The high temperature exchange of 14C between 14CO and 12C-graphite was used to label a large number of samples of various nuclear graphites. The technique has made it possible to obtain data on the self-diffusion of carbon in graphite. Three nuclear graphites were used, Pile Grade A and two isotropic varieties. Diffusion constants at 2473K lay in the range 0.64 x 10-19 to 2.97 x 10-19m2/s. The D0 values varied from 1.20 x 10-12 to 1.06 x 10-6m2/s and the activation energies ranged from 337 to 621kJ/mol. The D values found here were lower than those found by other workers. Activation energies were also compared with values found by other workers and discussed in relation to theoretical calculations on the activation energy for direct interchange, vacancy and interstitial mechanisms for diffusion. It was concluded that direct interchange was the predominant mechanism for the diffusion of 14C in the highly graphitised samples used in this work.

The Diffusion of 14C in Nuclear Graphites. Sach, R.S., Williams, W.J.: Carbon, 1974, 12[4], 425-32