Radiation stability of long-term annealed bi-phasic advanced ceramic breeder pebbles

Advanced ceramic breeder pebbles consisting of Li ₄ SiO ₄ and additions of Li ₂ TiO ₃ were tested regarding their long-term thermal and to their radiation stability. As-prepared and long-term annealed pebbles were irradiated with accelerated electrons (up to 6 MGy) to investigate the formation of radiation-induced defects and radiolysis products caused by ionizing radiation. By using Raman spectroscopy the formation of significant amounts of radiolysis products can be excluded. Electron spin resonance spectrometry revealed several paramagnetic radiation-induced defects, such as HC ₂ centres (SiO ₄ ^3- and TiO ₃ ^- ), E’ centres (SiO ₃ ^3- and TiO ₃ ^3- ), Ti ³⁺ centres and peroxide radicals ([tbnd]Si–O–O·). Radiation-induced defects forming in the first stage of the radiolysis seem to be more pronounced in long-term annealed samples. Thermally stimulated luminescence showed relatively low temperatures (40–200 °C) for the thermal recovery of the radiation-induced defects by accelerated electrons. Moreover, the main recovery process of defects takes place in the first 8–10 days after the irradiation.