On 2/24/2012 6:25 PM, Tim Wescott wrote:
On Fri, 24 Feb 2012 18:11:39 -0600, Richard wrote:

On 2/24/2012 6:04 PM, Jon Elson wrote:
Ed Huntress wrote:



Well, that *is* really a problem. All of the plutonium in the world
won't get them a bomb, but the gun trigger for Little Man could
probably have been made in a good basement shop. That's why it's a lot
scarier for them to have enriched uranium than plutonium. Any goof can
make a gun-trigger uranium bomb, if they have a plan that gives them
useable dimensions.
Anybody that has more than a gram of 239 Pu ALREADY has enriched
uranium. You need "weapons grade" enrichment, meaning about 90% 235U)
to build a breeder reactor to make 239 Pu. It has to be a fast neutron
reactor to transmute the 238 U at the edge of the core to 239 Pu, and
that requires a high proportion of 235 U for the chain reaction to
continue. (I'm not a reactor physicist, but that's my understanding.)
So, if they have kilograms of 239 Pu, they MUST have tons of pretty
pure 235 U.

Jon


I wonder where they got the 235U?

Any peaceable nuclear reactor needs U-235 to fire the reaction -- it's
just that the common type (non-breeder) doesn't need much.

I'm not so sure about the absolutely needing a breeder reactor -- AFAIK,
you get Pu from ordinary reactors, just in small quantities. In fact,
(again, AFAIK), part of the reprocessing of nuclear fuel is getting the
Pu out.




Yeah, that jives with what I think I remember.

But it takes a certain quantity of 235 to get rolling.

I seem to remember that it takes more material to build a reactor than a
bomb...