Characterisation of ceramic breeder materials for the helium cooled pebble bed blanket

In the European helium cooled pebble bed (HCPB) blanket slightly hyperstoichiometric lithium orthosilicate (Li 4 SiO 4 +SiO 2 ) and lithium metatitanate (Li 2 TiO 3 +TiO 2 ) pebbles are considered as candidate ceramic breeder materials. Such ceramic breeder pebbles and pebble beds were investigated in different types of experiments carried out at Forschungszentrum Karlsruhe. In longterm annealing experiments (96 days at 970 °C in He+0.1% H 2 atmosphere) the behaviour of the pebbles under DEMO blanket relevant conditions was investigated. Mechanical uniaxial and triaxial compression tests at temperatures up to about 850 °C were performed to determine the mechanical behaviour of pebble beds as a function of temperature (stress–strain dependence, thermal creep behaviour, friction coefficients). Thermal conductivity measurements up to about 800 °C were carried out with the aim to study the effect of creep on the pebble bed heat conduction. An overview of the experimental activities on ceramic breeder materials is given.