>> So, most of the worst radioactive elements are long gone
You're wrong. Just facts:
Cesium-137 half-life 30 years
Strontium-90 half-life 28 years
You're wrong. Just facts:
Cesium-137 half-life 30 years
Strontium-90 half-life 28 years
Less than half of strontium 90 is left, and vary close to half of Cesium-137 is gone, but together they make up a small fraction of overall radiation released.
Iodine 131 for example is one of the most dangrious isotopes after an event, but it's half life is 8 days.
But we need also to take in mind that when some of those compounds vanish in fact they aren't gone, they convert in other subproducts. Uranium creates Cesium (and Iodine I think, i'm not expert on this) when decays, so the real cesium should be now 50% plus X (where X is the cesium constantly created since the accident). And Thorium, Polonium, Radium...
What happens whith uranium in the subsoil when is burned in a fire?. Is its decay increased?
Anyway, the dust is something like 95% less radioactive now than it was right after the event and you get far less dust from a contaminated forest fire than you would from the initial fire.
PS: Inside the reactor there is new stuff being generated from fission, but that's contained right now.