液态熔盐堆芯石墨的结构调控及其与熔盐作用机制研究

In view of immediate contact between moderated neutron graphite and high temperature molten salt, the liquid molten fluoride salt and fission gas will diffuse and permeate into the graphite, even result in the corrosion of the graphite, which has disadvantage for stable operation of the reactors. As a nuclear material, the graphite should be provided with low porosity, high strength, corrosion resistant and excellent isotropic degree. In this work, the liquid slurrying-mixing technology is suggested to perpare the moderated neutron graphite by the subjecting mixture of binder of coal-tar pitch, filler of pitch coke. Depanding on structural design and technical optimization, the binder carbon and filler carbon in the graphite will be strengthen, and dispersible uniformity of pore size in the material will be improved. The mutual relationship between preparing parameters and properties of graphite will be studied. The deposition, diffusion and transfer characteristics of liquid molten fluoride salt（FLiNaK, FLiBe）in the graphite will be studied. Based on the distribution and diffusion characteristic of liquid molten fluoride salt in the moderated neutron graphite, the relationship between infiltration feature and pore structure of graphite will be clarified. After irradiation by neutron, the properties evolution, such as crystallite parameter, mechanical strength and thermal coefficient of expansion of graphite will be evaluated, and corrosion behaviors and irradiation damage mechanism will also be investigated. It would be provided with an innovative candidate material for moderated neutron graphite in liquid molten salt reactors in the future.

在高温液态熔盐堆中，作为慢化中子的石墨材料与熔盐接触，熔盐和裂变气体将在石墨孔隙中扩散和渗透并引起材料腐蚀，不利于反应堆稳态运行。本项目针对熔盐堆对石墨材料低孔径、高强度、抗腐蚀和各向同性等要求，提出了利用二次液相浆涂工艺制备石墨材料的路线。以粘结剂煤沥青和骨料沥青焦为原料，通过对液相浆涂工艺优化控制，来增强粘结剂炭和骨料炭之间界面结合能力，从而改善最终材料性能和结构，并掌握制备工艺参数和石墨理化性能之间的相互关系。通过考察不同粘度的流体熔盐（FLiNaK、FLiBe）在慢化剂石墨中的分布和扩散行为，研究熔盐对石墨的浸渗特性和对其孔结构与热力学性能的依赖关系。考察中子辐照条件对石墨材料的微晶参数、力学强度、热膨胀系数等性能的影响变化规律，探索对石墨辐照或腐蚀损伤机理。研究成果将是对传统慢化剂石墨结构设计和制备技术的重大创新，也将为今后我国液态熔盐反应堆用慢化剂石墨制备和候选提供重要依据。

在熔盐反应堆中，作为慢化中子的石墨材料与液态高温熔盐直接接触，熔盐和裂变产物将在石墨中扩散或渗透导致局部富集，甚至引起材料腐蚀，不利于反应堆稳态运行。针对熔盐堆用石墨材料低孔径、高强度、抗腐蚀和结构致密等要求， 本项目研究了核石墨材料界面缺陷和特定微观结构形貌的形成原因，探索石墨材料宏观的导热性能、力学强度和孔径结构与其界面缺陷和微观结构形貌之间的内在联系。项目研究采用原料预处理技术及热处理工艺掌握了石墨材料孔径调控技术，突破了平均孔径在100 nm的石墨材料制备技术；此外，系统研究了石墨材料的熔盐阻隔性能，阐明了石墨材料孔隙结构对熔盐浸渗行为的影响规律；最后采用离子辐照技术研究了几种所制石墨材料的辐照行为，研究其在辐照条件下的结构及性能演变规律，以进一步评价石墨材料核用性能。研究成果是对传统慢化剂石墨结构设计和制备技术的重大创新，也将为今后我国液态熔盐反应堆用慢化剂石墨选择提供重要技术支撑。