The B Reactor (105-B) at Hanford was the first large-scale plutonium production reactor in the world. It was designed and built by DuPont based on an experimental design by Enrico Fermi, and originally operated at 250 megawatts (thermal). The reactor was graphite moderated and water cooled. It consisted of a , graphite cylinder lying on its side, penetrated through its entire length horizontally by 2,004 aluminium tubes. (180 t) of uranium slugs, diameter by long, sealed in aluminium cans went into the tubes. Cooling water was pumped through the aluminium tubes around the uranium slugs at the rate of per minute.