Density functional theory metadynamics of silver, caesium and palladium diffusion at β-SiC grain boundaries

摘要: Abstract The use of silicon carbide in coated nuclear fuel particles relies on this materials impermeability towards fission products under normal operating conditions. Determining the underlying factors that control rate at which radionuclides such as Silver-110m and Caesium-137 can cross barrier layers, palladium could compromise or otherwise alter nature layer, are paramount importance for safety fuel. To end, DFT-based metadynamics simulations applied to atomic diffusion silver, caesium along a Σ5 grain boundary carbon-rich Σ3 cubic 1500 K. For calculated coefficients lie similar range (7.04 × 10 −19 –3.69 × 10 −17  m 2  s −1 ) determined experimentally. caesium, rates very much slower (3.91 × 10 −23 –2.15 × 10 −21 than found experimentally, suggesting different mechanism simulation. Conversely, is faster (7.96 × 10 −11 –7.26 × 10 −9 observed penetration nodules. This points slow dissolution rapid regrowth nodules possible ingress addition previously suggested migration entire boundaries. was be slightly (2.38 × 10 –8.24 × 10 −10 boundary. Rather diffusing precise plane boundary, atom moves through bulk layer immediately adjacent there greater freedom move.