nuclear ied's folder - Coal Ash Is More Radioactive Than Nuclear Waste By burning away all the pesky carbon and other impurities, coal power plants produce heaps of radiation At issue is coal's content of uranium and thorium, both radioactive elements. They occur in such trace amounts in natural, or "whole," coal that they aren't a problem. But when coal is burned into fly ash, uranium and thorium are concentrated at up to 10 times their original levels.

https://www.scientificamerican.com/article/coal-ash-is-more-radioactive-than-nuclear-waste/