Uranium -> thorium -> radium -> radon -> ... -> lead is a natural decay chain that does not typically activate other atoms to become unstable, so the decay ener

Uranium -> thorium -> radium -> radon -> ... -> lead is a natural decay chain that does not typically activate other atoms to become unstable, so the decay energy between uranium and lead represents all the radioactivity there will ever be from that uranium. You can't predict exactly when it will be released, and because radon is a gas, you can't as easily predict where it will be released, but once you get to stable lead, it's done. If you tack up a slab of any stable nucleus higher than iron on the nuclear binding energy curve to the inside walls of a neutron chain-reaction reactor, you can probably get it to absorb neutrons of the appropriate speed and become unstable, promising future radioactivity with an amount of energy between its current state and whatever its final decay product may be. That may be less total energy than the difference between uranium and lead, but it probably runs faster from start to finish than billions of years, and is probably more energy than the absorbed neutron. So aside from natural reactors, which mostly shut down a long time ago, the only increases in radioactive potential are going to be from human-built reactors. The radon is just moving primordial radioactive potential from where the radium is, which is also where the uranium or thorium is, to wherever heavier-than-air gases can accumulate. If you remove the radium, you stop that. If you encapsulate the radium in a glass that traps gas, you stop that. Mostly, we don't bother trying to remove trace amounts of uranium and other radioactive isotopes from mineral resources, but if a fungus could do it cheaply, it could make coal ash less dangerous to process and store.