Not that that should have of course…
Don’t very powerful blasts ruin land for thousands and thousands of years? I guess not. But toxic waste is toxic…forever. Millions of years, so they say. Why are Nagasaki and Hiroshima “clean” now (indeed, just shortly after the war)?
They were exploded in the air rather than on the ground. Much less fall out is produced this way.
An atomic bomb doesn’t produce that much waste. The uranium is scattered widely (which is a problem, but a diffuse one). The immediate radiation is brutal, and there were radiation death in high numbers. The “thousands of years” you’re thinking about are the waste from atomic reactors. The “spent” radioactives are still radioactive, but they’re not useful for a reactor any more, and the rods, shielding and etc. have been exposed to radiation for years, so they’re contaminated as well.
As hawthorne says, an air burst only scatters the material of the bomb, while a ground burst sends a bunch of pulverized (and radioactive) buildings and dirt into the atmosphere.
At Chernobyl (accident in 1986) the core is still hot, but that’s partly (mostly?) because there’s an undetermined amount of fuel still in there. Yikes. Nobody know when they’ll get that sucker cleaned up–the main plan seems to be to encase it all in concrete and just leave it.
Another aspect: the most intensely radioactive products of a fission explosion have short half-lives, from days to months. The decay in total activity is especially dramatic over the first few days (hence the civil defence advice to stay in a shelter for that time).