Comment by Aurornis

> What am I missing about how hard it is to enrich uranium?

The challenges are primarily geopolitical. There are uranium enrichment operations in a number of countries around the world. Weapons grade enrichment is a lot harder, but nothing that a sufficiently funded and motivated nation state couldn’t achieve if they wanted to and, most importantly, didn’t have any other countries discover it.

> Processing, 700kg of uranium does not sound insurmountable, even with a terribly slow and inefficient process.

You have to get enough uranium ore, process that down, then enrich it on a large scale. Uranium ore deposits aren’t very uranium dense except for a few known mines, so pulling rocks out of the ground in another country may produce extremely low yields.

Enrichment is a very slow process requiring a lot of stages because U235 and U238 are barely different, so they don’t separate much in each stage. Everything has to work together and work well. Like you said it’s not insurmountable, but by the time a country has spent years mining low-yield ore and building complicated many stage centrifuges they’re likely to make a mistake that leads to an intelligence agency catching on.