Diffusion coefficients for carrier-free strontium-85 in two types of reactor grade graphite and two types of bonded compacted graphite were determined at 1200 to 1600C. In all four types of material the diffusion coefficients at 1000C were found to lie within the range of 8.9 x 10-11 to 8.9 x 10-10cm2/s, with activation energies of 68 to 79kcal/mol. The diffusion of strontium in a graphite which had been previously loaded with strontium has also been studied and it was shown that quite small amounts of strontium previously diffused into the graphite could greatly influence the diffusion rate of strontium subsequently entering the graphite. At 1000C, a concentration of 2mg/g graphite increased the diffusion coefficient by 5 orders of magnitude. The measurements were considered to be suitable for use in predicting the long-term movement of strontium through fuel-tube walls in a high temperature gas-cooled reactor where the graphite was similar to the graphite used in this work, since comparison with data obtained from post-irradiation examination of fuel tubes suggested that strontium diffusion was not affected by either a neutron flux or a high pressure of helium.

Laboratory Determinations of Strontium Diffusion Coefficients in Graphite. Sandalls, F.J., Walford, M.R.: Journal of Nuclear Materials, 1976, 62[2-3], 265-72

Figure 14

Diffusivity of Sb clusters on graphite