Measurements of the effective thermal conductivity of a bed of Li 4SiO 4 pebbles of 0.35–0.6 mm diameter and of a mixed bed of Li 4SiO 4 and alu

Abstract

The Karlsruhe ceramic breeder reference design for a Demo relevant blanket is based on a concept where the breeder material is in form of a bed of a mixture of Li 4 SiO 4 pebbles in the diameter range 0.35–0.6 mm. The heat transfer parameters of this bed have been measured in an especially developed experimental apparatus. The bed is contained in an annular space between two concentric cylinders. The heat produced electrically in the inner cylinder flows in the radial direction. The agreement of the measured thermal conductivity data with the correlation of Schlünder is quite good. The measured heat transfer coefficients between pebble bed and bed wall show considerable scatter, because the temperature difference at the wall is small. Analogous experiments have been performed for a mixed bed of 2 mm aluminum pebbles and 0.1–0.2 mm Li 4 SiO 4 pebbles in the volume ratio 3 to 1. These measurements are required to calculate the temperatures in a mixed bed of 2 mm beryllium pebbles and 0.1–0.2 mm Li 4 SiO 4 pebbles. This kind of pebble bed is being developed for an alternative blanket design capable to withstand possible excessive beryllium swelling.