Behaviour of ceramic breeder materials in long time annealing experiments

In the development of the European Helium Cooled Pebble Bed (HCPB) blanket the reference material is slightly overstoichiometric lithium orthosilicate (Li4SiO4+SiO2) pebbles, fabricated by the melting–spraying method. Slightly overstoichiometric lithium metatitanate (Li2TiO3+TiO2) and lithium metazirconate (Li2ZrO3+ZrO2) pebbles, fabricated using a extrusion–spheronization–sintering process, are considered as alternative candidates for the ceramic breeder material. In order to compare the long-term behaviour of the three materials at HCPB-blanket relevant temperature and atmosphere (He+0.1% H2), a campaign of three long time annealing experiments were carried out at Forschungszentrum Karlsruhe (FZK). Pebbles of each ceramic breeder material (Li4SiO4+SiO2 from FZK, Li2TiO3+TiO2 and Li2ZrO3+ZrO2 from CEA) were annealed for 96 days at 970 °C. During this period the change of the mechanical characteristics, the microstructure, and the chemical composition of the pebbles was analysed. After the end of the annealing experiment, uniaxial compression tests of pebble beds were performed additionally. In the present paper the results from the second experimental campaign are reported and discussed.