THE DIFFUSION OF CESIUM IN THE GRAPHITIC MATRIX A3-3 UNDER IRRADIATION BY A FAST-NEUTRON FLUX OF 2X10(17) M(-2) S(-1)

The Cs-137 core release rate of High Temperature Reactors (HTR) is eff ected by the interactions of cesium with the graphitic material used a s a matrix for the coated fuel particles. The migration of Cs-137 in t he graphitic matrix A3-3 at a fast neutron flux of 2 x 10(17) m(-2) s( -1) was studied in short-term experiments using the thin-film techniqu e, The penetration profiles did not satisfy Fick's second law. The dif fusion/trapping/re-emission model was applied to determine the diffusi on coefficient D and the trapping coefficient mu for four profiles pro duced at 1088 and 1166 K. D, mu and the reemission coefficient b at 12 93 K were determined for two profiles. Compared to laboratory conditio ns no effect of the fast neutron irradiation on the Cs-137 migration i n matrix A3-3 was observed.