[It needs to have the materials. Fissile materials are pretty rare. Though well, maybe we could salvage some power supply generators.
[Three things. One, what would we do with a nuclear power plant. Two, how much power does a smoke factory need. And three, there is psychicness. Don't try and be physics. Physics and psychics look alike, but can't stand each other.]
[Oh, and you forgot Explosive Power Generators. Those are explosive by nature, but are usually pretty small. They're like ammo for laser weapons.]
We could use it to solve all our power needs, salvage it to make a dirty bomb, or trigger a runaway reaction(meltdown). It won't leave a big mark, but it will release quite a bit of radiation, and give those below something to think about.
Lots. Basically, the only thing a tier one terraforming plant has to work with are the underground, and the icelayers and gasses locked within. I assume that it works by melting the ice, running the result through the reactor(where it splices into oxygen and hydrogen), and then venting those into the surroundings. Needs quite a lot of temperature if you want to make a dent in the temperatures in the next 10 000 years.
And well yes, but those hardly make very big explosion. In general, power reactors focus on a controlled release of energy.
(( Not really, it's a game not a science report xo I'm pretty sure it doesn't have to be realistic. ))
I like realism. A lot. It allows me to make big assumptions like those above.