Elastic response of individual European advanced ceramic breeder pebbles during uniaxial compression

Abstract

Lithium orthosilicate (Li4SiO4, LOS) based advanced ceramic pebbles are currently the reference material in Europe for solid tritium breeder blankets. These breeder pebbles, as the constituent of pebble beds, are not structural members but undergo cyclic thermo-mechanical compression. To withstand these operational loads, lithium metatitanate (Li2TiO3, LMT) was added as a second strengthening phase during their development at Karlsruhe Institute of Technology (KIT) in the Institute for Applied Materials Energy Storage Systems (IAM-ESS). To capture the micro scale response of the pebble bed, Discrete Element Modelling (DEM) is currently used. These simulations use the Hertzian contact model and require the crush load and Young's modulus of individual pebbles as input. In this study uniaxial compression tests were done to obtain the mechanical response of individual 500 μm and 1000 μm diameter pebbles produced by the KALOS facility built and installed at KIT IAM-ESS. Correcting the Hertzian equation to account for pebble defects, the Hertzian contact assumption was validated. The crush load increased with LMT content but the Young's modulus appeared to be independent of the LMT content. The closed porosity prevalence and variation across various batches is low and did not show any influence on the crush strength or stiffness of the pebbles.