Nuclear power is sometimes described as being free of greenhouse gas emissions, and that’s true of the nuclear fission reactions themselves. But here is a list of all the stages of the nuclear power cycle at which greenhouse gases are emitted: uranium mining, uranium milling, conversion of uranium ore to uranium hexafluoride, uranium enrichment, fuel fabrication, reactor construction, reactor decommissioning, fuel reprocessing, nuclear waste disposal, mine site rehabilitation, and transport throughout all stages.

During these stages, greenhouse gases are emitted directly (for instance, by trucks) but also indirectly (such as through the use of materials such as steel and cement, which are manufactured using emissions-intensive processes). //

Quantifying all these emissions is a complicated prospect, but we can attempt to do it using a method called “life-cycle assessment”. The result of one such estimate (with which I agree) is quoted in the Intergovernmental Panel on Climate Change’s Special Report on Renewable Energy Sources and Climate Change Mitigation (see pages 731-2).

http://srren.ipcc-wg3.de/report/IPCC_SRREN_Ch09.pdf //

My review of various estimates suggests that the greenhouse emissions from nuclear power vary from 10 to 130 grams of CO2 per kilowatt hour of power, with an average of 65 g per kWh – or roughly the same as wind power. For comparison, coal power has emissions of about 900 g per kWh, and gas-fired power about 450 g per kWh. About 15-25% of nuclear’s greenhouse emissions come from building, maintaining and decommissioning the nuclear power plant.