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Joaquín description of the Brazilian and Iranian nuclear industry is 
spot on, which is why there is there huge disconnect among the public 
and 'leaders' as to the reasons why both countries want a closed fuel 
cycle (to be fully "closed" they would have to recycle their spent fuel, 
another story, though) so they are not beholden to the US ability to 
withdraw technology and fuel once it is given. This was also one the 
reasons there was much opposition to the Indian 1-2-3 agreement within 
India by those that wanted to develop an *indigenous* nuclear fuel AND a 
reactor industry. It's why in large part they are using proven Russian 
reactors and not American ones. Why they are reluctant to use the S. 
Korean models because they are too close to the US...and thus those 
nasty strings.

But Joaquín is very wrong about what he believes could be a "bomb" with 
low enriched uranium. In fact he's wrong about how 'easy' it is to 
fission U235 in low concentrations (LEU). There is an "architecture" to 
uranium placement and concentration that allows for fission to occur. 
Yes, the higher the concentration, he 'easier', rather faster, fission 
can occur. But it is actually a very difficult process to achieve. If 
you dumped a pile of LEU onto a barge and splashed it with a 
moderator...that is water...very pure, deminerialized water, you might 
be able to get a 'slow burn' of the U235 which would in essence be a 
sort of dirty weapon with very limited effect. But probably not.

Fuel rods are designed and positioned to GET a reaction. "Not getting" a 
reaction is what happens when the water moderator (water is used to slow 
down the neutrons so they can collide with the U235 and cause fission) 
can't access the U235 in *exactly* the right way or the pellets are 
designed wrong; positioned wrong; of a wrong U235-U238 'mix' or are 
other wise out of alignment.

As soon as the difference in fuel pellets in the rod changes, the 
reaction generally stops. If you piled in a few thousand tons of LEU in 
exactly the right proportion built to reactor specs and then figured out 
a way to dump water over them you would get a run-away reaction but they 
would not explode. This is where Joaquín is very wrong. The architecture 
of an A-bomb requires Highly Enriched Uranium (over 96%) to achieve not 
just the 'runaway" fission reaction but one that does it so fast, so 
uncontrollable that you get an explosion. It's never been done.

Scientists know this because of A-bomb development going back to the 1940s.

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