WhirledView: North Korea Sold Uranium Hexafluoride to Libya? The Evidence: "If the uranium hexafluoride was made from uranium recovered from reprocessing, then the U-234 signal would be scrambled by enrichment for use in reactor fuel or by nuclear processes in the reactor. So comparing U-234 with natural samples would make no sense, particularly if no North Korean samples were available. For the U-234 test to work, the uranium would have to be natural, not processed through a reactor.

The implications of the two are different, too. No enrichment apparatus is necessary to produce uranium hexafluoride from uranium ore, just a chemical processing plant. Plutonium traces in the uranium hexafluoride imply (as the Washington Post says) that North Korea has done reprocessing and may have done enrichment to produce the reactor fuel.

Another possibility for the origin of the uranium hexafluoride is that it could have come from the Soviet Union some long time ago. Soviet uranium processing usually combined ores and concentrates from many geographic sources, so the U-234 test would be less diagnostic and might well not fit any natural samples."

(Via ArmsControlWonk.com.)