Diffusion behaviour of fission product in pyrolytic silicon carbide

The concentration distribution of 133Xe, 140Ba, 89Sr, 141Ce, 103Ru and 95Zr-95Nb in a SiC layer and releases of these fission products from SiC coated fuel particles were measured in a temperature range from 16500 to 18500C, to obtain the diffusion parameters and to investigate the diffusion behaviours in SiC. Temperature dependences of the diffusion coefficients of these fission products except 95Zr-95Nb were obtained. In diffusion behaviours of the alkali earth fission product, volume diffusion occured considerably besides grain boundary above 16500C. 141Ce and 103Ru diffusions were almost through grain boundaries in the temperature range. 95Zr-95Nb showed volume diffusion besides boundaries diffusion in their distribution annealed at 18500C for 35 h, but those for the shorter time or at the lower temperature would be due to boundary diffusion. In comparison of the diffusion coefficients in SiC and PyC, it was proved that SiC was effective for retention of the solid fission products. (Auth.)