[John_KZ]

No, the idea that fly-ash is highly radioactive is a faux created by the nuclear lobby. Some coal is more radioactive than other, but in general they're very safe from this perspective. The real problems are is it's corrosiveness, it's heavy metal content (if any), and the particle size.

[Erlangolem]

I live and learn, thanks. The particle size I assume is an issue for pulmonary reasons? So sequestered in concrete that wouldn’t be an issue, smart.