Thursday, April 13, 2006

More on Iranian Nukes

Comment I left on the Cosmic Variance thread that mirrored my previous comment

Few more comments:

the Russians supply Iran with their technology, under the NPT.
The Bushehr reactor dates back to the Shah's rule. It is late in part because
the Iraqis bombed it in 1984 (if I recall correctly).
The fuel for Bushehr is supposed to be returned to Russia for reprocessing
to prevent plutonium extraction and is supposed to stay in the core for a year or longer to make sure the Pu-239 is contaminated with Pu-240 and Pu-241.

If Bushehr-1 is fueled and turned on, and the Iranians then block or expel the IAEA, with the acquiesence or expulsion of the Russians, then they can have bomb grade Pu-239 in 3-4 months by doing a short burn which creates minimal Pu-240/241. This is inefficient for power production, good for bomb making.
Depending on how good their design is, a 4 month run could make enough Pu-239 for 3-10 bombs, and same again every 4 months until they run out of fuel. If they can do their own enrichment, or if they build heavy water reactors, then they never run out of fuel to breed plutonium.

If they learned the plutonium chemistry from their lab experiments in the 90s, then they can get metallic Pu extracted, cast and machined very quickly. Weeks.

This is why the situation is escalating, Bushehr is supposed to go on the grid in 6 months. That means they must load the fuel now, and start test runs.

It would mean open defiance of IAEA and the UN, but that is right where the Iranians are headed now.

U-235 fission bombs, with yields up to some tens of kilotons of TNT equivalent are easy; you make 2-3 sphere segments, keep them apart and shoot them at each other inside a metal tube when you're ready. Boom.

If you try that with Pu-239, according to reliable sources, it squibs. It goes partly critical faster than it can assemble into a sphere, and the heat pushes the plutonium a part. You get a very incomplete explosion, with bits of melted and burned plutonium metal. Messy and mostly useless.
Similarly too much Pu-240 or Pu-241 in you plutonium and it can't be assembled without going critical prematurely, possibly spontaneously.

The way around that is to have a small plutonium core, with the remaining segments in spherical shell, like the skin of a soccer ball. Then you implode the segments onto the core using high velocity explosive in a simultaneous and very symmetric implosion. Tricky, but straighforward. Require fast detonation, high velocity, pure explosive (which can be bought); and fast switches (which can be bought) - this is 1940s tech.
This gives you controllable yield over maybe a factor of 10-100 without much fuss.

If you want much broader yield range, or very light compact warheads, or something that will trigger thermonuclear fusion reactions, then you need good engineers and some experiments (or experience for hire). 1950s tech.

If you want something that will make a very big boom as deterrent to attack or invasion, which can be installed as a mine, or in truck/ship, and you don't care if it is dirty due to incomplete burn or "only" 10 kilotons instead of 30 kT, then you're done.
Just churn them out one or two per month as long as the reactor runs and the labs are open.

Several actual issues are coming together, only one of which is the US internal political situation.

The Iranian government is acting as if it intends to exit the NPT and go nuclear.

The Iranians have completed the technology development to go indenpendent of the NPT signatories and can do the full cycle internally without relying on Russian fuel supply or reprocessing.

The Bushehr reactor is finally due to actually go on line full of moderately enriched uranium which could be used for quick production of an initial batch of bombs. This has been delayed to the point that the Iranians ought to be seriously annoyed about it, the reactor should have been on-line several years ago.

It seem neither side is negotiating in good faith.


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