Measurements of the effective thermal conductivity of a non-compressed Li4SiO4 pebble bed

•A new set-up to measure the effective thermal conductivity of a pebble bed was built.•Bare thermocouples were used to improve the measuring accuracy of the temperature.•Pebble bed container made of quartz glass improved the reality of the testing values.•Low temperature difference in the direction of heat flow was applied in the work.•The effective thermal conductivity increased with the increase of temperature.