Pebbles Making Waves

This paper describes various high-level nuclear researches including nuclear-fuelled pebbles that are being conducted across South Africa. The pebbles are ingenious industrial products, designed to passively limit the amount of heat unleashed by the nuclear fission reactions that drive the reactor. The spheres that give the pebble bed reactor its name enclose fissionable uranium inside layers that serve various roles, such as moderating fission, containing pressure, and accommodating deformation of the core. Nuclear-fuelled pebbles are introduced at the top of the reactor vessel and slowly wend their way down through the annular-packed bed under the action of gravity to the bottom of the reactor vessel. In a towering building at the headquarters of Nesca in Pelindaba, South Africa, reactor components are being tested for their ability to work with high-pressure helium. Those parts will go in the pebble bed modular reactor power plant to be constructed at Koeburg, near Cape Town. The plan of the pebble bed reactor power plant will use the helium coolant to run the turbine directly rather than heat a secondary fluid, as in a water reactor.