Yeah but a person with an AK-47 and TNT isn’t safe regardless of the setting

A person with an AK-47 and TNT can't render vast tracts of land uninhabitable for decades in the way that nuclear waste can.

I am very pro-nuclear in the US (and the EU etc.), but I think the concern about nuclear in potentially unstable nations is absolutely valid.

Sure they can. They are called minefields.

The Chernobyl exclusion zone is 1000sqmi (32mi by 32mi). That's not so vast if it's in low populated area.

That would be a significant area for most western countries.

It's a mistake to think of Chernobyl as anything near worst case, there were absolutely huge containment efforts that took place after that disaster that might not take place after a similar future disaster.

I think the comment's material point is, why put a nuclear plant in arms reach of such groups? It's a good point.

I would argue that most people are not talking about putting a nuclear plant in, say, Somalia. I think most people realize there have to be some preconditions met before you can really even think about using nuclear power. For the most part, if you are able as a nation to construct such a plant, you likely have the security infrastructure to secure the place. In fact, you likely have one of the more powerful security infrastructure buildouts in your region.

A hydroelectric power station is a far bigger risk if that's your threat model. A you have a relative eternity to get people out of harms way if a reactor goes pop compared to if a dam bursts.