It depends on how you look at it.
Nuclear power plants main emissions is water, in the form of steam, which is used in the cooling process.
Nuclear is sustainable energy source, but the problem is that we only use about 10-20% of the energy, which is a lot, but not particularly efficient.
Also, we have to deal with the used fuel rods, currently most of the are disposed off by, putting them in container to keep in the radiation, and are dumped to the bottom of the ocean, some are reused elsewhere.
So in terms of emission, yes nuclear is a clean energy, but we have to find better way to deal with the used fuel rods.
