In Sweden between 1930-1970 we produced building elements from concrete where oilshale was used to burn the chalk and the ashes of the fuel was mixed into the c

In Sweden between 1930-1970 we produced building elements from concrete where oilshale was used to burn the chalk and the ashes of the fuel was mixed into the concrete! That shale ash was so rich in uranium that the concrete turned blue! Since then thousands have died by passively breathing the radon evaporation from the walls in some Swedish houses. On the subject RTG elements are also used in space probes: https://www.youtube.com/watch?v=H62hZJVqs2o https://www.youtube.com/watch?v=H62hZJVqs2o