碳化硅基新型包覆燃料颗粒的设计及制备

摘要

Tristructural-isotropic (TRISO)coated fuel particle which can contain most gas and solid fission products within the coating layers provides the crucial safety of high temperature gas-cooled reactor (HTGR).To meet the requirements of very high tem-perature gas-cooled reactor (VHTR),which will be operated in higher temperatures with deeper burnups,two novel types of SiC-based coated fuel particles were designed. The porous silicon carbide layer is used to replace the PyC buffer layer in the first type. The coating layers from inside to outside are inner porous SiC layer,inner dense PyC layer,dense SiC layer and outer dense PyC layer,respectively.The second type is the coated particle with different SiC coating layers,and the coating layer sequences from inside to outside are inner porous SiC layer,SiC transition layer and outer dense SiC lay-er,respectively.The novel particle design can reduce the internal pressure of coated fuel particle which can further reduce the probability of pressure vessel failure by introducing the porous SiC inner layer.The formation mechanism and preparation parameters of the porous SiC layer were investigated.The two novel coated particles with designed coat-ing layers were successfully prepared by a fluidized bed chemical vapor deposition meth-od.Moreover,the novel SiC-based fuel element concept was also provided,and two types of fuel elements with spherical and columnar shapes were fabricated using surro-gate coated particles.%TRISO 型包覆燃料颗粒可将核裂变产生的气体、固体裂变产物束缚在燃料颗粒内部，是高温气冷堆安全性的重要保障。为满足未来超高温气冷堆在更高温度及更高燃耗条件下对燃料元件的要求，需对传统 TRISO 颗粒进行优化和改进。基于包覆颗粒的破损机制，设计了两种 SiC 基新型包覆颗粒，一种采用疏松 SiC 层替代疏松热解炭层，包覆层由内而外依次为疏松 SiC 层、内致密热解炭层、致密 SiC层、外致密热解炭层；另一种为全 SiC 包覆结构，包覆层由内而外依次为内层疏松 SiC 层、SiC 过渡层、外层致密 SiC 层。根据结构设计，采用流化床化学气相沉积法实验探索了疏松 SiC 的形成机制及包覆工艺条件，并利用 SEM、XRD 等进行材料分析，最终成功实现了两种新型包覆颗粒的大规模制备。更进一步，提出了全 SiC 基燃料元件的概念，并制备了球形和柱形全 SiC 基模拟燃料元件。