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Originally Posted by wolf
TW, there is no such thing as "weapons grade" U238. U238 makes up better than 99% of all Uranium mined, which is why it was so difficult to come up with the amounts of U235 necessary to make a bomb. .... The graphite and uranium pile at the Squash Court was a primitive precursor to today's breeder reactors, if I remember my Manhattan Project history correctly.
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Wolf has properly and accurately corrected my numbers. U235 is necessary for weapons grade uranium. It is quite easy to convert weapons grade uranium back into commercial grade. Simply mix U235 with U238. Seperating the stuff is so difficult that WWII and Cold War processing plants were located where electricity was plentiful.
The squash court chain reaction by Fermi and Sklar was simple uranium and graphite similar to how many early commerical nuclear reactors including (I believe) Chernoybl work. Don't know how much U235 was in that Uranium. But that world's first chain reaction was not bomb grade. Important point - graphite is a moderator.
Breeder reactors are a whole new concept originally pioneered after WWII. Because of how a breeder works, many breeder reactors use liquid sodium - not water. Sodium because it is not a moderator. How dangerous is liquid Sodium - a reference to some text in a very good citation by Troubleshooter? Simply put a little bit of sodium into water - and run.
All reactors create some plutonium. Idea is to design a reactor and its fuel so that minimal plutonium is created. But a breeder reactor has a completely different agenda. Its purpose is to create energy AND create more fuel than it 'burns'. We have a problem. There just is not enough Uranium to keep all these nuclear plants going. Idea is to put depleted uranium or other euqivalent materials (ie thorium) into a reactor that includes plutonium. Have no moderator that would slow down neutrons. It produced electricity and even more nuclear 'fuel' in its first demonstration reactor in the western desert. Reactor had initials something like ERMI. Have long since forgotten.
Fermi 1 which residents of Toledo and Detriot can visit was this nation's first commercial breeder reactor. The story goes largely untold. But those who love adventure books and detest a-hole fiction will read "We almost lost Detroit". In short, breeder reactors are unstable, not well understood, and have killed people. We gave up and entombed Fermi 1 (next door to Fermi 2 - a conventional reactor). Europeans tried and also failed (I don't know those details).
So where is most of the world's plutonium? I answered that some years ago in a post that truly defined a serious terrorism threat. Massive amounts of plutonium were processed in Britian and France. Then shipped to Japan without any military escort (Japan would not permit their warships to go international). Terrorists never expedited the oppurtunity.
So now most of the world's plutonium is in Japan supposidely to make a breeder reactor. (There are very good political reasons to believe that plutonium may have also had secondary purposes). But at any rate, Fermi and Sklar's chain reaction had little in common with breeder reactors other than both involve nuclear reactions and uranium.