Ceramic pebbles are foreseen to be used as tritium breeder in helium cooled pebble bed blankets in fusion reactors. The pebbles are subject to high temperature and irradiation. They may fail during thermomechanical loading. Failure of pebbles will influence the macroscopic thermomechanical response of pebble beds. Fragments of crushed pebbles can block the evacuation of purge gas. The influence of pebble failure, thermal stress and thermal conductivity is investigated to support blanket design.