There is no 100% clean nuclear power ever. Well as the articles explain, there is. If you search on the internet, there are even more options. For more information watch the documentary "Pandora's Promise". More to a Factorio related point: In the future it shouldn't be a problem to clean...

There exists an option to get rid of radio active wast, just search for TerraPower or "MIT Develops Meltdown-Proof, Nuclear Waste-Eating Reactor".
The end product is less radio active then a lot of cities are at the moment (radio activity is all around us).

100% clean power.