Study of mechanisms involved in thermal migration of molybdenum and rhenium in apatites

The aim of this work is to characterise the retention properties of apatites, studied as potential inert matrices, towards the long-lived fission product Tc-99 (T = 210 000 years) in radioactive waste disposal. The study was made using two stable homologous elements of Tc: molybdenum which has the same mass as technetium, and rhenium which is the chemical analogue of Tc. These elements were introduced in apatite samples by ion implantation and their profiles were determined by Rutherford backscattering spectroscopy (RBS). The coupling of X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) analysis showed the oxidation of molybdenum and rhenium during annealing. Using these results on Mo and Re behaviour, assumptions were made on the migration of technetium. (C) 2001 Elsevier Science B.V. All rights reserved.