Effect of carbon ion irradiation on Ag diffusion in SiC

Abstract

Transport of Ag fission product through the silicon-carbide (SiC) diffusion barrier layer in TRISO fuel particles is of considerable interest given the application of this fuel type in high temperature gas-cooled reactor (HTGR) and other future reactor concepts. The reactor experiments indicate that radiation may play an important role in release of Ag; however so far the isolated effect of radiation on Ag diffusion has not been investigated in controlled laboratory experiments. In this study, we investigate the diffusion couples of Ag and polycrystalline 3C-SiC, as well as Ag and single crystalline 4H-SiC samples before and after irradiation with C 2+ ions. The diffusion couple samples were exposed to temperatures of 1500C, 1535C, and 1569C, and the ensuing diffusion profiles were analyzed by secondary ion mass spectrometry (SIMS). Diffusion coefficients calculated from these measurements indicate that Ag diffusion was greatly enhanced by carbon irradiation due to a combined effect of radiation damage on diffusion and the presence of grain boundaries in polycrystalline SiC samples.

Ag diffusion in SiC high-energy grain boundaries: Kinetic Monte Carlo study with first-principle calculations

“…Although there are still many uncertainties about these mechanisms, it is suggested that a RED of Ag through a percolating network of amorphous-like HEGBs may explain the observed radiation effects on Ag diffusion in SiC. In addition to possible RED in disordered GBs, we recently proposed a Ag kickout mechanism [63], that can be active in GBs with crystalline qualities. It was shown in this argument that interstitial clusters formed under irradiation can dissolve during postirradiation annealing, and then kickout substitutional Ag, leading to its facile interstitial diffusion.…”

“…%, which is very close to the values of 2-4 at. % estimated from experimental solubilities [63] assuming they are dominated by HEGBs. This excellent agreement is somewhat fortuitous but further suggests that our Ag formation energetics are accurate.…”

FY18Q3 Quarterly Report: Radiation Enhanced Diffusion of Ag, Ag-Pd, Eu, and Sr in Neutron Irradiated PyC/SiC Diffusion Couples

“…As such other techniques such as SIMS may be required. The use of SIMS has been successfully demonstrated in prior studies of diffusion of fission product species in SiC [6][7][8].…”

Preparation of Diffusion Couples for Irradiation and High Temperature Testing of Representative TRISO PyC/SiC

“…Historically, 110m Ag release has garnered much attention due to its notable release relative to other fission products and lack of consensus regarding the release mechanism [8][9][10]. Concerning silver release, there is a reported discrepancy between the diffusion kinetics reported from in-pile release experiments, out-of-pile release experiments, surrogate experiments, and computational modeling efforts [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. The reported in-pile release is more rapid than out-of-pile release and surrogate experiments.…”