[astrodust]

Transport is the only problem here. If there's a way of reburning fuel, or of containing it on-site long enough that most of the most harmful radiation has subsided you'll be fine.

The shorter the half-life, the more dangerous the radiation is. Radioactive elements with long half lives are generally less damaging and it's only from prolonged exposure you're in trouble.

Polonium is notoriously toxic (https://en.wikipedia.org/wiki/Poisoning_of_Alexander_Litvine...) and has a furiously short half-life. Plutonium has a half-life of about 24,000 years so the radiation is spread out over a much, much longer period of time.

You can hold a plutonium sphere and suffer no ill-effects. The same cannot be said for one of polonium, something so nasty that nanograms of the material can kill you.

So basically it's the short-lived elements you need to worry about the most. The long-lived ones are relatively harmless. The biggest concern with those is securing them from those intent on using them for harm, as refining and weaponizing nuclear waste is a concern.