Chicago Pile No. 1, first man made nuclear reactor (Oklo). A group of scientists headed by Enrico Fermi succeeded with the first self-perpetuating chain reaction on 2nd December 1942 in Chicago, IL, USA. Natural uranium was used as a fuel and graphite as moderator. Due to the low power of the reactor a special cooling was not necessary.

Diagram CP-1

CP-1 during the critical test of the first self-perpetuat-ing chain reaction on 2nd Dec. 1942