Silicon carbide is the main diffusion barrier against metallic fission products in TRISO (tristructural isotropic) coated fuel particles. The explanation of the accelerated diffusion of silver through SiC has remained a challenge for more than four decades. Although, it is now well accepted that silver diffuse through SiC by grain boundary diffusion, little is known about the characteristics of the grain boundaries in SiC and how these change depending on the type of sample. In this work five different types (coatings and wafers) of SiC produced by chemical vapor deposition were characterized by electron backscatter diffraction (EBSD). The SiC in TRISO particles had a higher concentration of high angle grain boundaries (aprox. 70%) compared to SiC wafers, which ranged between 30 and 60%. Similarly, SiC wafers had a higher concentration of low angle grain boundaries ranging between 15 and 30%, whereas TRISO particles only reached values of around 7%. The same trend remained when comparing the content of coincidence site lattice (CSL) boundaries, since SiC wafers showed a concentration of more than 30%, whilst TRISO particles had contents of around 20%. In all samples the largest fractions of CSL boundaries (3 ≤ Σ ≤ 17) were the Σ3 boundaries. We show that there are important differences between the SiC in TRISO particles and SiC wafers which could explain some of the differences observed in diffusion experiments in the literature.

碳化硅是针对TRISO（三向同性）涂层燃料颗粒中金属裂变产物的主要扩散屏障。超过四十年来，关于银通过SiC加速扩散的解释一直是一个挑战。尽管现在人们已经普遍接受银通过晶界扩散通过SiC扩散，但是对于SiC中晶界的特性以及这些晶界如何根据样品类型而变化知之甚少。在这项工作中，通过电子背散射衍射（EBSD）对化学气相沉积生产的SiC的五种不同类型（涂层和晶片）进行了表征。TRISO颗粒中的SiC与高角度晶界（约70％）相比，其SiC晶片的浓度在30％至60％之间。相似地，SiC晶片的低角度晶界浓度更高，范围在15％到30％之间，而TRISO颗粒的值仅达到7％左右。比较重合点晶格（CSL）边界的含量时，仍保持相同的趋势，因为SiC晶片的浓度超过30％，而TRISO颗粒的含量约为20％。在所有样本中，CSL边界的最大部分（3≤Σ≤17）是Σ3边界。我们显示出TRISO颗粒中的SiC和SiC晶片之间存在重要的差异，这可以解释文献中扩散实验中观察到的某些差异。因为SiC晶片的浓度超过30％，而TRISO颗粒的含量约为20％。在所有样本中，CSL边界的最大部分（3≤Σ≤17）是Σ3边界。我们显示出TRISO颗粒中的SiC和SiC晶片之间存在重要的差异，这可以解释文献中扩散实验中观察到的某些差异。因为SiC晶片的浓度超过30％，而TRISO颗粒的含量约为20％。在所有样本中，CSL边界的最大部分（3≤Σ≤17）是Σ3边界。我们显示出TRISO颗粒中的SiC和SiC晶片之间存在重要的差异，这可以解释文献中扩散实验中观察到的某些差异。