Let me reinforce what Karen said, because this isn't written very often, and I figured it out independently. (Karen's only the second person I know who's stated it clearly.)
The fundamental economic problems with fission power all derive from this phenomenon: you're creating a soup of mixed chemicals, and it destroys nearly everything you try to use to contain it. This obviously leads to endless cost blowouts. The only way to avoid the cost blowouts is to just not worry about it, and let the reactor self-destruct and leak -- which was basically done during the Manhattan Project and the Russian equivalent -- but that obviously has its own problems (Chernobyl, poisoning everyone in sight, etc.), as well as being rather uneconomical due to the short lifespan.
Which, in turn, is due to the problem of transmutation, which is an insoluble problem of fission.
In most of industry, we go to massive time, trouble, and effort to purify chemicals and to remove toxic elements. A fission reactor inherently does the exact opposite: it un-purifies chemicals and adds toxic elements. Perhaps you can see why it can never, ever be economical.
Once I believed that fission was one solution to our CO2 pollution. That changed some years ago, when I got to meet a professional nuclear waste manager (from Belgium).
Over some of his country's beer, he explained all of the above to me. He paid for the beer, knowing that with the existing Belgian reactors he would never be out of a job.