What is the environmental impact of a nuclear-powered electrical generator versus a coal-fired electrical generator?
Good question. I will argue that a nuclear reactor has LESS an environmental impact than a coal powered fire station.
A nuclear reactor operates for a year; the bigger ones have a capacity to match or better that of the best coal-fired stations. The result is high level waste, but I believe the quantity of high level waste would not fill your bedroom. Granted that the waste is still dangerous for 1000's of years, and also that the waste must be held securely over this time, but contrast this with the impact of a coal-powered power station.
A 500 MW coal-fired power station will produce approx. 3,000,000 tonnes yearly of carbon dioxide, along with significant quantities of sulfur oxide, and nitrogen oxides - all of which is necessarily vented to the atmosphere. On this basis, and I am certainly willing to be corrected, I would argue that the nuclear power station has less of an environmental impact.
So to conclude, nuclear energy is not a green energy resource, but it is less likely to have a deleterious impact than burning coal.