Study of the thermal migration of molybdenum, technetium and iodine fission products in apatites

With a view to store long life nuclear wastes in a geological site, apatites are envisaged on the one hand as a containment matrix for actinides or fission products for a long life, and on the other hand, as materials incorporated in the building barriers. This study concerned migration of fission products in the apatites as a function of temperature. Iodine 129 (16 million years period) and technetium 99(210,000 years period) were chosen, with the aim to obtain a modeling of the behavior of these elements in order to extrapolate their future over a long period of time. The studied apatite is a hydroxy-apatite with a chemical composition known as Ca₁₀(PO₄)₆(OH)₂. In order to limit radiation protection issues, the behavior of technetium is studied via rhenium, its chemical counterpart, and molybdenum, whose mass is close to that of technetium. The coupling ion implantation - RBS allowed to show a volatilization of these elements during air annealing. molybdenum and rhenium were then chemically characterized by XPS and XANES (X-ray Absorption Near Edge Structure). An oxidation of these elements is shown, resulting in the formation of volatile oxides. In the case of iodine, experiments with radioactive iodine 131 and stable iodine are jointly conducted, showing a diffusion of this element in the grain joints of the material.