And Chernobyl isn't a nuclear bomb. Nuclear reactors only have a 2% ~ 5% mix of U235/238 (might have the order wrong; less than 5% of the radioactive isotope). Bombs are near 95%, or "highly enriched uranium" .. which would likely have less radiation in the aftermath than a nuclear plan since everything would be consumed in the detonation ... but everything would be dead for obviously other reasons.
Much of the fallout of a nuclear bomb comes from the dirt becoming so neutron irradiated that they become unstable isotopes. But also the daughter particles of a nuclear bomb are also unstable even if the u235/238 is consumed. If you explode a bomb in atmosphere the fallout concerns are much less because you aren't kicking as much irradiated dirt into the atmosphere.
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