I have an additional question about power plants. If you have both a coal and a nuke plant, will it always use the nuke plant? I was just considering the possible situation where you build a nuke plant to save the two unhealth, then later start running environmentalism or something, and now you'd rather switch back to the coal plant. Possible? Or does each built plant actually replace the previous one in the list of buildings such that you can switch back by building a new coal plant?
I've never built nuke plants, and you never want to switch out of hydro plants pretty much (give or take the other mad's noted event), so this isn't something I'd thought about much before.