In the 1950’s, Dr. Rudolf Schulten (later Prof. Dr. Schulten, “father” of the pebble bed reactor) had an idea. The idea was to compact silicon carbide-coated uranium granules into hard, billiard-ball-like spheres to be used as fuel for a new high temperature, helium-cooled type of reactor. The idea took root and in due course the AVR, a 46 MW_th (megawatt thermal) demonstration pebble bed reactor, was built in Germany. It operated successfully for 21 years.

Then, in the intense wave of post-Chernobyl anti-nuclear sentiment that swept Europe, particularly Germany, the idea almost submerged.

It is resurfacing in South Africa, and China... See Pebble bed reactor