The emission of fission products embedded in various graphites by fission recoil was studied by the post-irradiation annealing technique over the temperature range 500 to 1400C. Detailed studies of the emission of Xe133 showed the release to be in two parts: an initial rapid release lasting for about 16h and a slow diffusion process. The fraction evolved by the initial process increased with the temperature of annealing. Values were given to define its magnitude and some discussion of its origin was given. The latter portion of the release was described by a diffusion coefficient obtained from the application of Fick's law of diffusion to the release. Activation energies for the diffusion of Xe133 were calculated and the relation of the diffusion coefficients to graphite structure was discussed.

The Diffusion of Fission Products from Graphite. Findlay, J.R., Laing, T.F.: Journal of Nuclear Materials, 1962, 7[2], 182-91