I don't understand why the nuclear industry wouldn't pile in to fund research into this area (as a potential way to clean up nuclear waste). Probably I don't understand how this fungus actually works and it is impossible!
Even if it did somehow accelerate the decay, it wouldn't be that useful, since (Chernobyl aside), all the waste from the typical civilian nuclear reactor can fit in a side lot on the site of the reactor complex itself (and often does!). There just isn't that much radioactive waste to clean up!
Not to disagree with you, just to say that even though it's a minor nuisance it nevertheless occupies a lot of mental space because of how annoying it is.
A radiotropic fungus that’s in TFA can’t meaningfully affect the rate at which nuclear decay is happening. What it can do, supposedly, is to harvest the energy that the nuclear decay is releasing; normally there’s too much energy for an organism to safely handle.
At the risk of vastly oversimplifying, you can’t plug your phone into high voltage transmission lines. These fungi are using melanin to moderate the extra energy, stepping it down into a range that’s useful (or at least minimally harmful).