[JasonC]

Uranium 238 is not the sort that goes off. Uranium 235 is. Weapons grade U means refining U-235 out of the background U-238, which is by far the most common isotope in naturally occurring uranium. The U-235 typically runs 0.5% to 1% of the U content of a uranium ore. It has to be refined to more like 90% of a sample to sustain a chain reaction. U-238 can be used for nuclear fuel in reactors, but it reacts too slowly to be useful for explosions (its half life is on the order of 4 billion years, almost 10 times longer than U-235).

U-238 can be gradually enriched into plutonium in a special "breeder" reactor, absorbing particles emitting by a running reactor (actually, a tiny portion absorbs neutrons and then undergoes beta decay, emitting electrons and turning into plutonium - left running long enough this builds up and can be extracted from the remaining U-238 around it). But in itself it is not useful for bombs.

When the article says "weapons grade uranium", that means a sample of uranium that is around 90% U-235, seperated out of a much larger amount of uranium ore. The seperation process is quite difficult, and is the step the Iraqi's have not managed to solve on a large scale themselves. So U-238 getting to Iraq, while obviously not helpful, doesn't get them a bomb or solve the problem holding them up. Enough U-235 of high enough purity does. Or plutonium.

I hope that helps.

[bonesmccoy]

was the nuclear power plant hit by Israel a breeder reactor?