"Graphite reactor" directs here. For the graphite reactor at Oak Ridge National Laboratory, see X-10 Graphite Reactor.

A graphite reactor is a nuclear reactor that uses carbon as a neutron moderator, which allows un-enriched uranium to be used as nuclear fuel.

The very first artificial nuclear reactor, the Chicago Pile-1, used graphite as moderator. Two graphite moderated reactors were involved in major accidents: An untested graphite annealing process contributed to the Windscale fire (but the graphite itself did not catch fire), and a graphite fire during the Chernobyl disaster contributed to the spread of radioactive material (but was not a cause of the accident itself).