Associations of Pd, U and Ag in the SiC layer of neutron-irradiated TRISO fuel

Effect of carbon ion irradiation on Ag diffusion in SiC

“…However, the observed enhancement in diffusion coefficient in itself cannot account for the integral release measurements ((1.5-35.9)×10 -16 m 2 /s at 1500 o C). In addition to irradiation, the release of Ag can be affected by many other factors, such as the presence of nanocracks and voids [7,76,77], change in the microstructure (including degradation) of SiC [78,79], the effect of other fission products/impurities [80][81][82][83][84], and possibly combined effects of these factors with irradiation. Further investigation is necessary to provide quantitative measure for combined effects of radiation and other possible mechanisms for enhanced diffusion, such as interaction of Ag with other fission products/impurities, the annihilation of radiation damage during annealing, and the effect of the change in microstructure.…”

Effect of palladium on the microstructure and grain boundary complexions in SiC

“…The purpose of these coatings is to work as a miniature fission product containment vessel, capable of retaining within the particle all relevant fission products. [7][8][9][10] Recently, Cancino et al identified three types of Dillon-Harmer grain-boundary complexions 11 in SiC and suggested that the complex diffusion behavior of fission products could be explained through the existence of grain-boundary complexions and complexion transitions. [1][2][3] Among all the fission products generated in the kernel, Pd has received particular attention as it is capable of chemically interacting with SiC producing palladium silicides (Pd 2 Si at temperatures between 1000°C and 1300°C) and carbon.…”

“…[4][5][6] Furthermore, it has been suggested that Pd can enhance the diffusion of other relevant fission products such as Ag 110m (a strong γ-ray emitter), however, it is still unclear how Pd could enhance such diffusion since the original theory suggesting the formation of a solid solution has not been corroborated experimentally, since Pd and Ag have been observed to diffuse separately. [7][8][9][10] Recently, Cancino et al identified three types of Dillon-Harmer grain-boundary complexions 11 in SiC and suggested that the complex diffusion behavior of fission products could be explained through the existence of grain-boundary complexions and complexion transitions. 12 Therefore, in this work, we studied the effect of Pd on the microstructure of SiC.…”

Grain boundary complexions in silicon carbide

“…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.…”

“…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.…”