Experimental investigation of thermal diffusivity and heat capacity of ceramic breeder beds

In the solid Breeder Blanket (BB) concepts both tritium release and heat recovery depend on the thermal performances of the breeding zone. Within the R&D activities of the Helium Cooled Pebble Bed (HCPB) breeding blanket, the knowledge of the thermal diffusivity of the breeder beds is of fundamental importance to model the transient heat transfer during the power pulses of the fusion machine. The aim of the present study is to investigate the thermal diffusivity of the breeder beds at BB relevant conditions; to this end the line heat source probe method was employed together with differential scanning calorimetry. An experimental facility, based on the line heat source probe method, was devised for the investigation of the thermal diffusivity of granular beds at breeder blanket relevant temperatures, mechanical state, purge gas type and pressure. Besides the experimental approach, literature values were used to estimate the specific heat capacity of the breeder materials starting from the specific heat capacity of the constituent compounds based on the mole fraction. In addition to the thermal diffusivity and heat capacity, a preliminary insight on the phase transitions of the reference and advanced ceramic breeder beds is given.