【作者】 田宇； 严泽凡； 刘荣正； 刘兵； 邵友林； 唐亚平； 刘马林；

【Author】 TIAN Yu;YAN Ze-fan;LIU Rong-zheng;LIU Bing;SHAO You-lin;TANG Ya-ping;LIU Ma-lin;Institute of Nuclear Energy and New Energy Technology of Tsinghua University;

【机构】 清华大学核能与新能源技术研究院；

【摘要】 高温气冷堆(HTGR)采用三元结构各向同性(TRISO)的包覆核燃料,因其固有安全性和高温制氢等应用而著称。TRISO燃料颗粒采用碳化硅(SiC)作为裂变产物的屏蔽层,其对整个颗粒有着重要影响。因此制备高品质的SiC包覆层对提升TRISO颗粒整体性能有着重要意义。目前以MTS为前驱体,采用流化床-化学气相沉积(FBCVD)方法已经成功制备出SiC包覆层,但还存在包覆时间长(约2～3 h包覆35μm),包覆效率(MTS利用效率约87%)有待提高等一系列问题。随着更大规模高温气冷堆燃料元件生产线的研发和燃料元件制备经济性要求的提高,需对流化床-化学气相沉积制备SiC包覆层过程从晶体生长角度进行分析,从而获得各种参数对SiC晶体生长影响的规律。采用分子动力学(MD)方法可以模拟和描述沉积过程,有助于分析材料的微观生长机理。本文基于对FB-CVD过程的深入分析,拟将此多物理场耦合过程进行阶段性分析研究。选择SiC材料气相沉积过程作为研究对象,利用MD方法构建沉积模型,模拟了C、Si原子在基底上的沉积和SiC材料生长演化过程,从表面粗糙度、径向分布函数、配位数等方面定量分析了基底温度对沉积层质量的影响。本研究表明MD方法可以用于SiC材料的气相沉积过程模拟,并定量分析了温度对SiC层包覆的影响,未来可用于模拟TRISO颗粒包覆SiC层的过程,为核燃料包覆层制备工艺的优化提供理论依据和指导。更多还原

【Abstract】 High temperature gas-cooled reactor(HTGR) uses tri-structural isotropic(TRISO) coated nuclear fuel,and is characterized by its inherent safety and application in hydrogen production.TRISO fuel particles use silicon carbide(SiC)as the shielding layer of fission products, which has important effects on the whole particle.Therefore,the preparation of high quality SiC coating is of great significance to improve the overall performance of TRISO particles.At present,SiC coating has been successfully prepared by fluidized bed chemical vapor deposition(FB-CVD) using MTS as precursor,but there are still a series of problems such as long coating time(about 2～3 hours for 35 μm coating) and coating efficiency(about 80 %～87 % of MTS utilization efficiency) remaining to be improved.With the development of a larger-scale HTGR fuel element production line and the need to improve the economy of fuel element preparation,the process of SiC coating layer preparation by FB-CVD needs to be analyzed from the perspective of crystal growth to obtain the influence of various parameters on SiC crystal growth.The use of molecular dynamics(MD) methods allows to simulate and describe the chemical vapor deposition process and helps to analyze the microscopic growth mechanism of materials.Based on the indepth analysis of the FB-CVD process,this multi-physics coupling process will be analyzed and studied in stages.The vapor phase deposition process of SiC material is selected as the research object,and the deposition model is constructed by using MD method to simulate the deposition of C and Si atoms on the substrate and the growth evolution of SiC material,and the influence of substrate temperature on the quality of deposited layer is quantitatively analyzed in terms of surface roughness,radial distribution function and coordination number.This study shows that the MD method can be used to simulate the vapor deposition process of SiC materials, and the influence of temperature on the SiC coating is quantitatively analyzed.In the future,it can be used to simulate the TRISO particle coating process of SiC layer,and provide theoretical basis and guidance for the optimization of the preparation process of nuclear fuel coating.更多还原