Half lives range from extremely short to very long, but the great majority of radioactivity is from shorter-lived isotopes. Also, the isotopes that were released in significant amounts from the reactors (due to their physical and chemical natures) were almost entirely short-to-medium lived isotopes. Longer-lived isotopes, like plutonium, are heavy solids, and stayed put inside the reactors.
Virtually all of the elevated radiations levels (exposures) in areas around the plant are due to Cs-137 and Cs-134, which have half lives of ~30 and ~2 years, respectively. Tritium has already decayed away and the dose (radiation levels) from longer lives isotopes is negligible.
Due to other factors like cleanup efforts and environmental dispersion (i.e., the radioactive material being "washed away"), the radiation levels in the currently off-limits areas will fall faster than the 30-year half life suggests. Thus, the majority of those areas will have radiation levels within the range of natural background in a matter of years (i.e., not even decades).
That said, yes the areas around the plant would be a great place for disposal of low and intermediate level wastes (that decay faster) and storage site for spent fuel assemblies (long-lived wastes). Eventually, a deep geologic repository site would be found for those high-level wastes. (That or reprocessing.)
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