I can’t give you a direct quote about chlorine, fluorine and carbon, as I haven’t taken this stuff in about 3 years. BUT, Nuclear plants aren’t really 100% clean. They are better obviously than coal or gas plants, but they still produce nuclear waste among other byproducts (which could well include those gasses, and I believe it’s chlorocarbon and fluorocarbon, not all three separate). During enrichment yes, fission takes place. That’s how they get the uranium up to the required standard. What makes the energy is decay, the opposite of fission. (You could probably find this info, at least far better than I remember it, from any entry level college chem book….. I sold mine long ago or I’d look it up for ya).