two aspects should be attached great attention to,one is exploring the performance potential of existing materials with the help of new ideas and new methods of material design and preparation,the other one is development of new materials like the metallic glass composites and high-entropy alloys.According to the Roadmap of Fusion Reactor Materials of China,we review the development of the structural materials of the fusion blanket in this article.The development of RAFM steel,mechanical alloyed(MA)oxide dispersion strengthened steels(ODSs),vanadium alloys and SiCf/SiC has been introduced.In recent years,new types of structural materials emerge,such as mo-dified RAFMs and none-MA ODSs,which have also been described in this article.Finally,the authors look ahead the development of advanced structural materials with better performance.