First-principle studies of radioactive fission productions of Cs/Sr/Ag/I adsorption on silicon carbide in HTGR

Silicon carbide (SiC) is one of the important fuel-element materials in high-temperature gas-cooled reactors (HTGRs), and learning the adsorption behavior of radioactive fission products on the SiC surface is essential for source-term analysis in HTGR. In this study, the adsorption behavior of cesium, strontium, silver, and iodine on β-SiC is investigated using first-principle calculations. We find that the interactions between the adatoms and SiC substrate are strong for all four types of nuclides with binding energy of approximately 1-3 eV. These results are confirmed again by analysis of the charge density difference and density of state. Furthermore, the adsorption rates of the four nuclides are obtained, and we explain that these nuclides display significant adsorption rate on the SiC surface but are not easily desorbed, which shows that the solid fission products have difficulty penetrating through the SiC. These results demonstrate that in HTGR, intact SiC could effectively obstruct the diffusion of fission products from the uranium dioxide in tri-isotropic (TRISO) particles to the primary circuit, which are first obtained in a micro perspective.