I believe you've confused something. Almost all plutonium from the Manhattan project (e.g. 'Fat Man') was from graphite-moderated, light-water cooled reactors a

I believe you've confused something. Almost all plutonium from the Manhattan project (e.g. 'Fat Man') was from graphite-moderated, light-water cooled reactors at Hanford site in Washington, starting with the 'B reactor'. Plutonium: The First 50 Years (chapter 9) http://www.doeal.gov/SWEIS/DOEDocuments/004%20DOE-DP-0137%20Plutonium%2050%20Years.pdf http://www.doeal.gov/SWEIS/DOEDocuments/004%20DOE-DP-0137%20... http://en.wikipedia.org/wiki/B_Reactor http://en.wikipedia.org/wiki/B_Reactor The US did not build a heavy-water plutonium production reactor before those at the Savannah River Site (South Carolina), which did not start until 1953. These are all the plutonium production reactors the US has built (ref. DoE): 9 graphite-moderated light-water cooled reactors at Hanford, and 5 heavy-water moderated/heavy-water cooled reactors at Savannah River. In the Manhattan project, there were also tiny amounts of plutonium sourced from the X-10 reactor at Oak Ridge (also graphite-moderated): http://en.wikipedia.org/wiki/X-10_Graphite_Reactor http://en.wikipedia.org/wiki/X-10_Graphite_Reactor Separately, there was highly-enriched uranium produced at Oak Ridge (Tennessee), which was used in 'Little Boy'. And, CP-3 was a research heavy-water reactor (Chicago), built in 1944, which was not used for breeding plutonium. http://en.wikipedia.org/wiki/Chicago_Pile_3 http://en.wikipedia.org/wiki/Chicago_Pile_3 Hope this clears things up...