> If someone has a modest amount of money and no regard for safety, it's actually pretty easy to assemble a reactor.

My understanding is that building a reactor is fairly easy (possibly even in reach of a smart high-school kid). But that getting hold of the enriched uranium required to run a reactor is (thankfully) rather difficult due to trade and production being heavily controlled.

Yeah, a guy from my home high school built a nuclear fusion reactor: https://www.wired.com/2007/03/high-school-stu/

It's pretty cool. It's really cool.

Fusion is one thing. The farnsworth style fusors are relatively easy to make. I'm talking about fission, which is a bit more difficult, but actually could be made possible with the neutrons emitted by a farnsworth reactor(or a bunch of other ways that don't require high voltage/high vacuum).

I've made neither ¯\_(ツ)_/¯

But enriching uranium isn't rocket science. You gassify uranium as uranium hexifluoride, centrifuge it, extract the heavier (uranium-238) fraction, and then turn the uranium-238-enriched gas into solid uranium oxide (recycle the fluorine).

It's not rocket science, and there are other methods available as well. It does take a lot of energy and time though. Probably easier for a low tech setup to just bombard U-238 with thermal neutrons.

Once you get enough U-235, just use beryllium to reflect the neutrons back in and add a moderator(water, graphite, etc). Just don't be anywhere near it when it finally goes critical.

But working with fluorine compounds is seriously dangerous, and the process requires literally hundreds of centrifuges working day and night for months to produce the required amounts of 238

Enriched uranium is hard to acquire but it's not hard to make if you have a source of thermal neutrons. You can get thermal neutrons in a number of ways. I'm not going to get into the details, but establishing criticality is not easy, but it's not hard either, at least if you're not concerned with safety.

A small surprise for me was learning that you can buy a fully functional tank in America for relatively little cash. Where I come from, even the thought of anybody but the army owning a tank is absurd.

The tanks’ guns are disabled. They aren’t functional tanks in regards to the one feature that makes a tank a tank.

It can have another (dual-) use as armored bulldozer. See

[1] https://en.wikipedia.org/wiki/Marvin_Heemeyer

> but the fact is someone developed many of these technologies in more primitive times without access to modern materials or the internet.

With scraps, in a cave!

Stone knives and bear-skins...

The secret is to bang the rocks together, guys!