No, that's incorrect. Coal is mostly carbon, but almost all of that carbon burns with the coal -- what's left over in the ash is whatever didn't burn, which is

No, that's incorrect. Coal is mostly carbon, but almost all of that carbon burns with the coal -- what's left over in the ash is whatever didn't burn, which is mostly minerals like silicon/aluminium oxides. Even the source coal has relatively low levels of C14 (since it's been buried for millions of years), and nothing about the combustion process would be likely to concentrate that in the ash. Radioactivity in coal ash is primarily due to small quantities of uranium in the coal. It's not significantly radioactive, though; the hazards it poses are more due to other heavy metals which are often present in the ash (lead, mercury, etc).