Radiation-induced effects in neutron- and electron-irradiated lithium silicate ceramic breeder pebbles

Ceramic breeder (CB) pebbles consisting of lithium orthosilicate (Li4SiO4) as the main phase and lithium metasilicate (Li2SiO3) as a secondary phase were analysed with respect to radiation-induced defects and radiolysis products. Therefore, pebbles that were irradiated with neutrons in the so-called HICU experiment (High neutron fluence irradiation of pebble stacks for fusion) were compared to pebbles irradiated with accelerated electrons and to an unirradiated sample. Fourier transformation infrared spectroscopy was used to investigate changes in the phase composition. Beside an expected increase in the second phase in the neutron-irradiated samples, no further significant changes or additional phases were detected compared to accelerated electron-irradiated samples. Several paramagnetic radiation-induced defects and radiolysis products, such as E' centres, HC1 and HC2 centres, peroxide radicals and either colloidal lithium particles or F+ centres were detected by electron spin resonance spectrometry. Thermally stimulated luminescence revealed relatively high temperatures (200-450 degrees C) for the recovery of neutron radiation-induced defects and radiolysis products due to high irradiation temperatures. In general, accelerated electron irradiation can be used to mimic radiation-induced defects and radiolysis products in neutron-irradiated samples. (C) 2020 Karlsruhe Institute of Technology. Published by Elsevier B.V. All rights reserved.