Thermal Diffusivity Measurement of Graphite Pebble Bed by Laser Flash Method

Full text: In solid-type breeding blankets for fusion reactors, most of the concepts employ materials in the breeding zone to be packed as pebbles, which is called collectively as a pebble bed. For reliable blanket system design, thermo-mechanical properties of pebble beds have to be well understood and measured. Especially, in order to apply conventional continuum approach to predict thermo-mechanical behaviors of pebble beds, such as Finite Element Method (FEM), it is important to measure the effective properties of pebble beds as well as properties of the pebble itself. In the present work, thermal diffusivity of graphite pebble bed is measured. The graphite reflector is unique feature of Korean TBMs in that the amount of beryllium multiplier is considerably reduced by replacing some of it with the graphite reflector while tritium breeding capability remains almost the same. Therefore, establishing thermo-mechanical data for the graphite pebble bed is critical for Korean fusion programs. For measurements, Laser Flash Method (LFM), which is a non-contact and non-destructive method with covering a wide range of diffusivity with excellent accuracy, is applied and wall-influence effect on the minimum thickness required for the sample is investigated for future experiments. (author)