中国RAFM钢中氚及自衰变氦-3的驻留机制研究

As a highly recommended main structure material for the tritium breeding blanket in a future magnetically controlled fusion reactor, reduced activation ferritic/martensitic(RAFM) steels will be tested with the test blanket modules in ITER machine. The entry subsequently retaining of tritium and helium-3 from tritium decay in the material can lead to a significant loss of tritium as fuel produced in the breeders and cause damages to the performance. In this project, two candidated domestic RAFM steels nominated as China Low CLF-1 and CLAM will be focused on their properites of retaining tritium and helium-3. The occupancy and associated distribution of tritium and helium atoms will be investigated theoretically and experimentally. The diffusion constants of hydrogen isotopes including the solubility, diffusivity, permeability will be determined. The mechanism and discipline on the migration and retaining of tritium and helium-3 atoms in the two materials and its correlation to the micro-structure evolution will be explored in detail. The retainability of tritium will be evaluated for the two RAFM steels as a practical structure material in the tritium breeding blanket will be evaluated. And an efficient detritiation technology will be proposed accordingly. This project is aimed at obtaining some fundamental data on their tritium confinement capacities for the two candidated structure materials and a thorough understanding of some related disciplines on the tritium inventory and its internal distribution characteristics.

低活化铁素体/马氏体钢是未来磁约束核聚变堆产氚包层推荐的主体结构材料并将在ITER实验包层模块中考核，氚及氚衰变氦-3在钢中的驻留将影响所产生氚的有效利用并导致材料的结构损伤。本项目针对中国低活化铁素体（CLF-1）钢及中国低活化马氏体（CLAM）钢两种候选材料，通过理论模拟和实验手段，考察氚及氦-3在表面及内部晶格点阵及缺陷位的占位及分布特征，获取氢同位素在材料中溶解度、扩散系数和渗透率等扩散常数，重点研究氚及氦-3输运行为及与材料微观结构的相互制约关系并掌握其在晶格中的驻留规律；评价材料氚包容能力并初步探索驻留氚的去除与回收工艺。为两种在研候选结构材料提供氚驻留量、氚及衰变氦-3分布特征等涉氚相容性的基础数据并深入认识有关规律。

针对磁约束聚变堆包层候选结构材料低活化铁素体-马氏体（RAFM）钢在服役工况下的氢同位素驻留及由此产生的氢脆、氦脆及氚燃料损失等氢、氦相容性问题，采用理论计算、评估并结合实验测试手段研究了氢同位素（含氚）在CLAM及CLF-1两种国产RAFM钢的渗透、驻留、在线去除行为以及驻留氢同位素产生的力学损伤效应。结果表明：氢倾向于占据bcc晶格中的四面体间隙且与空位能较好地共存，而氦倾向于与晶格空位结合；两种国产RAFM钢具有高于气态氚常用的包容结构材料18-8型奥氏体不锈钢1~2个数量级的扩散系数和渗透率，其中CLAM钢具有稍更高的扩散系数；高的扩散系数也导致材料中驻留的氢同位素很容易通过400℃左右的高温下在线去除，加氢交换有助于进一步提高氘和氚的去除效率；两种国产RAFM钢均属氢脆敏感材料，尤以板条和碳化物颗粒密度均较大的CLF-1钢为甚，但在500℃、氢同位素分压仅为100Pa的正常服役工况下脆性化程度并不高；两种材料经620℃、1.2MPa（含10%氚）饱和充氘氚并在室温下存放5年后，内部驻留的氚原子由于高的扩散系数而大部分逃逸出样品，残余氚在2~5appm量级，形态以缺陷捕获的氢原子团簇形式为主，且由于氢同位素已逸出，材料仍能保持较好的塑性。研究结果证明了两种国产RAFM钢作为聚变堆包层结构材料在正常服役工况下可以不考虑氢脆效应，其驻留的氚量在可接受的克量级且容易通过氚提取间隙的高温原位热解析方法及时去除。项目研究工作中，培养了氢同位素与材料相互作用研究领域3名硕士研究生及1名博士研究生，发表论文12篇。