Pebble-bed reactor

Summary

A pebble-bed reactor (PBR) is a type of nuclear reactor where the nuclear fuel is contained within a bed of pyrolytic graphite spheres (pebbles), with the graphite serving as a neutron moderator. Pebble-bed reactors are typically high temperature gas-cooled reactors (HTGRs), and are capable of being refueled during operation. The helium-cooled PBR design is considered a type of very-high-temperature reactor (VHTR), one of the six classes of nuclear reactors in the Generation IV initiative.