HEAT-TRANSFER AND TECHNOLOGICAL INVESTIGATIONS ON MIXED BEDS OF BERYLLIUM AND LI4SIO4 PEBBLES

For the European BOT DEMO solid breeder blanket design the use of mixt ures of 2 mm beryllium and 0.1-0.2 mm Li4SiO4 pebbles with and without 0.1-0.2 mm beryllium pebbles has been proposed. A series of heat tran sfer and technological investigations are being performed for these pe bbles. 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 Li4SiO4 pebbles and of a bed with 2 mm Be peb bles plus 0.1-0.2 mm Li4SiO4 and Be pebbles. (b) Thermal cycle tests o f mixed beds of Li4SiO4 and beryllium pebbles; during these tests the pressure drop across the bed of the helium purging flow is measured. ( c) Annealing tests at 650 degrees C of the Li4SiO4 pebbles with and wi thout the beryllium pebbles. (d) Measurement of the failure loads of t he Li4SiO4 pebbles before and after annealing. Tests (a) and (b) have been performed for bigger Li4SiO4 pebbles (0.3-0.6 mm) as well. The re sults of the experiments are reported in the paper.