Chlorine speciation in nuclear graphite: consequences on temperature release and on leaching
Résumé
This paper aims to get information on pristine chlorine speciation and its evolution with temperature in nuclear graphite used as a moderator in the first generation UNGG French reactors. For this purpose, temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) have been carried out on samples annealed in the temperature range 200-1000 °C. Two chemical forms of different thermal stabilities have been identified. Around 70% of chlorine is assigned to stable organic chlorine bound to aromatic carbon whereas around 30% is assigned to inorganic thermally labile oxychlorinated groups. The consequences for direct disposal are discussed.