This is still theory unless they actually use it for that.
Also, Russia's own Kursk 2 isn't very far from the captured one. They could turn that into a dirty bomb too. Recency bias on a threat shouldn't overwhelm normal analysis.
Where I live is at risk of declining political stability in the near future. I don't worry about living next to a nuclear power plant because I'm worried about maintenance or operational safety or whatever, I worry about what happens when a thousand men with machetes and an apocalyptic ideology show up. And perhaps you look at the news in your country and wonder if you also may be heading towards declining political stability.
Note my example was also nuclear. I don't know what you're countering with this.
Also, nuclear plants can be a target for plenty of states or groups that don’t have nuclear weapons like terrorists.
As for your second claim: So can hydro plants, causing enormous destruction. So? Secure the vulnerable asset, create defensive and preventative strategies. You don't go through life not building genuinely useful things because somewhere, somehow, somebody might aim to do them harm. The logic is absurd if taken to any other level. For example, I should never buy or build a house because some group of landless lunatics might coalesce and try to take it from me one day. Better to not have my own useful home in the first place then? Absurd.
Hell at this point whoever does will just conquer whoever doesn't. Just like the industrial revolution let whoever burn coal take over the rest. I'm hoping to be in a country that isn't conquered, but the west seems to have entered a death spiral of self delusion.