Sample holder design for effective thermal conductivity measurement of pebble-bed using laser flash method

Highlights: • The effective thermal conductivity of a graphite pebble-bed was successfully measured by Laser Flash Method. • For the measurement on pebble-bed form, the new sample holder was specially designed. • The 3-layers measurement technique was designed in order to make the laser flash method successful. • The effective thermal conductivity of a graphite pebble-bed was converged around 3.2 W/m K. • The effect of the temperature (RT ∼ 200 °C) in a graphite pebble-bed was negligible. - Abstract: Since the stress due to the thermal load on breeding blanket structure is one of the main design driver, the thermal conductivity is necessary input data for thermal-structural and thermo-hydraulic analyses performed in order to understand the heat transfer phenomena and estimate the thermal stress. Since for the functional materials of solid type breeding blanket a pebble-bed form is mainly adopted instead of a bulk form such as a block or a disk, it should be needed to measure the thermal conductivity of pebble-bed. In this study, the effective thermal conductivity of pebble-bed is measured by laser flash method, which is one of the various thermal conductivity measurement methods, because this method has several advantages such as a wide thermal conductivity range of the measurement and a small amount of pebbles. A sample holder considering the heat transfer mechanism from the laser source to pebble-bed has been specially designed in order to apply the laser flash technique to the pebble-bed sample and it has been validated by the experiments. This paper introduces preliminary results of the effective thermal conductivity on the pebble-bed using this sample holder.