Or, we accept that people will occasionally have access to weapons-grade nuclear material and move on.
"But YellowApple!" I can already hear someone saying as I type this on a half-broken phone while sitting on a toilet, "That's a terrible idea!"
Yes, it is, but hear me out:
Let's suppose someone does skim nuclear material off the line. What's the likelihood of that nuclear material actually making it out of the facility? Geiger counters ain't a new invention; surely someone would notice if an employee is unexpectedly radioactive. If our thief opted to shield the material, we're talking a box that's probably too big to even carry, let alone sneak out in a pants pocket or something.
So by some magical miracle (or enough bribes, maybe) someone manages to snag a piece of nuclear material and escape. Now what? Nuclear weapons ain't exactly easy to build at home. Maybe sell it? Good luck advertising that: "FOR SALE: 1 gram of weapons-grade plutonium. Don't ask how I got it. NO FEDERAL AGENTS PLEASE! $42069 OBO 234-867-5309"
Aight, so let's say you somehow managed to figure out how to build a nuke (or you somehow managed to sell it to someone who does and not instead to an undercover cop). Now what?
- You could go be a terrorist, I guess. Good luck getting away with it, seeing as how that material you pilfered will almost certainly come up in a variance report and you're suddenly near the top of the suspect list.
- Strongarm some rival nation? If you're able to steal weapons-grade material, chances are they can, too. Congrats! You've rediscovered the art of mutually assured destruction!
- Let's say you don't give a damn about MAD and launch your nuke anyway. So now you're nuked back. A bunch of people die. That sucks. But! On the bright side, there's at least one less unhinged dictator in the world. Possibly two, if your rival was also a dictatorship. Do this enough times and we might end up with world peace.
All this being to say: yeah, sure, by some unlikely chain of events maybe there's a risk here, but considering the alternative right now can range from "millions of people displaced due to rising sea levels" to "billions of people dead due to global famine" to "humanity extinct because Earth is now Venus 2: Greenhouse Boogaloo", I'll take my chances, thanks.