It was recalled that the 137Cs core release rate of high-temperature reactors was affected by interactions between Cs and the graphitic material which was used as a matrix for coated fuel particles. The migration of 137Cs in a graphitic matrix, under a fast neutron flux of 2 x 1017m2/s, was studied during short-term experiments which used the thin-film technique. It was found that the penetration profiles did not satisfy Fick’s second law. A diffusion/trapping/re-emission model was used to determine the diffusion coefficient and the trapping coefficient for 4 profiles which were produced at 1088 and 1166K. The diffusion coefficient, the trapping coefficient, and the re-emission coefficient at 1293K were determined for 2 profiles. When compared with laboratory conditions, no effect of fast neutron irradiation upon 137Cs migration in graphite matrix was observed.

W.Hensel, E.Hoinkis: Journal of Nuclear Materials, 1995, 224[3], 230-5