Chicago Pile-5 (CP-5) was the last of the line of Chicago Pile research reactors which started with CP-1 in 1942. The first reactor built on the Argonne National Laboratory-East site, it operated from 1954-1979. CP-5 was a thermal-neutron reactor using enriched uranium as fuel and heavy water as coolant and as a neutron moderator. It produced neutrons for use in research. The reactor had an output rating of 5 megawatts.