I am puzzled as to where or who produced the U235 for the first nuclear pile. I read that graphite was used as a neutron moderator but only .7 % of natural uranium is U235.

He must have gotten it from Oak Ridge?. But I always thought that Oak Ride's uranium production came after the feasibility study that a pile was even possible. So where did the original batch come from ? Maybe from mass spectroscope or cyclotron but that wouldn't make enough uranium would it?

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    $\begingroup$ This reactor used natural uranium. See en.wikipedia.org/wiki/Chicago_Pile-1 $\endgroup$ Jun 6, 2018 at 20:27
  • $\begingroup$ Yes...interesting...50 tons uranium oxide and 6 tons uranium.....but now were both the uranium oxide and uranium .7 % U235 ? I thought maybe Fermi separated the U235 for the fast neutron source....but maybe he just used it as is and moderated it only ? and there lies the mystery ... $\endgroup$
    – Sedumjoy
    Jun 6, 2018 at 21:49
  • $\begingroup$ Did you read the Wikipedia article? It says " high-purity uranium dioxide from Mallinckrodt in St Louis, which was now producing 30 short tons (27 t) a month. Metallic uranium also began arriving in larger quantities, the product of newly developed techniques." $\endgroup$ Dec 23, 2021 at 9:30
  • $\begingroup$ @Stephan Matthiesen...thank you! That is a remarkable amount of uranium available at the time, $\endgroup$
    – Sedumjoy
    Dec 24, 2021 at 14:24

1 Answer 1


The uranium came from Belgian Congo, more precisely, from the Katanga Province. See this article explaining the central role of Edgar Sengier, ruler of the very powerful (Belgian) Union Minière du Haut Katanga (Katanga Mining Union), who in September 1940 secretly sent, without being ordered by anybody, around 1000 tons of especially rich uranium ore to Staten Island. The US Army was warned only afterwards, in 1942!

Some more details can be found into this book (in french): "Katanga" by I. Nagy, Ed. Rencontres, 1965.


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