Halls of Shrewd'm / US Policy
No. of Recommendations: 3
Stupid question: why the hell are
tens of thousands of centrifuges needed to enrich uranium?
The answer appears to be that only extremely high speed centrifuges can accomplish it, and those have to be small or else the forces would be too great. And so you need a lot of them to get any significant quantity.
See
https://en.wikipedia.org/wiki/Zippe-type_centrifug...
No. of Recommendations: 1
I'm not a nuclear physicist (my area was astronomical gamma rays), but I believe that is basically correct. Remember that uranium (U) is very heavy. Heavier than lead. If you have a large radius centrifuge, the angular momentum will be enormous spinning at tens of thousands of RPMs. You'd have to reinforce the thing greatly (impractically?) for it not to fly apart.
No. of Recommendations: 6
I was a chemist a lifetime or two ago. The uranium is enriched as uranium hexafluoride, which is a gas. The issue is separating U-235 (the fissile isotope) from U-238, which is the most common isotope. U-235 is only a tiny percentage of naturally occurring uranium and has almost the same atomic weight as U-238, and has the same chemical properties of course. In order to separate the two, the centrifuges have to spin at extremely high speeds for a long time. So fast and so long that even building a centrifuge that do that is technically very difficult. There are other separation methods, but they aren't any easier.
Separating the fissile material is a big enough challenge that it takes a state to accomplish it, isn't like mad billionaire could do it or something. Actually building a nuclear device is simple by comparison.
No. of Recommendations: 1
Thanks for the clarification. Obviously, I never worked on nuclear power (or weapons). My emphasis was astrophysics. I was only loosely acquainted with the general ideas. I was pretty sure they would have to separate fluids (solids don't separate very well), but I didn't remember that it was a gas until you said so.
All I know about nuclear weapons is that you want to achieve critical density at the moment of maximum neutron flux. I sorta know how they do the critical density bit, but I don't know how they affect the neutron flux. Of course, at that point they already have enriched product.
