Chemical reactivity of beryllium pebbles in air

In the design of the European Helium-Cooled Pebble Bed (HCPB) Blanket, the use of beryllium as a neutron multiplier in the form of a pebble bed is foreseen. In the development of the pebble bed, kinetic data are needed for the reaction between the beryllium pebbles and air. Therefore, thermogravimetric experiments were conducted to study the pebbles' behaviour when exposed to air in the temperature region 400-900 °C. The material tested consisted of beryllium pebbles produced by the Rotating Electrode Method. At temperatures up to 700 °C, the reaction kinetics is approximately parabolic, although a deviation from parabolic behaviour is observed after approximately 6000 s of air exposure. Above 700 °C, a combination of paralinear and accelerating behaviour is observed. From the experimental results the appropriate rate constants were determined by curve fitting.