> The shorter the half-life of an isotope is, the more radioactive and thus dangerous it is.
> The longer the half-life of an isotope is, the less radioactive and thus dangerous it is.
> Fukushima happened in 2011, almost 8 years ago. Almost everything dangerous had since decayed.
Plutonium-239 has a half-life of 24,100 years and is pretty dangerous AFAIK [1]:
> Radioactive contaminants are dangerous for 10 to 20 times the length of their half-lives, meaning that dangerous plutonium released to the environment today will stick around for the next half a million years.
[1] https://www.livescience.com/33127-plutonium-more-dangerous-u...