Why would we leave out terrorist attacks? Because they destroy your argument?
If you're imagining some kind of super coordinated military unit taking control of a powerplant yeah sure maybe? They'd be much better used just poisoning the water supply.
This is exactly the kind of baseless fear driven hypothetical sentiment that I'd like to understand.
[1] http://www.nbcnews.com/id/3072967/ns/business-check_point/t/...
For example, in 2014, rebels in Donetsk had attempt to create "dirty bomb" using radioactive waste from abandoned chemical plant. Fortunately, they were spotted and stopped.