It appears to be about as realistic as simcity. IOW, not. But it gives a basis for understanding just how simple, and complex, nuclear power generation is.
You could probably replace the nuclear core with a coal core for about the same realism but that would take the danger out of the game.
The starting goal is to get all those bars indicators right on the edge of yellow without quite touching it. The exception being emergency venting. That should stay zero.
It's web based so you can play right away.
Being in too much of a hurry to make money has negative effects. The readings all have inertia. Patience keeps things at the right temperature.
Do try not to kill civilization.
http://www.nuclearpowersimulator.com/