"Tom Cooper" wrote in message
m...
(phil hunt) wrote in message
...

The centrifuges are used to whirl UF6 gas ("Uranium Hexaflouride")
into highly enriched uranium, needed for building the weapon: i.e. for
getting HEU. Usual uranium has something like 20% of the U-235
isotope: you need 85-90% U-235 in Uranium in order to get weapon grade
material. Using the "gas centrifuge" for this is the simpliest and
cheapest (of three or four) mean of producing nuclear weapons. The
South Africans used this technique to produce their, just for example.
See also:
http://www.fas.org/nuke/intro/nuke/uranium.htm

The South African nuclear enrichment programme (using the Y plant at
Pelindaba for (90+%) HEU and the Z plant for the commercial (5%) LEU) was
not based upon gas centrifuges but on a local technology called "standing
wall centrifuges". The final progamme was to be based on molecular laser
enrichment. This program was canceled in ~1996.

Natual uranium has 0.71% U-235 and 99.29% U-238.

David Nicholls
South Africa