Might it have been Oakflat Nuclear Power Plant Simulator[1] you're thinking of? I'm not aware of a version that ran on the DEC but it might very well have existed and it sounds quite similar. I can certainly credit it for developing my unhealthy fascination with nuclear power. Also perhaps my unhealthy tendency to push buttons and see what happens!
I never realized this was the one I had on both C64 and DOS! When I played C64 I was too young (4-5yo) to actually play it. And the DOS version came on one of those disks comprised of half freeware games, half bootleg games. (Back when you could still buy those at legit retailers). Anyway that's germane because I seem to remember that once the reactor powered up it would immediately meltdown. I realized at the time - I think this was the developer's copy protection. Which struck me as much more entertaining and clever than just not working if it was a bootleg copy.
[1] https://www.mobygames.com/game/62490/the-oakflat-nuclear-pow...