Nothing Can Stop What's Coming

I’d like to add a bit more about uranium isotopes.
Note: if Keln comes over here I’d welcome any corrections he has; this is a hobby for me but he used to deal with nuclear power for a living.
U-238 is overwhelming more common than U-235, it’s over 99% of uranium as it comes out of the ground. It radioactively decays quite slowly, taking 4.5 billion years for half of it to decay. (It becomes thorium-234, which much more rapidly decays further, a chain that ends with lead-206.)
You cannot build a bomb out of U-238, although you can make plutonium 239 from it–which can be made into bombs (very difficult technically–a mass must be created AND compressed with high explosives). (A plutonium bomb was used on Nagasaki, and it was complex enough they had to test one beforehand in New Mexico.)
U-235 has a 700 million year half life, eventually becoming lead-207, and it can be made into bombs. In bombs, it doesn’t undergo that kind of decay, rather it undergoes the exact reaction shown in the “cover art” for this post. And a U-235 bomb is easy to make, provided you have a stock of U-235–just arrange for two smaller chunks to be brought together quickly to form a critical mass and KaBoom! (The bomb dropped on Hiroshima was a U-235 bomb. It’s so dead simple to make one of these, in fact, that they didn’t even bother with a test.)
The difficulty with making a U-235 bomb comes in the fact that the U-235 must be separated out from the U-238. There’s no chemical way to do this, because the two isotopes are both uranium.
A physical process is required and the most well-known of these is to react uranium with flurorine to make uranium hexafluoride (a gas), and then use centrifuges to separate out the heavy molecules (with U-238 in them) from the light ones (with U-235).
This is a very difficult, tedious process. One pass through a centrifuge only somewhat “enriches” the mixture, making U-235 slightly more common in the product than it was before (and the discarded fraction has less U-235 but not none of it). So it has to be done over and over again, removing more U-238 each time, leaving (proportionately) more U-235 behind.
This is known as enrichment. It’s not perfect. But it can raise the U-235 portion enough to be usable in a nuclear reactor (up to about 20 percent, known as low enriched uranium), or if even more enriched (20-80%, high enriched uranium), make bombs.
This is what Iran is doing with all those centrifuges we keep hearing about.
The U-238 rejected by this process is called “depleted uranium” and is often used by the military for bullets, and can sometimes be used as tank armor. It’s extremely dense material, much more so than lead.
There was a poster over on the other tree who kept claiming that Robert Mueller delivered our nuclear stockpiles to Russia (that’s an awful lot of stuff!). Or that (supposedly) he delivered a sample of highly-enriched uranium to Russia so they could see what they’re buying. (People would try to correct him, and he’d simply ignore them and paste the same one-paragraph diatribe over and over again into his posts.)
That’s just absurd, and now I can finally say something.
What Russia got in Uranium-1 (thank you, Hitlary!) was a lot of our uranium mines. It’s ore. It hasn’t been enriched yet. If they needed samples, they would have been given samples of the ore to see how much uranium is in it–but this uranium is NOT enriched, because it’s still in the ground and hasn’t been processed yet.
It’s like I am trying to sell you an iron mine, and I give you a piece of (highly processed) tool steel as a supposed sample. No, you’d want an ore sample, so you could see how much iron was in the ore.
From what I read (once, so take it with a grain of salt), apparently what Robert Mueller took to the Russians was a sample of HEU that came from some that was stolen and we had recovered. The Russians could analyze that (isotopically with a mass spectrometer, if not some other way), and determine it came from one of their enrichment facilities, and positively identify that we had recovered the stolen HEU.