The migration of 137Cs in a graphitic matrix was studied, at He pressures of 4 and 10MPa, by using a thin-film technique and vapor-deposited carrier-free 137Cs. It was found that the penetration profiles did not satisfy Fick’s second law, but the use of a diffusion equation which included terms for trapping and re-emission was successful. When compared with 137Cs migration in a vacuum, a high He pressure led to a decrease in the diffusion coefficient of 137Cs, and to an increase in the activation energies for diffusion and trapping. The diffusivity could be described by:

D (cm2/s) = 10.3 exp[-1.76(eV)/kT]

while the trapping coefficient was described by:

 (/s) = 2200 exp[-1.63(eV)/kT]

at temperatures ranging from 1073 to 1273K, under a He pressure of 4MPa.

W.Hensel, E.Hoinkis: Journal of Nuclear Materials, 1995, 224[1], 1-11