Posted 7/31/2010 3:52 am
Here is my dream: lakers full of good milled uranium with 1% U235 pull into a sepp harbour as they do every day. The engines keep running to power the derricks, which very slowly pull out the schoolbuses full of neutron absorbing boron. Just like Fermi's pile in chicago, but way bigger.
I'm changing out of my captain's uniform in a fast cab headed for the safe houses of Nashville tennesse. LA is hotter than chernbyl.
No. Natural uranium has decayed to the point where it requires exactly the right conditions to go critical - hence the need for nuclear reactors.
On top of this, the sort of criticality existing in a nuclear reactor is not the sort you need for a nuclear weapon - a fission event create both immediate ("prompt") neutrons and ones from delayed neutron decay (which can be emitted up to a few minutes after the initial event).
As long as there are enough neutrons from all sources to sustain criticality, then the reactor will carry on working.
In a bomb, delayed neutrons are no use and the chain reaction is caused just by prompt neutrons (the bomb will likely have blown up before the subsequent decay events) and you need very highly enriched material.
All the naturally occuring Hafnium isotopes are stable (well, one of them has a 1*10^15 year half-life, which is just about as good as stable). If he had access to a reactor to make hafnium, he would just be making 239Pu.
Yeah, I know - but that uses isotopes that are not naturally occuring - I think they were talking about 178m2 Hf (which has a halflife measured in uS) in those proposals.
Making that stuff requires either a reactor or a very large particle accelerator - not exactly the sort of zero-tech approach that Teapots was thinking of.
Which explains exactly why Iran is nowhere near producing a nuclear weapon - they simply do not have the capacity to do this in spite of a certain class of people belching a lot.
Did you read that article? One of the things that it explains quite clearly is that at the time fission was occuring the isotopic mix of natural uranium contained considerably more 235U than it does now. This is fairly obvious, since 235U is more radioactive than 238U and hence decays more quickly.
Note that you *can* sustain fission with the isotope mix of current natural uranium, but you need to get the conditions just right. The CANDU reactor is designed to work on natural uranium as were the British "Magnox" gas/graphite reactors, the piles at Hanford and the original design of the Russian RBMK - although in practice the RBMKs used slighly enriched fuel because this gave the plant better operating margin (which was somehing the RBMK really needed).
The PWR/BWR reactors typically used for power generation in the west use water as both a moderator and coolant, and have to use significantly enriched fuel or they won't work at all.
There are many different gamma isomers. Some of them are in the 15KeV X-ray range, some of them are so low energy that they are almost visible as a faint blue light. They all decay slowly, some of them almost instantly, some of them with a half life of more than a hundred years.
Yeah, you need high power X-ray lasers to just charge them. And lots of x-rays are going to go to waste from elastic collisions which would cause them to drop below the absorbtion threshold. Gamma isomers are a nice scifi concept but the practical implementation wont be easy or cheap.
You obviously have no idea just how inefficient this process is - this was the first isotopic separation method used at Oak Ridge, but was replaced by gas diffusion, since that required less than 1% of the energy input. The plant at Oak Ridge was consuming about 400MWh/SWU - the gaseous diffusion plant dropped this to 2.5-3MWh/SWU.
Centrifuges use about 50kWh/SWU, and LIS maybe half that (it's hard to be sure, since no full scall LIS plant has ever been constructed).
You dissolve it in acid, vaporize it, then sort the isotopes by various methods. They are of very slightly different mass so it is difficult and it takes a lot of juice.
It's not really more difficult to do than a lot of industruial processes but it has to be done thousands of times over and over again on a massive scale in order to get even a few grams a year of weapons grade uranium (95% uranium), and it takes almost unimaginable amounts of energy.
