The British Royal Navy did secretly run a reactor in the middle of London for decades without anyone really noticing though, but obviously they didn't really have to hide it from the security services which might be harder.
https://en.wikipedia.org/wiki/JASON_reactor
The British Royal Navy did secretly run a reactor in the middle of London for decades without anyone really noticing though, but obviously they didn't really have to hide it from the security services which might be harder.
https://en.wikipedia.org/wiki/JASON_reactor