Aren't there any serious studies done on people who live in areas with high natural radiation like Ramsaar in Iran? I guess that would be a closest thing to living on a slowly leaking radioactive waste dump and best place you could get on studying long term effects of weak radiation levels.
Not that I know. In Germany, the recently best in the field was the KIDD study about childhood chancer rates near nuclear power plants, which also correlate good to the nuclear waste dump.
Such a study would sure be interesting, also for spaceflight research.
Regarding nuclear vs fossil fuels. Problems with nuclear energy seems to be more managable than problems with fossil fuels. If we continue to burn everything that burns - oil, coal, conventional natural gas, shale gas, tar sands, maybe even develop ways to tap deep sea methane hydrates it all has the potential to cause severe impact on climate. What if major bread baskets of the world suddenly don't get any meaningful rainfall for several years in a row because of some climate shift. Now we have a Very Big Problem.
I think that both kinds of fuel lack control, but there are different kinds of being out of control there.
Most CO2 can be chemically filtered out of the gases, if you want to. It isn't effective, and only really works for power plants, but you can do that.
sulfur can be removed from fuel by carefully selecting the fuel or using special chemical filters in the power plant.
But nuclear waste is different there - nuclear waste isn't something you can easily filter out. Take Iodine for example, it is really nasty if released, since it can hide in many molecules, and only a mass spectrometer or centrifuge could separate a bit of it from normal Iodine.
Also, you can't even compare chemical power production with nuclear in terms of the exhaust/waste: chemical power plants have, if you use high enough temperatures and a long enough exhaust stack/filter system to let the exhaust cool, a very reliable output. Carbon and Oxygen become CO2. a bit of water forms. Other, more nasty chemicals form by contaminants alone.
Nuclear fission is different. You only know for sure that the resulting nuclei after the fission have only a small chance of being of similar mass. Everything else is possible - you can have a wide range of different isotopes. Harmless substances in a nuclear reactor can capture neutrons and become highly radioactive. The three classic kinds of radiation can also mess with the materials.
This is one big problem handling the waste - you don't really know what the waste is made of, until you analyzed it. The statistics tell you a reliable figure what you can expect, but then you don't even reliable know, what properties the fuel had that went into the reactor. Or what kind of radiation affected a certain junk part, that is now waste itself.
The many noble gases that are produced along the process are also highly radioactive and noble gases can't be chemically filtered, you need to use different technology there.
Nuclear waste has the nasty tendency to wait silently for a long time until you do an error. And then hell breaks loose. If you don't have the proper respect for the material, you are already gambling with the devil. But even if you do everything thinkable right, nuclear waste can trick you and contaminate a place and produce new nuclear waste.
The funny thing about nuclear fuel is also, that it does not even result in radioactivity constantly dropping - the way how it drops is the sum of many decay processes and many formations of new radioactive isotopes.