Influence of SiC grain boundary character on fission product transport in irradiated TRISO fuel

Abstract

In this study, the fission product precipitates at silicon carbide grain boundaries from an irradiated TRISO particle were identified and correlated with the associated grain boundary characteristics. Precession electron diffraction in the transmission electron microscope provided the crystallographic information needed to identify grain boundary misorientation and boundary type (i.e., low angle, random high angle or coincident site lattice (CSL)related).

Grain boundary complexions in silicon carbide

“…However, EBSD results, such as those recently published by Lillo and Gerczak,3,19 could provide a route to select conditions to produce more stable coatings with a lower probability of complexion transitions. However, EBSD results, such as those recently published by Lillo and Gerczak,3,19 could provide a route to select conditions to produce more stable coatings with a lower probability of complexion transitions.…”

“…During fabrication samples were cooled down at 5°C/min. 3,9 The presence of these intergranular films or other complexions with high diffusivities would lead to preferential diffusion routes compared to grain boundaries with lower complexions (e.g., mono-layer or clean grain boundary). The specimens were observed in a transmission electron microscope (TEM, FEI-TALOS F200X system, and JEOL JEM-2100Plus system, both operating at 200 kV).…”

“…1 The ease with which Ag can diffuse through SiC has baffled scientists leading to a wide range of experiments and theories trying to explain the origin of this behavior. 3,9,10 Furthermore, O`Coonell et al 11,12 raised further questions regarding grain boundary diffusion by showing that two SiC materials (one irradiated, one not) with almost identical grain boundary character (as characterized by electron backscatter diffraction, EBSD) exhibited very different Ag/Pd diffusivities. [2][3][4] Little is known however of the characteristics of the grain boundaries in SiC, there are even contradictory results regarding when, why and how it is that Ag diffuses.…”

“…The most recent experimental and theoretical evidence support the idea that silver diffuses through the grain boundaries. [2][3][4] Little is known however of the characteristics of the grain boundaries in SiC, there are even contradictory results regarding when, why and how it is that Ag diffuses. Recent experiments showed that Ag diffusion is strongly related to microstructure to the point that for some microstructures silver diffuses only after the sample has been heat treated above a specific temperature and that above some temperature Ag could even induce abnormal grain growth.…”

“…7,8 Although originally proposed that Ag would diffuse along with Pd as a solid solution, recent evidence from irradiated fuel has shown that Pd and Ag might not be diffusing together since Ag nodules could be found on several tests in the absence of Pd. 3,9,10 Furthermore, O`Coonell et al 11,12 raised further questions regarding grain boundary diffusion by showing that two SiC materials (one irradiated, one not) with almost identical grain boundary character (as characterized by electron backscatter diffraction, EBSD) exhibited very different Ag/Pd diffusivities.…”