The diffusion of uranium and thorium in columnar pyrocarbon between 1450 and 2065C was studied by using the thin‐layer depletion technique. Coefficients were obtained that were in good agreement with results reported elsewhere for uranium diffusion in the <a> direction at actinide concentrations of less than about 0.15mg∕cm3. The coefficients increased at higher actinide concentrations. The anisotropic pyrocarbons were well-oriented, with their basal planes parallel to the deposition surface. Diffusion coefficients parallel to the deposition surfaces were about three orders of magnitude greater than those in the perpendicular direction. This difference was due mainly to the pre‐exponential term in the Arrhenius equation. The data (tables 8 and 9) could be described by:

U, <a> :     D (cm2/s) = 1.84 x 104exp[-119(kcal/mol)/RT]

U, <c> :     D (cm2/s) = 1.29 x 100exp[-103(kcal/mol)/RT]

Th, <a>:     D (cm2/s) = 1.21 x 104exp[-127(kcal/mol)/RT]

Th, <c>:     D (cm2/s) = 8.90 x 100exp[-113(kcal/mol)/RT]

Diffusion of Actinides in Pyrocarbons. Thin Layer Experiments. Evans, R.B., Stiegler, J.O., Watson, G.M.: Journal of Applied Physics, 1970, 41[12], 4808-19