RA-1 Enrico Fermi is a research reactor in Argentina.
By contrast, the HIFAR reactor in Australia went critical just six days later, on 26 January 1958.
The RA-1 reactor produced the first medical and industrial radioisotopes made in Argentina, and was used to train staff for the first two nuclear power stations there.
It is a pool type, with enriched uranium oxide fuel (20% U-235), light water coolant and moderator, and a graphite reflector.
It produces 40 kilowatts of thermal energy at full authorized power.