Heat transfer and technological investigations on mixed beds of beryllium and Li4SiO4 pebbles

Abstract For the European BOT DEMO solid breeder blanket design the use of mixtures of 2 mm beryllium and 0.1–0.2 mm Li 4 SiO 4 pebbles with and without 0.1–0.2 mm beryllium pebbles has been proposed. A series of heat transfer and technological investigations are being performed for these pebbles. Namely: (a) Measurements of the thermal conductivity and of the wall heat transfer coefficient of a 2 mm Be pebble bed, of a bed with 2 mm Be plus 0.1–0.2 mm Li 4 SiO 4 pebbles and of a bed with 2 mm Be pebbles plus 0.1–0.2 mm Li 4 SiO 4 and Be pebbles. (b) Thermal cycle tests of mixed beds of Li 4 SiO 4 and beryllium pebbles; during these tests the pressure drop across the bed of the helium purging flow is measured. (c) Annealing tests at 650°C of the Li 4 SiO 4 pebbles with and without the beryllium pebbles. (d) Measurement of the failure loads of the Li 4 SiO 4 pebbles before and after annealing. Tests (a) and (b) have been performed for bigger Li 4 SiO 4 pebbles (0.3–0.6 mm) as well. The results of the experiments are reported in the paper.